get power from pci bus

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i want to connect a cart to pci bus just to use +12,-12,0&+5 v power
lines of it
now i want to know if i need to change any settings for the bus or its
enough to connect the board to the bus
and also what should i do to protect my pc from damages may be happens
after connnecting the card like overcurrent or etc

Re: get power from pci bus

On 10 Jun 2006 01:12:27 -0700, wrote:

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I believe it is possible to pull juice directly off the PCI bus but
the risks are high in trying.  What exactly do you want to power?

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Even if you don't screw up and short something out, if the connected
device sucks too much juice it can do nasty damage like melting the
ATX connector, etc.  IMO shorts or meltdown are more likely damage
than "overcurrent."  I mean, are you saying you want to hot-plug a
homemade card safely to suck DC power off the PCI bus to power some
other device?  Isn't a PSU molex plug easier?

Re: get power from pci bus wrote:

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The power is always present, so there are no BIOS settings.

You should remember that the gold fingers on a PCI card,
have limited current carrying capability. If you wanted
to draw 10 amps, the pins would burn off. Each gold
finger will have a much lower current rating, like maybe
1 amp or less.

To protect the motherboard, you should use fuses on each
voltage line. Then, if there is an accident, the fuse
will open. If you use a fast blow fuse, like a Picofuse,
that affords maximum protection, but if the load you
are plugging in has quite a surge current when it is
first powered up, the fuses may not last.

I think your question would be answered better, if you
told us something about the load you were hoping to power.

The -12V on a lot of power supplies, is very weak, and
would not be a good option for driving heavy loads.

A Molex disk drive connector, gives you access to +5V
and +12V, at reasonable current levels (at least 6 amps).
You don't need to fabricate a PCI card, to get at
the power.


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