Modded power supply??

[doanster]

So I have a spare power supply layin around... want to use the +12V and +5V rails for some DIY projects (non-computer related). How do I control the on/off signal manually like how the mobo does? Which wires to bypass?

 

[Jiggz]

Here's some sites:

PSU to DC Power

Another one

 

[bX510]

Very interesting. What can you use the converted PSU for?

 

[doanster]

I dunno what other people use it for, but for me it's gonna power a 150W subwoofer amp for testing. My old power supply can pump 8A into the +12V rail... which should be enough just for testing purposes.

 

[JimPhelpsMI]

Hi, No big mods necessary. If it's an AT PSU then a DPDT switch can be added to the 4 conductor heavy AC leads to turn it on and off. If an ATX PSU then a momentary N. O. push button switch can be connected between the Green wire and any Black wire in the Mother board connector. Hope this helps a bit, Jim

 

[doanster]

Originally posted by: JimPhelpsMI
Hi, No big mods necessary. If it's an AT PSU then a DPDT switch can be added to the 4 conductor heavy AC leads to turn it on and off. If an ATX PSU then a momentary N. O. push button switch can be connected between the Green wire and any Black wire in the Mother board connector. Hope this helps a bit, Jim

Excellent.. exactly what I needed.

Now how would I turn the power supply off?

 

[Jiggz]

To turn it off I guess you can either unplug it from the wall or turn off the power switch on the PU itself if it's equipped with one. Although, it is true you can just use a momentary sw (ATX) or dpst maintaining sw (AT), remember switching PS requires a constant load (usually 1 Amp) either on the 5V or 12V line to stay on.

 

[JimPhelpsMI]

Hi, If you used the AT PSU with a toggle switch that switch would turn it on and off. If you use the ATX then the momentary button will turn it on an off same as if in your machine. Jim

 

[Zepper]

And you also want to put a minimum dummy load across the +12 and +5 rails to keep the PSU stable. (approx 12 Ohm at 20 Watts across the +12 and 5 Ohms at 10 Wats on the +5 rail),. That PSU can deliver maybe 96 Watts of 12V downhill with a tail wind. So be sure to keep the amp turned down.

.bh.

 

[doanster]

Originally posted by: JimPhelpsMI
Hi, If you used the AT PSU with a toggle switch that switch would turn it on and off. If you use the ATX then the momentary button will turn it on an off same as if in your machine. Jim

How convenient...

thanks!

 

[doanster]

Oh, where can I find power resistors that can dissipate the said amount of heat? I only have a bunch of 1/4W ones right now 🙁

 

[Zepper]

Radio Shack carries a small selection of high power resistors - as would any halfway decent electronic parts store that supplies the service trades. You can parallel lower power capacity resistors to get what you need. Say if you need ~12 Ohms at 20W, you could use two ~24 Ohm at 10Watts resistors in parallel or two ~6 Ohm at 20 Watt units in series to give the same end result. If you have an actual load like your power amp on the +12 then you don't need a dummy load there. You just need the dummy load on the rails that lack a real load. The idea is that you don't want to run switching PSUs without a load on all the high capacity rails (both the 5V and 3.3V rails are supplied from the same winding so a load on the +5 will do for both). In the old days, computers (that shipped without a full complement of drives) and better brand case/PSU combos would come with a dummy load hooked up so you could power up and test w/o worrying about damage to the PSU.
. Places like bgmicro.com or allelectronics.com carry a varying selection of power resistors (they are odd-lot resellers) if you don't have anything local to you.

.bh.

 

[JimPhelpsMI]

Hi, Try Radio Shack or your local Radio, TV wholesale parts store. If you can't find anything you can use an old HD or CD drive or MB. Modern PSUs dont seem to have a real problem with no load. I assume that if you are using it for testing or etc you will always have a load on when you turn it on. I use spare PSUs all the time for testing.
Good Luck, Jim

 

[doanster]

Thanks for the help everyone!