
So Where’s My Low Voltage DC Wall Socket? - kyancey
https://hackaday.com/2016/12/21/so-wheres-my-low-voltage-dc-wall-socket/
======
MisterTea
We don't need DC sockets as they dont solve any problems. The stupid simple AC
mains distribution system is well tested and proven. Who cares that they
provide up to 3kW. The "last meter" problem is perfectly solved using AC-DC
wall warts and bricks. If the power supply dies, you buy a new one and just
plug it in. No electrician required. Putting things in wall or central
distribution is not a solution to any existing problem and introduces needless
cost and complexity.

A better solution would be to get everyone on board with a single DC voltage
and connector. Then we can buy larger multi socket bricks that are just AC-DC
power strips. You can then add batteries and give it UPS functionality. But
good luck getting everyone to agree on a single standard.

~~~
Wowfunhappy
Wouldn't it be more efficient to have e.g. one DC power supply for the house
that can power everything that needs DC power, instead of lots of individual
(and likely cheap/inefficient) power supplies?

~~~
laurencerowe
Most electronic devices require low voltage DC, so resistance losses in
cabling across even quite short distances (10+ metres) would be significant.
This is why DC distribution in data centres if it is used is normally 48V.

~~~
snuxoll
It’s also more difficult do do straight transformation on DC voltages, it can
be done but the reason our power grid settled on AC was getting high voltage
transmission levels down to reasonable ones for use is simple with some wound
coils.

It’s really easiest to just keep everything AC until the point of use, putting
a transformer and a bridge rectifier in most devices is a better solution than
needing switching power supplies everywhere to convert DC voltages (or wise
options like linear regulators).

Switched mode power supplies also have EMI to deal with due to the higher
switching frequencies, an AC transformer runs at line frequency (50/60Hz).

~~~
MisterTea
Dumb DC supplies using just a bridge rectifier and filter cap(s) isn't really
ideal if you need a stable voltage. If the mains voltage sags, so does output.
Then factor in ripple from the cap bank under higher loads and the associated
nonlinear harmonics and power factor issues from the rectification. You could
add a linear regulator and increase the transformer output and burn the excess
off as heat but efficiency goes down the toilet.

Switchers, for all their complexity, are pretty damn clean in terms of output
and input PF correction. Even in audio and sensitive analog applications where
dumb supplies were preferred have been replaced by switchers. A good design
goes a long way and it's unfortunately easy to design junk switchers because
of the complexity involved.

------
rhinoceraptor
It seems like USB A/C are going to be that. You can already buy outlets that
have both mains and USB ports, there are even dual USB C outlets now, that can
do 30 watts:

[https://www.amazon.com/dp/B07PTWG5DV](https://www.amazon.com/dp/B07PTWG5DV)

~~~
Spooky23
The author makes the valid point that USB-A is too low power, and USB-C
requires active cables. (Translation: expensive or dangerous)

~~~
Johnny555
If you want one port that can charge multiple devices of varying needs safely,
you need smarter cables. Sounds like a reasonable tradeoff.

Otherwise every single cable would have to be built to handle the highest
possible power delivery rate (100W for USB-C).

~~~
lostlogin
Looking at that plug and how chunky the holes are for ac power, when access is
limited and you can’t see, shoving a usb c plug into the ac hole is going to
happen often.

~~~
Johnny555
You'd have to shove awfully hard -- hard enough to crumple the metal shell of
the USB connector, since it's wider than the opening in 120VAC socket. (I just
tried it with a spare electrical outlet, and even with a fairly hard push and
wiggling it around, I couldn't make it fit)

~~~
lostlogin
Yikes and thanks - I’m in New Zealand and our plugs are way smaller so you
couldn’t make that mistake here, but it’s good to know the terminals are far
enough in that it’s safe. I’ve seen some surprising things people have forced
into the wrong port. USB into Ethernet etc.

------
ethagknight
Is "Digital Electricity" a real thing? Its billed as an alternative to AC or
DC. This may be as good a place as any to ask this question, but I am a hotel
developer, and we've had a few people reaching out to us trying to sell
"digital electricity" that sends high voltage over cat5 (up to 2000w per the
Belden materials) by essentially sending high voltage for very brief blips
with the ability to switch off before any damage occurs if a short is
detected. they claim it is supposed to be significantly more efficient,
doesn't require electricians to run cables, and its safer. I declined... but
im still curious. basically every device in the room is connected via lan to a
power server.

[https://www.belden.com/blog/smart-building/digital-
electrici...](https://www.belden.com/blog/smart-building/digital-
electricity-5-things-you-need-to-know)

~~~
allovernow
Looks like buzzword marketing bullshit to me. Apparently they're just sending
pulsed DC power over Ethernet cables? Nothing else in that article is as new
or exciting as they dressed it up to be. GFCI outlets are standard in modern
houses, they claim to be safely transmitting "high voltage" but 120V is not,
and the "digital" buzzword stinks of marketing.

>It transfers high levels of power over non-power cable

You can't beat physics. Wires heat up from current, regardless of whether it's
AC, DC, or "digital" pulsed DC. I doubt Ethernet cable is rated for any
significant amount of power, but searching for "cat6 max power" doesn't return
any relevant results because search is broken in 2019.

It's also likely to be rather inneffecient, as they are converting from AC to
DC and then potentially back to AC? There may be an advantage to pulsing DC
but I'm not sure, typically AC is more efficient for power transmission
because of lower losses for the same power over distance and higher
transformer efficiency (no need for an inverter).

~~~
lopmotr
It's apparently a bit smarter than GFCI. [1] says it measures the loss in the
wire to determine if a person or whatever is touching it. So that would
protect people against shocks from touching both wires, which GFCI can't do.

[1]
[http://magazine.connectedremag.com/publication/?i=488126#{%2...](http://magazine.connectedremag.com/publication/?i=488126#{%22issue_id%22:488126,%22page%22:6})

I think this is a pretty nice idea except for the patents and only having one
or two suppliers and lack of technical details.

------
forgotmypwd123
I always thought running low-voltage DC through a house from a single supply
was doomed due to voltage drop over the distances required....

~~~
aivisol
That absolutely is. You could be better with 48 or even 24 volts, but then you
are out of luck if you want to power a majority of devices which are 12v. So
your only option is to go for USB-A wall socket which essentially is a wall-
wart hidden in your wall. I do not see a good solution here.

~~~
JoeAltmaier
A buck convertor in the socket (cost: $1) with a voltage dial or selector
would do the trick.

------
rb808
I dont think DC wall socket is the problem - its the small electronics that
each have their own power pack.

Ideally to me every led lamp, settop box, alarm clock, phone, laptop would not
come with a power supply box. It would just take a USB cable or similar
standard. Then you could buy a good quality power supply adapter that you can
reuse for lots of products - and avoid the abundance of random adapters
everywhere.

~~~
atonse
That is sort of happening already. A lot of devices are just using USB
standard for their power supplies.

I suspect that with PD, that allows even lamps to negotiate that they need
more power, maybe?

------
alexhutcheson
Interesting idea, but running an extra set of cables is a non-starter. The
cost/benefit analysis would never make sense for existing structures, and
newly built structures wouldn't do it unless it was almost certain to become a
universal standard. This is a classic chicken-and-egg problem.

You would also still need something similar to a wall-wart to step down the
voltage to whatever your device actually uses (e.g. from 12 V to 5 V to charge
your phone), so its not clear how much benefit there would really be from such
a system.

Whatever specs we adopted would probably also end up not being appropriate for
some future devices, so we'd probably go back to a substantial number of
devices bundling their own PSUs anyway.

Interesting idea, unlikely to ever be worth the cost. If wall-warts really
bother you, then just invest in some wall outlets with integrated USB sockets
- there are many good options on the market.

~~~
gwbas1c
Also, the biggest non-starter is just how _inefficient_ it is to move 12v any
reasonable length. 12v domestic wiring only makes sense in very tiny small
dwellings. (Think studio apartment or 3rd world country shack.)

Otherwise the voltage sag and resistance makes it cheaper and more efficient
to do normal 120/240 voltage with device-specific converters. (For example, if
I had to run 0-gauge cable from my breaker box throughout my house to support
12v, the cost of copper alone would be prohibitive.)

I honestly think standardizing on USB for devices that can use it is the best
approach, given that we already have tiny AC->USB converters that don't block
other plugs, and outlets with USB built-in are on the market. Furthermore, I
wonder just how much we can shrink the typical wall-wart so it won't cover
other plugs?

(I also think we're better off trying to do a global domestic 200 or 400 volt
DC standard.)

------
kjs3
The solar/RV/golfcart world has and entire ecosystem of standardized 12v DC
power distribution and the appliances that use it if you really feel the need
to have DC. Works pretty good...last year wired up a friends mountain cabin
with 12v solar, batteries, inverter for AC, led lights, fans, dorm room sized
DC fridge. Different manufacturers and everything popped together fine.

~~~
iamnothere
Most laptops can be charged from 12V auto-style sockets as well.

12V DC is fantastic for a solar setup (vacation cabin, off-grid home, or
whatever). You can still have some standard AC outlets using an inverter, but
there's no reason to have lights running off of AC -- especially if you have
LEDs! Since inverters cause a slow but constant power drain, it makes sense to
leave them off most of the time.

Edit: I also wanted to mention the amazing "3-way" fridges, which I was not
aware of until looking into solar a few years ago. They can run on AC, DC, and
propane, giving you an alternative if the power goes out. The RV world has
tons of this stuff, and the appliances usually aren't that much more
expensive. Some are even cheaper than regular appliances since they are
usually more compact.

~~~
nybble41
Keep in mind that your typical RV refrigerator capable of running on AC or
propane, and possibly DC, will run much less efficiently on electric power
than a standard electric refrigerator. That might make them less-than-ideal
for a solar + battery configuration. In an RV context one typically uses the
electric mode only when connected to "shore power", where the lower efficiency
is less of an issue.

Propane-based refrigerators use an absorption cycle which depends on heat
produced by burning the propane; in electric mode they just substitute
resistive heating. A pure electric refrigerator would use a compressor-driven
heat pump, which is considerably more efficient.

------
205guy
I think that with low power LED lighting, as well as all rechargeable devices,
there is a case for some (not all) 12VDC sockets around the house (and
cars/vans/RVs). Actually, I think mobile applications will be first: in an RV,
it makes no sense to have a big inverter to take your 12V batteries to 120V
AC, just to plug in wall warts to charge to camera, phone, etc.

I have a friend who installed 12V in parts of his house, backed by a solar
charged battery system. See my previous comment for some details:

[https://news.ycombinator.com/item?id=21109247](https://news.ycombinator.com/item?id=21109247)

Talking to this friend, we discussed the same problem as the OP. In RVs that
are wired for battery power, they use wall-mounted cigarette lighter plugs,
and you can buy some small appliances that use them. They are ugly and take up
too much space, it would be so much better to have a plug of a regular shape
and size. Of course it has to be polarized for DC, so something like ( - | ).

There is also the problem of breaking the arc in DC, so one prong needs to be
longer and making contact further in so it can't arc outside the plug. Or
maybe it needs some internal mechanism such as plastic slot covers that close
and break the ark (like child-protected sockets have now). Anyway it
definitely needs some research and design, but I think it would be cool to
have a new 12VDC standard plug, then people could start designing products
that use it to get the whole ecosystem started.

------
jon-wood
I don't get why they write off USB so quickly. It's small, it's reasonably
convenient, and is almost ubiquitous already.

~~~
ocdtrekkie
The article explains: USB A's power is too limited for a large percentage of
household uses, and USB C is complicated and expensive, requiring digital
circuitry to negotiate.

------
theandrewbailey
> ...and incorporate a fuse to protect the appliance cable from fire. Those
> British BS1363, fused-mains-plug habits die hard.

Lots of car barrel connectors have fuses inside. I'm not seeing much reasoning
behind not using the car barrel connectors, aside from 'it was designed for
cars, not as a general purpose connector'.

~~~
consp
They break easily. Spring loaded bits (actual springs). No properly defined
standard and they vary a lot. Come out easily depending on quality. Easy to
contact center pole to side poles on insertion. No ability to add earth.

~~~
Jamwinner
12v plugs are indeed a standard, and can be quite robust. Other than size and
cost, there are no such downsides. On DC there is seldom an 'earth', gound is
analougous to dc negative/neutral depending on local standard.

ANSI/SAE J563 and UL2089

[https://en.m.wikipedia.org/wiki/Cigarette_lighter_receptacle](https://en.m.wikipedia.org/wiki/Cigarette_lighter_receptacle)
shows the UL standard.

~~~
consp
The case was made as a dc plug in general. Though 12V does definitely not
require "earthing", you are correct about that. With earth in this case it is
not the ground perse but some connection schemes (and standards) require
either a third connector or open return path for DC which this connector
cannot provide.

Apparently they decided to make it a standard in 1994 after years of
mismatching equipment all over the world, which is longer than I would have
ever guessed. Interesting to see. Apparently UL "standard" does not translate
well to actual standard. My experience is that most devices fail on the spring
center contact, and do not fit for all cars. Anecdotal but still: even the
expensive charger I have doesn't work in one car I've owned (opel) due to the
misalignment of the outer contacts and it jumps out too much). It says it's
UL2089 compatible though so I guess opel was at fault. There are so many
"extension cords" out in the wild which hardly work or go lose after time due
to bad design or because they are just a bit too wide. I own several of them
and have thrown most away.

The funny thing is the standard describes two sockets with differing size
which is not helpful in any way and looks like a legacy of some manufacturers
made into the standard.

The article also mentions other bad characteristics about the connector and
plug like bad contact causing high resistance which is simple due to the
design but might also be present with other designs of course.

I mean, it's nice it became a standard as it was in every car anyway since
everybody smoked in them but there are way better solutions which do not have
the problems I already mentioned and are way better solution for home
appliances. If there is not yet a proper standard, why chose one which is not
designed for this usage and most definitely was never designed for what it is
used for today with all kinds of side effects (good or bad).

------
jhallenworld
Crazy, USA needs higher voltage AC, not DC...

People in the 240V world get to pull 3KW from their wall sockets, I'm jealous.

[http://wordpress.mrreid.org/2012/04/16/why-kettles-boil-
slow...](http://wordpress.mrreid.org/2012/04/16/why-kettles-boil-slowly-in-
the-us/)

------
nickhalfasleep
No mention of Power-over-ethernet?

~~~
mark-r
What is the maximum power provided by PoE? Wikipedia is surprisingly vague on
the subject, probably because there are multiple standards. PoE was never
intended to power more than just network equipment.

~~~
steve19
I am not sure how Wikipedia can be more explicit, they even have a table
showing the voltages and wattages of the different standards. [0]

According to that table, the latest standard, 802.3bt Type 4, can provide 71 W
to the device at the end of the cable (and inject 100W into the otherside).

[0]
[https://en.wikipedia.org/wiki/Power_over_Ethernet](https://en.wikipedia.org/wiki/Power_over_Ethernet)

~~~
mark-r
Clicking on the link "Power capacity limits" brings you to nothing useful. Are
you looking elsewhere?

~~~
steve19
Scroll down to the table "Comparison of PoE parameters".

------
errantspark
I have to deal with this problem constantly and I haven't figured out a good
solution yet. I'm not sure this is particularly meaningful in a normal mains-
connected environment but as someone who's base power source is a finite
amount of 24v DC, I hate eating the inversion losses when I could save ~7-16%
using switching supplies off the main bus.

Currently everything I have is connected up with a hodgepodge of those green
pluggable terminal blocks. It's not an elegant solution but it's hard to
standardize on something, especially when I have devices that run off 5, 9,
12, 24 and 48 volts. I still run an inverter most of the time (I have two,
pure and modified depending on the load).

I think it's possible to devise a decent solution here, I like the XLR based
designs but I'm afraid of plugging things into the wrong voltage. I think
maybe the good solution is to make a color-mapping for the common voltages up
to 48v (past that you require an electrician to do wiring in the US iirc) and
then make cables that are XLR on one end, and whatever-plug on the other end
with an LED that lights up corresponding to the voltage. That way you know if
your barrel jack is 12 or 5. It doesn't have to be foolproof, or even customer
friendly really. People setting up DC buses to run all their electronics
should be able to accept the responsibility of frying something if they give
it too much juice.

------
baybal2
The telecom industry has 48 volt as a de-facto standard, bur never came to a
mechanical standard.

Thus you see daisy chains of mechanical adaptors in telecom closets.

~~~
kjs3
Well...the daisy chains were the standard for mechanical connections. :-)

What there never was was a connection standard safe enough to put in a house,
made to be (ab)used by normal people. 48v DC as it lives in the telco world is
flat out dangerous if you aren't careful.

------
unilynx
If none of the current plugs are usable, can we have a low-power plug standard
based on PoE?

Having both ethernet and low power from one socket would be perfect for IoT
devices, save people from having to run Ethernet wiring themselves afterwards,
and cut down on wireless spectrum use.

And your 'smart fridge' would just plug into both outlets and use a relay to
cut 230V if the motor doesn't need to run.

~~~
atourgates
Wouldn't the labor/effort cost to run and terminate Ethernet vs. 120v wiring
be significantly higher?

My perspective is just that of someone who's run a bit of both at an amateur
level through my house, and finds terminating stupid-simple 120v wiring much,
much easier than ethernet.

------
upofadown
Yeah, we are kind of running low on actual high power devices to plug into
residential outlets these days. Those that remain are pretty much confined to
specific parts of specific rooms. Various stand alone cooking things on the
kitchen counter. Hair dryer in the bathroom by the mirror. The vacuum cleaner
seems to be the exception and there is a tendency toward built ins.

Heck, I don't know that there is even much need for high power ceiling
lighting any more. Everything that people want to see with any detail is self
illuminated these days. Just scatter some low power LEDs around (you don't
even have to provide a way to turn them off) and you are done. If you actually
want to read a paper book or do some knitting then an appropriate lamp is not
going to take hardly any power as it would only have to illuminate a small
area.

------
lostlogin
More than a low voltage plug (which I’d love) is the need for in wall smart
plugs that have a wired connection rather than wifi. I can’t believe I’m the
only person that wants this and while I’ve found a few in wall smart plugs,
I’ve never found a wired one.

~~~
paulfurtado
There are classic home automation systems like x10 that potentially predate
wifi and offer wired solutions that use the power lines themselves for wired
communication, you might want to check these out

~~~
dboreham
Powerline Gigabit Ethernet is a thing, but it's bordering on wireless (uses
the power wiring as a "guideline" as to where its RF energy should go). This
makes the network attachment unit costly and adoption low. For most
applications WiFi is cheaper and more convenient. Anyone who wants really
solid connectivity will lay Cat5.

~~~
paulfurtado
The use case here is turning an outlet or light on/off, so latency matters,
but it requires nearly zero bandwidth (assuming that you're not talking tcp).
Granted, x10 security cameras exist.

x10 speaks a protocol designed for this purpose and requires a base station.

------
gok
> USB C meanwhile requires active cables, sockets, and devices, sacrificing
> any pretence [sic] of simplicity.

Passive USB-C cables should be fine up to 60 watts. Beyond that you need a
chip to certify safe construction but that's a good thing.

------
8bitsrule
A DC solution is WAY overdue. Put your hand on your AC->DC converter, or your
wall-wart. Above ambient room temperature? Wasted energy. "It's only 2-10
watts." Multiply by 5 units (underestimated) per 100 million households.
That's >= a gigawatt. 8700+ GwH / year.

That's aside from the environmental costs of making & disposing of these
pernicioius devices. Time for that decades-old solution to retire.

------
fsh
I don't see how going to 12 V would help simplifying devices. Most chips don't
run on 12 V, so one will anyway need a switch-mode power supply or linear
regulators with big heat sinks inside each device. The added expense of a
rectifier and mains-capable transformer is minimal.

On the other hand, at least fewer people would be electrocuted by their crappy
Amazon USB chargers.

------
fortran77
We don't want low voltage distribution. It's dangerous. The currents have to
be MUCH higher, and actually increases fire risk.

------
alexhutcheson
Comments below the original post are great.

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moonbug
go look at copper prices...

------
jhoechtl
2016

