ESR testing

[barry wilkins]

I would be interested in any information on the results obtained when testing electrolytic capacitors using an ESR meter . It seems the reults obtained are not quite as straight forward as expected .
For an example the esr for a 4.7uF 100V polyester capacitor shows virtually zero esr ,but a 4,7 uF 450V electrolytic capacitor has an esr of about 7 ohms ?

Barry Wilkins

[ratdude747]

Re: ESR testing

remember that each type of cap has different qualities, one of which is esr. that is normal... but idk about the numbers...


edit- either he meter is not zeroed or you have a bad cap, 7 ohms is high.

[Krankshaft]

Re: ESR testing

The lower (fractional capacitance and single digit caps) will show higher ESR readings in the whole number range this is normal.

[barry wilkins]

Re: ESR testing

It is a brand new capacitor ,shop only had one in stock @450 volts .
When you look at data sheets there does not seem to be any mention of esr ?
When I get a chance I am going to check a number of caps. and make a chart of results .
One thing I have noticed is the fact the ripple current increases with the working voltage .

Barry Wilkins

[PCBONEZ]

Re: ESR testing

If they don't mention ESR they are GP [General Purpose] caps.

450v caps are rarely low ESR.
Look at the Ripple Current spec instead.
That will tell you how much they can handle without over-heating internally.
.

[barry wilkins]

Re: ESR testing

Yes think you are right if you look at the same value of capacitor and different working voltages ,you see the ripple current increases with the voltage .
I saw a complicated formula that included ripple current and esr ,if I can find it again I will see if I can reaarange it so that esr is the subject

Barry Wilkins

[PCBONEZ]

Re: ESR testing

Those formulas tend to be inaccurate because of all the assumptions you have to make.

Within a series [model line] of capacitor the Ripple and ESR follow the can size.
Higher volt caps tend to have larger cans.

If ESR is not shown in the data sheet for the original cap then just look at the Ripple rating because ESR isn't important to the application. [Usually, sometimes the original caps aren't good enough to be there in the first place, meaning: they aren't low ESR but should have been.]
.

[PCBONEZ]

Re: ESR testing

Back to the question:

Tested a 2200uF 16v 12.5mmx30mm w/ESR meter today.
Not low ESR but not quite GP either.
Was a Test equipment cap from a +/- 0.02% accuracy DMM.
Not a 'normal' cap as the tolerance was +50%/-10% so it's probably better quality and ESR than average GP cap.
ESR = 0.150

2200uF 16v low ESR for comparison
Panny FC 12.5mmx25mm ESR = 0.030
Panny FM 12.5mmx25mm ESR = 0.015
UCC KZJ 12.5mmx20mm ESR = 0.009
.