Pilot Light Calculation

[starfish]

DIYing for a few years, but new at the math. So - I'm building a mic power supply. Have a 28v 40ma light that fits an existing hole and I like the look of. If I were to run it off 120 ac then 120 - 28 = 92v  92/.04 = 2300ohms    .04 x .04 x 2300=3.68w  So I would need a 2k3 5watt series resistor? Is my math right? Probably not a good idea? I want to avoid using the heater supply as the transformer is already close to its max current rating. I have a 125v light I could use, but I was trying to avoid any more metal work.

 

[JohnRoberts]

Unless the pilot light is double insulated and/or meets pretty substantial safety spacing requirements I wouldn't power it from mains power. Stuff happens and you don't want it to happen to you or friends. A 125v lamp is probably better insulated, designed for the application.

Can't you use a high efficiency LED? That would draw much less current than 40 mA.

JR

 

[starfish]

Thanks, I'll check out a high efficiency LED, was just trying to use what I have here.