12V from Computer PSU

[Monsters_Inc]

To all electronics CPF wizards,

I just came up with an idea this afternooon, don't know how laughable it is yet. I was thinking of drawing the 12V DC from my computer's power supply hooked up to a 'car charger' of a rechargeable flashlight.

It's the most cost effective way of transforming a US device to work in Aust. AC inverters for 110V to 240V will cost >$60-80, whereas a 300W PSU is around $30.

Plus, I don't think it's practical to drive for the 10 hours needed for a light to fully charge.

Am I insane? Is there a flaw in my thinking that should be addressed?

Thanks.

 

[Klaus]

Hmmh - it will be noisy, suck a lot of power and might blow on you if no load is attached (its a switching PS which needs a load) - besides that its a great idea IMO - maybe just the effect of mass production - you might look into buying a smaller PS for that purpose (100W or 150W will be sufficient) which might also be cheaper and quiter - on the other side why not just use one 12V connector off your PC (when its ON long enough) ?

Klaus

 

[James Van Artsdalen]

The load might not be enough to drive it into regulation. This is a common problem in PCs: not only do you have to make sure you can power all of the power-hog devices that might be installed but you also have to test and make sure it works right empty

 

[evan9162]

I've run several old AT PC power supplies with no load, and have had no problems. They supply the correct voltage, even under no-load situations. Most that I've found are also short protected. If you do short one of the rails, the supply will shut down. You have to power cycle the supply to get it back on.

-Darin

 

[snakebite]

you can use a pc supply as long as you put a load on the +5.this keeps it in regulation.
a car taillight bulb will do.
but not good for things like ham gear as they are noisy.
btw at supplies can be gotten cheap or even free since they are obsolete.

 

[Entropy]

Check out either http://www.bit-tech.net/ or www.virtual-hideout.net - If it's not a problem to only use this charger when your PC is on, one of those sites has an article on bringing the power from inside your PC to external power jacks for powering "external mods" (Note: These guys like their LEDs too... They haven't discovered Luxeons yet though.

 

[Tsao]

Hi Onyx
I got few this

it was power for HD in a disk array. I don't have spec buy it shows "AC input 115V 230V" It can drive 12V@2A, 5V@3A. The I've used one for my PC extra fan. Not bad. I can give it to you for free if you want to do some mod with it. Let me know if you want.
FYI

 

[Monsters_Inc]

Thanks for all the info guys. Tsao - thanks for the offer, but looking at that pic has be put off somewhat. I'm not THAT into electronics to be able to figure out what to do with that...

The extent of my PSU modding is 7V fans to lower noise. And yes, AT PSU should work fine, ATX's require shorting the brown pin (#14?!) to ground and a load applied. I'm a little hesitant to use my working PC's 12V line, in case something shorts or blows, could cause quite some damage...

 

[Graham]

I've run ATX and AT PSUs using just the 12v rail and had no problems. Although given the huge variety of PSUs out there anything is possible.

You could always look for an old second hand PC, or even something someone is throwing away (even an old 386 PSU would probably do - in fact older is better, since old AT supplies have an actual switch on them, unlike ATX supplies)

Actually, I've been scavenging old supplies here at work to use at home for electronics (and torch!) experiments - I've been using one to power a 50W MR16 lamp, and it does the job perfectly.

I suspect a lot of people don't realise just how handy the PSU in an old PC can be.

Graham

 

[Tsao]

Originally posted by Onyx:
Thanks for all the info guys. Tsao - thanks for the offer, but looking at that pic has be put off somewhat. I'm not THAT into electronics to be able to figure out what to do with that...

<font size="2" face="Verdana, Arial">ya, even me, electronic engineer, still afread to touch some thing should touch on it.

 

[PsycoBob[Q2]]

I can get rid of some of the worries about shorting.

Find a molex 4-pin pass-thru meant for powering a fan. Either rip the fan off, and use those 2 wires, or clip off the male (uh, downstream end- those things are male-shroud and female-pin) end and attach wires to the yellow and black wires. Yellow is +12v. An inline fuse-holder soldered direct to that wire with a chunk of heat-shrink to cover the connection. Nice, fast-blow 2-amp fuse...

And the nice plug will let you disconnect it from the PSU if you want. I'll let you figure out the rest. (Hm, a little more shrink-tube might be useful...)

 

[Zelandeth]

Well, until I actually got around to building a specifically designed regulated DC supply (1.5V - 12V), an old 100W AT PC PSU was used. Runs fine with or without load, and shuts down if short circuited. All I've done to it is cut a hold in the case and replace the original switch with a rocker which fits in that hole, and remove all leads apart from +12, +5 and ground, which have small crocodile clips on. Does the job fine, and appears to be pretty solid (has survived many a drop off the desk anyway). Presently it's just powering a 20W haologen desk lamp (manufacturer had fitted only a 15Ah transformer for goodness sake! which promptly went up in smoke after a very short time), and does the job just fine. Purpose made PSU on the other hand usually passes the time running a pile of cheap LEDs which are tied by supply wires to a couple of supply rails. Very handy. Could post schematics of that PSU I guess if anyone's interested.