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Indicator LED wiring?

rmartingt

Well Known Member
I’m planning to install a “smoke on” indicator LED. I already have the LED itself; it’s a small 12V unit. My question is, can I simply wire this LED in parallel, or do I need a resistor to protect it?

I plan to wire the smoke system as follows:
Smoke arm switch “on” passes power to the input side of an automotive relay and a small jumper puts power to one side of the coil. Pressing the smoke switch on the stick grounds the relay, causing it to close and send power to the pump (which pulls about 7 amps, IIRC0.

My thought was to pick off either the ground side of the relay coil, or the output side of the relay, and use that to power the LED.

Will this work, or will I pop my LED?
 
If your LED is labeled ‘12 volts’ then it will have a resistor built into it. Remember it’s directional, there should be a ‘+’ label on one lead. It won’t work if wired backwards.
 
If the LED does not have an internal LED, one needs to be installed in series.
An online LED Resistor Calculator will come in handy.
You need to know the voltage drop across the LED. It depends on the LED color and
could be anywhere between 1.8 and 3.2 volts. The resister will likely be
somewhere between 470 - 560 ohms. Error on the high side.
 
I’m planning to install a “smoke on” indicator LED. I already have the LED itself; it’s a small 12V unit. My question is, can I simply wire this LED in parallel, or do I need a resistor to protect it?

I plan to wire the smoke system as follows:
Smoke arm switch “on” passes power to the input side of an automotive relay and a small jumper puts power to one side of the coil. Pressing the smoke switch on the stick grounds the relay, causing it to close and send power to the pump (which pulls about 7 amps, IIRC0.

My thought was to pick off either the ground side of the relay coil, or the output side of the relay, and use that to power the LED.

Will this work, or will I pop my LED?
You can't use the ground side of the relay coil.

FWIW I would put it in parallel right where the pump gets power, no resistor required. This way it comes on when the pump has power and generating smoke.

:cool:
 
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