Use secondary PSU for GPU only

[46godric]

Okay, so I have two older systems where one is working except for the GPU and the other one is so old that it's not worth to use. In the working one I have a 375w PSU and the other a 350w.
I was thinking about buying some cheaper/older graphics card. I found a used gtx 460 for a good price. But according to psu calculators my system would use 368w and with a probably halfbad psu it might not be enough.

So could I use the 350w psu's 6pin to connect to the gpu and everything else on the 375 one?

 

[DSzymborski]

What are the exact power supplies?

 

[Karadjgne]

Sure, with separate power plugs, gotta stick it somewhere, bolt it so the case is grounded to the frame (or attach by wire) and figure some way to turn it on. Kinda more of a pita than the $40 for a single psu large enough to cover both.

 

[46godric]

What are the exact power supplies?

Well those are old (up to 10 years) prebuilt machines so on one of them it says Dell and I cant check the other right now, but probably similar.

 

[46godric]

Sure, with separate power plugs, gotta stick it somewhere, bolt it so the case is grounded to the frame (or attach by wire) and figure some way to turn it on. Kinda more of a pita than the $40 for a single psu large enough to cover both.

So i can't just connect the 6 pin? Do I have to find a way to turn it on? Thought it would give out power just by having the power plug in the back, or no?

 

[Karadjgne]

No. The psu will be off if just plugged in. When you push the button on your pc, it's not the pc you startup, but the psu which powers everything else. So you'll need to figure out a way to power up both psus at the same time, and be able to turn off the psus at the same time. They must also be linked at least via common ground at the pc or you run the risk of creating feedback since the gpu will be powered by separate sources.

It's not something commonly done, having separate sources for a single pc, basically only miners using massive banks of gpus will even attempt it because the potential for disaster is quite real. You've got a specific frequency, carrier wave, amplitude etc coming from one psu at 12v, and a different one coming from the other psu. Being 12v DC, that power all goes back to ground. Not being tied together means that if the pc unit is putting out 200w and the gpu unit 100w, the return will be 250w and 50w as that 100w will be split after joining in the gpu.

You can do it successfully, if you can keep the loads somewhat balanced between the psus it's better, but trying this on 10year old, low grade (Dell is possibly a Delta unit and quite good), unknown or rediculous limit protection circuitry psu's is just asking for a giant ball of smoke which may or may not happen.

Personally I'd recommend giving up on the idea unless the pc in question isn't something you are afraid to lose.

 

[kerberos_20]

if u like to dyi u can interconnect green wire (should be only one) and ground both psus together
that green wire is on that big ATX connector (20/24 pin)

 

[DSzymborski]

Really, the best option is to bite the bullet and just buy one modern, competent, budget GPU, and not have to jury-rig ancient power supplies.

PCPartPicker part list / Price breakdown by merchant

Power Supply: Corsair - CXM (2015) 450W 80+ Bronze Certified Semi-Modular ATX Power Supply ($26.99 @ Newegg)
Total: $26.99
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2018-09-11 20:45 EDT-0400