Testing High Farad Capacitors

Kornbread

We use capacitor banks for batteries in our remote controlled sleds. One cap bank exploded a while back. It cost ~$3k to replace the bank. Another one of our rc's is down and one of the guys is saying it's another bad capacitor bank. I'm not sold. Capacitor banks like these should have several years of life, not one year. Each cap is 400farad, and IIRC, 2.7v, 16caps wired in series w/another 16bank wired in parallel.

Is there an easy way to test for a bad cap? These things look to be ~$20each and once the bank is out of the rc, fairly easy to replace individual caps.

If anyone is interested, this is one of our two storage systems. The other storage system uses 130' cranes to access all the racking. Any yes, the rc has pulled a Bo and Luke Duke by leaping out of the rack and onto the floor. $$$ day.

kenrhodes

For what the machines do if you can replace all the capacitors for $320. Then replace them and ASAP and enjoy the uptime. You can't diagnose them for $320.
Next I would work with the engineering team to figure out why are the banks dying so fast. Tuning the motor drives might save a lot of money in the long run.

Kornbread

So far, we have to order pre-assembled capacitor banks for $3k. Long lead time and this is the third bank in ~6months. Someone dropped the top of the rc onto one bank. Lucky it didn't pop. They make a big bang and stink when they do that. Replacing all 32caps is still way cheaper than $3k.

4thtry

Does anyone make an LCR meter that can test a 400 farad capacitor? The most expensive LCR meters that I could find at Mouser can only range out to 10 farads.

PWRRYD

Just set up a simple circuit to measure the RC time constant. Apply a fixed DC voltage to charge through a fixed resistance and measure the time (5 time constants).

Kornbread

@PWRRYD said:
Just set up a simple circuit to measure the RC time constant. Apply a fixed DC voltage to charge through a fixed resistance and measure the time (5 time constants).

I think that's going to be what happens.