Acceptable esr limit?

[ohmmy]

I have an esr meter and I googled an esr chart.

Couple questions:

Is an onboard test accurate?
How much can the esr value be different from the chart before it's considered bad?

Example: 1000uf 25v - chart says .14ohms esr. Tester indicates .25ohms esr in circuit. Is that considered bad enough to replace?

[stj]

Re: Acceptable esr limit?

the chart is rubish, you need the datasheet for the part your testing because they vary so much.
btw, a panasonic FR series 1000uf 25v is rated at 0.018 ohms
a rubycon YXF series is 0.062 ohms

so 0.25 ohms sounds pretty bad!!!

[budm]

Re: Acceptable esr limit?

"Example: 1000uf 25v - chart says .14ohms esr. Tester indicates .25ohms esr in circuit. Is that considered bad enough to replace?" Always test it out off the board and use the MFG spec to verify.

[mariushm]

Re: Acceptable esr limit?

The chart you get with esr meters is one made up based on the average ESR of capacitor series from about 10-20 years ago.
Most charts were copied or based upon Bob Parker's esr meter project ... see the pictures on this old page: http://members.ozemail.com.au/~bobpar/esrmeter.htm

Modern capacitors nowadays have much better specifications so you can't really rely on those charts. It's better to get the datasheet and compare the measurements with the information in the datasheet.
Once you work on lots of things, you get an experience and tend to know how much a good capacitor should measure.

A good low esr capacitor of 1000uF 25v should measure less than 0.25 ohm, but the value is really not that big. I would be worried with values above.. let's say 0.4 ohm. It could be that you have a not so low esr capacitor series installed, and maybe the circuit doesn't even have a low esr capacitor in the first place.

Oh.. also make sure your leads don't add to the resistance measured by the meter.

[ohmmy]

Re: Acceptable esr limit?

You mean the datasheets for the capacities being tested not the board they're installed to?

[mariushm]

Re: Acceptable esr limit?

You look at the capacitor, you determine the brand and series from the text on the capacitor and then you look in the datasheet for that series at the impedance value measured at 100kHz.

The ESR of your capacitor should be close to that value, give or take some percentage... only natural that the specs will degrade a bit over time, but shouldn't be 3-5 times the original value.