Adding a second motherboard to a power supply

Hi folks,
My present situation finds me with a honking big Lian Lee tower case that holds an ATX MoBo and three internal drives. I'm using it essentially as a file server. It uses 95 watts as measured using a kill-a-watt meter. My plan is to combine with with another PC such that I wind up with an existing ATX motherboard and a second mini-ITX motherboard running off the same power supply. The case has plenty of room for the extra motherboard and sufficient drive space for the drives I'll want. My question revolves around splitting the power supply cables between two motherboards.

The primary mobo is an Abit AV8 which uses a 20 pin ATX PSU connector and a separate 4 pin PSU connector.

The secondary mobo will be an Intel D510 mini-ITX board that uses a single 24 pin ATX PSU connector

The PSU is an OCZ-420ADJ. It has a 20 pin ATX connector with a 4 pin connector that can attach to it. It also has two extra 4 pin (12V) connectors. It also has lots of connectors for powering the hard drives.

I intend to get a 20 pin ATX PSU splitter and run that to both boards. The 4 pin connector paired with the 20 pin connector will go to the Abit AV8. To power the mini-ITX board I'll extend the splitter with a 20 to 24 pin converter.

The one down side to this is that only one motherboard can control the PSU as far as I know. And I'll be constrained to operating the board that controls the PSU all of the time. And I don't really know how that is done. I wonder if I have to disconnect some of the pins on one of the motherboards to allow one to control the PSU.

So... That's what I have in mind and I would appreciate feedback on how I can expect this to work or factors that I've overlooked. If someone has already done this, please let me know how it worked!

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  1. Welcome to Tom's Forum! :)

    Bad idea, one failed PSU to knock down two systems with one stone. By the time you get done with your Jerry-Rigging and time it makes absolutely no sense.
  2. Hi jaquith,
    Thanks for the reply and thanks for the welcome.

    Part of this that I didn't much emphasize is to decommission another PC. That would leave me with an additional spare PSU. Time is less an issue these days... unfortunately.

    I suppose another thing to do would be to put a separate PSU in for the Micro-ITX board and just let them share the case with no other connection.

  3. I 'get it' but too what's at the outlet is different than whats required, therefore use the following estimator for both systems to get a total. Go to Radio Shack and pick-up the 24-pin and 4/8-pin, extra wire and solder the connections.

    PSU Estimator ->

    Good Luck!
  4. You could always look into one of the flex format power supplies. Here's what a quick search on turned up:
  5. Thanks for the additional replies.

    This is probably the PSU I'd go with at the moment:

    It's a bit of overkill for a system that will probably run at about 35W (Based om my experience with a previous system.)

    If I was weighing features higher than cost, I'd probably select:
    But I wonder if it would directly support a mobo with a 24 pin connection (and I'm not sure that FSP/Frotron is particularly high quality.)

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