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Dual PSU with a non-standard primary PSU

post #1 of 5
Thread Starter 
I'm trying to upgrade a generic HP desktop with a second hand 7970 GPU. The system has proprietary power connectors, so I can't just replace the existing PSU with a more powerful ATX unit. I've seen a few threads about multi-PSU builds here and there but I'm still not sure what to do because this situation seems to involve more complications than regular multi-PSU builds that are made for extreme power or redundancy.

Those are the HP connectors:



I'd like to see some comments from you experts on whether if it's safe to add a secondary ATX PSU on this system. Currently there are a few potential pitfalls I can think of:


The secondary PSU (with PS_ON shorted to power on) would have no load on 5V or 3.3V. Given that I'm aiming for small and cheap here group regulated PSUs would make it worse. (Any indy regulated PSU that has just the needed capacity and relatively cheap?) Maybe a fan or two on the 5V to provide load can help?

The two power inputs would not share a common ground, as I don't know the pinout on the proprietary connector, and those 20pin/24pin multi-PSU adapters won't work. (Edit: just realized the PSUs are simply grounded to the case, or a common AC source. No problems here. It's the voltage matching that's tricky. A powered PCIe riser cable should take care of it though.)

It would be difficult to build a power-on switch relay to turn on both PSUs simultaneously. I would need to turn on the secondary PSU before boot and off after shut down. Will voltage on the 7970's PCIe power connector do any damage when the card is not turned on? This would also cause 12V to have no load until boot. Do I need another 12V fan or something?


Will those be show-stoppers? Anything that I missed?


I'm working on a very tight budget. The price of the 7970 and a PSU would be the upper limit of what I can pay for. Swapping out the mobo is not an option. The 7970 is a used card that just happened to be available from a source I trust at a low price I can take, so it's either this card or nothing.
Edited by MrKoala - 12/11/14 at 2:17am
post #2 of 5
What do the proprietary power connectors look like? Maybe it's possible to remove the old connector head to use for the new power supply. Before removing the connector, just need to note which wire goes where.

If you can't remove the old connector, you can make an adaptor. Cut off the old connectors leaving like 5-6 inches of wire and crimp a standard female atx connector to it. You'll have to buy some pins, crimping tool and female connector. Maybe some money you won't be willing to spend.

Something like this. Then you connect the new power supply to the female connector end and proprietary end to the motherboard.
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post #3 of 5


I've run dual PSUs before, but just one for the motherboard and cards, and the other for fans and watercooling stuff.
I'd be really leery of a graphics card getting power from both the motherboard slot and a different PSU.
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post #4 of 5
How old is that HP with a proprietary PSU?

HP stopped using those quite awhile ago.... Does the motherboard even have a PCIe slot?
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post #5 of 5
Thread Starter 
Thanks for the replies. smile.gif
Quote:
Originally Posted by DuckieHo View Post

How old is that HP with a proprietary PSU?

HP stopped using those quite awhile ago.... Does the motherboard even have a PCIe slot?

It's a quite new Haswell system. The PCIe should be fine.
Quote:
Originally Posted by redxmaverick View Post

What do the proprietary power connectors look like? Maybe it's possible to remove the old connector head to use for the new power supply. Before removing the connector, just need to note which wire goes where.

If you can't remove the old connector, you can make an adaptor. Cut off the old connectors leaving like 5-6 inches of wire and crimp a standard female atx connector to it. You'll have to buy some pins, crimping tool and female connector. Maybe some money you won't be willing to spend.

Something like this. Then you connect the new power supply to the female connector end and proprietary end to the motherboard.

The HP connectors look like this:


The 4pin CPU power plug appears to be standard. The rest two are definitely not. All the three go into the mobo. SATA and fans are powered by cables from the mobo.

If I know which pin is which, asking some electronics repair shop to make the adaptor won't cost much. But my attempt on Googling the pinout has failed.


I'll try opening up the HP PSU and see if I can have any luck taking out the connector head. But even if I do, will I be able to plug both heads into the new ATX PSU? There's no PCIe power connector on this PSU. The original dGPU is a 8350 which doesn't need much power.
Edited by MrKoala - 11/3/14 at 9:13pm
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