2 GPU's on a Switch via Separate PSU

[Bad213Boy]

I have 3 video cards in SLI. I know you can have 2 PSU's to power your system. And yes I know it's not recommended to run 2 PSU's. But if you're broke, you're broke. I already know I can run my CPU and 1 video card on the 1st PSU, and 2 video cards on the 2nd PSU.

The kicker is this. I want to put a rocker switch on my case to control the on/off switch for the 2nd PSU. So when I'm doing just basic stuff, I'm only using 1 video card. Having older GTX 400 cards eat up a lot of wattage, regardless of whether they're in use or not. So if I can turn 2 video cards off when not needed, I'll probably save some money on my electricity bill. And I don't want to hear about buying new video cards.

I need to know if this will fry my motherboard. Also, will the 2 video cards on the 2nd PSU even be recognized after the system is booted? I'm not even sure if all the cards need to be running during boot for them run in SLI. In theory it should be safe as long as you don't have the 2nd PSU running without the 1st PSU running. But if the operating system wont recognize the cards after boot, then this whole idea is pointless, which would suck.

[werdwerdus]

I'm guessing the gpu will hold up the boot process when it detects no power connected. If you tried to boot with power on, then turn off after boot, my guess is that would probably crash your system. Just a guess though..

[Snow Crash]

I'm guessing the gpu will hold up the boot process when it detects no power connected. If you tried to boot with power on, then turn off after boot, my guess is that would probably crash your system. Just a guess though..

I ran with 2 PSUs for a while. I can say that when I first set it up I forgot to turn on PSU 2 before booting and it was not well received but no damage to any components happened.
Nothing bad happened to my mobo when PSU 2 was powered up without PSU 1 (of course it won't boot but you knew that :-)
SLI is going to compound the issue but ... you could probably safely try the following at your own risk.

Switch BIOS to halt on NO ERRORS.
Turn both PSUs on and boot for max performance
After max boot, when you want to run low ... turn SLI off, turn PC off, turn off PSU2, boot.
Then reverse the process to get back to max ... PC off, PSU2 on, boot, SLI on

It sounds like a pita and depending on your mobo it may or may not work but if you spend a lot of time running with 1 card it might be worth trying.

[Bad213Boy]

I know I can unplug the 2 extra video cards and still have the SLI connector connected and my system will boot up perfectly fine. It's only when you try unplugging the video card in the 3rd SLI slot will it post an SLI error. I hate that, that's sooo dumb how you have to have a huge space in between 2 SLI cards. I know it's better for air flow, but the concept of it not being flexible is stupid. Mobo manufacturers put so many on/off settings in the BIOS, I can't believe they didn't include options to disable each pcie slot. I could have just used profiles then. Thx guys.