Instead of buying a $40 LED stick, I decided to try making my own.
My question is about the resistance. I used this calculator:
http://led.linear1.org/led.wiz
The LEDs are 3.5v foreward voltage, 30mA foreward current.
with a 12v source, it tells me to wire in groups of 3 (series) with a 56 ohm resistor.
If I input 14v, I get 4 in series with a 1 ohm resistor.
My question is, if I do the 14v wiring, will it hurt to run them on 12v (engine off).
Replies (2)
swez on 12/23/2007 07:58:06
Nope, not at all. They will just be less bright is all. The worst case here, they may not get enough voltage to light at all @ 12 volts and that 1 ohm resistor. A possible solution would be a variable resistor, (Pot) to add or subtract the net ohmic load to adjust LED brightness at any voltage present.
You can also employ a series/parallel configuration here and change the resistor values off each parallel leg. (2 in series per leg, 2 legs) The resistance value at 12 volts is 180 ohms per leg to get the proper voltage drop for each series lamp per leg.
Run the calculator at both 14 and 12 volts and see how they choose the configuration and resistors.
Note: Even if the LED's get too much power, they will be a little brighter and not last as long is all. Consider using 13 volts as your voltage supply and a pair of 220 ohm resistors. (Series/parallel) When they see 12 volts, they will be less bright. At 14 volts, max brightness is achieved. A combination of fixed and variable resistors, (In series) would help adjust lamp output under all voltage conditions.
Swez
ttocs on 12/23/2007 14:09:02
as long as everything is fused correctly you should have no problems.
My question is about the resistance. I used this calculator:
http://led.linear1.org/led.wiz
The LEDs are 3.5v foreward voltage, 30mA foreward current.
with a 12v source, it tells me to wire in groups of 3 (series) with a 56 ohm resistor.
If I input 14v, I get 4 in series with a 1 ohm resistor.
My question is, if I do the 14v wiring, will it hurt to run them on 12v (engine off).
Replies (2)
swez on 12/23/2007 07:58:06
Nope, not at all. They will just be less bright is all. The worst case here, they may not get enough voltage to light at all @ 12 volts and that 1 ohm resistor. A possible solution would be a variable resistor, (Pot) to add or subtract the net ohmic load to adjust LED brightness at any voltage present.
You can also employ a series/parallel configuration here and change the resistor values off each parallel leg. (2 in series per leg, 2 legs) The resistance value at 12 volts is 180 ohms per leg to get the proper voltage drop for each series lamp per leg.
Run the calculator at both 14 and 12 volts and see how they choose the configuration and resistors.
Note: Even if the LED's get too much power, they will be a little brighter and not last as long is all. Consider using 13 volts as your voltage supply and a pair of 220 ohm resistors. (Series/parallel) When they see 12 volts, they will be less bright. At 14 volts, max brightness is achieved. A combination of fixed and variable resistors, (In series) would help adjust lamp output under all voltage conditions.
Swez
ttocs on 12/23/2007 14:09:02
as long as everything is fused correctly you should have no problems.
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