Hi everyone
I own a mac pro (old one, not the tin can) and i'm perfectly happy with it except for the GPUs.
I currently have a GTX 780 which is kinda greedy and causes some shutdown because it pulls too much electricity from the system. I also would like to add a second GTX to the system (i use all of that for 3d renders) so i will definitely need more power.
 
My plan is to add a secondary PSU for GPU only.
Some years ago, manufacturers created extra PSU, especially for big GPUs,  that could be inserted in a HDD bay.
All of them have been discontinued so i think maybe something was wrong with the concept or the achievements.
 
Anyway, i plan to buy a PSU, put it outside the machine, with only the needed cables going inside. It will be full modular so i will only plug the GPU on it.
 
Possible problem : On the Dedicated auxiliary GPU PSU, you could plug one of the motherboard molex in, so the PSU would know when the system is on or off.
My question is : if i buy a full modular PSU, will it need a connection to a motherboard to be on? would i have to "trick it" into believing there's a motherboard plugged to it? Will it work right off the box and send the electricity to the GPU when turned on without anything else done?
 
If my idea is doable, what PSU would you recommend?
 
Thank you for your help.
 

bob16314
Just to add a little more, a reference is a 250-watt card..Of that 250 watts, 75 watts is taken from the mobo PCIe slot and the remaining 175 watts (~15 amps @ 12 volts) is supplied by the 6/8-pin supplemental power connectors..You'll only be powering the supplemental power connectors with the secondary PSU, so you won't need a huge one as far as watts go..But you'll need to get up into the 650W/750W neighborhood to get a PSU that has all the neccessary 6/8-pin supplemental power connectors for two cards, like an EVGA 650 G1/GS or 750 B2/G2..PSU's and specs are ..I'd roll with a single 12 volt rail unit.

Thank you for all those useful infos.


I think the ADD2PSU might be a nice opportunity to try and see if i can connect one of my old PSU to see how it works and buy a good one in case everything is fine.
Indeed my 780 is under fed : it's connected with 2x6 pins instead of one 6 pin and one 8 pin and this explain probably why it works but fails under heavy load (big 3D Renderings).
 

seth89

 
That is a new and sealed 450w 5.25" dedicated GPU power supply for a buy now of $59.99.
I used a unit like it back in the day when I have two GTX295 (qsli) and a BFG PPU. There is nothing wrong with them, power supplies just got more powerful and cheaper. For example my 1100 ABS PSU was 450 bucks in 2008, the same company (now Rosewill) sells a 1,100w PSU for 150 bucks.
 
PS I have no affiliation with that ebay link, I just did a quick search.
 
here is another one on amazon for the same price:

 

Thank you for the search.
 
I also found those earlier but the issue is i live in Europe so those might not be as interesting as they look :
I made a cart at amazon to check how it would cost to have it sent over here. With shipment and duty taxes, the Juicy box has a total cost of $120 which just doubles its price... At this price, i have a more than correct real full modular PSU.
This is what i was looking for this alternative, but thanks anyway :)
 
I might be able to get one from someone i know in europe (if he can find where he put it) so we'll see.
 
 

bob16314
Just to add a little more, a reference GTX 780 is a 250-watt card..Of that 250 watts, 75 watts is taken from the mobo PCIe slot and the remaining 175 watts (~15 amps @ 12 volts) is supplied by the 6/8-pin supplemental power connectors..You'll only be powering the supplemental power connectors with the secondary PSU, so you won't need a huge one as far as watts go..But you'll need to get up into the 650W/750W neighborhood to get a PSU that has all the neccessary 6/8-pin supplemental power connectors for two cards, like an EVGA 650 G1/GS or 750 B2/G2..PSU's and specs are here..I'd roll with a single 12 volt rail unit.

Go with what this guy said... I'd get all technical and what not, but this is enough...