I acquired a box of large (50,000-320,000 uF) capacitors for $7. They have various voltage ratings, from 10-90V.

These caps are old. Not sure exactly how old, but 30 years wouldn't surprise me. I want a quick and dirty way to make sure they're still OK. Since I have 20-30 of them, a faster method is better. If it takes an hour to test each cap, and I only have about 20 free hours a week, it will take a week plus to test them all. I want something much faster than that.

I don't care about ESR, so I won't test the caps for that.

To test leakage, I will charge them up to rated voltage and make sure they hold that voltage to within 1% for at least 100 seconds. If the dielectric is compromised, this should show it.

But the hard part is... How can I make sure the capacitance rating written on them is accurate? The best I can come up with is to use a 1 mA constant current source (made with a LM234 or LM317) to charge the cap from 0V to 1V, and time how long it takes. Since C = I * dV/dt, and dV will be 1, the capacitance in mF should be equal to the seconds it takes to charge them.

Admittedly, with the 320,000 uF cap this will take 320 seconds, or about five and a half minutes. I guess I can up the constant current to 10mA for that one, then it'll only take 32 seconds.

Is there a faster, cheaper way? I'm not afraid of opamps, but this has to be doable on a college student budget. No $50 opamps. And remember I don't have a lot of free time either.

P.S. I'm not spending $50 on a high-capacitance LCR meter. If I have to spend more than $7 on the test setup, that's more than the caps cost me, and I'll just throw them away. Also, I already have an AADE LC-IIB meter that works fantastically (better than 1%) on caps <= 100 uF.