Many of us have lots of devices that uses AC mains (110V/220V) to DC (typically 12VDC, 9VDC and sometimes 15VDC) adapters. There's my Wi-Fi router, my powered speakers, printer, scanner, etc.

So I would like to combine all these into a single device; do the AC/DC conversion once and have everyone tap the DC line, instead of each doing the conversion themselves.

Regarding to this, I have two questions:

  • is there any commercial solution out there to do this? (bench power supply for example)?
  • suppose I have one of these beauties powering my stuff and this power supply can deliver 100W of power. Will the device always be consuming 100W of power or will the consume increase as I hang more devices?



Your last question first: no it won't always consume 100 W, that seems to be a common misunderstanding. A 100 W power supply will supply 1 W if that's what the load needs. It's what you attach to the power supply which determines the actual power consumption. The 100 W is just the limit.

Bench power supplies are a possibility, but they are too sophisticated for this: they are designed to deliver 1 or more variable voltages, while you can do with fixed voltage levels. Also, a bench power supply usually has only a couple of voltage outputs, so it may depend on your needs if that's sufficient. You already mention three different voltages, but you might also add 5V DC, maybe others.

The lack of a standard makes it hard to design a universal supply; there's not even agreement on a standard polarization for the DC connector. So each power supply is designed for its own purpose: a given voltage at a given current. Today many adapters use switch-mode regulators for more efficiency, but also these are optimized for a certain output voltage. You could go from 15 V to 12 V to 9 V, but each level has its efficiency, and for the last link in the chain you would have to multiply all previous efficiencies, and the 15 V will need to be higher power than when it just has to power that router.

What you could do is remove the electronics from the adapters and put them all in a single enclosure, that would at least save you a couple of wall sockets. But you'll lose the possibility to wire every device up where you want; do you want to place your speakers in the same closet as your router?

Final note: a PC power supply delivers different DC voltages, but most power is available at the lower 5 V, maybe not enough at 12 V, and at tens of amperes at 5 V it's way overkill.

  • \$\begingroup\$ @Desperate - you're welcome!!!!!!!!! ;-) \$\endgroup\$ – stevenvh Jun 26 '12 at 10:16
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    \$\begingroup\$ @stevenvh Actually today PC power supplies provide most of their power at 12 V rail since that rail is used to power pretty much all big consumers such as CPUs and GPUs. \$\endgroup\$ – AndrejaKo Jun 26 '12 at 11:44
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    \$\begingroup\$ @stevenvh that page's recommendations look seriously out of date. Intel's been primarily 12V on the mobo since the P4, Amd since the Athlon 64. The reason they use 12V for input is to keep the amperage down on the PSU wires. The 4/8pin 12V connectors on a modern mobo are intended as dedicated CPU power links. PCIe slots can deliver upto 75W of power to the GPU via 12V; higher performance cards use 6/8 pin 12V connectors to deliver an extra 75/150W of power each to the card. \$\endgroup\$ – Dan is Fiddling by Firelight Jun 26 '12 at 12:40
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    \$\begingroup\$ @stevenvh Also look at new PSU designs. Antek's 450W 80+ platiunum model (picked because the oldest platinum models are only about a year old) is rated for only 16A on the 3.3/5v rails (85W combined max); and 34A (408W) of 12V power. You'll see something similar on any other new PSU. Even on a 1000W model, enermax only provides a max 20A on the 3.3/5V rails (100W combined max). newegg.com/Product newegg.com/Product/Product.aspx?Item=N82E16817194097/… \$\endgroup\$ – Dan is Fiddling by Firelight Jun 26 '12 at 12:44
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    \$\begingroup\$ @stevenvh Make that very dated. Look at section 26.4 of the guide. They discuss low end PCs with 128MB of ram, and high end ones with 512MB. Despite the 2008-2012 copyright, the contents there probably dates back to ~2000. \$\endgroup\$ – Dan is Fiddling by Firelight Jun 26 '12 at 12:47

I too think that this superficially would be a great idea. When you look into the detail though, it's virtually impossible. What voltage would you distribute? A DIY magnetic in-defibrillator controlled by an Arduino might take 3.3v. But your door bell's buzzer takes 12v. And a LED night light might run on 2.4v. The industrial PLC watering those plants in the attic runs on 24v.

If you distribute 2.4v, you're going to lose a lot of power just through cable resistance.

If you have multiple voltages, you'll need multiple (somewhat redundant) circuits reaching all parts of your house.

If you have multiple parallel cable runs, that will significantly raise the material /installation costs of the building. This would be a difficult and unwanted proposition for starter home builders.

And how would you future proof it? When 0.5v CPUs become available for PCs, where would you get 0.5v from? So you're left with the lowest common denominator - 240VAC.

  • \$\begingroup\$ not to mention the ground loops and short circuits created by connecting all those previously isolated devices to the same common. \$\endgroup\$ – Jasen Jul 24 '16 at 21:26
  • \$\begingroup\$ @Jasen That's right. I forgot to consider safety. Your house would look like the inside of a Cray super computer. Which wires would average Joe connect his tri voltage computer controlled massage chair to? Ban him from all electrical work? Are we now making social policy? \$\endgroup\$ – Paul Uszak Jul 24 '16 at 21:35
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    \$\begingroup\$ You're just naysaying, being all dramatic about voltage conversion, and that's bunk. All my routers and laptops use 12V or higher even though they're 5V or 3.3V devices, My LED lighting is perfectly efficient on mains power. Voltage conversion, done deal. Second once a standard is picked, everyone will build to that, including solving the ground loop "problem". For now, the quasi-standard is 12V, and thousands of off-grid homes use it as their primary bus. It's being done. For real. \$\endgroup\$ – Harper - Reinstate Monica May 20 '17 at 3:17
  • \$\begingroup\$ @Harper Hmm, I'm not sure that the bunkers of 5000 post apocalyptic survivalists in Utah, America constitutes an emerging standard for LG, Toshiba and Apple or the house building industry in Germany... \$\endgroup\$ – Paul Uszak May 20 '17 at 22:38
  • \$\begingroup\$ @Jasen is quite on spot, ground loops are not a minor issue nor an easy one to cope with, shall we add a second isolated DC/DC in each appliance? But even worst, what about short circuit current? A one off adapter can probably supply a few hundred mA but a centralised power supply will probably set 10s amperes short circuit, enough to melt down cords and sockets, so we have come to the need of an individual current limiter in each socket... We are slowly building up a new DC/DC adapter in place of existing ones. \$\endgroup\$ – carloc Sep 30 '18 at 8:07

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