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USB power - how much is too much?
BobA:
Just tap off the power connector. Drawing more than 500 ma from USB will damage it.
orchidius:
So there's no harm in just tapping the red wire from a molex plug, wire it to the PCB and complete the circuit with the ground? The LED's won't protest?
gryhnd:
My preference for powering anything not directly involved with the PC (LEDs, extra cooling fans, other bling) is to run them off a second power supply...removes the strain from the PSU as well as the :banghead: when something fubars. That can be as simple as extra wall warts you have laying around, to a full blown spare AT/ATX power supply.
BobA:
It is fine to wire your LEDs off of a drive power connector. Make sure you have the proper limiting resistors or LED with built in resistors.
See link on power connectors PC Power Connectors
MonMotha:
Not that it's commonly done, but if you go tapping the 5V line on a big PC power supply, I'd recommend installing a suitable fuse. PC power supplies can often source 50 AMPS or more on their 5V lines (hey, that's only 250W) which is more than enough to heat up and melt insulation on AWG22 commonly used for wiring arcade cabinets. I've accidentally shorted the 5V rail on a modest (230W) supply with a ~1' piece of AWG26 before: the supply did not go into shutdown but rather started making my wire's insulation melt. That was fun... I suspect the short circuit protection on those supplies has gotten better, but why chance it?
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