Bad... 2F cap?

[eccerr0r]

A while ago I bought a 2F cap intending to use it as a spot welder. But when I got it, it was well below expectations. I don't have a meter that goes up to 2F but I found that it was around 220mF at most. ONE TENTH the expected value. It had a "snazzy" voltmeter on it but it was coming off for its intended application...

I did not check its ESR yet, I didn't bother...

It was BOSS branded.

Anyone into high end car stereo and actually measured the capacitance in their caps? (I surely am not, but capacitors are capacitors ...)

(Photographed: the 2F cap and a 220mF cap that I measured to be around the same in capacitance).

[PeteS in CA]

Re: Bad... 2F cap?

That 220mF reading might be an artifact of your meter's measurement limitation. It may be that your meter recognizes the 2F cap as a cap, but is displaying the maximum value it can. Try charging it with a 1.5V battery through a 1K resistor, and see how long it takes to charge fully (the 10-20 M-Ohm internal resistance of your DMM should be irrelevant if you use a 1K charging resistor; OTOH, if you use a 10K or higher your charge time should be ginormous). With a 1K resistor the charge time will be pretty long, and the 2F cap should take 8X-10X the time for the 220mF cap.

BTW, haven't seen a Sangamo brand 'lytic in a really long time. I think Sangamo was bought by Cornell-Dubilier, one of the very few remaining US 'lytic capacitor companies.

[eccerr0r]

Re: Bad... 2F cap?

Yes, my Sencore LC meter tops out at around 200mF. I had to use another method which is pretty much what you suggest: I charged the cap with a power supply and counted how many seconds it took for a light bulb to extinguish during discharge. They both counted at around the same time so they are both around the same capacity -- which is way too small for 2F vs 220mF.

I actually do have a constant voltage/constant current power supply, technically I could derive an exact capacitance by measuring the voltage increase over any fixed amount of time... But too lazy with accurately measuring voltage and time. Technically simply using CC/CV mode and timing how long it takes to get to 0 current flow should do it too...

Yeah that 220mF Sangamo is ancient. I have a few Sangamo caps (which I googled sangamd *shh*) "Made in the USA" - I'd say these are at least 40-50 years old now.

300mF 7.5WV
220mF 15WV
67mF 35WV
41mF 50WV

My father salvaged them from equipment that he scrapped from a long time ago.