I know that there is still power in my pc when it's off, I see the little led on my mobo. But how can I hook-up something else that will work when my pc is off? For example, I have a gadget that works on 24v. How could I hook that up so that it's running, even though my pc is turned off? Dig? Oh, one more thing. If the PSU doesn't have 24v, how much can I get out of it when it's off? Where are those wires?
The only active line when a PSU is on while the system is off is the +5vsb line, which only supplies anywhere between 1-3A (depends on the power supply in question). If you wanted to power something that runs at 24v, then you'd need a step-up transformer. The thing about this is that you're basically trading volts for amps. If you had a 24v .5A device, then on the 5v supply side, you'd be drawing at least 2.5A (more because of losses). That'll be too much for most power supplies.
Just a note to avoid confusion to curme, a step up transformer cannot be used directly from the output of the power supply, in fact a step up transformer would be difficult to find that had the correct turns ratio. You'd need a DC-DC converter, or a simple charge pump.
A simpler way would be to use the 5v VSB supply to keep a relay on whilever the PSU is plugged in, switching a separate mains:24v supply. It means tapping into the mains inside the PSU, so make sure your skills are up to it.
You're right Stevey, I tend to get the two mixed up in my head. edit: cool, 1234 posts. Now I know my ABCs! </Ralph Wiggum>
following on from our local superhero, you might find these monolithic regulators handy - they produce a regulated 24V (well, the 24V version does, anyway) from an input of anything between 27V and 40V. All you need to make them go from the mains is a transformer with a rectifier and a suppression capacitor or two. Add in a relay for the switching, and you're off. As has been said, though, you'll be working with mains-grade power, not to mention poking around in your PSU, so if you aren't sure of your skills, then don't
