A multi power supply for your desk from a PC power supply


I've blogged several times before about my desire for universal DC power -- ideally with smart power, but even standardized power supplies would be a start.

However, here's a way to get partyway, cheap. PC power supplies are really cheap, fairly good, and very, very powerful. They put out lots of voltages. Most of the power is at +5v, +12v and now +3.3v. Some of the power is also available at -5v and -12v in many of them. The positive voltages above can be available as much as 30 to 40 amps! The -5 and -12 are typically lower power, 300 to 500ma, but sometimes more.

So what I want somebody to build is a cheap adapter kit (or a series of them) that plug into the standard molex of PC power supplies, and then split out into banks at various voltages, using the simple dual-pin found in Radio Shack's universal power supplies with changeable tips. USB jacks at +5 volts, with power but no data, would also be available because that's becoming the closest thing we have to a universal power plug.

There would be two forms of this kit. One form would be meant to be plugged into a running PC, and have a thick wire running out a hole or slot to a power console. This would allow powering devices that you don't mind (or even desire) turning off when the PC is off. Network hubs, USB hubs, perhaps even phones and battery chargers etc. It would not have access to the +3.3v directly, as the hard drive molex connector normally just gives the +5 and 12 with plenty of power.

A second form of the kit would be intended to get its own power supply. It might have a box. These supplies are cheap, and anybody with an old PC has one lying around free, too. Ideally one with a variable speed fan since you're not going to use even a fraction of the capacity of this supply and so won't get it that hot. You might even be able to kill the fan to keep it quiet with low use. This kit would have a switch to turn the PS on, of course, as modern ones only go on under simple motherboard control.

Now with the full set of voltages, it should be noted you can also get +7v (from 5 to 12), 8.7v (call it 9) from 3.3 to 12, 1.7v (probably not that useful), and at lower currents, 10v (-5 to +5), 17v (too bad that's low current as a lot of laptops like this), 24v, 8.3v, and 15.3v.

On top of that, you can use voltage regulators to produce the other popular voltages, in particular 6v from 7, and 9v from 12 and so on. Special tips would be sold to do this. This is a little bit wasteful but super-cheap and quite common.

Anyway, point is, you would get a single box and you could plug almost all your DC devices into it, and it would be cheap-cheap-cheap, because of the low price of PC supplies. About the only popular thing you can't plug in are the 16v and 22v laptops which require 4 amps or so. 12v laptops of course would do fine. At the main popular voltages you would have more current than you could ever use, in fact fuses might be in order. Ideally you could have splitters, so if you have a small array of boxes close together you can get simple wiring.

Finally, somebody should just sell nice boxes with all this together, since the parts for PC power supplies are dirt cheap, the boxes would be easy to make, and replace almost all your power supplies. Get tips for common cell phone chargers (voltage regulators can do the job here as currents are so small) as well as battery chargers available with the kit. (These are already commonly available, in many cases from the USB jack which should be provided.) And throw in special plugs for external USB hard drives (which want 12v and 5v just like the internal drives.)

There is a downside. If the power supply fails, everything is off. You may want to keep the old supplies in storage. Some day I envision that devices just don't come with power supplies, you are expected to have a box like this unless the power need is very odd. If you start drawing serious amperage the fan will need to go on and you might hear it, but it should be pretty quiet in the better power supplies.



Interesting idea; however, simply swap the + 12 and non-chassis ground negative for -12 v. Same goes for +/- 5V (or any other voltage)

Re DC power, I wish that automakers would develop and implement a different interface, as opposed to the cigarette lighter plug. First of all, its too large (I know there is an in-line fuse, but no matter, its diameter is way too big. Secondly, we need more of them (I'm not speaking of large SUVs, etc, where there might be multiple receptacles). If the plus was smaller, more of them would fit in the same space, and a few extra could be spread out around the dash. If youw ant to charge your cell-phone (that's 1), play your MP3 while charging it (that's 2), have a radar detector (that's 3) and a portable GPS (that's 4 - I know they run on batteries, but that would be for handheld usage). You can buy a 2 way cigarette plug spliiter from RS, but that is big and bulky. Plus, I'd like for each receptacle to be separately fused. Thanks!

12v is 12v, reversing the poles doesn't do anything. The reason the -12v from these power supplies is important is that combined with the +12 (from the same ground) you have 24v and all the other useful voltages, but not at high current.

Some airlines developed a different plug, you will find it in the seats of UA, and I have the adapter, but it never caught on.

Brad, PC power supplies aren't designed for this application. They can overheat and blow out under "no load" conditions.

Would they need load on all the outputs? I mean I have a dozen power supplies under the desk, many at 5v, 6v and 12v, so I would be drawing a couple of amps at those voltages. Don't know if I would be drawing as much at 3.3v, but I would have to presume the supplies can handle low load at that voltage as older motherboards don't use it at all.

Or are you just saying we would need to have the fan going?

Hi guys, can anyone tell me (or point me where to read about) where in _modern_ PC hardware utilised -5 and -12 volts output? Some old expanshion cards used -12v (DAC/ADC, for instance) - but this was a quite long time ago - what for now?
Sometime, when I repair one of modern PSU, I discover (with great surprise) that -5v line whithin it connect to "air" (e.g goes to "nothing"), and "Health monitor" in BIOS shows something like -61,55v in "-5v" line.
Tnx in advance,
regards, Benny.

PS Sorry for my ugly English.

Don't know about -5v but RS232 still uses -12v and you still find serial ports, at least one, on desktop PCs. Laptops have pretty much given up on them. Desktop motherboards have headers on them even when there's no port at back.

http://www.igo.com/home.asp seems to put you a bit closer to the goal.

But powers only one powerful device and has a module to do some low power devices. That's more towards my goals for a universal power supply. This thread's about doing something cheap with the cheap and plentiful power supplies I have several of in my closet!

This is an idea I ran across at another site as well..
It pays to look around and re-use whatever locally
available technology we have...

Case in point:
We have a Sustainable Energy class at our university.
We're modifying electric bicycles to run from NiMH
battery packs, and needed a DC source that wasn't common:
32v @ 18 amps ( to fast-charge a 16-cell 12AH pack ).
If you hook up 3 PC power supplies in series ( the 12v
outputs), you can get 36v @ as many amps as the supply
is rated for - I found 18-24A models ). We are also
building battery management boards ( to oversee the
fast-charge termination - necessary) we can use one of
the +5 outputs to run the chip on these boards.

You can put a small power resistor across the +5 output
to draw enough current to keep the PS happy so it doesn't

BTW, the NiMH packs we are planning to use were
originally for Laptops - 9.6v @ 1700 maH -
put a bunch in series/parallel and they can spin
an ebike motor without an issue...

The issue of course is charging them..

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