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Ancient_Hacker Ancient_Hacker is offline
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Default Using DMM on Possibly Charged Caps

On May 29, 9:21 am, Rob wrote:
Is
it safe to use the DC voltage measurement function to see if the cap
has been safely discharged?


If you put the DMM on the 200 volt range.

Or if the DMM has an "Auto range" feature. With Auto-range, the DMM
has to be capable of standing full rated voltage even on the most
sensitive range. You see with the leads disconnected, the auto range
feature is going to change ranges down until it's on the most
sensitive range, typically 200mv full scale. Then when you put the
leads on a high voltage, for a few milliseconds the meter is getting
up to 2000 volts into the most sensitive range. The design of the
front-end has to be able to handle this. Typically they use a large
series resistor and clipping diodes to limit the peak voltage going
into the A/D chip. No problem at all.

But in general it might be simpler to just have a discharging resistor
handy. A 5-watt wirewound resistor of around 1000 ohms will do the
job safely and quietly. Solder some stranded wires with clips on the
ends.