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How do I build a simple 120v/240v ac voltage indicator? Answered

I want to build a small voltage indicator light which will tell me whether a circuit is putting 120vac or 240vac. I will also put in a fuse tester (easy enough) but these functions will give me nearly everything I need for my job (unless someone can think of a good ammeter circuit which would indicate at 0-40A in 5A imcrements- I'm not getting my hopes up on that...)


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12 years ago

a small neon discharge lamp strikes on about 80 V AC you can connect it to 240 V thru 150 K or larger resistor now add a second 150 K resistor parallel to the neon lamp. you get a voltage divider the lamp gets 1/2 of the input voltage now. if its 120 V it will get 60 V and stay dark. if its 240 V it will get 120 V and light up experiment with the value of resistors if needed. dont use resistor lower than 150 K for the master one (the one thru which current from the live wire comes) cause the lamp needs current limitation the 40 A - is it ac ? ac is hackable and it'd be possible to come up with something