what tool identifies bad caps on live circuit?

[PCBONEZ]

Re: what tool identifies bad caps on live circuit?

depends, if it's wet then it's fresh electrolyte.

Or someone sneezed.

[Krankshaft]

Re: what tool identifies bad caps on live circuit?

There is one exception you can use an ESR meter to measure the ESR of batteries since their ESR goes up as they age. This is especially true of sealed lead acids.

I would qualify a battery as a live circuit of sorts.

But yes the only way to measure live caps is with a scope checking the ripple.

I had a Uniden phone from 03 it's handset was humming like crazy to the point where I could barely hear someone on the line. The wart had a 470uf 16V cap in it ESR measured 7.8 I thought it was kind of high. But before I condemned it I checked the ripple it was so bad it was almost as if I was looking at pulsed DC. The GP replacement cap which I checked before installation later had an ESR of 0.32. The old cap showed no outward signs of failure.

As you can see measuring ESR and if you're unsure about the proper ESR checking ripple can help sniff out most caps.