Reply to "Wiring Multiple LEDs with SPST Switches"

Consolidated LeoOGR Forum Member

You'll certainly need to add resistors. Your diagram shows all of the LEDs wired in parallel. You will want resistors for each LED like this:

For warm white LEDs, the forward voltage (Vf) to each should be 3.3 volts. Depending how bright you want them, the forward current (If) should be between 10 and 20 milliamps. In the configuration shown in the above diagram, we can use the following formula to calculate the resistor value that you'll need.

R = (Vs - Vf) / If -- or --
R = (Supply Voltage - LED forward voltage) / Forward current
R = (12v - 3.3v) / .020A
R = 8.7 / .02
R = 435Ω

The nearest higher common resistor value is 470 ohms which is fine. The same calculation at 10ma gives a result of 870 ohms. So even a 1k (1000 ohms) would be alright in this situation.

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