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COMMENT PAGE FOR:
(HTM) Data centers are transitioning from AC to DC
ykonstant wrote 6 hours 21 min ago:
Soon they will replace all the iron railings with maiden.
mikewarot wrote 10 hours 33 min ago:
Ok, this is just plain nuts.
800 volts DC, at the megawatt power supply levels, implies fault
impulses of more than a megajoule. Google tells me that's about 2 hand
grenades worth of boom. That's an optimistic lower bound.
The resulting copper plasma cloud is a burn and inhalation hazard,
along with the overpressure.
Let's say you get a 10 kiloamp fault current, this will then induce
voltages everywhere you don't want it to go. If all the interconnects
are fiber, that's really not a problem, but you have to have everything
EMP shielded if you don't want boards popping randomly after such an
event.
The "efficiency" of removing the extra power conversions also removes
filtering and surge suppression. It's entirely possible that one power
supply over-voltage takes out half of your racks. The MOSFETs used
tend to fail closed instead of open, making failures far worse than a
simple outage.
Very smart people are making very smart mistakes.
redm wrote 15 hours 37 min ago:
I guess we've come full circle. It was just 20 years ago that my
datacenters gutted DC in favor of AC.
Rapzid wrote 16 hours 40 min ago:
I somehow made it to middle age without making the connection from
AC/DC to electricity. Or I never thought about it till now.
tezza wrote 18 hours 22 min ago:
They were Thunderstruck?
wolvoleo wrote 19 hours 14 min ago:
Well they're kinda transitioning back. When I grew up most DCs (and
telecom facilities) were running on 48V DC. Easy to back up with a big
room full of lead acid batteries (just keep an eye on that hydrogen gas
lol)
Xcelerate wrote 19 hours 56 min ago:
I set up my own home network with a Vertiv Liebert Li-ion UPS a few
years ago and was thinking about how inefficient the whole process is
regarding power. The current goes from AC to DC back to AC back to DC.
Straight from the UPS as DC would work much better, and as I was
teaching myself more about networking equipment, I was surprised to
learn that most of it isn't DC input by default (i.e., each piece of
equipment tends to come with built-in AC-DC conversion).
Then I started routing ethernet with PoE throughout my house and
observed that other than a few large appliances, the majority of
powered devices in a typical home in 2026 could be supplied via PoE DC
current as well! Lighting, laptops, small/medium televisions. The
current PoE spec allows up to 100 W, which covers like 80% of the
powered devices in most homes. I think it would make more sense to have
fewer AC outlets around the modern house and many more terminals for
PoE instead (maybe with a more robust connector than RJ45). I wonder
what sort of energy efficiency improvements this would yield. No more
power bricks all over the place either.
ssl-3 wrote 16 hours 27 min ago:
It's fun to think about. There's advantages both ways, but I think
it leans most-heavily towards keeping AC.
1. One of these is simplicity. With AC, one single home run of
cabling (eg, Romex) can feed a whole room full of stuff, like a
bedroom or a living room. At one end of the run is a circuit breaker
(a fairly simple electromechanical device) and at the other end is a
series of outlets (which are physically daisy-chained, but are
functionally just wired in parallel with eachother).
Since one single run of cable can feed many devices, it is easy to
accomplish.
2. Another advantage is that it is universal. Anything can plug
into these outlets. Whatever a person brings into the home to use,
they can plug it into an outlet and it works. It works this same way
in every home.
3. And there's quite a lot of power available: A common 20A 120v
branch circuit cabled up with 12AWG Romex is stated to supply up to
16A continuously, or 1920W. For intermittent loads, it can supply
20A -- or 2400W. That's tiny by European standards, but it's still
quite a lot of power. It's plenty to run a space heater when Grandma
visits and she complains about the guest room being cold (even as you
start to sweat when you cross the threshold to investigate) and a big
TV and a whole world of table lamps, all at once. And you can plug
this stuff into any outlets in a room, and it Just Works.
4. But, sure: Lots of devices want DC, not AC. So there's a
necessary conversion step that is either integral to the device being
plugged in, or in the form of the external wall warts we all know
very well.
So let's compare to power-over-ethernet.
1. It's also simple, but only tangentially-so. One home-run cable
per outlet, whether that outlet is used or not, is something that can
be rationalized as being a simple topology. A PoE switch at the
head-end instead of a central box with circuit breakers is a
simple-enough thing to transition to. And a lot more individual
cables are required, but they're relatively small and are generally
easier to install.
2. It's standardized, but it's not universal at all. I've got a few
PoE widgets around the house, but I'm pretty friggin' weird when it
comes to what I do with electricity. I can't go to Wal-Mart and buy
more PoE widgets to use at home, and when people visit they aren't
bringing PoE adapters to charge their phones and other electronics.
My computer monitor doesn't have a PoE input. I can easily imagine a
table lamp or a fan that connects to PoE, and also uses it as a
network connection for automation, and that sounds pretty sweet in
ways that tickle my automation bones in the most filthy of
fashions... but that's getting even further into the weeds compared
to how regular people expect to do regular things.
3. There isn't a lot of power available. 802.3bt Type 4 is the
highest spec. And within that spec: While switch ports can output
up to 100W, a device being powered is limited drawing no more than
71.3W. Now, sure, that's 71.3W per port, but in a room with 10 ports
that's still only ~700W -- at most -- in that room. And Grandma's
space heater won't run on 71.3W, nor her electric blanket. My laptop
wants more than this. The list of useful, portable things that we
casually plug into a wall that only draw less than 71.3W is pretty
short and most don't benefit from the main advantage of PoE, which is
a combination of [some] power alongside high-speed Ethernet data.
4. We still need wall warts since PoE is nominally ~48VDC. For
example: Phones use less than 71.3W while charging, but they don't
run on 48V. That means 120V AC comes in from the grid, gets shifted
to 48VDC for distribution within the dwelling, and then gets shifted
yet again to the produce the power (5, 9, 15, and 20V are
common-enough in USB PD world) that devices actually want. That's
more lossy conversion steps, not fewer -- and we still get to keep
the extra conversion (wall warts) as punishment for our great ideas.
This is not the path towards increased energy efficiency.
---
PoE is great for the things we use it for today. A camera, a
wireless access point -- you know, fixed-location stuff that uses
networked data as its primary function and also requires power.
Installed PoE light fixtures (like, say, task lights in a kitchen)
also sounds neat -- unless they die prematurely and no PoE
replacements are to be found. (Now, you have not just one or two
problems, but many: The lights aren't working in that space and they
can't be replaced with a trip to Lowes because the Romex that would
normally have been installed was deliberately deleted from the plan.
It could have been a 20-minute DIY fix that costs less than $100, but
now it involves drywall and paint and retrofitting new cabling. Or
maybe PoE replacements do exist, but it's now 2035 and the new ones
don't talk the same network protocols as the old ones did.)
But there are other upsides: I've got an 8-port PoE-powered network
switch that works a treat. It's a dandy little thing. And it sure
would be neat to plug my streaming box in with PoE and kill two birds
with one cable; I would like that very much.
But most people? Most people don't give a damn about ethernet (PoE,
or not!) these days, or streaming boxes, and that trend is
increasing. They just plug their lamp into the regular outlet on the
wall like they always have, and deal with whatever terrible UI is
built into their smart TV, and use wifi for anything that needs data.
And when they buy a home that is filled with someone else's smart
infrastucture, their first task (more often than not) is to figure
out who to call to erase those parts completely and put it back to
being normal and boring.
matt-p wrote 17 hours 27 min ago:
One of the main problems is conductor size. I wish we could access
22AWG copper in cheap and cheerful cat5e/cat6 format cable. 24AWG
cat5e, sometimes CCA is not great for doing large amounts of POE.
Xcelerate wrote 16 hours 54 min ago:
22AWG Cat6A is actually what I used (cheap it was not however).
crote wrote 17 hours 50 min ago:
The problem is that all of those DC devices don't operate on 48V
either. The vast majority of chips require a 5V or lower input, so
with a 48V DC supply you're still going to need a per-device PSU to
do DC-DC conversion. In other words: no getting rid of power bricks.
Efficiency isn't as straightforward either. You're still being fed by
120V/230V AC, so you're going to need some kind of centralized
rectifier and down converter. It'll need to be specced for peak use,
but in practice it'll usually operate at a fraction of that load -
which means it'll have a pretty poor efficiency. A per-device PSU can
be designed exactly for the expected load, which means it'll operate
at its peak efficiency.
We also don't use 5V DC grids because the wire losses would be
horrible, so a domestic DC grid should probably operate at pretty
close to regular AC voltage as well. In practice this means the most
sensible option would be to have a centralized rectifier and a grid
operating at whatever voltage it outputs - but what would be the
point?
As to PoE: I personally really like the idea, but I don't believe
it'll have a bright future. For its traditional use the main issue is
that there doesn't seem to be a future for twisted-pair beyond
10Gbps. 25GBASE-T might exist as a standard on paper, but the
hardware never took off due to complete disinterest from the
datacenter market, and it is too limited to be of use in offices and
homes. I fully expect that 25G will arrive in the home and office as
some form of fiber-optic interconnect - with fiber+copper hybrid for
things like access points.
On the other hand, for a lot of IoT applications PoE seems to be too
complicated and too expensive. It makes sense for things like
cameras, but individual lights, or things like smoke sensors are
probably better served in office/industrial applications by either a
regular AC supply or a local DC one, plus something like KNX, X10,
CAN, or Modbus for comms: just being able to be wired as a bus rather
than a star topology is already a massive advantage. And for domestic
use the whole "has a wire" thing is of course a massive drawback -
most consumers strongly prefer using Wifi over running a dedicated
wire to every single little doodad.
matt-p wrote 16 hours 3 min ago:
What if all homes had battery storage and or solar? You could then
simply use it's rectifier as needed or direct 48v from the solar
panels. That would be even more efficient than 230v.
marcosdumay wrote 14 hours 55 min ago:
I'm not sure converting the solar and battery to 48V,
distributing it around, and converting it to the needed voltage
at the point of use is any more efficient than inverting it into
230V and distributing it around.
Also, you'll need wires that 5 times thicker. Instead of needing
a reasonably 1mm^2 for a normal 16A line, you'll need 5mm^2 for
the same power.
matt-p wrote 4 hours 8 min ago:
Solar and battery are already at 48v in most cases, so you are
avoiding converting it to AC.
I agree, it's unserious to suggest a cooker or something high
power is going to run off of 48v. But for loads like lights,
PC/Laptop/TV/Audio 16a at 48v is ~770W which is adequate for
these devices.
marcosdumay wrote 1 hour 5 min ago:
Both solar and batteries voltages vary wildly and require a
converter to use.
ssl-3 wrote 15 hours 25 min ago:
That'd be neat. But there's no standard for voltage for home
solar: The batteries might be 12, 24, 48v, 60v, or even much
more. Meanwhile, the panel arrays commonly output anything as
low as 0V and up to ~600V. There's not much for rules and norms
here.
Even if we were to standardize a low (<50V) voltage for DC
distribution within homes, we'd still need ~120/240VAC to power
big stuff, or we'd instead need even-larger conductors (more
copper) than we use today to do the same work with low voltage.
But, sure -- we can play it out. So let's say we have an in-home
48VDC distribution standard and decide that this is the path
forward and we enshrine it in law.
We need to convert whatever the solar system has available to
48VDC. Then, we need to distribute that 48VDC using a completely
separate network of cabling. Finally, we still need to convert
48VDC to whatever it is that devices can actually use.
That's not representative of a reduction in steps, or an increase
in efficiency.
That is instead just an increase in installed infrastructure
expense, and a decrease in device compatibility. It takes what
we have, which is simply universal (at least within any given
geographical area) and adds complexity.
And for what? What's the perceived benefit?
matt-p wrote 4 hours 13 min ago:
Almost all home batteries are 48v, I think it would be
reasonable to standardise on that.
ssl-3 wrote 1 hour 8 min ago:
So 48v it is.
Is the juice worth the squeeze, though? Two sets of home
wiring voltages? Substantially bigger copper wire inside the
walls instead of existing copper, in order to do the same
work? Two sets of appliances (of all sizes) on shelves at
the store? More adapters?
Billy now needs to bring 2 wall warts to make sure he can
charge his portable gear at a friend's house instead of just
1, because he's never sure until he gets there if they've got
a 120 or 240v house like they all used to be, a combination
house, or if it's one of those solar-only places that only
has the weird plugs.
What we have now is 1 cable plant connecting the rooms of a
home, and an increasing number of hybrid solar inverters that
-- on a sunny day -- cheerfully convert solar power directly
from whatever the panels are outputting to the 120/240 VAC
wiring that both existing and future appliances know how to
use. At night, these hybrid systems do do the same thing
from whatever voltage the battery uses and convert that to
AC. There's only 1 voltage, and only 1 plug; Billy brings 1
wall wart and knows he can charge his stuff.
To be sure: What we have not strictly ideal, but then
neither is changing things without a clear positive benefit.
Again: What's the qualitative advantage of changing this,
other than change for the sake of change?
DC might feel nice and neat, but in reality it doesn't seem
to be shaped that way at all to me.
lillecarl wrote 15 hours 32 min ago:
We live on societies, switching from AC to DC because your
low-power home appliances doesn't need AC makes no sense. Home
power usage is dominated by heating and cooling not by your 45w
laptop charger.
DC infrastucture makes sense in highly specialised
environments.... Like new gigawatt AI farms
shiroiuma wrote 13 hours 25 min ago:
Large home appliances probably mostly need DC power these days
too. Look at clothes washers: they all have variable-speed
reversing motors, so they're probably using brushless DC motors
(which use motor drives that are fed with DC, and output
variable-frequency and variable-amplitude sinusoidal waves to
drive the motor). HVAC seems to be similar, with
variable-speed motors and compressors.
I don't think that much stuff is left which actually needs AC
power (usually to run an AC induction motor).
matt-p wrote 3 hours 58 min ago:
[HVAC] true for the fans and controllers but surely you
wouldn't DC feed a compressor.
pdpi wrote 17 hours 57 min ago:
> maybe with a more robust connector than RJ45
USB-C could be that connector, using USB-PD instead of PoE. Though
I'm not sure I'd want to need that much smarts for every single power
outlet.
kjs3 wrote 17 hours 33 min ago:
Considering the number of times I've sheared off a USB-C connector
vs ethernet, I wouldn't consider USB-C to be more robust than RJ45.
YMMV.
pdpi wrote 16 hours 54 min ago:
How often do you unplug RJ45s versus USB-C, though?
kjs3 wrote 16 hours 30 min ago:
I'm not talking about unplugging. Normal use.
Brian_K_White wrote 12 hours 41 min ago:
And in normal use, how often do you handle or cycle an rj45
vs a usb?
Even when it's your job the usb are still handled and cycled
way more often. You might handle 100 ethernet jacks today,
but it won't be the same one 100 times. You plug it in and
don't touch that one again for 5 years.
dmonitor wrote 12 hours 56 min ago:
USB-C devices tend to be mobile. Flexing and disconnecting
are much more common.
sneak wrote 17 hours 58 min ago:
I think Ubiquiti (makers of the UniFi wifi products, as well as some
of the most popular managed PoE switches) also make a ton of other
PoE products such as the usual stuff like cameras, ip phones, network
switches, access card readers, door locks, and, now, ceiling lights
(presumably due to the latest PoE standards delivering significant
wattage).
It's super nice because you only need to put the UPS/ATS at the PoE
switch and then you get power redundancy everywhere you have ethernet
running (i.e. the phones don't go down).
zahlman wrote 18 hours 11 min ago:
> Lighting, laptops, small/medium televisions. The current PoE spec
allows up to 100 W, which covers like 80% of the powered devices in
most homes.
I find it a little hard to imagine that those devices outnumber
things like stoves, dishwashers, washers/dryers, kettles, hair
dryers... by 4:1.
Unsure why PoE would be better for LED lighting than the standard
approach of screwing a bulb directly into AC, either. How many lumens
do you get out of strip lights these days? And you still have AC-DC
conversion for whatever's sourcing power onto the Ethernet link.
formerly_proven wrote 18 hours 4 min ago:
PoE is also fairly bulky, requires large connectors, and either
requires a wholly isolated PD or what's basically a class 2 DC/DC
converter. That's why PoE-powered stuff usually has that big
transformer cube in it with a lot of clearance, slotted PCB, 2-4 kV
capacitors etc.
In practice PoE will have lower efficiency than mains powered,
since it'll usually be at least double conversion, often three
converters in series, plus the losses of the thin network wires,
and the relatively high idle losses / poor low-load efficiency of
the necessarily over-dimensioned PSE.
throw0101d wrote 19 hours 0 min ago:
> I set up my own home network with a Vertiv Liebert Li-ion UPS a few
years ago and was thinking about how inefficient the whole process is
regarding power. The current goes from AC to DC back to AC back to
DC.
With double-conversion, generally yes.
I recently ran across the (patented?) concept of a delta
conversion/transformer UPS that seems to eliminate/reduce the
inefficiencies:
* [1] * a bit technical: [2] * Figures 6 to 8 [pdf]: [3] The
double-conversion only occurs when there's a 'hiccup' from utility
power, otherwise if power is clean the double-conversion is not done
at all so the inefficiencies don't kick in.
(HTM) [1]: https://dc.mynetworkinsights.com/what-are-the-different-type...
(HTM) [2]: https://www.youtube.com/watch?v=nn_ydJemqCk
(HTM) [3]: https://www.totalpowersolutions.ie/wp-content/uploads/WP1-Di...
rsync wrote 19 hours 20 min ago:
"... throughout my house and observed that other than a few large
appliances, the majority of powered devices in a typical home in 2026
could be supplied via PoE DC current as well!"
We installed 120 LED ceiling lights in our home circa 2020, all of
which were run with high voltage (romex) and accompanied by 120
little transformer boxes that mount inside the ceiling next to them.
Later ...
We installed outdoor lighting with low voltage, outdoor rated wiring
and powered by a 12V transformer[1] and I felt the same way you did:
why did we use a mile of romex and install all of those little mini
transformers when we could have powered the same lights with 12V and
low voltage wire ?
I then learned that the energy draw of running the low-volt
transformer all the time - especially one large enough to supply an
entire house of lighting - would more than cancel out energy savings
from powering lower voltage fixtures.
You don't have this problem with outdoor lighting because the entire
transformer is on a switch leg and is off most of the time.
So ... I like the idea of removing a lot of unnecessary high voltage
wire but it's not as simple as "just put all of your lights behind a
transformer".
(HTM) [1]: https://residential.vistapro.com/lex-cms/product/262396-es-s...
shiroiuma wrote 13 hours 46 min ago:
These days, you should not be using transformers to power small
loads at all, you should be using switching power supplies. They
have negligible power draw when there's no load attached.
eqvinox wrote 18 hours 38 min ago:
> I then learned that the energy draw of running the low-volt
transformer all the time - especially one large enough to supply an
entire house of lighting - would more than cancel out energy
savings from powering lower voltage fixtures.
That's not a constraint of physics, you can absolutely build a DC
power supply that is efficient in a wide load range. (Worst case
it might involve paralleling and switching between multiple PSUs
that target different load ranges.) But of course something like
that is more expensive...
Dylan16807 wrote 17 hours 21 min ago:
> But of course something like that is more expensive...
More expensive than an inefficient unit, but it should still be a
lot cheaper than 120 separate units, right?
And I expect one big fat unit to do a better job of smoothing out
voltage and avoiding flicker than a bunch of single-light units.
Especially because the output capacitors are sized for the entire
system, but you'll rarely have all the lights on at the same
time.
Though for efficiency I'd think you'd want 48v and not 12v.
phantom784 wrote 1 hour 14 min ago:
Plus you save money on the conductors running to the lights.
estimator7292 wrote 19 hours 41 min ago:
I think we're slowly, slowly coming around to the idea of domestic DC
distribution. The vast majority of consumer electronics would be
perfectly happy to consume 12v. It's cheaper, safer, more efficient.
Less design work and certification on inbuilt AC adapters.
I think it's highly unlikely we'll see mass scale retrofits, but if
enough momentum builds up, I can see it as a great bonus feature for
new builds.
I got lucky with my house and every room has a dedicated phone line
meeting at a distribution panel (a couple of 2x4s with screw
terminals) built in the 50s. I'm in the process of converting it to
light duty DC power. The wiring is only good for an amp or two, but
at 48v that's still significant power transmission.
matt-p wrote 16 hours 30 min ago:
48v is what most home battery/solar systems run off. Also
coincidentally POE, IMO it makes a much more sensible candidate as
it is still 'safe' while carrying 4x as much power for a given
cable gauge. Consider laptops are 19 or 20v so you would
essentially /need/ a minimum of 24v.
zahlman wrote 18 hours 5 min ago:
> I think it's highly unlikely we'll see mass scale retrofits, but
if enough momentum builds up, I can see it as a great bonus feature
for new builds.
I imagine rooftop solar could also source DC for the house directly
(or via a battery), before hitting the inverter... ?
The main problem I see is educating consumers. Maybe that starts
with a standard for DC outlets and plugs that can't be confused
with AC... ?
(Now I'm imagining desktop computers with much simpler power
supplies; but you'd presumably have to wire for dozens of amps
incoming...)
p0w3n3d wrote 20 hours 42 min ago:
Hard as a rock!
Well it's harder than a rock!
BorisMelnik wrote 21 hours 17 min ago:
its really wild at all the AC to DC changes. for those non electric
engineers / hardware hackers (like myself) one of the biggest
"examples" I've seen of this has been ceiling fans.
Installing a ceiling fan used to be treacherous and so heavy. Also loud
and buzzy after installed. Now the fans in these things are so
lightweight and easy.
seeing the same in many more areas (lighting, etc)
hamdingers wrote 20 hours 27 min ago:
Would love to see more mainstream DC lighting options and an updated
code to match. I just finished a remodel of my workshop and blew over
a hundred bucks on 14/2 for a 15 amp lighting circuit that is
unlikely to ever see more than a 1 amps load.
The irony is all the recessed lights I picked out are DC, they all
have little AC-DC boxes hanging off them using a proprietary
connector. If I hadn't needed to pass a rough-in inspection going all
DC would've been trivial.
everdrive wrote 21 hours 53 min ago:
"How can we turn this technical story into a story about people and
their conflicts?"
tibbydudeza wrote 22 hours 2 min ago:
Have a solar system at home and from the panels it is DC into the
batteries but then the inverter needs to convert it to 220V/50Hz AC for
home use.
sholladay wrote 22 hours 30 min ago:
Is there anything left in a modern home that really needs or is better
on AC?
We have some old ceiling and exhaust fans, but I know those can be
replaced. Our refrigerator is AC, but extended family with an off-grid
home has a DC refrigerator that cycles way less, probably due to
multiple design factors but Iâm sure the lack of transformer heat is
part of it. Iâm not as sure about laundry machine or oven/cooktop
options but I believe those are also running on DC in the off-grid home
without inverters.
Most of these AC appliances also have transformers in them anyway for
the control boards. It seems kind of insane to me that we are still
doing things this way.
samus wrote 21 hours 54 min ago:
Any appliance with strong motors should be more efficient with AC
supply. But almost anything else can be regarded as a heater that
doesn't care much as long as it is fed with the correct voltage.
Which is actually the core issue.
A DC household would have to choose a trade-off between multiple
lines with different voltages or fewer voltages that need to be
adapted to the appliances. And we're right back at the AC situation,
but worse since DC voltages are more difficult to change.
But consumers like datacenters can very well plan ahead and
standardize on a single DC voltage. They already need beefy equipment
to deal with interruptions, power sourges, non-sinus components, and
brownouts, which already involves transformers, condensators, and DC
conversion for battery storage. Therefore almost no additional
equipment is required.
sholladay wrote 20 hours 24 min ago:
What qualifies as a strong motor here? Are you comparing to a
brushed DC motor? Do you think a washer/dryer would have worse
overall efficiency with a BLDC in a DC home compared to what we
have today? If so, thatâs news to me. Where can I learn more
about that?
The trade-off between, say, one (relatively) high voltage DC bus
throughout the home vs many branches with lower discrete voltages
is indeed a problem. With AC, we took the bus approach, running
120v everywhere (in the U.S., higher elsewhere). Iâm inclined to
say we should keep doing that for flexibility and predictability.
But itâs a trade off, like you said. It would obviously help if
regulatory and standards bodies came out with official
recommendations.
samus wrote 19 hours 17 min ago:
Things like washing machines, dryers, dishwashers, air
conditioners, or fridges spend a lot of energy by running
powerful electrical motors, which should benefit from AC.
Everything else I can think of in a typical household is
basically a mere heater that in principle works equally well with
AC and DC of the correct voltage. Even computers can be said to
mostly care about the correct voltage since AC->DC conversion is
vastly easier than voltage conversion.
shiroiuma wrote 13 hours 3 min ago:
>Things like washing machines, dryers, dishwashers, air
conditioners, or fridges spend a lot of energy by running
powerful electrical motors, which should benefit from AC.
No, they don't, not at all.
Most modern appliances have variable-speed motors these days.
You can't do that by just connecting AC to a motor; you need a
control board to generate the waveforms necessary to make the
motor turn at the speed and direction you want. That control
board has to be fed with DC power. (Source: I used to design
BLDC motor control systems)
Only really simple appliances, like old-fashioned
horribly-inefficient clothes dryers, still use AC induction
motors, and those are mostly being phased out. (Bathroom fans
also need AC; they're usually cheap synchronous reluctance
motors.)
So it really doesn't matter much whether the incoming power is
AC or DC these days, unless you have a bunch of ancient
appliances that still use induction motors. If it's AC, it's
going to be rectified and fed into a DC-to-DC converter to
create the lower DC voltages needed. If it's a higher DC
voltage, we can skip the rectification step and not worry much
about ripple.
zarzavat wrote 19 hours 49 min ago:
Probably 90% of my devices run 5V DC or similar, but you can't
run that through a home so you're back to needing AC. If you're
going to have AC and DC then you might as well just have AC.
sholladay wrote 17 hours 24 min ago:
> Probably 90% of my devices run 5V DC or similar,
Indeed. And thatâs quite normal. Our electrical system should
serve our modern needs.
> but you can't run that through a home
5V might be too low for that length of wire. But you could most
definitely have a low voltage line in your house that we could
design around, maybe 12V. Electric vehicles are moving towards
48V for accessories. It seems like lack of a standard is
holding us back more than anything else.
Or we could just keep doing 120V in the walls, with a DC
supply. Modern DC-to-DC voltage converters are very efficient
and small. But maybe Iâm wrong. A lot of people seem to
believe they are still not good enough yet for such a change to
make sense.
> If you're going to have AC and DC then you might as well just
have AC.
I arrive at the opposite conclusion. Most things are natively
DC. So therefore, power in the walls should be DC and we should
covert it to AC near the endpoint where necessary.
Retric wrote 22 hours 25 min ago:
Of grid homes are vastly more concerned with the energy efficiency of
their appliances and thus DC refrigerators generally have more
insulation. Most AC customers prefer more internal volume for food
over slightly increased efficiency.
AC motors are using way more power than the puddly control boards in
most home appliances. So you lose a little efficiency on conversion
but being 80% efficient doesnât matter much when itâs 1-5% of the
devices energy budget. You generally gain way more than that from
similarly priced AC motors being more efficient.
sholladay wrote 21 hours 42 min ago:
I agree with everything you said, except it seems like a false
dichotomy. We can clearly build DC refrigerators with more or less
insulation. We can clearly build them large or small. If you want
to prioritize volume, then surely you could do that with DC. Right?
I know that a long time ago DC-to-DC voltage converters were very
large in size, which meant AC would win on space efficiency. But
unless Iâm mistaken, thatâs no longer the case. Wouldnât a DC
refrigerator with equivalent insulation and interior volume have
nearly identical exterior dimensions as an AC refrigerator?
Retric wrote 18 hours 36 min ago:
> Wouldnât a DC refrigerator with equivalent insulation and
interior volume have nearly identical exterior dimensions as an
AC refrigerator?
Sure, but itâs important to separate what could be built from
what is being built based on consumer preferences and buying
habits. The average refrigerator could be significantly quieter,
but how often do people actually listen to what they are buying?
People buying Teslaâs didnât test drive the actual car they
were buying so the company deprioritized panel gaps. And so
forth, companies optimize in ways that maximize their profits not
arbitrary metrics.
notorandit wrote 23 hours 15 min ago:
It does make a whole lot is sense.
The amount of energy you loose to convert AC to DC can be humongous .
And useless if you produce your own power (normally already in DC).
gwbas1c wrote 1 day ago:
Anyone notice that 400V and 800V are also used in EV battery
architecture? I wonder if there's any sharing of technology?
pjdesno wrote 1 day ago:
90% of the power in our academic data center goes 13.8kV 3-phase ->
400v 3-phase, and then the machines run directly from one leg to
neutral (230v). One transformer step, no UPS losses, and the server
power supplies are more efficient at EU voltages.
But what about availability? If you ask most of our users whether
theyâd prefer 4 9s of availability or 10% more money to spend on
CPUs, they choose the CPUs. We asked them.
There are a lot of availability-insensitive workloads in the commercial
world, as well, like AI training. What matters in those cases is how
much computing you get done by the end of the month, and for a fixed
budget a UPS reduces this number.
poemxo wrote 20 hours 22 min ago:
Really you're down for over an hour a year? Unscheduled?
chromacity wrote 1 day ago:
> and then the machines run directly from one leg to neutral (230v)
And then every machine has a switching power supply to convert this
to low-voltage DC, and then probably random point-of-load converters
in various places (DC -> AC -> DC again) for stuff like the CPU / GPU
core, RAM, etc. Each of these stages may be ~95% efficient with
optimal load, but the losses add up, and get a lot worse outside a
narrow envelope.
Dylan16807 wrote 15 hours 18 min ago:
Yes, but it's not like any other layouts avoid those issues.
You could feed your servers off fat 12/24/48 volt supplies but with
how much power a modern server can pull you're already converting
in bulk even if you don't do that, limiting the potential
advantages. For running CPU/GPU/RAM, there is no other option.
When you need hundreds of amps at 1-2 volts, you convert that
centimeters away if at all possible.
A datacenter using DC distribution is still using high voltages and
stepping them down in layers. The hassle it avoids is in other
aspects of power delivery.
flossly wrote 1 day ago:
AC is also waaaay safer for households: since the power drop to to zero
100x (50Hz) per second switches are cheaper and safer, and
electrocution is less likely to happen.
fredgrott wrote 1 day ago:
That is about like aying the band AC DC had its revenge.....
can we stop vibe generating headlines?
saltyoldman wrote 1 day ago:
The large brick you have on all your tech when you plug it in is the
converter. AC works great for some applications, none of them really
technical in nature.
amluto wrote 1 day ago:
I wonder how much of the benefit is simpler redundant power equipment.
For AC, you have standby UPSes and line-interactive UPSes and frequency
and phase synchronization. And everything needs a bit more hold-up
time because, in case of failure, your new power supply might be at a
zero crossing.
For 800V DC, a simple UPS could interface with the main supply using
just a pair of (large) diodes, and a more complex and more efficient
one could use some fancy solid state switches, but thereâs no need
for anything as complex as a line-interactive AC UPS.
Animats wrote 1 day ago:
800V to each rackmount unit, with hot plugging of rack units? That's
scary.
The usual setup at this voltage is that you throw a hulking big switch
to cut the power, and that mechanically unlocks the cabinet. But that's
not what these people have in mind.
They want hot-plugging of individual rackmount units.
GE has a paper about the power conversion design, but it doesn't
mention the unit to rack electrical and mechanical interface. Liteon is
working on that, but the animation is rather vague.[2] They hint at hot
plugging but hand-wave how the disconnects work.
Delta offers a few more hints.[3] There's a complex hot-plugging
control unit to avoid inrush currents on plug-in and arcing on
disconnect. This requires active management of the switching silicon
carbide MOSFETs.
There ought to be a mechanical disconnect behind this, so that when
someone pulls out a rackmount unit, a shutter drops behind it to
protect people from 800V. All these papers are kind of hand-wavey
about how the electrical safety works.
Plus, all this is liquid-cooled, and that has to hot-plug, too. [1] [2]
(HTM) [1]: https://library.grid.gevernova.com/white-papers-case-studies/a...
(HTM) [2]: https://www.youtube.com/watch?v=CQOreYMhe-M&
(HTM) [3]: https://filecenter.deltaww.com/Products/download/2510/20251016...
chris222 wrote 10 hours 28 min ago:
A high powered EV charger is 800 volts. Totally safe and outdoors in
thousands of places.
brucedawson wrote 12 hours 39 min ago:
It's easy to make these 800V systems totally safe. You just have to
combine this idea with the extremely sensible plan to put data
centers in space and then there will be no worry about when "someone
pulls out a rackmount unit" because there not be someone within
hundreds of kilometers.
hinkley wrote 19 hours 20 min ago:
The power connectors will be on the far side of the rack from the
service side so shouldnât be a problem for humans touching the
third rail so to speak.
With that sort of voltage you should be able to use a capacitive or
inductive sensor to activate a relay.
mikewarot wrote 16 hours 23 min ago:
With a power rail that could supply kiloamps of fault current, thus
megajoules of energy into an arc, I wouldn't be so sure of that.
Copper vapor inhalation is a definite possibility and a horrible
way to die.
riedel wrote 20 hours 54 min ago:
An EV fast charger can do 1000V, so with a bit of logic that sounds
doable.
t0mas88 wrote 20 hours 29 min ago:
EV chargers take a different approach. There is no power on the
connector while you're plugging it in. It then locks in place
before the contactor closes and power is delivered. Unplugging is
the same, power is removed before the plug is unlocked for release.
reportingsjr wrote 11 hours 14 min ago:
This is effectively how hot swapping is done for may modern
systems. It seems counter intuitive to call it hot plugging, but
itâs what youâll find if you look up âhot swap
controllerâ.
dotancohen wrote 12 hours 27 min ago:
Do the EV chargers not have an alternative disconnect sequence
for when the two sides are forcibly mechanically separated?
Either by accident, malicious intent, or mechanical failure of
some component.
elif wrote 21 hours 1 min ago:
As long as you can control for fire, electrical safety seems like a
temporary condition as robots and intelligent machines are cheaper
and more available long term solution to hot swap blades in
datacenter racks.
elif wrote 17 hours 20 min ago:
Dear downvoters: softbank has been optimizing their datacenters
for robotic technicians since 2020.
They are about to have fully human free datacenters by the end of
this year.
When you are designing long term goals with datacenters, as I
explicitly mentioned talking about, you can't ignore automation.
lmm wrote 12 hours 17 min ago:
> Dear downvoters: softbank has been optimizing their datacenters
for robotic technicians since 2020.
> They are about to have fully human free datacenters by the end
of this year.
What I'm hearing is that they've been trying to build a
human-free datacenter for 6 years and they haven't done it yet.
What's the betting that that "end of this year" schedule slips
further?
QuantumGood wrote 20 hours 44 min ago:
I think you're being downvoted for speaking of a complex future
possibility ("robots and intelligent machines ... solution") as if
it was a proven commodity. There will be many twists and turns in
the path to the possible reliability, scalability, and cost
effectiveness of robots and intelligent machines.
elif wrote 19 hours 54 min ago:
It is a proven commodity already. Just not in our
behind-the-curve country.
Look at NTT Data or SoftBank.
(HTM) [1]: https://www.softbank.jp/en/sbnews/entry/20250917_01
QuantumGood wrote 11 hours 30 min ago:
Appreciate your effort to provide reference info. Near the end
it says "part of SoftBankâs efforts to implement robotic
automation at [one] Data Center scheduled to start operating
[no later than April 1 2027]".
They literally speak of preparing for a future that does not
yet exist. I am optimistic it will exist, but that's not the
same thing as it already happening and having a track record of
reliability and profitability. I could find no mention of
robots actually doing anything at that link. The article is
about prepping servers, not specifically about robotics, in the
same sense that planning hoses for gas pumps at gas stations is
not about building cars.
elif wrote 20 hours 10 min ago:
Yea I literally said long term but HN voters have such a hate
boner for anything adjacent to AI
dist-epoch wrote 1 day ago:
Or maybe you can require technicians to be in full-protection
electrical suits.
rdtsc wrote 1 day ago:
It is a pretty clever design
> When it is detected that the PDB starts to detach from the
interface, the hot-swap controller quickly turns off the MOSFET to
block the discharge path from Cin to the system. After the main power
path is completely disconnected, the interface is physically
detached, and no current flows at this time
> For insertion, long pins (typically for ground and control signals)
make contact first to establish a
stable reference and enable pre-insertion checks, while short pins
(for power or sensitive signals)
connect later once conditions are safe; during removal, the sequence
is reversed, with short pins
disconnecting first to minimize interference.
contravariant wrote 1 hour 7 min ago:
The phrase "when it is detected" makes me nervous.
Animats wrote 1 day ago:
Yes, I read that. There had better be a backup system. MOSFETs tend
to fail ON, and there's a megawatt going into each rack.
Somehow this seems the wrong approach to AI.
rdtsc wrote 10 hours 50 min ago:
I figure the latch-up failure mode is a known failure mode. It's
not something totally unexpected.
> Somehow this seems the wrong approach to AI.
One a more ironic level, it's seems on par with the whole AI
approach!
superxpro12 wrote 23 hours 52 min ago:
Fail spectacularly
Data center workers are gonna need those big yoink sticks and
those thick arc-fault bibs that furnace operators wear.
Animats wrote 21 hours 29 min ago:
McMaster-Carr has the personal protective equipment required
for 800V:
Flash protection face shields [1] and Class 0 electrical
protection gloves.[2]
It's not that bad. It's just ordinary industrial protective
gear. [1]
(HTM) [1]: https://www.mcmaster.com/products/arc-flash-protection...
(HTM) [2]: https://www.mcmaster.com/products/electrical-protectio...
neoCrimeLabs wrote 1 day ago:
The datacenter I built in 2007 was DC.
Many datacenters I'd been to at that point were already DC.
Didn't think this was that new of a trend in 2026, but also acknowledge
I did not visit more than a handful of datacenters since 2007.
It just seemed like a undenyably logical thing to do.
jeffbee wrote 22 hours 19 min ago:
It's obviously not new. ±400VDC architecture was presented at Open
Compute last year, which is a fair indicator that the presenter had
put it into practice at least 5 years prior to disclosing it. 48VDC
distribution within a rack, and 48-to-1V direct regulators for CPUs,
were both contributed to OCP 7 years ago, at which point they were
both old hat. And 48VDC telco junk is, of course, totally ancient.
b00ty4breakfast wrote 1 day ago:
They're still converting from AC to DC at the datacenter, it just isn't
being stepped down at the perimeter. There is no transmission of HVDC
going on. This isn't really Edison's revenge, more like his consolation
price, ha!
skullone wrote 1 day ago:
Transitioning? It already happened decades ago. Only smaller
scale/generic or less proficient "we bought all Dell and HP" use AC. At
large scale it's been a ton of DC for literally decades. And for 70
years in telco and network gear.
KnuthIsGod wrote 1 day ago:
Waiting for home DC.
It is silly to have AC to DC converters in all of my wall connected
electronics ( LED bulbs, home controller, computer equipment etc )
gwbas1c wrote 1 day ago:
Assuming you live in a "large" western home, it's impractical.
Remember, Edison's first power grid operated at 110/220v DC to the
home. If there was lower voltage (IE, 12 volts) going from the street
to your walls, the line loss would be significant. It only works in
RVs and shacks because the wires are short.
Thus, even if you had DC in the walls, it would be 100+ volts, and
you'd still have conversion down to the lower voltages that
electronics use. If you look at the comments in this thread from
people who work in telco, they talk about how voltage enters
equipment at -48V and is then further lowered.
hahn-kev wrote 1 day ago:
It's called USB power delivery
est wrote 1 day ago:
home appliances have lower voltage, like 12V or 5V. The wire loss and
heat would be a problem.
scarecrowbob wrote 1 day ago:
Well, having spent some time operating a 12VDC system last year when
I moved into some shacks, I will say that I find it a lot more
convenient to run 120VAC.
I end up converting stuff anyhow, because all my loads run at
different voltages- even though I had my lights, vent fan, and heater
fans running on 12V I still ended up having to change voltages for
most of the loads I wanted to run, or generate a AC to to charge my
computer and run a rice cooker.
Not to mention that running anything that draws any real power
quickly needs a much thicker wire at 12V. So you're either needing
to run higher voltage DC than all your loads for distribution and
then lowering the voltage when it gets to the device, or you simply
can't draw much power.
Not that you can't have higher voltage DC; with my newer system the
line from my solar panels to my charger controller is around 350VDC
and I can use 10awg for that... but none of the loads I own that draw
much power (saws, instapot, rice cooker, hammond organ, tube guitar
amp) take DC :D
mauvehaus wrote 23 hours 14 min ago:
Do you have a website with your system on it? I have an off-grid
building I need to add solar to in the next year or so. After I fix
the foundation and roof, of course. Naturally Iâm exploring
options for item 387 on the todo list instead of think about how
Iâm going to jack the building up.
scarecrowbob wrote 21 hours 59 min ago:
It's a pretty simple system:
4KW of panels, 400W 48V
EG4 6000XP charge controller/ inverter
3x EG4 LifePower4 48V batteries
a raspberry pi running solar assistant
I feels like a bit overkill, and there is still a whole mppt
unused on the 6000xp so I could still double my panel input.
Also solar assistant tells me that I rarly go below 75% battery
storage. If I just wanted to run my fridge and assorted
convenience loads (and ran things like table saws off a
generator) then I could get away with a lot less of a system.
But I'm operating a recording studio, and there were a couple
days this winter where I had a full-band session and a couple
days of storms and got down to below 50%.
jazzyjackson wrote 1 day ago:
Catch me wiring my house with 20V USBC ;)
ternus wrote 1 day ago:
The lesser-known instance of this is RV power. When you're running
off small batteries and solar, you want to make the best use of the
watt-hours you have, and that means avoiding the DC-to-AC-to-DC loop
wherever possible. So you run 12V (or in newer models, higher
voltage) versions of everything, upconverting as necessary.
amluto wrote 1 day ago:
I am really skeptical that 12VDC power distribution in RVs actually
saves power compared to a high-quality (hah!) higher voltage AC or
DC system. 12V is absurdly low and you canât easily lose quite a
few percent in resistive losses even with fairly large cables, and
those large cables are quite unpleasant to work with and rather
dangerous.
ternus wrote 11 hours 38 min ago:
The vast majority of what you're running from RV DC are things
like lights, fans, phone chargers, and other
cigarette-plug-adapter type devices. My RV has a 12V DC fridge.
For anything more - particularly air conditioning - you need AC
for sure.
My inverter-charger is connected to my batteries with 4/0 cable.
That wasn't fun to run.
saltyoldman wrote 1 day ago:
I tried using a microwave off the RV batteries, your inverter
needs 4/0 cable. Very "fun".
jacquesm wrote 1 day ago:
Not going to happen. For the same reason that the US never converted
to a higher domestic voltage even though there are many practical
advantages. The transition from one system to another at the consumer
level would be terrible, even if there would be some advantage (and
I'm not sure the one you list is even valid, you'd get DC-DC
converters instead because your consumers typically use a lower
voltage than the house distribution network powering your sockets) it
would be offset by the cost of maintaining two systems side by side
for decades.
You could wire your house for 12, 24 or 48V DC tomorrow and some
off-grid dwellers have done just that. But since inverters have
become cheap enough such installations are becoming more and more
rare. The only place where you still see that is in cars, trucks and
vessels.
And if you thought cooking water in a camper on an inverter is tricky
wait until you start running things like washing machines and other
large appliances off low voltage DC. You'll be using massive cables
the cost of which will outweigh any savings.
zahlman wrote 17 hours 58 min ago:
... or we could have both sets of wiring, and use what's
appropriate for the task/appliance?
throw0101c wrote 1 day ago:
> Not going to happen. For the same reason that the US never
converted to a higher domestic voltage even though there are many
practical advantages.
It would be relatively easy for the US to go to 240V: swap out
single-pole breakers for double-pole, and change your NEMA 5 plugs
for NEMA 6.
For a transition period you could easily have 240V and 120V plugs
right next to each other (because of split phase you can 'splice
in' 120V easily: just run cable like you would for a NEMA 14 plug:
L1/L2/N/G).
What would be the real challenge would be going from 50 to 60Hz.
rkomorn wrote 1 day ago:
> What would be the real challenge would be going from 50 to
60Hz.
Other way around, no? The US is already 60Hz.
Edit: I mostly remember this because the SNES games I used to buy
in the US and brought back to Europe ran noticeably slower.
wincy wrote 1 day ago:
I just wish I could run my air conditioner and my desktop computer
at the same time without flipping the breaker. The RTX 5090 is a
space heater and will easily peg at the 600W itâs rated for, and
so with that and an air conditioner window unit, I have to run a
long cable from another unused room if I want to do anything that
stresses the video card.
zahlman wrote 17 hours 29 min ago:
If you're running an air conditioner and a "space heater" at the
same time it might be worth reconsidering your priorities.
I can watch 1080p video on YouTube and it runs in an up-to-date
web browser using less than 50% CPU on 12-year-old hardware with
8GB of RAM and a graphics card that was a budget option at the
time (my searches indicate it draws at most 80W, though it
expects a 500W PSU for some reason).
jacquesm wrote 1 day ago:
You can use nvidia-smi to reduce the powerdraw of the card to
just below what will trip the breaker.
SoftTalker wrote 1 day ago:
I'm not sure it's likely, but I could see DC lighting start to
happen in new construction. Have a single AC-to-DC converter off
the main service entrance that powers hard-wired LED lighting
fixtures in the house. Would probably be better than running the
individual (and usually very low quality) converters in dozens of
standard LED light bulbs. Would need to be standardized, codified,
etc. so probably not happening soon.
ansgri wrote 1 day ago:
Would be more practical to have a single 50-300W AC-DC 24V PSU
per room or group of rooms, then pull relatively short DC cables
to each light. A multichannel light controller could also be
placed nearby, and then if you need fully-featured brightness and
color control, only a small PWM amplifier could be placed at each
light if distance from controller to each light is too long to
transmit PWM power directly.
manwe150 wrote 1 day ago:
I suppose that still begs the question somewhat, since the US does
have 240V (2 phase) already driving many appliances. Why hasnât
it ever become standard for luxury kitchens to have a
European-style outlet for use with a European kettle? I know the US
already has a different 240V plug shape, so it might have to be an
unlicensed installation, but surely someone wanted hot tea faster
and did that calculus before?
shiroiuma wrote 9 hours 3 min ago:
>Why hasnât it ever become standard for luxury kitchens to have
a European-style outlet for use with a European kettle? I know
the US already has a different 240V plug shape, so it might have
to be an unlicensed installation, but surely someone wanted hot
tea faster and did that calculus before?
I've heard of Americans getting EU plugs for things like this,
but it's extremely uncommon. The simple answer is: Americans
just don't drink tea very much, and the ones who do aren't going
to go to this much trouble and expense just to be able to boil
water for their tea twice as quickly.
fragmede wrote 8 hours 44 min ago:
If speed is the issue, Japanese water boilers keep water at or
near boiling so there's less of a wait, and they operate on
110v.
xoxxala wrote 1 day ago:
Technology Connections did this with an EV battery charger:
(HTM) [1]: https://youtu.be/INZybkX8tLI
bregma wrote 1 day ago:
> but surely someone wanted hot tea faster
No one in the USA drinks hat tea. The choices (and it tends to be
regionally-based) is sweet or unsweet tea. No need to boil a
kettle quickly for that.
zahlman wrote 17 hours 55 min ago:
> The choices (and it tends to be regionally-based) is sweet or
unsweet tea.
... Unless you're buying it pre-made, does this not still start
with making hot tea the regular way? Or what exactly are you
doing with the tea bags and loose tea from the supermarket?
vel0city wrote 22 hours 41 min ago:
As a counter argument, things like pour over coffee is getting
to be more popular in the US and older drip coffee makers seem
to be getting slightly less popular.
Still though, I don't seem to see most of those people
seriously clamoring for the electric kettle to go a bit faster.
The cost for the wiring difference and dealing with odd
imported kettles just isn't worth it generally.
mauvehaus wrote 23 hours 19 min ago:
> No one in the USA drinks h[o]t tea.
There are dozens of us.
Perplexingly I was traveling in one of the iced tea regions of
the country in need of a cup of hot tea, and they had no way to
make it. Like, you have a commercial coffee maker and hot cups,
the coffee maker has a hot(ish) water tap. All you need is a $4
box of teabags thatâll last until the heat death of the
universe. Nope.
margalabargala wrote 23 hours 25 min ago:
What? Plenty of people in the US drink hot tea.
fc417fc802 wrote 1 day ago:
Ahckhually US residential is split single phase, not two phase.
[1] I think the answer to your question is that it mostly doesn't
matter for personal mug size quantities of hot water and if it
does matter to you there are readily available competing options
such as dedicated taps for your kitchen sink.
Perhaps the biggest reason is that a traditional kettle on any
half decent electric range will match if not exceed the power
output of any imported electric kettle. Many even go well beyond
that with one burner marked "quick boil" or similar.
(HTM) [1]: https://en.wikipedia.org/wiki/Split-phase_electric_power
lostlogin wrote 20 hours 12 min ago:
I use an induction stove on maximum to boil water as I get
irritated at the time it takes to boil water with 240v.
Iâm surprised that American exceptionalism can tolerate half
powered sockets.
MrBuddyCasino wrote 10 hours 31 min ago:
The induction stove boost function is glorious. Using twice
the power temporarily is such a timesaver!
vessenes wrote 1 day ago:
Most important comment here!! I would love to buy like a 6kw
battery induction kettle for the states. As far as I can tell,
they donât exist.
jcalvinowens wrote 1 day ago:
I wired a UK kettle to an unused 240V range outlet in the US
once. It was amazing, boiled a liter of water in just under a
minute. Obviously kinda sketchy.
zahlman wrote 17 hours 57 min ago:
"Wired"?
...There was some kind of switch involved, I hope?
jacquesm wrote 1 day ago:
That's more like it :)
tbrownaw wrote 1 day ago:
> I know the US already has a different 240V plug shape, so it
might have to be an unlicensed installation, but surely someone
wanted hot tea faster and did that calculus before?
How expensive would a proper AC->DC->AC brick for that power
level be?
jacquesm wrote 1 day ago:
Not so simple, you'd have to use a 'drier' or 'welder' socket
for that otherwise you won't have enough power. A single
circuit in Europe is 240V 16A or 3840W!
A pure sinewave inverter for that kind of power is maybe 600 to
1000 bucks or so, then you'd still need the other side and
maybe a smallish battery in the middle t stabilize the whole
thing. Or you could use one of those single phase inverters
they use for motors.
ianburrell wrote 1 day ago:
You can run 240V circuit to kitchen for kettle and put in NEMA 6
outlet. But few people care about fast boil and importing
European kettle. Most people use the microwave or stovetop, and
120V kettles are fine in most cases. It will never become a
standard thing.
jacquesm wrote 1 day ago:
Well, as you say, it would not be according to code and the
insurance company might have something to say about it. It's also
single phase but not quite the way you do it in the USA, it would
be a neutral and a phase whereas in the USA I think it is 2x110.
Finally, it's 50 Hz rather than 60 which would work fine for
resistive loads but not so well for inductive ones such as
transformers and motors.
In all likely not worth the trouble. When I moved to Canada I
gave away most of my power tools for that reason and when I moved
back I had to do that all over again.
aidenn0 wrote 1 day ago:
> In all likely not worth the trouble. When I moved to Canada I
gave away most of my power tools for that reason and when I
moved back I had to do that all over again.
If you ever have to do it again, you can probably get a
transformer rated high enough for power-tools for cheaper than
replacing all of your power tools.
mauvehaus wrote 23 hours 24 min ago:
The line frequency tends to screw with things with motors
too. Moved from the US to Belgium back when compact cassette
was a common format for music.
Killed a few tapes with a transformer on a US tape deck
before buying a 220V 50Hz unit. No, I donât remember if the
pitch was grossly off, but Iâm guessing it wasnât.
jacquesm wrote 1 day ago:
Of course you can. That's kind of obvious. It is also highly
impractical. Besides the frequency delta you end up having to
lug a heavy transformer along and then you have to alternate
it across your tools so you don't end up frying the
transformer.
Aloisius wrote 1 day ago:
This article seems to imply that 800V DC is high-voltage DC, but that
seems quite low.
bigiain wrote 1 day ago:
I think there'a a regulatory "Low Voltage" definition of "below 50V",
which has implications around whether you need to be a licensed
electrician to install it or not. Anything above that is - for at
least some purposes - considered "High Voltage".
Other people, of course, have other definitions of high voltage:
"This resonant tower is known as a Tesla coil. This particular one
is just over 17 feet tall and it can generate about a million volts
at 60,000 cycles per second."
and:
"This pulse forming network can deliver a shaped pulse of over 50,000
amps with a total energy of about 1,057 times the tower primary
energy"
(HTM) [1]: https://www.youtube.com/watch?v=RoGbrgOhPes
MathMonkeyMan wrote 1 day ago:
Quite low compared to a power utility's HVDC, but quite high compared
to the 5/12/24 V output of most AC/DC converters used for
electronics.
adrr wrote 1 day ago:
Our houses should be DC. So wasteful to have all these bricks to
change to AC to DC.
flowerthoughts wrote 1 day ago:
I'm renovating a house, and have been considering 24V or 48V DC
outlets in a few rooms. Semiconductors become more expensive above
~32V, so 24V might be the sweetspot.
However, there's also PoE (24 or 48V!), so maybe that's the right
approach. It's not like each outlet is going to run a heater anyway.
fc417fc802 wrote 1 day ago:
Lower voltage makes voltage drop across the line proportionally
worse. Depending on the purpose PoE is probably the way to go since
the wiring and hardware is all standardized and safety certified.
Unless you mean running AC and installing inverters in the wall?
What is this even for? All my electronics are DC but critically
they all require different voltages. The only thing I might benefit
from would be higher voltage service because there are times that
15 A at 120 V doesn't cut it.
flowerthoughts wrote 5 hours 23 min ago:
No, I meant running separate DC wires. I'm Europe, so it's 240
VAC vs 24/48 VDC. For small devices, 24 V would be useful in that
you don't require an isolated SMPS, so cheaper endpoints are
possible. Slightly less risk of burning down the house with some
cheap Chinese AC/DC. 24 V is still high enough to use USB PD/PPS
at 20 V, and I doubt I'll run enough current that the losses due
to lower voltage would be a problem.
For PoE, I thought it was standardized at 48 V, but I see lots of
cameras run at 24 V, and I think I've even seen 12 V. Seems a bit
of a mess.
Mistletoe wrote 1 day ago:
Modern bricks really arenât that inefficient though. An Apple
charger is like 90% efficient. A DC to DC converter is about that
efficient or worse.
catlikesshrimp wrote 1 day ago:
The power adapters became so efficient that we have to transition
to wireless charging to keep it down
The irony...
epx wrote 1 day ago:
Having a single big DC converter at a home would help a lot with
power factor (LED lamps connected directly to AC have terrible power
factor).
jwilliams wrote 1 day ago:
There are niches where DC makes sense - low-voltage lighting, USB/LED
ecosystems.
Once you get into higher power (laptops and up), switching and
distribution get harder, so the advantages fade.
For bigger appliances (fridge, etc), AC is fine + practical.
adiabatichottub wrote 1 day ago:
Your modern fridge is probably going to have an inverter-driven
motor, so you're right back to using DC.
adrr wrote 1 day ago:
All modern appliances and HVACs are using inverter drive motors
for efficiency. Brushless DC motors are more efficient though.
userbinator wrote 1 day ago:
"Brushless DC motors" are actually just AC synchronous motors.
bigiain wrote 1 day ago:
Sure, maybe?
If your house gets 800V DC you're still gonna need "bricks" to
convert that to 5VDC of 12VDC (or maybe 19VDC) that most of the
things that currently have "bricks" need.
And if your house gets lower voltage DC, you're gonna have the
problem of worth-stealing sized wiring to run your stove, water
heater, or car charger.
I reckon it'd be nice to have USB C PD ports everywhere I have a
220VAC power point, but 5 years ago that'd have been a USB type A
port - and even now those'd be getting close to useless. We use a
Type I (AS/NZS 2112) power point plug here - and that hasn't needed
to change in probably a century. I doubt there's ever been a low
voltage DC plug/socket standard that's lasted in use for anything
like that long - probably the old "car cigarette lighter" 12DC thing?
I'm glad I don't have a house full of those.
torginus wrote 1 day ago:
I've had discussed with people familiar with the matter, and they
convinced me its really not worth it for many reasons, the main one
being safety - DC arcs are self sustaining - AC voltage constantly
goes to zero, so if an arc were to form, it gets auto extinguished
when the voltage drops. With DC this never happens, meaing every
switch or plug socket can create this nice long arcs and is a
potential fire hazard.
jacquesm wrote 1 day ago:
The 'what is safer' question for DC and AC at the same effective
current and power has a mixed set of answers depending on
conditions. For instance, DC is more likely to cause your muscles
to contact and not let go (bad), but AC is more likely to send your
heart into ventricular fibrillation (sp?, also bad).
AC arcs are easier to extinguish than DC arcs, but DC will creep
much easier than AC and so on.
From a personal point of view: I've worked enough with both up to
about 1KV at appreciable power levels and much higher than that at
reduced power. Up to 50V or so I'd rather work with DC than AC but
they're not much different. Up to 400V or so above that I'd much
rather have AC and above 400V the answer is 'neither' because
you're in some kind of gray zone where creep is still low so you
won't know something is amiss until it is too late. And above 1KV
in normal settings (say, picture tubes in old small b&w tvs and
higher up when they're color and larger) and it will throw you
right across the room but you'll likely live because the currents
are low.
HF HV... now that's a different matter and I'm very respectful of
anything in that domain, and still have a burn from a Tronser
trimmer more than 45 years after it happened. Note to self: keep
eye on SWR meter/Spectrum analyzer and finger position while
trimming large end stages.
Tempest1981 wrote 1 day ago:
> DC will creep much easier than AC
Can you say more about "creep"? Is the resistance changing? Or is
material actually migrating?
Also curious why it's worse using DC.
jacquesm wrote 1 day ago:
(HTM) [1]: https://www.eevblog.com/forum/beginners/understanding-...
Tempest1981 wrote 21 hours 11 min ago:
Thanks Jacques. So creepage is when current flows/arcs across
the surface of an insulator, vs through the air. And it's
worse with DC due to its unidirectional nature. Worsens when
pollution builds up, or the surface degrades.
jacquesm wrote 20 hours 16 min ago:
Indeed. And it's a really nasty thing to properly protect
against because that pollution, especially with stuff that
is unattended for a long time has a habit of ending up much
worse than your worst fantasies. I've taken more than one
electrocuted mouse out of the HV section of older color TVs
for instance. Up to 250V or so it is manageable, above that
you can get the weirdest problems including completely
invisible arcing where the only giveaway is the ozone smell
and the occasional click. Looking at HV circuitry in the
dark or by putting a flame near a suspect spot is a great
way to spot these kind of issues.
adiabatichottub wrote 1 day ago:
Really depends on what we're talking about. A lot of electrical
safety equipment has a DC rating, usually something like
90VDC/300VAC. Also, most DC equipment just isn't going to have the
stored energy to generate a big arc. Well, except batteries, and
we're already piling them all around us.
torginus wrote 1 day ago:
I mean it depends, but for dual rated stuff has both a voltage
and current limit, both of which are way lower.
Like typically a 230V/20A AC switch can switch 24VDC/2A. And the
energy is not in the equipment, its in the mains (or batteries
like you said, or PV panels)
adiabatichottub wrote 1 day ago:
Right, but that's why I mentioned safety equipment. Your
common DIN-mount UL-489 branch circuit breaker will be rated
for the same trip current, same short circuit current rating
(SCCR), but lower voltage. So you can use the same wiring and
breakers as you might have with AC and your 48V battery bank
won't vaporize the $5 hardware store toggle switch that somehow
became a shunt.
torginus wrote 1 day ago:
I mean, most AC circuit breakers use electromagnets to trip
on overcurrent (as well as bimetallic strips using thermal
methods for sustained high current).
Electromagnets dont work for DC, so your breaker will never
trip. For thermal protection, you need current, so that
checks out, and it would make sense for it to be rated under
50V as thats considered the highest voltage thats not life
threatening on touch.
PV Batteries in general have a very high current (100s of A)
at ~50Vish volts, so I dont think there's a major usecase for
using household breakers for them.
Im still not getting your point BTW, switches and breakers
are two separate things, with different workings, and
household (and datacenter) DC would be I think around 400ish
V, which is a bit higher than the peak voltage of AC, but
still within the arc limits of household wiring (at least in
230V countries).
The advantage of DC is that you use your wiring more
efficiently as the mean and peak wattage is the same at all
times. Going with 48V would mean high resistive losses.
adiabatichottub wrote 19 hours 43 min ago:
> Electromagnets dont work for DC, so your breaker will
never trip.
If electromagnets don't work for DC then what am I supposed
to do with this pile of DC solenoids and relays? ;)
> PV Batteries in general have a very high current (100s of
A) at ~50Vish volts, so I dont think there's a major
usecase for using household breakers for them.
That's what the SCCR rating is for. When there's a fault
you're going to have a LOT of current flowing until your
safety kicks in. Something like the grid or a battery bank
will happily provide thousands of amps almost
instantaneously. Breakers designed for protecting building
wiring are rated for this. Now, most household breakers
aren't dual DC/AC rated, but you can actually buy DC rated
breakers that fit in a home panel (Square D QO series).
> Im still not getting your point BTW, switches and
breakers are two separate things, with different workings,
and household (and datacenter) DC would be I think around
400ish V, which is a bit higher than the peak voltage of
AC, but still within the arc limits of household wiring (at
least in 230V countries).
My point is that there isn't any material reason why DC
can't be as safe as AC, all the proper safety equipment
already exists. Extinguishing a DC arc during a fault is a
solved problem for equipment at household scale.
> The advantage of DC is that you use your wiring more
efficiently as the mean and peak wattage is the same at all
times. Going with 48V would mean high resistive losses.
I just mentioned 48V because it's a common equipment
voltage for household DC systems. 400V would be good for
big motors and resistive heating loads.
Regarding DC vs AC and wiring efficiency, talking about
mean vs peak wattage just confuses the issue. 1 volt DC is
1 volt RMS. It is an apples-to-apples comparison. If you
want to say "we can use 170VDC or 120VAC with the same
insulation withstand rating, and at lower current for the
same power", then that is absolutely true. But your
common 600V THHN building wire won't care if you're using
400V AC or DC, so it's mostly immaterial.
kccqzy wrote 1 day ago:
Thatâs actually a recent phenomenon. Before the age of electronics
most household appliances either worked with AC or DC equally well
(like incandescent bulbs) or worked well with AC only given the
technology at the time (think anything with a motor, fans, HVAC
compressors etc).
analog31 wrote 1 day ago:
Taking it to an extreme, the house I lived in while in grad school
had wall lamp fixtures that doubled as electric and gas lamps. At
some point I imagine it would have been possible to choose between
using electric or gas by either flipping the switch or turning a
valve. They said "Edison Patent" on them. We could have lit the
house on AC, DC, or gas.
Thinking about the failure modes gave me the heebie jeebies, but
the gas had been disconnected ages prior.
eszed wrote 1 day ago:
I lived in a 19th century house in San Francisco that had
gorgeous plaster work medallions on the ceilings - think cherubs
and fruits - in the middle of which were the light fixtures. One
day my dumb-ass flatmate made an ill-advised attempt to DIY his
light fixture and cracked the still-active gas line embedded in
the ceiling. Sometime in the 1920s - the date was printed on a
sticker in the electrical panel - when they electrified the
house, they'd wrapped the electrical wires around the gas pipes,
and left them otherwise in situ. Crazy stuff.
jazzyjackson wrote 1 day ago:
Itâs kind of fun that light switches predate electricity. I
think you used to turn a key, I guess you were turning a valve?
Now that I think of it using a key to operate a valve makes a lot
of sense but you donât see it too often, well, I guess you want
to turn things off without needing to find a keyâ¦
ericd wrote 1 day ago:
Something to consider, and something I got a vivid demonstration of
while playing with solar panels, DC arcs aren't self-extinguishing,
unlike AC arcs. At one point I stuck a voltage probe in, and the arc
stuck with it as I pulled the probe away. It also vaporized the metal
tip of the probe.
My understanding is that DC breakers are somewhat prone to fires for
this reason, too.
KaiserPro wrote 23 hours 31 min ago:
> My understanding is that DC breakers are somewhat prone to fires
for this reason, too.
I think its that DC breakers are more expensive, so people use AC
rated breakers instead. They are both rated for 400v @10 amps, its
the same thing right?
It turns out they are not, and most people, even electronics types
rarely play with 200v+ of DC.
ericd wrote 21 hours 27 min ago:
Yeah, I think this array was pushing 350-400V
toast0 wrote 1 day ago:
> DC arcs aren't self-extinguishing, unlike AC arcs. At one point I
stuck a voltage probe in, and the arc stuck with it as I pulled the
probe away. It also vaporized the metal tip of the probe.
It would have self-extinguished if you waited long enough for the
probe to vaporize.
bigiain wrote 1 day ago:
Heh - I vaporised a fairly large soldering iron tip (probably 4mm
copper cylindrical bar?), when I fucked up soldering a connector to
a big 7 cell ~6000mAHr LiPo battery and shorted the terminals.
Quite how I didn't end up blind or in hospital I don't know. It
reinforced just how much respect you need to pay to even low-ish
voltage DC when the available current was likely able to exceed
700A by a fair margin momentarily. I think those cells were rated
at 60C continuous and 120C for 5 seconds.
jacquesm wrote 1 day ago:
You got super lucky.
bigiain wrote 1 day ago:
Yep. Super super lucky. I suspect my reading glasses are the
only reason I can still see anything.
jacquesm wrote 1 day ago:
I have a couple of those narrow escapes one of which led me
to put a significant chunk of Eastern Amsterdam out of power.
Another involved Beryllium oxide. 9 lives are barely enough.
swamp_donkey wrote 1 day ago:
Ah! Perhaps you are a member of the gigawatt club? Eligible
for entry once you have accidentally tripped off 1000 MW of
load or generation! No sweeping that under the table
bigiain wrote 15 hours 58 min ago:
Somehow I simultaneously desperately want to be in that
club, and never want to be responsible for an event that
would let me join that club...
jacquesm wrote 1 day ago:
I'm the idiot that sent a fairly high voltage spike into
the grid setting off a cascade. Even years later I do not
fully understand how it could happen, you'd think the
grid would be low impedance enough to absorb a spike like
that. But it set off a cascade on a part of the local
grid that was known to be weak.
bigiain wrote 1 day ago:
I would read that book...
jacquesm wrote 1 day ago:
'Stupid stuff I've done and survived'...
ericd wrote 1 day ago:
heh man, I'm glad you got out of that easy, I definitely wore
safety glasses 100% of the time after my experience. I think a
lifetime of experience with dangerous wall outlets and harmless
little 1.5V/9V DC cells teaches us the wrong lessons about DC
safety. I've since heard stories of wrenches exploding when they
fall across EV high voltage battery terminals. Wrenches aren't
supposed to be explosive.
The electricians I was working with also told me stories about
how with the really big breakers, you don't stand in front of it
when you throw it, because sometimes it can turn into a cloud of
molten metal vapor. And that's just using them as intended.
scheme271 wrote 1 day ago:
A bunch of those big breakers require two people. One person in
a flash suit and another with a 2m long pole around the first
person. That way if an arc flash happens, the second person
can yank the first person to safety without also getting hurt.
pocksuppet wrote 1 day ago:
Why don't they use the pole to flip the breaker from 2m away?
defrost wrote 1 day ago:
Ruins the fun and interrupts instilling respect deep into
the bones of interns.
Allegedly
While on "work experience" from high school I was put on
washing power lines coming straight out of the local power
station near the ocean - lots of salt buildups to clear.
Same deal, flashover suits and occasional arcs .. and much
laughter from the ground operators who drifted the work
bucket close.
jacquesm wrote 1 day ago:
Those harmless 9V DC cells can do a lot of damage if you use
them right.
sobjornstad wrote 1 day ago:
This reminds me of the sailor who [decided]( [1] ) to measure
his internal resistance by pushing probes through the skin on
his thumbs and electrocuted himself with the 9V multimeter
battery.
(HTM) [1]: https://darwinawards.com/darwin/darwin1999-50.html
jacquesm wrote 20 hours 10 min ago:
Mythbusters time. Salty fluids can be remarkably
conductive. Blood qualifies. What's interesting though is
that you have to wonder if there isn't some contributing
factor here, as a kid I did this quite a few times, so
that's one more for that list of stuff that could have
killed me. At the same time: I didn't have nice insulation
piercing tips back then (I do now) and that may be what
saved me. I will definitely not try this again.
Another story in the same line is that I heard that a horse
got killed by contact with a lantern battery, but I don't
have any reference for that, just a story by a family
member that collected coaches.
bluGill wrote 1 day ago:
Amps - the old 48vdc telco data centers vaporized wrenchs once
in a while.
bandrami wrote 1 day ago:
I've worked overseas a lot and one thing that's really different from
2 decades ago is that I simply don't need a step-down transformer
anymore because every single thing I plug in converts to DC (or
otherwise accepts dual-voltage) anyways. So I have a giant collection
of physical plug adapters because every device I use just needs to
fit into the socket and takes care of it from there.
(My stand mixer is the lone sad exception)
747fulloftapes wrote 1 day ago:
Agreed!
I spent a few years getting flown out around the world to service
gear at different datacenters. I learned to pack an IEC 60320 C14
to NEMA 5-15R adapter cable and a dumb, un-protected* NEMA 5-15R
power strip. While on-site at the datacenters, an empty PDU
receptacle was often easy to find. At hotels, I'd bring home a
native cable borrowed from or given to me by the native datacenter
staff or I'd ask the hotel front desk to borrow a "computer power
cable," (more often, I'd just show them a photo) and they generally
were able to lend me one. It worked great. I never found a power
supply that wasn't content with 208 or 240V.
Example adapters: [1] or [2] *: Some fancier power strips with
surge suppression have a MOV over-voltage varistor that may burn up
if given 200V+, rendering the power strip useless. Hence,
unprotected strips are necessary.
(HTM) [1]: https://www.amazon.com/dp/B0FD7PHB7Y
(HTM) [2]: https://www.amazon.com/dp/B01IBIC1XG
umvi wrote 1 day ago:
I don't understand why new houses don't just have one high quality
AC/DC converter so you can just use LED lighting without every bulb
needing its own AC/DC converter. I imagine the light bulb cartel
wouldn't really like that.
amluto wrote 1 day ago:
Every decent LED would then need ⦠a switching power supply. LEDs
are current-driven devices, and you get the best efficiency if you
use an actual current-controlled supply. And those ICs are very, very
cheap now.
The part that would genuinely be cheaper is avoiding problematic
flicker. It takes a reasonably high quality LED driver to avoid 120Hz
flicker, but a DC-supplied driver could be simpler and cheaper.
ianburrell wrote 1 day ago:
What voltage do you use? Most DC stuff wants low voltage (5-48V), but
appliances need higher voltage like AC-level to get enough power over
existing wiring. The result is DC-DC converters every place that have
transformers now.
The gain from DC-DC converters is small and DC devices are small part
of usage compared appliances. There is no way will pay back costs of
replacing all the appliances.
gizmo686 wrote 1 day ago:
LED light bulbs exist exclusively for compatibility with Edison
sockets. Every LED fixture I have seen had a single transformer for
the entire fixture; and that transformer was reasonably separate from
the LEDs themselves.
fragmede wrote 1 day ago:
because shorts and voltage loss are a real issue at that scale.
Majromax wrote 1 day ago:
With modern technologies, that's power over ethernet or USB-C. Other
comments in this thread point out that the telephone service also
routinely used 48V for the ring signal.
However, higher DC voltage is riskier, and it's not at all standard
for electrical and building code reasons. In particular, breaking DC
circuits is more difficult because there's no zero-crossing point to
naturally extinguish an arc, and 170V (US/120VAC) or 340V
(Europe/240VAC) is enough to start a substantial arc under the right
circumstances.
Unfortunately for your lighting, it's also both simple and efficient
to stack enough LEDs together such that their forward voltage drop is
approximately the rectified peak (i.e. targeting that 170/340V peak).
That means that the bulb needs only one serial string of LEDs
without parallel balancing, making the rest of the circuitry
(including voltage regulation, which would still be necessary in DC
world) simpler.
fortran77 wrote 1 day ago:
Do you want your house to burn down? Lower voltages for LED lights
mean higher current.
bigiain wrote 1 day ago:
That's traded off against the increase efficiency of LED lighting,
at least compared to incandescent lighting. An LED "equivalent
replacement" for a typical incandescent globe is down around 1/10th
of the power. A 7Watt LED bulb is typically marketed as "60W
equivalent". If that configured as a bunch of LEDs in series (or
series/parallel) that need 12VDC, it's right about the same current
draw as the 120V 60W incandescent equivalent. (Or perhaps double
the current for those of us who get 220VAC out of our walls.)
(Am I just showing my age here? How many of you have ever bought
incandescent globes for house lighting? I vaguely recall it may be
illegal to sell them here in .au these days. I really like quartz
halogen globes, and use them in 4 or 5 desk lamps I have, but these
days I need to get globes for em out of China instead of being able
to pick them up from the supermarket like I could 10 or 20 years
ago.)
throw0101d wrote 1 day ago:
> I don't understand why new houses don't just have one high quality
AC/DC converter so you can just use LED lighting without every bulb
needing its own AC/DC converter.
IEEE 802.3bt can deliver up to 71W at the destination: just pull Cat
5/6 everywhere.
* [1] *
(HTM) [1]: https://en.wikipedia.org/wiki/Power_over_Ethernet#Standard_i...
(HTM) [2]: https://www.usailighting.com/poe-lighting
elcritch wrote 1 day ago:
And pay $60 per Ethernet POE+ light bulb.
throw0101d wrote 23 hours 47 min ago:
> And pay $60 per Ethernet POE+ light bulb.
In the commercial/industrial space this may be worth it: how long
do these bulbs last? how much (per hour (equivalent)) do you pay
your facilities folks? how much time does it take for employees
or tenants to report an outage and for your folks to get a ladder
(or scissor lift) to change the bulb?
bluGill wrote 1 day ago:
It wouldn't work. leds need low voltages, meaning massive wires. you
can run the voltage change on ac or dc. Ac just needs a few capacters
to smooth the wave out.
sghiassy wrote 1 day ago:
Iâve always wondered about these new High-Voltage DC (HVDC)
transmission lines.
I always thought ACâs primary benefit was its transmission
efficiency??
Would love to learn if anyone knows more about this
topspin wrote 1 day ago:
> I always thought ACâs primary benefit was its transmission
efficiency??
There are many factors involved, and "efficiency" is only one. Cost
is the real driver, as with everything.
AC is effective when you need to step down frequently. Think
transformers on poles everywhere. Stepping down AC using
transformers means you can use smaller, cheaper conductors to get
from high voltage transmission, lower voltage distribution and,
finally lower voltage consumers. Without this, you need massive
conductors and/or high voltages and all the costs that go with them.
AC is less effective, for instance, when transmitting high power over
long, uninterrupted distances or feeding high density DC loads.
Here, the reactive[1] power penalty of AC begins to dominate. This
is a far less common problem, and so "Tesla won" is the widely held
mental shortcut. Physics doesn't care, however; the DC case remains
and is applied when necessary to reduce cost.
(HTM) [1]: https://en.wikipedia.org/wiki/Electrical_reactance
prezk wrote 1 day ago:
Important factor is that AC at given nominal voltage V swings between
1.41V and -1.41V, so it requires let's say 40% better/thicker
insulation than the equivalent V volts DC line. This is OK for
overhead lines (just space the wires more) but is a pain for buried
or undersea transmission lines; for that reason, they tend to use DC
nowadays.
BTW, megavolt DC DC converters are a sign to behold:
(HTM) [1]: https://en.wikipedia.org/wiki/File:Pole_2_Thyristor_Valve.jp...
cogman10 wrote 1 day ago:
The primary benefit of AC is it's really easy to change the voltage
of AC up or down.
The transmission efficiency of AC comes from the fact that you can
pretty trivially make a 1 megavolt AC line. The higher the voltage,
the lower the current has to be to provide the same amount of power.
And lower current means less power in line loss due to how
electricity be.
But that really is the only advantage of AC. DC at the same voltage
as AC will ultimately be more efficient, especially if it's humid or
the line is underwater. Due to how electricy be, a change in the
current of a line will induce a current into conductive materials. A
portion of AC power is being drained simply by the fact that the
current on the line is constantly alternating. DC doesn't alternate,
so it doesn't ever lose power from that alternation.
Another key benefit of DC is can work to bridge grids. The thing
causing a problem with grids being interconnected is entirely due to
the nature of AC power. AC has a frequency and a phase. If two
grids don't share a frequency (happens in the EU) or a phase (happens
everywhere, particularly the grids in the US) they cannot be
connected. Otherwise the power generators end up fighting each other
rather than providing power to a load.
In short, AC won because it it was cheap and easy to make high
voltage AC. DC is comming back because it's only somewhat recently
been affordable to make similar transformations on DC from High to
low and low to high voltages. DC carries further benefits that AC
does not.
adgjlsfhk1 wrote 1 day ago:
AC is less efficient than DC at a given voltage. The advantage of AC
is that voltage switching is cheap, easy and efficient. Switching DC
voltage is way harder, more expensive, and less efficient. However
the switching costs are O(1) and the transmission losses are O(n) so
for some distance (currently somewhere around 500 km) it's worth
paying the switching cost to get super high voltage DC. The big thing
that's changed in the last ~30 years is a ton of research into high
voltage transistors, and fast enough computers to do computer
controlled mhz switching of giant high power transistors. These new
super fancy switching technologies brought the switching costs down
from ludicrous to annoyingly high.
arijun wrote 1 day ago:
> AC is less efficient than DC at a given voltage
To expand on this, a given power line can only take a set maximum
current and voltage before it becomes a problem. DC can stay at
this maximum voltage constantly, while AC spends time going to zero
voltage and back, so it's delivering less power on the same line.
adiabatichottub wrote 1 day ago:
Maybe if by "same voltage" we mean DC voltage the same as AC peak
voltage. When we talk about AC voltage we are referring to
root-mean-square (RMS) voltage. It's kind of like saying the
average, though for math reasons the average of an unbiased sine
wave is 0. Anyhooo, 1 VRMS into a load will produce the same
power as 1VDC. If AC delivered less power than DC at the same
voltage then life would be very confusing.
manwe150 wrote 1 day ago:
Thatâs true, but my understanding is the main contributor is
skin effect, since AC travels only on the surface of the wire,
while DC uses the whole area, resulting in lower resistance loss
( [1] )
(HTM) [1]: https://en.wikipedia.org/wiki/Skin_effect
adgjlsfhk1 wrote 1 day ago:
this iirc is the smallest of 3 problems. the other 2 are skin
effect (AC wires only store power on the outside of the wire) and
capacitive effects (a write running parallel to the ground is a
capacitor and AC current is equivalent to constantly charging and
discharging the capacitor)
cjbgkagh wrote 1 day ago:
(HTM) [1]: https://en.wikipedia.org/wiki/High-voltage_direct_current
hristov wrote 1 day ago:
It is absolutely stupid to talk about this as edisons revenge. If Tesla
had the modern high power transistors needed to get high voltage dc out
of the ac produced from a spinning turbine he would be all for high
voltage dc too. Tesla understood that high voltage was needed for
efficient long range transmission. He also understood that transformers
were the inly remotely efficient way to climb up to and down from these
high voltages. And transformers only work with ac. So he designed an ac
system and even designed some better transformers for it.
If there was anything like a high power transistor back then he would
have used that. High power transistors that are robust enough to handle
the grid were designed inly recently over 100 years after the
tesla/edison ac/dc argument.
dang wrote 21 hours 26 min ago:
Ok, we've deposed Edison from the title above.
altairprime wrote 21 hours 34 min ago:
Note that one could email the mods to de-clickbait/enrage the title,
especially with such a concrete point as this commentâs. (I
havenât done so as TIL is a poor basis for such an argument.)
metalliqaz wrote 22 hours 49 min ago:
yes, this! thank you good post
crimshawz wrote 23 hours 37 min ago:
Agree, clickbait.
superxpro12 wrote 23 hours 56 min ago:
Yeah this isnt an argument. It was far simpler to wrap some copper
wire around a chunk of metal than it was to fire up a mosfet
fabrication plant in the 1800's.
You can have the best idea in the world, but if you cant manufacture
it you're SOL.
ghighi7878 wrote 1 day ago:
Title is clickbait. Edison is not mentioned anywhere else in article.
I am okay with it.
amelius wrote 1 day ago:
But there was an equivalent: a mechanical switch. Or an
electromechanical relay. Or a spinning wheel with electrical
contacts.
mr_toad wrote 1 day ago:
> If there was anything like a high power transistor back then he
would have used that.
Mercury arc rectifiers were used long before his death.
crote wrote 1 day ago:
Yes, but a rectifier only rectifies. That's not going to give you
DC-DC conversion - let alone converting it to a higher voltage for
long-distance transmission.
wildzzz wrote 21 hours 38 min ago:
DC-DC before the transistor was difficult to do at scale.
Vibrators and relays existed but were not reliable long term.
fsh wrote 1 day ago:
It was Westinghouse who pushed the AC grid against his rival Edison's
DC approach. Tesla was a minor figure working for both of them for a
bit.
bryanrasmussen wrote 1 day ago:
sure, and also Montezuma didn't actually plan on diarrhea ruining
people's vacations, but vernacular usage being what it is we have the
phrase Montezuma's revenge.
I only found Edison in the headline, I didn't find it anywhere in the
body, nor did I find Tesla. Glancing through the article it almost
seems like someone tried to make a catchy headline to get clicks.
teleforce wrote 1 day ago:
>It is absolutely stupid to talk about this as edisons revenge. If
Tesla had the modern high power transistors needed to get high
voltage dc out of the ac produced from a spinning turbine he would be
all for high voltage dc too.
This!
The soon people realized these facts the better. The pervasive high
rise buildings did not happen before the invention of modern cranes.
Exactly twenty years ago I was doing a novel research on GaN
characterization, and my supervisors made a lot money with
consulations around the world, and succesfully founded govt funded
start-up company around the technology. Together with SiC, these are
the two game changing power devices with wideband semiconductor
technology that only maturing recently.
Heck, even the Nobel price winning blue LED discovery was only made
feasible by GaN. Watch the excellent video made by Veritasium for
this back story [1] Why It Was Almost Impossible to Make the Blue
LED:
(HTM) [1]: https://youtu.be/AF8d72mA41M
asah wrote 1 day ago:
> The pervasive high rise buildings did not happen before the
invention of modern cranes.
yyy! if we're going to wander off-topic :-) then I should mention
elevators, water pumps, fire suppression including fire truck
ladders and more! :-)
da02 wrote 1 day ago:
What are some novel processes or technologies you see becoming more
important in the next 5-10 years?
ta9000 wrote 1 day ago:
Does that mean when we run out of Ga there are no more LED TVs?
adrian_b wrote 20 hours 51 min ago:
Gallium is expensive to extract because it is extremely diluted
in the environment.
It accompanies in very low quantities aluminum and zinc, so it is
extracted only in the mines of aluminum or of zinc, as a
byproduct.
However, the abundance of gallium is similar to that of lithium,
while gallium is used in smaller amounts, so there is no risk to
not have enough gallium in the near future.
On the other hand, all semiconductor devices with gallium also
use some indium. Indium is used in even greater quantities in all
LCD or OLED displays, to make transparent electrodes.
Indium is an extremely rare element in the entire universe,
comparable with gold, so for indium there is a much greater risk
that its reserves will become insufficient.
This could be mitigated by extracting such critical elements from
the dumped electronic devices, but this is very expensive,
because only small amounts of indium are used per device, so very
large amounts of garbage would have to be processed in order to
extract a sizable amount of it.
nancyminusone wrote 1 day ago:
Except for gaseous hydrogen and helium, and some spacecraft, all
other atoms remain on the earth and are recoverable with enough
energy and effort.
philipkglass wrote 21 hours 42 min ago:
One more exception: uranium. It actually splits into smaller
atoms when it's used as fuel.
myrmidon wrote 1 day ago:
Sidenote: Whenever someone tells you that (vital) reserves of
some ressource are going to run out soonish (implying drastic
consequences), you should be extremely skeptical:
Such predictions have an abysmal historic track record, because
we tend to find workarounds both on the supply side (=>
previously undiscovered reserves) as well as flexibility on the
demand side (using substitutes).
This applies historically for oil, lithium, rare earth metals and
basically everything else.
edit: I'm not saying we're never gonna run out of anything-- I'm
just saying to not expect sudden, cataclysmic shortages in
general, but instead steadily rising prices and a somewhat
smoothish transition to alternatives.
marcosdumay wrote 14 hours 20 min ago:
"Reserves" are the name of something that exists only at a set
price. Change the price, and the reserves change too.
The people that rush to tell you that reserves are running out
tend to omit what price they are talking about. That way of
expressing oneself is normally called "a lie".
reylas wrote 1 day ago:
I always add "cheap" to the sentence. It seems they are
always talking about the cheap version of anything. Going to
run out of water? Or are we running out of the "cheap" version
of water that does not have to be processed?
myrmidon wrote 1 day ago:
This is a valid point: quickly depleting reserves often
indicate that pricing is not sustainable. Which is bad.
But non-sustainable pricing is very different from
"cataclysmic collapse", and too many people expect the latter
for too many things, which is just not realistic in my view
(and historical precendent makes a strong case against that
assumption, too).
A society where water prices gradually increases to
"reverse-osmosis only" (instead of
"pump-from-the-ground-everywhere") levels is very different
from a society where water suddenly runs out.
mschuster91 wrote 1 day ago:
> Such predictions have an abysmal historic track record,
because we tend to find workarounds both on the supply side (=>
previously undiscovered reserves) as well as flexibility on the
demand side (using substitutes).
That's a classic example of the "preparedness paradox" [1].
When no one raises the alarm in time or it is being ignored,
resources can go (effectively) exhausted before alternatives
can be found, or countries either need to pay extraordinary
amounts of money or go to war outright - this has happened in
the past with guano [2], which was used for fertilizer and
gunpowder production for well over a century until the
Haber-Bosch ammonia process was developed at the start of the
20th century.
And we're actually seeing a repeat of that as well happening
right now. Economists and scientists have sounded the alarm for
decades that oil and gas are finite resources and that
geopolitical tensions may impact everyone... no one gave too
much of a fuck because one could always "drill baby drill", and
now look where we are - Iran has blasted about 20% of Qatar's
LNG capacity alone to pieces and blocked off the Strait of
Hormuz, sending oil prices skyrocketing. [1]
(HTM) [1]: https://en.wikipedia.org/wiki/Preparedness_paradox
(HTM) [2]: https://en.wikipedia.org/wiki/Guano
bluGill wrote 21 hours 17 min ago:
I've seen articles from the 1880s claiming oil will run out
by 1890. 140 years latter...
Yes we can run out of oil, but nobody really knows if or even
when that will happen. Right now I'm guessing we won't run
out because wind and solar is so much cheaper for most
purposes everyone is shifting anyway - this will take decades
to play out.
mschuster91 wrote 13 hours 43 min ago:
> Yes we can run out of oil, but nobody really knows if or
even when that will happen.
We can run out of cheap and accessible oil very, very fast
if the shitshow in MENA continues to escalate. Qatar
already lost 20% of their LNG capacity in a single strike.
The US may have enough domestic oil production to sate its
domestic demand, but the prices would still skyrocket even
for them. Europe meanwhile, we're straight fucked here.
Technically the oil hasn't run out, it's still in the oil
fields of the journalist-butcher country and other
sheikdoms, but that doesn't matter if it cannot be pumped
out any more because the wells got blasted to pieces or if
it cannot be transported thanks to Iranian mines, Europe is
still running out of oil in practice.
myrmidon wrote 12 hours 31 min ago:
What does "Europe running out of oil" mean to you? Gas at
the pump for >10â¬/l, potentially with some rationing
scheme? Do you honestly think that's gonna happen?
It is easy to get infected by the media narratives that
are notoriously biased towards maximum drama, but I
firmly believe that we are not gonna escalate into such a
scenario.
There's always options; sorting priorities because of
price, radical electrification of transport, or, at the
extreme end, picking up coal hydration again (worked well
enough to keep the Nazi war machine running for quite a
while, with much worse access to crude).
For comparison: Copper prices did increase by 500% since
2000, but people barely even care, and that's how I would
expect "shortages" to typically go.
myrmidon wrote 1 day ago:
I don't see the Guano industry as a straight counter-example,
it even illustrates my point:
If you had made predictions/scenarios in 1850 based on Guano
deposits running out within a decade or two, you would have
mispredicted completely, because a lot of the industry just
transitioned to sodium nitrate (before synthetic fertilisers
took over). Nowadays media landscape would've gladly made
such doom-and-gloom predictions for global agriculture back
then.
I completely agree that quickly depleting reserves often
indicate non-sustainable pricing for ressources (which is
obviously bad long term), but that is very different from
sudden collapse.
AndrewDucker wrote 1 day ago:
Why would we run out of Ga?
mikkupikku wrote 1 day ago:
There's a component of modern culture that trains and expects
people to be extremely pessimistic about long term human
development. It results in situations above, where without
any further information people just assume by default that were
going to run out of a thing and are on some collision course
with not just a disaster, but every single conceivable one.
(Gallium is a byproduct of aluminum production. We aren't
going to run out.)
bananaflag wrote 1 day ago:
On the other hand, it is possible to run out of a metal when
all of it is either somewhere in some device or scattered
among landfills (i.e. not concentrated in a place like a
mine).
pyrale wrote 17 hours 57 min ago:
> On the other hand, it is possible to run out of a metal
when all of it is either somewhere in some device or
scattered among landfills
The metal isn't going to disappear, but it won't be
concentrated enough to be as easily retrievable.
pwndByDeath wrote 23 hours 16 min ago:
Its concentrated in a place like a landfill that already
has access for large vehicles.
margalabargala wrote 23 hours 40 min ago:
It's a byproduct of aluminum production.
The earth's crust is 8% aluminum.
We will have bigger problems before hitting this one.
adrian_b wrote 20 hours 45 min ago:
That is true, but gallium is present in the aluminum and
zinc ores only in minute quantities.
We will not remain without gallium, but it is impossible
to scale up the gallium production to a higher level than
provided by the current productions of aluminum and zinc.
So there is a maximum level of gallium that can be used
per year and it would not be possible to increase the
production of blue and white LEDs and of power
transistors above that level.
Fortunately, the amount of gallium used per device is
very small, so it is not likely that we will hit that
level soon. A much more serious problem is the associated
consumption of indium, for which the resources are much
less.
ta9000 wrote 15 hours 19 min ago:
Thanks for providing a real answer.
nkrisc wrote 1 day ago:
Thatâs still not running out. Itâs still there, just
more effort to get.
PowerElectronix wrote 23 hours 46 min ago:
Effort high enough to consider that material lost to any
practical purpose like a tv.
nkrisc wrote 20 hours 4 min ago:
If prices of certain metals were high enough I bet
people would stop throwing out TVs and dig up old ones
from the dump.
swiftcoder wrote 21 hours 54 min ago:
Cost scales with refinement effort, so it just results
in more expensive TVs. That said, pretty sure we'll
have drowned the planet in landfilled TVs long before
this becomes a serious issue
card_zero wrote 1 day ago:
"At 10 parts per quadrillion, the Earth's oceans would
hold 15,000 tonnes of gold", says the Wikipedia page on
gold.
I'm inclined to think we've lost that gold.
nkrisc wrote 20 hours 5 min ago:
Practically speaking, sure. It's obviously not
cost-effective to extract it. But it's there if someone
can get it. I don't expect anyone to be extracting gold
from ocean water, but there are other source of other
elements that may not be cost-effective now but could
be in the future or may simply become necessary despite
the cost.
threetonesun wrote 1 day ago:
My understanding of most elements is if we want more itâs
either pretty easy to make from something else we have a lot
of, or we need to redo the Big Bang, the latter being, in my
opinion, a bit of a disaster scenario.
nkrisc wrote 1 day ago:
Even synthesizing helium is prohibitively expensive. Unless
you want whatever heavy decay products we have from nuclear
waste, synthesizing elements at industrial scale probably
isnât happening.
Unless by âmake from somethingâ else you mean extract
the element from existing chemical compounds found in
Earth, in which case weâre still just using existing
deposits on Earth.
jibal wrote 1 day ago:
(HTM) [1]: https://shrunk.ai/research-journals/f/cranes-skyhooks-and-...
mcbishop wrote 1 day ago:
I've heard the EV charging has played a big role in the maturation
of GaN / SiC.
teleforce wrote 1 day ago:
Yes, EV and high frequency electronics (microwave, mmWave,
photonics) that require very fast switching capability.
UltraSane wrote 1 day ago:
And military radars love GaN
chrneu wrote 1 day ago:
the internet really needs to stfu about tesla and get over that
oatmeal comic that spawned a billion internet myths. dude was a
decent inventor but suffered from chronic mental health issues and,
in his lifetime, wasted so much time/energy/money and burned so many
bridges with his horrible attitude. there's a reason most people
didnt like him in his day, he was a depressed asshole who alienated
everyone around him, and yes I know he was likely gay in a time when
that wasn't cool. the fact still remains; his inventions are
massively overblown by internet nerds.
the podcaster Sebastian Major from "Our Fake History" did a looonnngg
patreon episode on tesla and debunked most of the weird myths around
tesla. Sebastian doesn't have a vendetta or anything, it's just
amazing how much of the Tesla stuff is just nonsense or is viewed
through a very weird bias nowadays. Major also briefly touches on the
weird Edison stuff and how the internet has twisted Edison into a
villain.
tibbydudeza wrote 22 hours 5 min ago:
Did he also not fall in love with a pigeon ?.
throw4847285 wrote 23 hours 38 min ago:
Software engineers idolize Tesla because they see themselves as the
Tesla (a selfless devotee of the abstract idea of technology)
against evil Edisons (businessmen who only care about money and
steal other people's ideas). They've basically projected the
Jobs/Woz divide back onto two historical figures who, in reality,
barely interacted.
The funniest part is that The Oatmeal comic didn't invent this
concept, but drew on pre-Internet narratives put forward by The
Tesla Society, who were mailing busts of Tesla to universities
around the country since the 70s at least. And that organization is
explicitly nationalistic and religious, tied to other
Serbian-American heritage organizations, and doing events with the
Orthodox church.
balamatom wrote 17 hours 10 min ago:
> And that organization is explicitly nationalistic and religious
So are many Serbs (more so if emigrants from atheist-socialist
Yugoslavia, or descendants of folks who moved before WW2) as well
as many other nations and organizations (America itself lol). So
are many Something-Or-Other-American individuals and communities.
I presume that the organization(s) sending Tesla busts, being
American-rooted, have had no illusions about which matters will
forever remain impossible to communicate to Americans. (Such as
anything not reducible to paperclip optimization.)
Instead, I consider it more likely that the point of promoting
Tesla was not to impress anyone in America, but to uplift Serbia
and generally the South Slavs of the Balkans who'd only gained
national sovereignty in Tesla's day: "look, our heritage has
already produced an honest-to-god American inventor half a jebani
vek ago, so you guys have zero excuse to act as if you're stuck
in the middle ages - do join the cargo cult of mordorn
civilization instead, will ya - we got value to extract from ya!"
>They've basically projected the Jobs/Woz divide back onto two
historical figures who, in reality, barely interacted.
I'd rather say this has been projected for them, but by whom is
anyone's guess; not like there's a shadowy cabal operating.
Besides said Serbian-American heritage promoters and whatever
their game is, I guess - but here we're not talking mid-XX
century Serbian diaspora any more, but a "culturally nonspecific"
audience.
Much safer to call it "a hivemind situation" when nobody knows
where some idea comes from, and nobody is accountable for
rebroadcasting it either, since it comes pre-tagged as Good and
True and Useful and it is wrongthink to doubt those. Especially
when the idea is so obviously Useful for excusing nonaction. ("I
can't be bothered to learn the first thing about electricity,
even the history of why I have access to it in the first place -
but now that Tesla guy I've vaguely heard of, he was the great
genius of the people! What better reason to Experience a Positive
Emotion!")
KaiserPro wrote 23 hours 42 min ago:
> he was a depressed asshole who alienated everyone around him,
enough Edison bashing!
Look, Tesla was a weirdo, but, he was a very good inventor who
actually invented shit.
Edison was an industrialist, who knew the price of everything, and
wasn't above spending a lot of money to destroy a rival.
Do I idolise Tesla? no, but I respect his understanding of high
frequency electronics with really primitive tooling.
Do I despise Edison? also no, but he is a massive prick. Excellent
buisness man, but an abrasive prick never the less.
boomskats wrote 1 day ago:
I mean yeah, but it's not like the guy's 'horrible attitude' came
from nowhere. He naiively romanticised migrating to the US thinking
the game was about scientific progress rather than capital, and so
he got repeatedly screwed over by almost everyone around him for
decades.
If I was in his position I'm not sure I'd have taken it as well as
he did.
wil421 wrote 1 day ago:
Thereâs no way he suddenly developed autism or whatever mental
illness plagued him upon arrival to American. Like most absolute
geniuses he struggled in other areas. He said he had visions as a
child.
balamatom wrote 17 hours 17 min ago:
But there is: his neurotype suddenly became considered
"whatever mental illness" upon arrival in Eugenicsland.
elar_verole wrote 1 day ago:
People need heroes. It's like the Keanu Reeves or Musk era, all the
""badass"" stories about this or that soldier / local hero / w/e
that are very often overblown and get further and further away from
the initial facts every time they resurface.
No hate here, just noticing there is a weird visceral need to
distill stories to their most essential, good vs evil, and the
Tesla v Edison thing embodies this perfectly I think.
ngvrnd wrote 1 day ago:
Except for Keith Moon. All the stories about him are true and if
anything underplay the truth. :-)
Imustaskforhelp wrote 1 day ago:
Keanu Reeves and Nikola Tesla to a degree as well, are decent
figures.
Aside from all the cult classics Keanu is part of like john wick
and the matrix, even discounting that, he is a good person in it
of itself who is genuinely humble and might be one of the best
persons within hollywood.
What I feel pissed about is that people like Andrew Tate and
others like them took the concept of Matrix and the contributions
Keanu did within that movie and tried to capitalize on that cult
classic decades after in the most toxic form that might be the
issue if we are talking about an era
To be honest, Nikola tesla is also a great person within the
context of his time. GGP's comment is still true but Tesla's
contributions can hardly be reinstated and I'd much rather people
believe these to be the heros (Keanu/Tesla) rather than Tate/Musk
etc.
If I take anything from Keanu, I would like to take his
humility/humbleness.
ndsipa_pomu wrote 1 day ago:
Whilst I agree that Keanu is a most excellent human, he was
hardly responsible for the concept of the Matrix. In my
opinion, Philip K Dick was a major influence (I'm a fan and
consider him the prophet of the modern age), though Gibson's
Neuromancer was likely a big influence too. (Also, there's the
old Doctor Who episode "The Deadly Assassin" which features the
Matrix).
It always seems to me that the far right are bereft of original
ideas and always co-opt other pre-existing concepts. There's
exceptions, but I always find that right wing works are always
lacking humour or irony (c.f. Ayn Rand's works).
something765478 wrote 23 hours 17 min ago:
> the far right are bereft of original ideas and always
co-opt other pre-existing concepts.
That's not unique to them: Good artists copy; great artists
steal.
tomtomtom777 wrote 21 hours 49 min ago:
"It is only the unimaginative who ever invents. The true
artist is known by the use he makes of what he annexes. And
he annexes everything."
- Oscar Wilde
ndsipa_pomu wrote 22 hours 20 min ago:
Yes, but I'd have difficulty in pronouncing Andrew Tate as
a good or great artist. Maybe con-artist would be the
highest that I'd go.
giancarlostoro wrote 1 day ago:
Tate is just attention hungry. Itâs pretty obvious. If you
feed no attention to him, he will go back to where he crawled
from.
aaronbrethorst wrote 1 day ago:
Weâre talking about Nikola Tesla, not Elon Musk, and I donât
think Musk is gay.
beAbU wrote 1 day ago:
I think you need to read the post you are responding to again.
anonymousiam wrote 1 day ago:
Tesla was an outstanding technologist, but a poor businessman. He
had a "vision" (actually more than one) about how his ideas could
transform the world. Some of his ideas were amazing, but he was
swindled out of his patents because the investors knew he had a
passion and wanted to see them in use. The polyphase AC motor or
fluorescent light bulb could have made him millions.
IMHO, the vision he had about universal free electricity
(transmitted wirelessly) was the dumbest. It was a novel idea, and
he invested a lot (his time and other people's money) in it. The
problem with his idea is that there was no way to monetize it (and
profit from it). (There were also the technical issues of the
power loss over distance (1/R^2), the harm to the environment, and
the interference with radio communications.)
Edison was quite a villain. He stole many of his "inventions", and
orchestrated a PR campaign against Tesla touting the "evils" of AC
power. AFAIK, the electric chair was either invented or inspired
by him.
I know these things because I've read many books on various topics
related to Tesla, and all of this knowledge predates the Internet.
fsh wrote 1 day ago:
Essentially none of this is true. The war of the currents was
between Edison and Westinghouse, not Tesla. Tesla's downfall was
that he turned into a crackpot who rejected modern science, such
as Maxwell's equations, and started defrauding investors. Edison
was an outspoken opponent of the death penalty, and the electric
chair used AC simply because it is much more deadly.
chipster_f00 wrote 1 day ago:
> The war of the currents was between Edison and Westinghouse
[...]
Thank you for quashing the gross misinformation. I was going to
post this, but searched and found your comment. `\m/`
(I learned of the "Current War" in the 70's, since the Edison
Museum was in my "backyard" -- and was a common destination of
local school field trips.)
HWR_14 wrote 1 day ago:
Edison did not invent the electric chair. When the inventors were
trying to choose between using AC or DC he helped them decide on
AC as part of his PR campaign.
Georgelemental wrote 1 day ago:
It's just a fun title, you are overthinking it
jacquesm wrote 1 day ago:
Agreed, for the IEEE to go down this route is more than a little
weird.
bluGill wrote 1 day ago:
Tesla also design the modern induction motor which needs ac. Though
these days we often run them on a phase generator which has a dc
step.
arijun wrote 1 day ago:
Also, if anything would have been Edison's revenge it would have been
HVDC, where they're sending power long distances with DC. (But as you
said, even there it wouldn't make a ton of sense, since they were
arguing in a different era).
themafia wrote 1 day ago:
The two primary reasons to do that are to allow the intertie of two
AC grids that are not otherwise synchronized, and to take
advantage of "earth return" paths when necessary to double the
capacity of the line. The latter you may need to consider just to
make the line cost effective over an equivalent AC span.
stego-tech wrote 1 day ago:
I've been hearing this line for over a decade, now. "Immersion cooling
will make data centers scale!" "Converting to DC at the perimeter
increases density!"
Yes, of course both of those things are true, and yes, some data
centers do engage in those processes for their unique advantages. The
issue is that aside from specialty kit designed for that use (like the
AWS Outposts with their DC conversion), the rank-and-file kit is still
predominantly AC-driven, and that doesn't seem to be changing just yet.
While I'd love to see more DC-flavored kit accessible to the
mainstream, it's a chicken-and-egg problem that neither the power
vendors (APC, Eaton, etc) or the kit makers (Dell, Cisco, HP,
Supermicro, etc) seem to want to take the plunge on first. Until then,
this remains a niche-feature for niche-users deal, I wager.
_zoltan_ wrote 20 hours 47 min ago:
I recommend reading these two: [1] [2] almost everybody in the
industry is embracing 800V DC mostly because of Vera Rubin and the
increased electricity requirements.
(HTM) [1]: https://developer.nvidia.com/blog/nvidia-800-v-hvdc-architec...
(HTM) [2]: https://blogs.nvidia.com/blog/gigawatt-ai-factories-ocp-vera...
jeffbee wrote 22 hours 13 min ago:
It is weird to me how far from the state of the art mainstream server
equipment is. I can't imagine anything worse than AC-AC UPS, active
PDUs, and redundant AC-DC supplies in each rack unit, but that's
still how people are doing it.
KaiserPro wrote 23 hours 35 min ago:
Immersion cooling was/is so fucking impractical it is only useful for
very specific issues. If you talk to any engineer who worked on CRAY
machines that were full of liquid freon, they'll tell how hard it is
to do quick swaps of anything.
Its much cheaper, quicker and easier to use cooling blocks with leak
proof quick connectors to do liquid cooling. It means you can use
normal equipment, and don't need to re-re-enforce the floor.
A lot of "edge" stuff has 12/48v screw terminals, which I suspect is
because they are designed to be telco compatible.
For megawatt racks though, I'm still not really sure.
kjs3 wrote 17 hours 6 min ago:
We had a cluster of liquid cooled CDC Cyber mainframes. One of
them developed a bad leak and managed to drain itself into the
raised floor. This was a Very Bad Day for many folks in the
computer center.
Edit: s/have/had/
crote wrote 1 day ago:
As seen on HN a few days ago, immersion cooling is dead: turns out
the risks of getting sued to oblivion due to widespread PFAS
contamination isn't worth it. [0]
DC doesn't have such a killer. There are a decent bunch of benefits,
and the main drawback is gear availability. However, the
chicken-and-egg problem is being solved by hyperscalers. Like it or
not, the rank-and-file of small & medium businesses is dying, and
massive deployments like AWS/GCP/Azure/Meta are becoming the norm.
Those four already account for 44% of data center capacity! If they
switch to DC can you still call it "specialty kit", or would it
perhaps be more accurate to call it "industry norm"?
It is becoming increasingly obvious that the rest of the industry is
essentially getting Big Tech's leftovers. I wouldn't be surprised if
DC became the norm for colocation over the next few decades.
[0]:
(HTM) [1]: https://thecoolingreport.com/intel/pfas-two-phase-immersion-...
mrguyorama wrote 20 hours 51 min ago:
They poison water supplies, knowingly, for decades, and it only
takes $12 billion dollars to finally get them to stop?
Fucks sake.
dist-epoch wrote 1 day ago:
These are GigaWatt data centers. For a single one they buy equipment
by the container ship. Nothing is niche about it.
gizmo686 wrote 1 day ago:
At least for servers, power supplies are highly modular. It just
takes 1 moderately sized customer to commit to buying them, and a DC
module will appear.
Looking at the manual for the first server line that came to mind,
you can buy a Dell PowerEdge R730 today with a first party support DC
power supply.
arijun wrote 1 day ago:
Surely if it makes sense for the big players, they will do it, and
then the benefits will trickle down to the rest? Like how Formula 1
technology will end up in consumer vehicles.
otterley wrote 1 day ago:
Those vendors all have DC power supply options, to my knowledge.
Itâs hardly new; early telco datacenters had DC power rails, since
Western Electric switching equipment ran on 48VDC.
(HTM) [1]: https://www.nokia.com/bell-labs/publications-and-media/publi...
stego-tech wrote 1 day ago:
Thatâs just it though, telco DCs != Compute DCs. Telcos had a
vested interest in DC adoption because their wireline networks used
it anyway, and the fewer conversions being done the more efficient
their deployments were.
Every single DC Iâve worked in, from two racks to hundreds, has
been AC-driven. Itâs just cheaper to go after inefficiencies in
consumption first with standard kit than to optimize for AC-DC
conversion loss. Iâm not saying DC isnât the future so much as
Iâve been hearing itâs the future for about as long as Elmoâs
promised FSD is coming ânext yearâ.
jacquesm wrote 1 day ago:
I think the real reason is because battery power didn't have to
be converted twice to be able to run the gear in case of an
outage, so you'd get longer runtime in case of a power failure,
and it saves a bunch of money on supplies and inverters because
you effectively only need a single giant supply for all of the
gear and those tend to be more efficient (and easier to keep
cool) than a whole raft of smaller ones.
otterley wrote 1 day ago:
DC power has been an option for datacenter equipment since I was a
young lad racking and stacking hardware. Cisco, Dell, HPE, IBM, and
countless others all had DC supply options. Same with PDUs. Whatâs
old is new again.
See e.g.
(HTM) [1]: https://www.dell.com/support/kbdoc/en-us/000221234/wiring-inst...
_zoltan_ wrote 20 hours 50 min ago:
800V DC is definitely not "old".
_fizz_buzz_ wrote 1 day ago:
Obviously 48VDC has been around and internally they will probably
still step down to 48V. But these 48V islands are nowadays inter
connected by regular AC grid. They want to replace that
interconnection with a 800VDc bus. I kind of assume they chose 800vdc
because there are already bunch of stuff available from EVs which
also have 800vdc battery packs now.
15155 wrote 1 day ago:
They chose 800VDC because it's a convenient multiple that is the
peak possible with a two-level 650V (probably GaN) FET arrangement.
eternauta3k wrote 1 day ago:
And why is 650V special?
15155 wrote 1 day ago:
Historical, physical, engineering reasons.
Much of the world's mains-voltage electronics run at 240V
(historical) and have PFC circuits (which are essentially just
boost converters) that run at ~400V DC link voltages. 650V
gives you enough headroom to tolerate overshoots and still have
an 80% safety margin with a single level topology.
This voltage also coincidentally is a convenient crossover
point where silicon MOSFETs start to become inefficient and GaN
FETs have recently become feasible and mass-produced.
bluGill wrote 1 day ago:
48vdc was common in phone exchanges. They filled the basement with
lead-acid batteries and to could run without the grid for a couple
weeks. In turn the phone was 99.999% reliable for decades.
superxpro12 wrote 23 hours 53 min ago:
This reminds me of the early google data centers that directly
soldered those massive duracell lantern batteries directly to the
motherboards as a primitive battery backup. I'm struggling to
google examples of it, this would have been back around 2008, but i
have a vivid memory of it.
edit: found it
(HTM) [1]: https://www.cnet.com/tech/tech-industry/google-uncloaks-on...
amelius wrote 1 day ago:
You need thick cables if you want to power a rack with 48V.
boricj wrote 1 day ago:
I'm working on stuff in that market, it's still largely is. DC
Power System Design For Telecommunications is still a must read and
it doesn't even cover the last 15 years or so of development,
notably lithium batteries and high efficiency rectifiers.
I will say that this is a surprisingly deep and complex domain. The
amount of flexibility, variety and scalability you see in DC
architectures is mind-boogling. They can span from a 3kW system
that fits in 2U all the way to multiples of 100kWs that span entire
buildings and be powered through any combination of grid, solar
and/or gas.
tverbeure wrote 1 day ago:
-48V! :-)
idiotsecant wrote 1 day ago:
I still have a bunch of 48vdc comms gear in my powerplant.
beAbU wrote 1 day ago:
Why do you have a powerplant?
bluGill wrote 1 day ago:
Power plant is the convention for any large company that has
backup power. A few UPSes for the server room - they are the
power plant. A backup generator - power plant. Sometimes even
just the room with all the break boxes from where the grid
comes in is called the power plant (though normally power plant
is reserved for backup power). It is extremely common for
commercial buildings to have their own power plant. Most of
their power comes from the grid in all cases, but they have a
power plant. At commercial scale you can often save money by
buying a backup generator powerful enough for your whole
building so you disconnect from the grid when grid power is in
highest demand (see your utility, then your accountant: for
details if you can afford a generator this large)
MathMonkeyMan wrote 1 day ago:
Yeah I always heard that the phone lines carried their own power,
and in Florida the phones did keep working when the power went out,
but I never knew why.
So the grid was always charging up the lead acid batteries, and the
phone lines were always draining them? Or was there some kind of
power switching going on where when the grid was available the
batteries would just get "topped off" occasionally and were only
drained when the power went out?
ssl-3 wrote 10 hours 54 min ago:
Neither.
The batteries, the grid/generator-supplied power supplies, and
the telephone switch equipment are all connected in parallel --
as if the entire DC power infrastructure consists of only two
wires, and everything involved with it connects only to those two
wires.
1. In normal operation, the batteries are kept at a constant
state of charge. The switches are powered from the same DC bus
that keeps the batteries charged.
2. When the power grid goes down, the batteries slowly discharge
and keep things running like nothing ever happened (for
hours/days/weeks). There is no switchover for this; it's just
the normal state, minus the ability to juice-up the batteries.
(Remember: It's just one DC bus.)
3. When the grid comes back up (or the generators kick in), the
batteries get recharged. There is no switchover for this either;
nothing important even notices. (Still just one DC bus.)
4. If the grid stays up long enough, go to 1. Repeat as the
external environment dictates. (And as you might guess, it's
still one DC bus and there's also no switchover here. Things
just continue to work.)
--
You can play with this at home with a capacitor (which loosely
acts like a battery does), an LED+resistor combo (which acts as a
load), and a small power supply that is appropriate for
LED+resistor you've chosen (which acts as the AC-DC converting
grid input).
Wire them all 3 parts up in parallel and the light comes on.
Disconnect the power supply, and the light stays on for a bit --
it successfully runs from power stored in the capacitor.
Reconnect the power supply, and the light comes on and the
capacitor ("battery") recharges -- concurrently.
Improve staying power by adding more parallel capacitance.
Reduce or eliminate it by reducing or eliminating capacitance.
Goof around with it; it's fun. (Just don't wire the capacitor
backwards. That's less fun.)
SigmundA wrote 1 day ago:
The batteries and phone lines were one system at -48v with power
supplies converting AC power to DC while grid / generator is up.
The batteries are floated at the line voltage nothing was really
charging or discharging and there was no switchover.
This is similar to your cars 12v dc power system such the when
the car is running the alternator is providing DC power and the
batteries float doing nothing except buffering large fluctuations
stabilizing voltage.
qingcharles wrote 1 day ago:
It's a pretty decent chunk of power down a POTS cable too, as it
was designed to ring multiple big chunky metal bells in the days
of yore.
I was wiring in a phone extension for my grandma once as a boy
and grabbed the live cable instead of the extension and stripped
the wire with my teeth (as you do). I've been electrocuted a
great number of times by the mains AC, but getting hit by that
juicy DC was the best one yet. Jumped me 6ft across the room :D
elcritch wrote 1 day ago:
I discovered the same exact thing wiring a second phone line to
my bedroom as a teenager. I jumped into a pile of fiberglass
insulation! :/
rdtsc wrote 1 day ago:
The teeth. Yikes! But yeah, I remember having the rotary phone
disassembled and touching the wires adjusting something when a
ring came. Gave me enough of a jolt to remember.
pocksuppet wrote 1 day ago:
The phone grid predated the electrical grid. There was no other
choice for power.
Actually, there was one. Even earlier phones had their own power.
A dry-cell battery in each phone, and every 6 months, the phone
company would come around with a cart and replace everyone's
battery. Central battery was found to be more convenient, since
phone company employees didn't have to go around to everyone's
site. Central offices could economize scale and have actual
generators feeding rechargeable batteries.
bluGill wrote 1 day ago:
Grid charging batteries, phone draining them as I understand. Of
course there were switches all over the us so I can't make
blanket claims but from what I hear that was normal.
divbzero wrote 1 day ago:
Interesting, so this is why the phone line still worked when power
was out across the whole town.
eqvinox wrote 18 hours 33 min ago:
Yeah, it used to be that you could still make calls (particularly
to emergency services) even in complete power outages, for as
long as your local exchange has batteries for. (AFAIR that
tended to be on the order of hours, but probably differs quite a
bit across locations and regulatory domains/countries.)
Another thing we lost in the age of VoIP landlines, but then
again mobile towers also have batteries. Just don't be unlucky
and have a power outage with 3% battery on your phone...
shiroiuma wrote 13 hours 16 min ago:
Luckily, phone batteries and phone power consumption seem to
have improved a lot in the last half-decade.
mjuarez wrote 1 day ago:
Not to be _that_ guy, but it was technically -48V DC.
Honestly, that was pretty surprising to me when I had to work with
some telco equipment a couple of decades ago. To this day, I don't
think I've encountered anything else that requires negative voltage
relative to ground.
swed420 wrote 1 day ago:
> I don't think I've encountered anything else that requires
negative voltage relative to ground
Automotive collectors can probably still relate to cars from the
1920s-50s having a "positive ground."
fuzzfactor wrote 23 hours 32 min ago:
With positive ground the traditional more-sacrificial spark
plugs lasted longer.
fecal_henge wrote 1 day ago:
I am STILL designing hardware for -48v telco standard. The first
thing we do is convert -48 -> 48v. That's 4 square inches of PCB
space we waste.
eqvinox wrote 1 day ago:
What do you need +48V for?
fecal_henge wrote 1 day ago:
We go -48 -> 48 -> 12 -> 3v3,1v8 etc etc. If you went 48
straight to POL voltages then you would have horrific
converter performance.
mastax wrote 12 hours 1 min ago:
I was just looking at these funny parts: [1] 130A, 48V ->
1.2V @ 94% efficiency! Except:
- $100 ea.
- Fixed 1/40 voltage ratio, regulation done by upstream
regulator.
- Look at the minimum specs for efficiencyâ¦
(HTM) [1]: https://www.vicorpower.com/products?productType=cf...
eqvinox wrote 1 day ago:
> If you went 48 straight to POL voltages then you would
have horrific converter performance.
What's horrific converter performance in numbers?
An isolated flyback (to 12V) should be able to hit >92% and
doesn't care if it's fed -48V or +48V or ±24V. TI webench
gives me 95% though I'd only believe that if I'd built and
measured it. What's the performance of your -48V â +48V?
[with the caveat that these frequently require custom
transformers... not an issue with large runs, but finding
something that can be done with an existing part for
smaller runs is... meh]
fecal_henge wrote 1 day ago:
-48 to 48 claims something like 97% (load dependent of
course). It also needs to arbitrate between two input
supplies for glitchless redundancy, plus have PM bus and
other spec mandated stuff. There is no technical reason
why you cant go -48 -> 12 as you state with good
efficiceny, but we cant get hold of a part that ticks all
the boxes.
Horrific performance by my definition would be 48v to say
1v. We only realistically use buck topologies for POL
supplies. Such a ratio is really bad for current
transients, not to mention issues like minimum on times
for the controller.
eqvinox wrote 18 hours 50 min ago:
I'm just surprised that either input isolation isn't on
your spec, or it still somehow works out better with
isolated to +48V than straight to 12V... but I guess if
your spec requires other things, it makes sense.
(Thanks for the info!)
djmips wrote 1 day ago:
Likely as a basis for converting to other useful DC voltages.
pluies wrote 1 day ago:
Well if it's negative 48V the electricty flows out of your
circuit and back to the grid, so you need to make it positive
to have the electricity come in.
HWR_14 wrote 1 day ago:
Can you explain why it's -48 VDC as opposed to 48 VDC with the +
and - inputs mislabeled?
crote wrote 1 day ago:
Because the chassis is connected to ground (as in, a literal
grounding rod hammered into the soil) and by definition your 0V
reference point.
The crucial difference is the direction in which the current is
flowing: is it going "in to", or "out of" a hot wire? This
becomes rather important when those wires are leaving the
building and are buried underground for miles, where they will
inevitably develop minor faults.
With +48V corrosion will attack all those individual telephone
wires, which will rapidly become a huge maintenance nightmare
as you have to chase the precise location of each, dig it up,
and patch it.
With -48V corrosion will attack the grounding rod at your
exchange. Still not ideal, but monitoring it isn't too bad and
replacing a corroded grounding rod isn't that difficult.
Telephone wires will still develop minor faults, but it'll just
cause some additional load rather than inevitably corroding
away.
HWR_14 wrote 23 hours 56 min ago:
So, there is a true value for 0?
Does that mean when you have electronics and use multiple
dc-dc converters all the inputs and outputs share the same
ground, it's not just the values for that pair of wires?
And if I want to use a telephone on an incorrectly wired 48dc
circuit, I could switch the positive and negative wires, as
long as the circuit in the telephone is isolated and never
touches ground?
Thanks. Somehow I got in my head that all circuits were just
about the delta from neutral and therefore nothing outside
them mattered.
bonzini wrote 17 hours 46 min ago:
> all the inputs and outputs share the same ground, it's
not just the values for that pair of wires?
No, it depends on the converter. There are converters that
leave 160V on the DC power rail for a 110V AC input, and
155V on the DC "ground" rail.
They are economic and you could find then when galvanic
isolation is at least in theory not important, but they're
terribly unsafe when used on PCBs that people might muck
with.
If you have some "normal" converters and some of this kind,
sharing the ground would be quite dangerous.
HWR_14 wrote 14 hours 11 min ago:
I have done some projects that needed some generic dc-dc
converters from aliexpress (eg stepping down 12v to 5 or
3.3) I alway treated the output of each step down as a
pair of wires that share no ground. It sounds like that
would be overkill if they were reputable but it's
probably best to not try tying the grounds together.
I figured any happenstance from the multimeter that the
grounds match was transitory and not to be trusted.
wat10000 wrote 21 hours 16 min ago:
There is a true zero potential. You can detect this because
two charged objects with zero delta between them will still
repel each other.
I think a circuit should mostly care about the deltas, but
when youâre talking about things like phone lines, the
earth becomes part of your circuit. You canât influence
its potential (itâs almost exactly neutral because any
charge imbalance gets removed by interaction with the
interplanetary medium) so everything else is going to end
up being determined by what you need for their relative
potential to that.
the_cosmos wrote 6 hours 28 min ago:
Voltage is _always_ relative; you only ever measure
differences between two points. Voltmeters have two
probes. Ground is just a convenient reference, not a
universal zero. And while Earth can act as a reference or
return path in some systems, itâs not perfectly neutral
or fixed...itâs just large enough to approximate that
in practice. (The interplanetary medium aka aether
doesn't exist)
Objects donât repel because theyâre at the same
potential. Electrostatic force comes from electric fields
due to charge. If two objects truly have zero potential
difference and no field between them, thereâs no force.
Youâre correct that circuits care about voltage
differences. After all, all work requires a force
gradient of some kind.
tinyhitman wrote 1 day ago:
Do you also happen to why this is not more common? Must be
useful for more than just telephone wires.
nhecker wrote 18 hours 18 min ago:
I ran into a guy at a hardware store who ran just such a
power supply attached our city's water (or was it natural
gas?) infrastructure. I was incredulous, but the idea that
it helped prevent corrosion did make sense.
crote wrote 18 hours 36 min ago:
It is! Look up "impressed current cathodic protection": you
apply a small DC voltage to, say, pipelines to prevent
corrosion.
bluGill wrote 1 day ago:
Most large scale systems are AC because transformers are
relatively cheap, low maintenance, and efficient. When the
system is AC ground makes no difference.
With DC systems you generally think about the issues -
which is why modern cars are negative ground. However
other than cars most people never encounter power systems
of any size - inside a computer the voltages and distances
are usually small enough that it doesn't matter what ground
is. Not to mention most computers don't even have a
chassis ground plane (there are circuit board ground planes
but they conceptually different), and with non-conductive
(plastic) cases ground doesn't even make sense.
marcosdumay wrote 14 hours 39 min ago:
> because transformers are relatively cheap, low
maintenance, and efficient
And because that problem of galvanic corrosion the GGP
talked about, and the mirror one of material aggregation
don't happen. And it also makes switches more reliable.
Both are less dangerous on telephone lines. But are very
important on electricity ones.
1 - It won't break your posts, but can easily short small
contacts.
jcalvinowens wrote 23 hours 42 min ago:
> When the system is AC ground makes no difference.
With AC it's about where the ground is attached along the
length of the transformer secondary. In the EU they
ground one of the ends of the secondary, in the US we
ground the center point.
I don't get to say this very often ... but the US way is
objectively safer with no downside: 99% of human shocks
are via ground, and it halves the voltage to ground (120V
vs 240V). A neutral isn't required if there aren't 120V
loads.
crote wrote 18 hours 24 min ago:
In the EU it is quite common for houses to have
three-phase power. If you squint a bit, the grounded
neutral of the Y transformer isn't entirely unlike the
grounded center tap in the US. The voltage is a lot
higher, of course!
Dylan16807 wrote 15 hours 31 min ago:
> If you squint a bit, the grounded neutral of the Y
transformer isn't entirely unlike the grounded center
tap in the US.
Yes, but you only get the safety benefit on three
phase equipment.
In the US there aren't a lot of 240V plugs, but if
you get some installed you can get the safety
benefits with plain old consumer goods.
Liftyee wrote 20 hours 3 min ago:
I agree that the US voltage is safer (with the tradeoff
of lower output powers available at your outlets).
However, I suspect this is more than negated by the US
plug design, which carries a much larger risk of shocks
than almost all EU plug designs (Schuko, British/Type
G, etc...)
- uninsulated metal pins make contact with supply while
partially exposed
- much smaller distance between metal pins and the edge
of the plug
jcalvinowens wrote 19 hours 50 min ago:
100% agree the US plug designs are terrible.
But there's no inherent power tradeoff: you can have
240V outlets in the US, with the two prongs both 120V
to ground. They're just really uncommon in
residences.
bluGill wrote 17 hours 7 min ago:
Dryers and Stoves/range outlets are very common in
US houses. Of course they are generally hidden
behind the device and so most people are not sure
if they have them at not. They are also reasonably
common in garages (welders, air compressors, table
saws... - if your hobby needs them you install
them, otherwise you won't have them).
jojobas wrote 1 day ago:
In short, ground.
em3rgent0rdr wrote 1 day ago:
Some old guitar effects used -9V DC.[1] And the convention with
guitar effects power adapter is the barrel is center negative
(which is motivated with facilitating easy wiring of the socket's
switch to connect to a 9V battery inside).
(HTM) [1]: https://www.analogisnotdead.com/article26/what-is-going-...
aidenn0 wrote 1 day ago:
RTL and DTL both needed negative-voltage relative to ground, as
do many analog circuits.
SAI_Peregrinus wrote 1 day ago:
Lots of amplifier circuits need a bipolar supply: both positive
and negative voltages with respect to ground.
jacquesm wrote 1 day ago:
Yes, and that tiny little difference can cost you a lot of
expensive gear if you run it off the battery and plug in a serial
port or something like that. You'll also learn first hand what
arc welding looks like without welding glass.
servo_sausage wrote 1 day ago:
Is that something other than a labelling convention? Is ground
actually connected to a earth stake?
magicalhippo wrote 12 hours 11 min ago:
> Is ground actually connected to a earth stake?
Yes, or something similar[1]:
A few of the more efficient grounding electrodes for buildings
and structures are:
- Metal Underground Water Pipe
- Metal In-ground Support Structures
- Concrete-Encased Electrode (also known as âfooter groundâ
or âUfer groundâ).
- Ground Ring
As mentioned this is particularly important for telecom and
similar systems which have signal wires going literally through
the ground.
[1]
(HTM) [1]: https://www.nfpa.org/news-blogs-and-articles/blogs/202...
CamperBob2 wrote 1 day ago:
Cathodic protection against corrosion was the goal of using
-48V, in the telcos' case.
myself248 wrote 1 day ago:
And the telegraph lines before that.
bluGill wrote 1 day ago:
positive ground used to be in all cars. When they went from 6
volts to 12 the disadvantages became appearant fast and so
everyone went negative ground then (mid 1950s). I am not clear
why positive ground was bad (maybe corrosion?)
yostrovs wrote 1 day ago:
Check out older English cars.
bandrami wrote 1 day ago:
I stg if I see the kids talk about Westinghouse being batterymogged I'm
leaving the Internet
shdudns wrote 1 day ago:
How is DC better than a three phase delta 800Vrms, at 400Hz?
- Three conductors vs two, but they can be the next gauge up since the
current flows on three conductors
- no significant skin effect at 400Hz -> use speaker wire, lol.
- large voltage/current DC brakers are.. gnarly, and expensive. DC does
not like to stop flowing
- The 400Hz distribution industry is massive; the entire aerospace
industry runs on it. No need for niche or custom parts.
- 3 phase @ 400Hz is x6 = 2.4kHz. Six diodes will rectify it with
almost no relevant amount of ripple (Vmin is 87% of Vmax) and very
small caps will smooth it.
As an aside, with three (or more) phase you can use multi-tap
transformers and get an arbitrary number of poles. 7 phases at 400Hz ->
5.6kHz. Your PSU is now 14 diodes and a ceramic cap.
- you still get to use step up/down transformers, but at 400Hz they're
very small.
- merging power sources is a lot easier (but for the phase angle)
- DC-DC converters are great, but you're not going to beat a
transformer in efficiency or reliability
hrmtst93837 wrote 1 day ago:
400Hz is an aircraft hack. In a data center, where batteries and most
of the stuff behind the PSU already want DC, cutting conversion
stages and a bunch of UPS weirdness is a boring win even if DC
breakers are nastier and pricier. If you want switchgear with
aerospace pricing in a building full of racks, AC at boutique
frequencies is one way to get there.
prezk wrote 1 day ago:
An advanced AI rack might use 100kW = 800V 125A, requiring gauge 2,
quarter inch diameter---this isn't your lol speaker wire. Actually, I
apologize, I realized I may be talking to a serious audiophile,
didn't mean to disrespect your Monster cables.
The skin depth by the way is sqrt(2 1.7e-8 ohm m / (2 pi 400Hz
mu0))=~3mm for copper---OK for single rack, but starts to be
significant for the type of bus bars that an aisle of racks might
want.
As for efficiency, both 400Hz transformers AND fancy DC-DC converters
are around 95% efficient, except that AC requires electronics to
rectify it to DC, losing another few percent, so the slight advantage
goes to DC, actually.
As for merging power, remember that DC DC converter uses an internal
AC stage, so it's the same---you can have multiple primary windings,
just like for plain AC.
bigiain wrote 1 day ago:
> I realized I may be talking to a serious audiophile, didn't mean
to disrespect your Monster cables.
I am a recovering audiophool.
I do own a pair of 2m long Monster Cable speaker cables (with
locking gold plated banana plugs). I am fairly certain I've used
welders with smaller cables.
(In my defence, I bought those as a teenager in the late 80s. I am
not so easily marketed to with snake oil these days. I hope.)
(On the other hand, I really like the idea of a reliably stable
plus and minus 70V or maybe 100V DC power supply to my house.
That'd make audio power amplifiers much easier and lighter...)
adamking wrote 1 day ago:
> no significant skin effect at 400Hz -> use speaker wire, lol
now run that unshielded wire 50 meters past racks of GPUs and enjoy
your EMI
> The 400Hz distribution industry is massive; the entire aerospace
industry runs on it
nothing in that catalog is rated for 100kWâ1MW rack loads at
800Vrms
> 3 phase @ 400Hz is x6 = 2.4kHz... Your PSU is now 14 diodes and a
ceramic cap
you still need an inverter-based UPS upstream, which is the exact
conversion stage DC eliminates
> large voltage/current DC breakers are.. gnarly, and expensive. DC
does not like to stop flowing
SiC solid-state DC breakers are shipping today from every major
vendor
> DC-DC converters are great, but you're not going to beat a
transformer in efficiency or reliability
wide-bandgap converters are at 95%+ with no moving parts
shdudns wrote 1 day ago:
"now run that unshielded wire 50 meters past racks of GPUs and
enjoy your EMI"
Multipole expansion scales faster than r^2.
Also, im not in the field (clearly) but GPUs cant handle 2.4 kHz?
The quarter wavelength is 30km.
"nothing in that catalog is rated for 100kWâ1MW rack loads at
800Vrms"
Current wise, the catalog covers this track just fine. As to the
voltages, well that's the whole point of AC! The voltage you need
is but a few loops of wire away.
"you still need an inverter-based UPS upstream, which is the exact
conversion stage DC eliminates"
So keep it? To clarify, this is the "we're too good for plebeian
power, so we'll transform it AC->DC->AC", right?
"SiC solid-state DC breakers are shipping today from every major
vendor"
Of course they do. They're also pricey, have limited current
capability (both capital costs and therefore irrelevant when the
industry is awash with GCC money) and lower conduction, and
therefore higher heat.
They're really nice though.
"wide-bandgap converters are at 95%+ with no moving parts"
transformers have no moving parts. Loaded they can do 97%+
efficiency, or 2MW of heat eliminated on a 100MW center.
shiroiuma wrote 1 day ago:
>- no significant skin effect at 400Hz -> use speaker wire, lol.
What are you talking about? There's a very significant skin effect
at 400Hz. Skin effect goes up with frequency. These datacenters use
copper busbars, not cable, so skin effect is an important
consideration.
shdudns wrote 1 day ago:
At 100 000 A for a 100 MW data center at 1000 V, speaker wire is a
joke.
You obviously need at least a dozen stands in parallel!!
Clearly skin effect scales with frequency but, 400 Hz is still low,
only 2.5x lines frequency (the scale is by the root); so the skin
depth is 3mm. 3mm on each side makes for a pretty hefty rectangular
cross-section.
bigiain wrote 1 day ago:
If you could get that 100,000Amps flowing through your speaker
wire, the vaporised copper and the plasma channel would probably
keep your 100MW flowing, at least until your building caught
fire.
jacquesm wrote 1 day ago:
Even your monster cable? ;)
bigiain wrote 1 day ago:
Well, it'd still vaporise, but it'd sound smoother and more
musical as it did it, and the soundstage from the plasma arc
would be _stunning!_
jacquesm wrote 1 day ago:
It's almost worth the experiment and your cables are a
sacrifice I'm willing to make. For science, of course.
bigiain wrote 1 day ago:
You're _so_ right!
I'm pretty sure you have my delivery address from when I
bought sorted Lego from you about 10 years back.
Let me know when to expect the 100,000Amp test equipment!
I shall make sure I wear better PPE than just my reading
glasses.
:-)
jacquesm wrote 1 day ago:
This would be the funniest thing to do. 100K Amps is
doable, the question is for how long. That would be one
very impressive bank of capacitors. And to turn a 00
into plasma would have some spectacular side effects,
such as raining molten copper across a sizeable area.
Just your reading glasses would indeed not be enough,
there probably isn't any PPE that I would consider
entirely safe other than sufficient distance from
ground zero. But now I'm really curious. I have a spot
welder that will do bursts of 5KA and that will happily
throw the breaker every so many welds. 100KA sustained
will be a fair engineering challenge.
Ah, that lego project... that was one I always wondered
if I should have industrialized it but sourcing enough
lego was a real problem.
adiabatichottub wrote 1 day ago:
Ho ho ho, you asked for it:
(HTM) [1]: https://www.youtube.com/watch?v=OC7sNfNuTNU
jacquesm wrote 1 day ago:
Holy crap. That's a whole series of bad ideas
extremely well executed. That guy probably has
never seen what a lead acid battery can do when it
explodes. He keeps hiding away from the hot metal
but in the path of ~half of those batteries.
Ignorance is bliss.
That's low voltage lightning :)
adiabatichottub wrote 1 day ago:
He was gifted an arch flash suit by the guys from
Lightening on Demand :D
jacquesm wrote 1 day ago:
"The gift of life". Complete madness.
bigiain wrote 1 day ago:
See also (as posted elsethread):
(HTM) [1]: https://www.youtube.com/watch?v=RoGbrgOhPe...
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