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Brians256 · 11-09-2002, 01:27 PM

I can answer that because I researched it a bit and I've used PSU's for lots of hobby experiments.

1) Using the negative voltage rails is dangerous because they are very low capacity. They can only supply a bit of current before they lose regulation (that means that the output voltage droops). Even large wattage PSU's don't rate the lesser rails at higher capacity. This is because the negative voltage rails are mostly used for ISA, RS232 and other older I/O standards. There isn't any point at making the -12VDC rail a 30amp circuit. All (or nearly all) the extra headroom in a 500W PSU goes into the 12VDC and 5VDC rails.

2) You can't tap into the ATX power "cable" without splicing into it or soldering an extra wire into the PSU interior.

Be careful. That doesn't mean you can't do it, but it does mean you should think about how much current you are demanding of those lesser rails.

11-09-2002, 01:27 PM	#24
Brians256 Pro/Staff Join Date: Oct 2001 Location: Klamath Falls, OR Posts: 1,439	I can answer that because I researched it a bit and I've used PSU's for lots of hobby experiments. 1) Using the negative voltage rails is dangerous because they are very low capacity. They can only supply a bit of current before they lose regulation (that means that the output voltage droops). Even large wattage PSU's don't rate the lesser rails at higher capacity. This is because the negative voltage rails are mostly used for ISA, RS232 and other older I/O standards. There isn't any point at making the -12VDC rail a 30amp circuit. All (or nearly all) the extra headroom in a 500W PSU goes into the 12VDC and 5VDC rails. 2) You can't tap into the ATX power "cable" without splicing into it or soldering an extra wire into the PSU interior. Be careful. That doesn't mean you can't do it, but it does mean you should think about how much current you are demanding of those lesser rails.