I am running a LED as an alternator indicator light, I have read a lot of notes which say it needs to have a resistor and diode to create enough resistance to excite the circuit. Any ideas what resistor and diode to use, and how to wire it?
Thanks,
Ed
Full Version: Alternator Light Help
I strongly suggest switching back to incandescent for that bulb. The circuit is designed to have power flow through it both ways under different circumstances, and an LED only allows power flowing through it in one direction.
--DD
--DD
Not worth the effort. What Dave said, + how often do you expect to see the light on?
LED will not work.
QUOTE(ConeDodger @ Jan 8 2017, 10:47 PM) 
Not worth the effort. What Dave said, + how often do you expect to see the light on?
Hopefully I won't see the light on at all, I am running LED because I am running aftermarket gauges and my alt light will be in the console, and it will match the other warning / indicator lights.
As I was told... The alternator will not charge if there is an LED light in the gauge
My car currently has an LED indicator for the ALT LIGHT.
It DOES work, but not by itself.
You have to put a ~70 Ohm high power (~1watt) resistor in PARALLEL with the diode.
One thing above that IS correct about Diode indicator: The stock incandescent bulb will light up if the Battery is "bootstrapping" the field winding in the alternator (key on but engine not running) OR if the Alternator has a much higher voltage than the Battery.
This is because current can flow both ways in the incandescent bulb and it will illuminate either way.
If you use the LED, then it will only illuminate in the first case (Battery providing current to field winding), but will not illuminate in the second case.
There are some LED indicators that will illuminate with both polarities, but I cant recall where I saw them.
It DOES work, but not by itself.
You have to put a ~70 Ohm high power (~1watt) resistor in PARALLEL with the diode.
One thing above that IS correct about Diode indicator: The stock incandescent bulb will light up if the Battery is "bootstrapping" the field winding in the alternator (key on but engine not running) OR if the Alternator has a much higher voltage than the Battery.
This is because current can flow both ways in the incandescent bulb and it will illuminate either way.
If you use the LED, then it will only illuminate in the first case (Battery providing current to field winding), but will not illuminate in the second case.
There are some LED indicators that will illuminate with both polarities, but I cant recall where I saw them.
QUOTE(stugray @ Jan 10 2017, 12:01 PM)
My car currently has an LED indicator for the ALT LIGHT.
It DOES work, but not by itself.
You have to put a ~70 Ohm high power (~1watt) resistor in PARALLEL with the diode.
One thing above that IS correct about Diode indicator: The stock incandescent bulb will light up if the Battery is "bootstrapping" the field winding in the alternator (key on but engine not running) OR if the Alternator has a much higher voltage than the Battery.
This is because current can flow both ways in the incandescent bulb and it will illuminate either way.
If you use the LED, then it will only illuminate in the first case (Battery providing current to field winding), but will not illuminate in the second case.
There are some LED indicators that will illuminate with both polarities, but I cant recall where I saw them.
Thank you, it works perfectly
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