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led current problems? Answered

Im running some leds off a 12v sealed lead acid battery and i need to know the best way to keep it from drawing to much current. Perhaps a fuse or large resistor? 



8 years ago

Ideally, drive it using a constant current source.


8 years ago

Depends on the led.

Small leds use ohms law to drop the excess voltage.

Large leds you need a driver circuit. (both have MULTIPLE instructables on the topics)

Try to get as many leds in series as the forward voltage will allow. a 12v SLA battery charges to about 14 volts and is dead at 11.5
Thus, you can expect 14 as your max.

If your led's forward voltage is say, 3, you can get 4 in series (Adds up to 12v) and you need to drop 2 volts with a resistor. the leds current is specified on the spec sheet, usually 20mA for small leds.
V=IR. 2 = .02*R
2/.02 = R
R = 100 ohms. (in this example)

If you're powering high power (500+mA) leds then you want to use a driver circuit that doesn't burn off power.