# LEDs and reverse voltage question



## Bwells (Mar 30, 2014)

I would like to install an LED for a backup light on a DC loco (HO) so that it comes on when backing. I figured that to wire it wrong would work but I read something about reverse voltage protection. Are LED sensitive to polarity when wired backwards as the LED would be off 95% of the time? I googled it and found a lot of info that was over my head, reverse voltage breakdown, avalanche effect etc, so my thought was to add another diode in one leg as follows.


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## Dennis461 (Jan 5, 2018)

Our model train power supplies do not go high enough in 'reverse' to destroy LED backup lights. Most diodes, including LED's have numbers published for a 5V reverse voltage, but that does not mean LED failure voltage.
terms used;
reverse voltage some spec sheets list 5VDC
peak repetitive reverse voltage (for example used in an AC circuit)
reverse breakdown voltage 30VDC or higher

now for a real problem...
some of my LOCO's backup lights (LED's) flicker when running forward due to voltage spikes caused by motor brush arcing (I think)

http://www.modeltrainforum.com/showthread.php?t=156922


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## wvgca (Jan 21, 2013)

sure, that will work


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## Bwells (Mar 30, 2014)

Thanks Warren. So just a standard diode, nothing fancy like a Zener?


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## wvgca (Jan 21, 2013)

nope, just a standard 1N400X diode...
it will change the resistor value sightly, but you don't have to be very concerned


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