Using an ESR/Capacitance meter

[PRNDL]

I just got a BP Precision 830 capacitance meter and was wondering how to use it properly.

It's pretty simple to measure caps - I found 2 bad ones - it kept switching between two ranges.

I'm wondering how good this is to use with capacitors in a circuit - both electrolytics and coupling, and how much the neighboring resistors effect the readings.
Is it similar to checking resistors -- if they're off a lot, unsolder one end and check again?

Does anyone have info on the BK 830?

Thanks!!

[Iannone]

You can download the manual at this URL:

https://www.bkprecision.com/products/docs/manuals/300_manual.pdf

[Greasehorse]

ESR is a measurement of the resistance through a capacitor. It is for electrolytics (only I think). Apparently, the older the caps gets, the more fluid dries up. This increases the internal resistance. At some point on the ESR scale, the cap is no longer working right anymore. Then it has to be replaced. Example. I used the meter on some 20uf 500 volt Spragues the other day will looking for an oscillation problem in the AB763 I built. Three of them read 14 or so on the meter, two read in the 50's. I assumed that the 50's were bad or going bad. Shelf time has likely dried them up. Still didn't fix the oscillation but I need this to work for a long time...anyway, that's my understanding of it. And my ESR will supposedly check them in circuit..make sure they are drained...hot caps hurt things and people...

[PRNDL]

The 830 is a capacitance meter, not and ESR meter.

I see that ESR meters are much more expensive.

Will a capacitance meter tell you if a cap is bad?

Or, is the ESR meter what you need to test electrolytics?

[PRR]

> ESR ... is for electrolytics (only I think).

Film-caps have ESR.

It is almost NEVER important to audio. It is either too low to matter, or the cap is so sick it won't be showing a good capacitance.

Electros do "dry up". Even when fully wet (modern ones are just damp), current flows through "salt water" (actually a borax solution) to get to the actual capacitor. This is resistance. When we want to "clamp" voltage, as with a B+ filter, resistance is bad. However a electro has so many more uFd/$ than a film cap, we get better clamping even with some ESR.

> some 20uf 500 volt .... Three of them read 14 or so on the meter, two read in the 50's. I assumed that the 50's were bad or going bad.

Rule Of Thumb: most electros are sold to clamp 120Hz B+ rails. Therefore a "good electro" will have ESR much-less than its capacitive reactance at 120Hz.

Turning to a reactance chart: 20uFd at 120Hz is 66 ohms. We expect ESR to be much less, though perhaps never much-much less. 14 ohms is plausible: if you just figured "20uFd" you'd expect 66R impedance, you really get 66+14= 80R, no big difference. But 66+54= 120 ohms, twice the expected 55 ohms, the cap works half as good as you'd figured, you may notice. So while the ~~50R ESR caps are not for-sure bad, they do seem to be poor performers, probably worse than the designer and cap-maker counted on.

As dry-out is a major cause of electrolytic trouble, it may be worth knowing.

A pure capacitance meter is handy for sorting hard to read film/disk caps.
 
> You can download the manual at this URL:

That's an insulation tester.

I think you want (depending if we talking 830A or 830B):

http://www.bkprecision.com/products/docs/manuals/830A_manual.pdf
http://www.bkprecision.com/products/docs/manuals/830B_manual.pdf