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I have noticed that slowly raising the track voltage the LED's on Fastrack switches illuminate pretty brightly well before the track voltage gets up to 18 volts.

I would like to get some LED's for a control panel that will work in conjunction with a toggle switch that turns power on/off on a siding.  I have found some nice panel mounted green LED's that are rated for 24vac. Using 18 volts for the track (DCS and Legacy), will the 18 volts be sufficient to illuminate the panel LED's (kind of like lower voltage illumination I see on Fastrack switches)?

The panel LED's that I have found tend to be available for 12vac or 24vac.  If the 24 volt LED's won't be bright enough, I would think I could put the 12 volt LED's in series with a resistor to work with 18 volts.  If I did that, what resistance and power rating would I need for the resistors?

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LEDs that are marketed for 12 or 24VAC are actually LEDs with a diode and a resistor already wired in series.  John's use of the LED calculator is correct for 18v DC source (not AC). and no other resistor in the circuit.  Not knowing what resistor is already in the circuit, it is difficult to know for sure what additional resistor to use.  Once you set the safe minimum resistor size, you will be stuck with whatever minimum voltage the LED lights.

An easier approach is to use a diode (converts to pulsed DC) and a CL2 LED driver in series with a plain LED.  The CL2 maintains a safe 20ma current supplied to the LED over a wide voltage range (5-90v).

CL2s are about a buck apiece, diodes maybe 10 cents, and LEDs 2-3 cents in quantity shipped from China.  This is far less expensive than the 12 or 24v AC LEDs.

Bob

@VinceL posted:
I would like to get some LED's for a control panel that will work in conjunction with a toggle switch that turns power on/off on a siding.  I have found some nice panel mounted green LED's that are rated for 24vac. Using 18 volts for the track (DCS and Legacy), will the 18 volts be sufficient to illuminate the panel LED's (kind of like lower voltage illumination I see on Fastrack switches)?

18 volts will be fine, you will probably not be able to see the difference between 18 volts and 24 volts on those.  The light output of an LED is linear to the current through the LED, but your eye does not respond in a linear way to light intensity, so it's likely you'll see little or no difference.

Last edited by gunrunnerjohn

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