2 PSU in one case serious problem

john959

Distinguished
Nov 4, 2006
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18,510
hello

i used two power supplies.. one is the main to power the motherboard and everything els and the 2nd for my GF 7900 video card
when the mainis off and i power the 2nd for the video card manually the main power suppy fan start turning on even when the PSU is off.. why? is the 2nd PSU connected only the GF card powering the main PSU throught the PCI express slot on the motherboard? what if both turned on
overload the motherboard and something blow up?
i want 2 PSU for DX10 video card and am trying to figure out this problem
any ideas?
 
Yes that is nothing to worry about.

Once the primary unit comes on line the mobo will POST and once the GPU comes to life it will properly use both PSU sources, I believe up to 75w are used from the 20+4 ATX connector for the PCIE slots, and 75w for each 6-pin PCIE GPU connector... So in theory a 300w GPU will have three 6-pin PCIE GPU connectors.

I would connect a CD or DVD device to the secondary unit to have some +5v load as well since some PSUs act funny without some load on both the +5 and +12 rails...