I need to build a power-supply to run a PC in a car, so I'm
trying to figure out why I really need +/- 12V, which may be
tough to produce with the ignition off (not enough overhead
for the regulator).  I could build a DC-to-DC coverter that
would raise the voltage, but that means $$$.

Thinking of a regular desktop PC with a MB, audio card, video
card, fan, and IDE drive only (no floppy or CD)...

- MOTHERBOARD:
    - 5V around board, which may be regulated to lower for
      processor, etc, but that should not affect me.
    - The motherboard has a 12V requirement (standard ATX
      PS), but does it really need it, or does it pass on
      the 12V to other devices?
    - AFAIK, the parallel port does not require 12V.
    - AFAIK, USB does not require 12V.
    - Does the built-in serial require a +/-12V supply?  Or
      does it generate +/-12V (like a MAX232 for example)?
      If I need to supply it, and decide not to use serial
      comms, then can I just ignore it?  Or can I just supply
      it with +/-5V (as an RS423 device) and make sure the
      other end handles that level?

- COOLING FAN:
    - I can always get or modify the fan for 5V use, or I
      could generate 10-ish volts for that.  So no prob
      here.

- AUDIO CARD:
    - I believe line-out sound levels go to 10V, so +/-12V
      is probably needed there.  Any way around this?

- VIDEO CARD:
    - No idea?  Anyone know anything about these?  Or would
      it vary by manufacturer?  (Which I doubt).

- HARD DRIVE:
    - Have an IDE laptop drive which says 5V at 500ma, so I
      should be okay here.

Anything else I'm missing?

Cheers,
-Neil.

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