Two power supplies?

needhelpnoobie

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May 29, 2006
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I have two 400 watt power supplies. I'm running one of them in my main machine which I use primarily for gaming. I have a 3.4ghz cpu/2gbs pc3200/7800GS video card and 6 fans powered off of it. My +12V is showing 6.5V - 9V when I should be almost twice that.

Is it possible to use my other 400watt power supply to power my video card and something else to take the strain off the other? Or should I just buy a better PSU
 
Hmm I see a thread a few down and a guy shows his dual PSU but doesnt explain what he had to do to make it work.

Can i just plug in the second PSU then connect it to what I want it to power and it will start up? I always thought the 20/4 pin connectors had to be plugged in before it would power anything?

😳 IF you can tell i dunno wtf im doing lol
 
Turn the PSU off and unplug it. Find a paper clip. Find the green wire on the 20+4 connector, and any black (ground) wire. Stick one end of the paper clip in the green connector and the other in a ground connector. Wrap it all in electrical tape, just to be careful. The PSU should now "think" it's connected to a motherboard, and work to power various devices.

I just learned this a short while ago in a thread I started on problems with my latest homebuilt system. Oh, and I claim no responsibility for any damages, injuries, or other negative results incurred if you attempt this procedure. Just so ya know.
 
I used an old AT unit in both my dual psu mods so they operated independently, I just turned them on at the same time. For the first one I cut out the old power cable and found a smaller DPDT switch that fit the hole where the power cable used to fit, on the full atx I just let the old power switch hang out the second 3.5" cutout :lol: lots of zip ties...

This should be much more detailed in showing how to connect two AT or ATX units:

Using a Second Power Supply @ directron

edit: You can always sacrifice the reset switch to power on/off the second unit if it is ATX...
 
Well, 'tis generally cheaper to get one larger PSU than two smaller ones, but if you recall the original post of this thread, the guy already has two, so just doing a mod or two is a much more efficient option.

Oh, and having a switch between the power on lead and the ground is probably a good idea (over what I suggested, I mean), though if you've got a power switch on the back of the PSU, it really wouldn't matter.
 
2psfig6.gif


The quick-and-dirty:

1. Remove connector, tag wires for reference (to be safe, but they ARE color coded).
2. Find a 12v relay (power rating shouldn't matter, you will be passing less than 500mA.
3. Solder leads on to said relay, and shrink wrap bare metal.
4. Connect wires 14 and 15 (or 16 and 17 if you have a 24-pin EPS12v PSU) on the "slave" power supply to the switch portion of the relay, and the coil leads to the 12v +/- leads on the "master" power supply:

[code:1:f66819b1c8]
| | (---------- (coil +)
(switch +)----o \____ | | (
(switch -)___________| | | (---------- (coil -)[/code:1:f66819b1c8]

Mind you, polarity doesn't matter, just an indication as to what's what.

5. Splice all remaining wires from "slave" PSU into the corresponding wires on the "master" PSU.
6. Plug in your devices (estimate, and balance the load, if possible). Give it some juice.

Now, an explanation:

The "master" PSU, when powered on, will trip the relay coil, which will activate the switch, and ground the PS-ON lead, in effect "fooling" the "slave" PSU into thinking it is receiving the power-on signal from the motherboard (PS-ON will be pulled low when it receives the signal). The motherboard will then send the PG (power good) signal to the power supplies to let them know that the voltage has stabilized, and that it is OK to continue output.

2 reasons it has to be done this way:

1. The PS-ON logic will not likely be rated to pull both PS-ON leads low (out of ATX spec), which will either not power on either PSU, or fry the motherboard. Either way, no es bueno.

2. The PG signal is somewhat complicated; it must be signalled between 10 and 300 msec after power on, not simultaneously, and not too latent. Again, the logic circuitry is not rated for 2 PSUs.

So... sorry about going all Mr. Wizard on y'all...

Hope that helps!

Cheers,
 
Oh, and one more thing...

In case you hadn't gathered, this small circuit will automatically power the second power supply on when the first one is activated.

Now, all you have to do is find a place for it...

Cheers,