Discharging filter caps

[Hotwatt]

I unplug my amp discharge filter caps with a 5w 250ohm resistor and when I put my DMM on the cap I see millivolts climbing upward. .009, .014, .027, etc. and it keeps going. Why is this? Can millivolts hurt me? Also if I leave the discharge lead on the amp for a few hours when I come back it measures negative .025 and slowly begins to climb.

[bal704]

If you're filter caps are charged, you'll be seeing hundreds of volts. Put your DMM on 1000V if it's not auto-ranging. One end of the resistor to ground, the other on your filter caps. You should see a slow bleed. mV level voltages aren't a problem.

I always put a bleed resistor on my builds so it bleed automatically.

[romberg]

Some of the energy in an electrolytic capacitor is not just charge on the plates. It is also chemical:

https://www.robotroom.com/Capacitor-Sel ... rge-5.html

This effect is also spooky to me. I always take a big BRITE PINK alligator clip lead and short out a big filter cap after I've discharged them safely with an resistor like you describe. This keeps the caps all at zero and is mostly for my own piece of mind. The reason the lead is a big obnoxious BRITE PINK is so that I remember to disconnect it before powering back up the amp. You can guess why I know this is important

Mike

[Stevem]

Wow! " can millivolts hurt me?"

[Hotwatt]

@romberg thanks that’s exactly what I was looking for and yes it’s a piece of mind thing.

[johnny riff]

I believe the term is called "dielectric absorption". I'm pretty sure millivolts won't shock you. I've seen the high voltage oil-run caps with a resistor strapped across the terminals when stored to prevent this.
You can touch the ends of a 9v battery fine..

[johnny riff]

make up a jumper with 10k 1-2w resister in serious insulated/heat shrunk with insulated alligator clips. less spark than just a wire.

[R.G.]

Even better, put 100K to 200K bleeder resistors across the filter resistors so they will, in a few seconds, pull down the filter caps and help keep them down to very low voltages when AC mains voltage is turned off.

[johnny riff]

that is true! if it is an unknown circuit a 10k or what have you jumper is not a bad thing to have. I agree a bleeder should be a standard issue.