Secondary power supply for GPU only, will it work?

[Mr_Koala]

I'm trying to get one 7970 GPU into a very generic HP desktop, whose PSU uses non-standard connectors and therefore can't be replaced with a more powerful one. The existing PSU is rated at only 300W and won't be able to handle the whole system once the 7970 goes in.

This upgrade is happening on a very tight budget. Buying a new standard ATX mobo plus a power supply is not an option. Alternatively, I'm think about buying a secondary PSU which will be wired only to the 7970. When the system needs to boot simply short the PS_ON pin on the mobo connector to turn it on, and then boot the system regularly with the original PSU.

Laptop eGPU builds are powered in a similar manner, so I feel the plan should work. However I've never heard of anything like this. Can hardware experts on this forum help me to evaluate this idea? Is there any potential pitfalls I should be looking out for?

 

[dottorrent]

Impossible. You need to buy a new case just for a standard ATX PSU to fit, let alone a secondary unit.

 

[Newbbuilder11]

I'm trying to get one 7970 GPU into a very generic HP desktop, whose power supply uses non-standard connectors and therefore can't be replaced with a more powerful one. The existing power supply is rated at only 300W and won't be able to handle the whole system once the 7970 goes in.

This upgrade is happening on a very tight budget. Buying a new standard ATX mobo plus a power supply is not an option. Alternatively, I'm think about buying a secondary power supply which will be wired only to the 7970. When the system needs to boot simply short the PS_ON pin on the mobo connector to turn it on, and then boot the system regularly with the original power supply.

Laptop eGPU builds are powered in a similar manner, so I feel the plan should work. However I've never heard of anything like this. Can hardware experts on this forum help me to evaluate this idea? Is there any potential pitfalls I should be looking out for?

I would advice against this seeing as how 1 mistake could possibly mess some things up. If you are using a 20-pin mobo then I would get something like this.

http://www.showmecables.com/product/ATX-Power-Cable-6-in-0-1524-m-20-to-24-pin-connectivity.aspx?utm_source=google&utm_medium=cse&utm_campaign=1035&zmam=49733141&zmac=5&zmas=1&zmap=1035&gclid=Cj0KEQiA7NyiBRCOhpuCm9Dq6b4BEiQA9D6qhUNnBu-pJdP6qh16RrT54u0_s_GxEE8NujaI6BGIoWUaAnjD8P8HAQ

And then buy a ATX PSU.

 

[Mr_Koala]

Did some Googling and it looks like there are people trying this idea. It should work in general.

However some posts pointed out since the GPU is powered partly by PCIe as well the two 12V rails should have common ground, which I can't satisfy. I don't know the pinout on the non-standard connector and I don't want to take any risk testing the original PSU which I can't replace easily.

The secondary PSU would need a bit of load on the 3.3V/5V for the 12V to work stably even though I only need the 12V. I might provide the needed load with a fan or something.

There is also the concern of secondary PSU's power on/off timing. Will anything bad happen if the GPU has voltage on the PCIe power connectors but is not turned on? Again, I can't make a relay to power on both PSUs' 12V simultaneously becaue I don't know the pinout.

Impossible. You need to buy a new case just for a standard ATX PSU to fit, let alone a secondary unit.

Space isn't a concern. The secondary PSU can sit outside the case if it has to.

I would advice against this seeing as how 1 mistake could possibly mess some things up. If you are using a 20-pin mobo then I would get something like this.

http://www.showmecables.com/product/ATX-Power-Cable-6-in-0-1524-m-20-to-24-pin-connectivity.aspx?utm_source=google&utm_medium=cse&utm_campaign=1035&zmam=49733141&zmac=5&zmas=1&zmap=1035&gclid=Cj0KEQiA7NyiBRCOhpuCm9Dq6b4BEiQA9D6qhUNnBu-pJdP6qh16RrT54u0_s_GxEE8NujaI6BGIoWUaAnjD8P8HAQ

And then buy a ATX PSU.

The HP proprietary conncetors look like this: i.imgur.com/41N9FEV.jpg.

24pin to 20pin won't help much here.