powering 4x 3w rgbs

Hey dweenose,

I'm building a lighting set up driven by audio data in max, and i was planning on powering it all from an old PC PSU.

I am driving 4 of these:


with 12 of these:


from the 12v line on the PSU, utilizing the dim pin of the pt4115 on those each of the driver boards with a PWM pin on my mega.

I am planning on cooling each of the LEDs with a CPU heatsink/fan (and thermal paste of course), will that be enough cooling? will the drivers need to be cooled as well? I plan on running this for at most 4 hours a session, not running them at full blast all the time.

Also, will the voltage drop be too much between all of the LEDs for the PSU to handle?

Thanks in advance -z

Both your driver and LED are typically used inside a lightbulb housing -- no fan but they do use a decent cone of aluminum for the heatsink. A heatsink/fan used for a CPU should be much more than would ever be used in a production bulb.

Not sure what you mean by the voltage drop and the PSU. That shouldn't be a consideration.

nevermind about the drop question.

the red channels run at around 7-8v
while the blue and green are around 10-11

This might seem foolish, but do you think I’ll fry it by running it from my PSU 12v line without a resistor? I cant find 3w tolerant resistors anywhere (locally)

A 7-8V string of LEDs with no current limiting resistor or LED driver connected to 12V? Yes, you'll definitely pop it. As to the 10-11V string it's only highly likely that you'll pop it. Depends on how quickly you can shut off the power ;)

If you're looking for a locally-available solution then you should look for a ~1A transistor (google: transistor as switch) and pulse the current to the LEDs with PWM.

bahh yeah kinda figured (mostly really hopeful i could swing it).

but alas! i forgot about 269 electronics (a component store hidden behind a tourist luggage / watch / perfume store in chinatown) which doesn't carry most ICs, but does have a comprehensive line of NTE resistors and caps. XD