Capacitor polarity, is the outer foil to ground?

[@matambale]

A fine, simple and cheap means to test for foil side - where we actually get to exploit all the RFI in the lab. I guess if you were testing dozens and dozens of caps for foil sides, you might want to build a device to speed it up, but certainly the scope technique is quick and easy enough. Thanks Timothy.

[@Timothycan]

I considered the easiest way to speed this up would be a set up with two croc clips (alligator clips if you prefer) and a changeover switch to reverse the polarity. Then, just put the capacitor leads in the croc clips, the 'scope connected after the reversing switch, and (holding the cap) just switch between the two polarities. You could do dozens in minutes that way.

[@matambale]

@@Timothycanthat's a quick, simple build right there. Nearly suggested filming it but it would take 10x longer to edit and post it than to just wire it up.

[@Snowsea-gs4wu]

Thanks for the video!

[@enewsdikgang5150]

What you're doing is not visible. You've enough space on your table

[@Timothycan]

I should have used a more sensitive oscilloscope, but the only other 'scope I have is enormous and heavy. I'm not skilled at making videos and I know it - but essentially the 'scope used here measures 15 mV of noise if foil is not to ground, and does not detect noise if foil is grounded. That's enough to know the polarity of the capacitor. My only point is that loads of test equipment and complex circuits are NOT necessary in order to do this.