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Reply to "Lionel O Gauge Switches run with DC Wiring Question....."

JohnGaltLine posted:

All the theory aside, Junior, use a 1.5k Ohm resistor in series with your LEDs and they should work well at voltages of 10-20 VAC on the input side.  Assuming a typical LED designed for maximum output at 20mA of current.  

JGL

Actually John, you can use a whole lot lower resistor than that as long as you have reverse voltage protection using a diode or you've connected two LED's in reverse polarity to protect each other.  Let's just assume you have .707 of the RMS voltage to consider since the LED only see half of the cycle.  I get around 14 volts, and I'm dropping at least two across the LED.  So, we're talking about 12 volts or less, at 20ma, that's a 600 ohm or larger resistor.  LED's will tolerate peak currents of multiple times their continuous rating, so this is a pretty safe number.

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