8 GPU node with 4 x GTX295 double-gpu cards powered by dual Chieftec 850W PSU's
So, why 2 PSU’s instead of 1 powerful?
Say, that we have to drive 4 x GeForce GTX295 cards ‘a max 289 Watts. It’s combined load is 1360 W, including rest of the system (CPU, chipset, HDD, etc…). So, minimum requirement is 1400W PSU. But this is bad idea — PSU’s are efficient in 40-75% load range, in that range they meet 80Plus and other promises. At 90-100% load they get un-efficient, dissipate extra heat and get loud, fans are running at max speed. So, at 1360 W load we need 1800 W PSU to run it in sweet-spot. Here we have few serious issues: (1) they are not widely sold; (2) they are not cost efficient, cost per watt gets very high, eg 2 x 750 W PSU-s sell 50% less than 1 x 1500; (3) PSU’s with 4 pairs of 6-pin anf 8-pin PCI-E connectors are rare.
And how to run them synchroneusly
One solution is to make cable. In that case You dont need to modify PSU cables and all remains original:
Dual PSU solution, master PSU, slave PSU remains original
Second solution is to modify ONE psu cable to control other:
Using one of these solutions Master PSU controls Slave PSU, switches it on and off.
In my case I run:
Master PSU
- System board
- HDD
- 2 x GTX 295
Slave PSU
- 2 x GTX 295
Both PSU-s run cool and quiet and I can sleep well, knowing that I don’t push my system to limit.
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Estonia Donates 
ok i have a question. what modifications you did ?
I mean i can understand that you took the power wire (green) and the ground wire (black) and put them in a female 20 or 24 pin connector. and you connect second PSU’s male 20 or 24 pin connector to the modified female connector of first PSU. But question is will you place the wires in front of same color wires or you will do cross connecting ? like green of first PSU with black of second PSU and black with green.
And one more question after doing all this the slave power supply will be the one which is not modified. am i right ?
this should be explane: http://www.coolermaster.com/UserFiles/Image/FAQ/CM_Stacker_dual_psu_cable450.jpg
I think this is the one 80plus silver 1500W PSU, rebranded as silverstone: http://www.fudzilla.com/content/view/15004/1/
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