> Curt wrote: > > Tonight while I was not watching television I learned how > to wire in a diode. I'm rebuilding the light I use over my > bed at camp converting it from fluorescent to LED.
> I'd wired the LEDs in 2 strings with a 3 position switch, I > wanted one position to turn on one string and the other > position to turn on both. I harvested a diode from an old > computer power supply to make that work and I think it > would work except I discovered that what I THOUGHT were 6v > LEDs turned out to be 3.6v. You push 6v (ie 4 D cell > batteries in series) into a 3.6v LED and it cooks off > pretty quick, whoops! I'm curious how bright the LEDs will > be at 3v, they were SUPER bright at 6. LEDs don't work like that. It is the _current_ (amps) that matter. The 3.6 V is not supply voltage - it is the voltage drop across the diode when conducting. And if you are supplying DC, you don't need a diode with it. And it's usually not a good idea to wire LEDs in parallel. So - do you know the current rating of those LEDS? 20 ma is typical for "old fashioned" general purpose LEDS. Newer, brighter LEDs can be designed for a whole lot more. The you subtract the LED voltage from the supply voltage (6 minus 3.6 equals 2.4) and then using ohm's law figure out what size resistor you need to drop 2.4 V at the design current. So if those are 200 ma LEDs, and R=E/I, then 2.4/0.2 = 12 ohm. Then we need to be sure you won't fry the resistor. Watts = current X voltage, so 2.4 X 0.2 = 0.48 Watt. A half watt resistor would be big enough - just. But it's a good idea to always overrate wattage a bit. I would use a 1 W resistor. With a 6 V supply, for each of the 3.6 V LEDs (if they are rated for 200 ma), you would need a single one watt 12 ohm resistor in series with it. If that's not clear enough, let me know and I'll answer questions or go into more detail. *smiles* _______________________________________ http://www.okiebenz.com To search list archives http://www.okiebenz.com/archive/ To Unsubscribe or change delivery options go to: http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
