dual power supplies? questions!

The_TailGunner

The_TailGunner

The_TailGunner

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lo all - longish post, so please bear with me...

im about to get an nvidia gtx 460 1gb, and i suspect my psu may not be up to it. because i am a cheap git at the best of times, im going to run a second power supply (as I have one spare) to help matters.

if i have my wiring diagrams right, i'll need the green and any black wire from the 24 pin mobo connector in order to turn the second psu on.

rather than bother wiring in a new switch or a relay (and paying for same), would i be ok to splice these into the wires that come from the case switch to the power-on pins on the mobo? Would i be right in thinking this would work? seeing as you can start an atx mobo by shorting the pins with a screwdriver, i assume all the case switch does is short them in a more elegant manner?

With this problem solved, am i best using the second psu for the gfx card, and leave everything else alone?

thanks in advance!

TG

tl:dr - i want to do something ill-advised with power supplies. i could die without your sage advice!
 
From the many years ago that it was that I needed to do this (think Celeron 300A times) here are a couple of pics.

Wiring
IMAGE1.gif


ATX connector
CONNEC1.jpg


Basically connect the green from the two supplies and a ground from the two supplies, short the grey and a ground on the second supply.

If you come to any harm doing this then it is through your own misadventure.
 
Hi
To run my 24 hour water test I just removed the 24 pin connector from the Mob and shorted out the green and black to run the PSU, why do you need to connect two together, why don't you just short them out , when you switch on the PSU it will power up.
I would not link them together, if one shorts it could take the Mob out.

I would just buy a better PSU and make it easy
ALan
 
to all you 'just buy a bigger/new one' naysayers - that would be less exciting! (and im a cheapskate)

the 2 power supplies have both been in use for a couple of years in machines i currently use for gaming. I assume if they were going to blow up, they would have by now.

:D
 
You can buy a duel psu "y" cable with a breakout cable for the sake of about 3 quid. Does the same thing as described above but properly terminated and probably neater.
 
I did this for about a year, never had any problems with it. I just shorted the wires on the 2nd psu and turned the rocker switch on before turning the pc power on everytime. was messy but it cost me nothing as i happened to have a spare psu lying around. I only used it for the gfx card.
If i knew about that adapter mattyfez mentions i would def had got one of them -.-
 
mattyfez said:
You can buy a duel psu "y" cable with a breakout cable for the sake of about 3 quid. Does the same thing as described above but properly terminated and probably neater.
Click to expand...

excellent! i'll trawl my local catalog-toting electical component selling high street store...or attempt to find a wiring diagram and make my own...

thanks a mil!

TG
 
I should imagine the adaptor does the same thing as the wiring diagram above (assuming that diagram is correct). To those asking why - so that the main power button controlls both PSUs, dur :).

But out of interest what is the rating of your existing PSU? The 460 isn't exactly a power hungry beast.
 
What's the benefit to shorting the grey wire to earth on the second psu? I've also used a psu to run a pump overnight by shorting green to black, but I've not done anything with the grey one.

I vaguely remember that it's important for the power supplies to agree on what earth is, but if they're both firmly bolted to the same case that should do it.
 
The grey is the "Power Good" line, it's just a safeguard to keep the 2nd PSU running properly.

As said by Liampope the point of joining green to green and one ground from each supply is so that both supplies turn on when you press the power switch on your PC.

I used a 200w and a 250w supply like this for around three years without issue to run a Celeron 300A at 450 system quite happily. Had the bits lying around so didn't see the point in buying a new PSU at the time.

These days I use a single Seasonic 650w.
 
JonJ678 said:
What's the benefit to shorting the grey wire to earth on the second psu? I've also used a psu to run a pump overnight by shorting green to black, but I've not done anything with the grey one.

I vaguely remember that it's important for the power supplies to agree on what earth is, but if they're both firmly bolted to the same case that should do it.
Click to expand...

Actually, looking at the diagram properly I also am not sure why you'd want to ground the PWR_OK signal on the second PSU?? It's an output from the PSU to the MOBO to say 'yep I'm good - away you go and boot up'. My initial skim-over interpretation of that diagram was that an LED was installed (would also have to have a resistor) to monitor the happiness (or otherwise) of the second PSU - the LED would be lit if the second PSU was happy. You'd of course know about the first PSU's happiness already - if it withdraws its PWR_OK signal the MOBO will reset :)
 
Liampope said:
Actually, looking at the diagram properly I also am not sure why you'd want to ground the PWR_OK signal on the second PSU?? It's an output from the PSU to the MOBO to say 'yep I'm good - away you go and boot up'. My initial skim-over interpretation of that diagram was that an LED was installed (would also have to have a resistor) to monitor the happiness (or otherwise) of the second PSU - the LED would be lit if the second PSU was happy. You'd of course know about the first PSU's happiness already - if it withdraws its PWR_OK signal the MOBO will reset :)
Click to expand...

Yeh you dont need a pwr ok, all you need is someting like this, 2 wires, an earth and a power on, to make the secondary PSU fire up.

cpa-167.jpg
 
Last edited:
alan whitaker said:
why do you need to connect two together
ALan
Click to expand...

If you don't have the two linked, then you potentially end up with a floating reference that isn't a true 0V throughout the system. Cue all manner of problems. Making the earth common is absolutely the right thing to do.
 
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