I have a capacitor which can charge up to 1500 V that is connected to another circuit. During maintenance, I have to go and work on the circuit and before doing so, I need to make sure that the capacitor is completely deenergized. I would like to have an LED installed which goes ON for voltages higher than 100 V and goes off when it is below 100 V. I thought of connecting an LED in parallel with a series resistor, however doing so will probably damage the LED as it would be designed for voltages greater than 100 V and not as close to 1500 V.
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1\$\begingroup\$ How much capacitance? How much current draw is acceptable? \$\endgroup\$– Matt YoungCommented Nov 15, 2019 at 2:13
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1\$\begingroup\$ Why have you not specified, ON load current and OFF Current and Voltage Threshold tolerance ? along with budget \$\endgroup\$– D.A.S.Commented Nov 15, 2019 at 3:51
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\$\begingroup\$ Besides agreeing with Neil_UK answer, I would add that such a indicator should not use semiconductors. Maybe a little neon indicator lamp, connected in series with high ohm resistors. But I wouldn't risk myself. \$\endgroup\$– mguimaCommented Nov 16, 2019 at 17:58
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I need to make sure that the capacitor is completely deenergized.
The way you make sure a high voltage capacitor is completely safe before working on it is to have a wire connecting both terminals together. Clip a wire onto both terminals. Use a conventional multimeter, with a HV probe if necessary, to see whether it's safe to attach the wire.
An indicator LED system is prone to all sorts of failure. If the light is off, then is that because the cap is at a safe voltage, or is it because the light has failed? Are you feeling lucky?
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\$\begingroup\$ Beyond the indicator LED system beeing prone to all sorts of failure, in this case there are high voltages which could zap the semiconductor junctions, turning the system even more prone to failure. \$\endgroup\$– mguimaCommented Nov 16, 2019 at 17:56