Improving simple filter cap tester.

[JHAnd]

Hi,

I made a simple filter cap "tester". It's just a 100uF 500V capacitance with crocodile clips for positive and negative. I use it to find 100hz buzz from bad filter caps, paralleling one cap at a time until the buzz goes away... then I have found the bad cap that needs replacing.

When done I discharge the "tester" through a resistor.

I usually have the amp on while testing and change the positive lead from cap to cap. Each time I clip the positive lead to a cap I get a tiny arc.

Is there a way to not have this happen? I find it startles/scares me even though I know it is going to happen.

Would paralleling a resistor work?

[iMo]

Yes, that is the standard way people do it.
The value should be large enough not to affect your measurement, and its time constant RC low enough to discharge the capacitor fast enough. So you have to find a compromise with the resistor value.
Also the voltage/power rating of the resistor is important provided you operate it at large voltages.

[shapirus]

I'd wire it up in some primitive enclosure with two buttons like this:

[MarkT]

Power down before connecting it or disconnecting it, then you won't have any arcs.  Also this greatly reduces chance of fumble-induced shorts which can be expensive if something blows up - yes its a lot slower, but you have peace of mind.

Recommend wearing eye protection when working with significant stored energy in electrolytics.

[Vovk_Z]

Each time I clip the positive lead to a cap I get a tiny arc.

Voltages about 200VDC and higher tend to create small arcs. It even can be seen just when you are measuring voltage with some DMMs.