[SOLVED] Would high voltage AC switches with LEDs work for low voltage

[Zak28]

Will LEDs inside illuminated switches light in a 12v circuit for switches rated for 125-250Vac?

 

[FvM]

It depends on AC, high or low frequency or DC 12V supply, switch type.

 

[Zak28]

It depends on AC, high or low frequency or DC 12V supply, switch type.

Regardless of frequency current is limited by resistors hence voltage determines what resistors should be inside switch.

 

[FvM]

You didn't say anything about the switch type. Resistive behavior is true for mechanical switches, but not for semiconductor switches.

 

[Zak28]

You didn't say anything about the switch type. Resistive behavior is true for mechanical switches, but not for semiconductor switches.

This case is for mechanical switches.

 

[FvM]

Then you are asking just for current rating. DC switching power can matter for higher DC voltage than 12 V.

 

[Zak28]

Then you are asking just for current rating. DC switching power can matter for higher DC voltage than 12 V.

What if the switch is illuminated with a neon bulb instead of LED?

 

[FvM]

It can't light.

 

[betwixt]

Zak28 - Neon lamps, which are more commonly fitted in side switches than LEDs, need around 90V across them before they start to conduct. They will work on AC or DC but they need high voltage to ionize the gas inside them before they conduct at all.

You can see why they are used in preference to LEDs if you do some math: an LED running at say 10mA would need a series resistor of (250-Vf)/If Ohms, if Vf is around 2V it would have to be 248/.01 = 24.8K and rated at more than 2.5W so it would run very hot!

Brian.

 

[Nik_2213]

Could OP's LED be a 'bidirectional' (back to back) driven via a small capacitor rather than a resistor ?

Much less heating...

 

[betwixt]

I doubt it would be economical to use an LED as you describe. The capacitor would have to be highly safety rated and have a series resistor and fuse. A failing capacitor would virtually short out the AC. Neons cost almost nothing and only need a high value, low power rated resistor (typically 180K/0.25W) and they are inherently reliable and safe.

If an LED was used and the capacitor broke down and the fuse popped, the light would no longer show whether the switch was on or off, that would be a safety risk in itself.

Brian.