loading

a few LED questions

I have been modding my ps2, It's been painted a window mod, and I'm thinking about adding a flip top. but for my next mod I'm going to install 2 yellow LEDs, to light up the window mod, so far I have 3 places I can wire them to, directly to the mother board which is12v of power, on the fan power supply which is around 7v, or the usb which I read was 5v, the LEDs are 2.1v and I have 2 of them. Which area is the best to hook them to, and is their any way I could do this without using a resistor, radio shack is closed, and I would like to finish this tonight, so the only way I could get a resistor would be to steal one from some other random electronic thing I have laying around. also (just making sure) if LEDs are wired in series, will the voltage be halved between the 2, if so then the 5 volt usb, will be at 2.5v when it's split, will this work or is a resistor still needed?

arch_angel07 (author) 9 years ago
oh ok, so im not far off from what I need, but wanting to do it right I should probably find a resistor correct?
LasVegas9 years ago
I wouldn't suggest connecting them directly to the USB's power output. That power is limited to 500mA and by connecting the LEDs to it, would take from whatever device is ever connected there. The fan supply wouldn't create much a a burden on the system, but I'm sure you could find other 5V or 3.3V sources elsewhere on the logic board, such as supplies for ICs. You should be able to find the regulators themselves supplying the logic board with those voltages. Doing this without current limiting resistors wouldn't be safe in any case.
arch_angel07 (author)  LasVegas9 years ago
yah I guess im going to have to salvage a resistor from the nearest remote controlled car, I never plan to use the usb, these LEDs are 20mA, im guessing that 500mA is a bit to much for them?,
500mA isn't the current output of the port, but the current limit. The output is actually determined by the load.