0.1uF ESR ?

[Flump]

I have a 0.1uF electrolytic cap which
my tester measures as 107nF
but it cant get a ESR reading from the cap.

Is this normal on caps this small ?

[c4757p]

Very low-value electrolytics tend to have very high ESR. It's possible that it's overrange.

[Flump]

thanks very much

[PedroDaGr8]

thanks very much

I have a 0.1uF that I read an ESR of around 160. I think tan delta is a better indicator of health for these size caps (plus its in the datasheet)

[Flump]

never heard of tan delta so will do some research on it
thanks Pedro 

[SeanB]

Tan delta is basically how lossy it is. Even on electrolytics it gives a good idea of the health of a capacitor. The smaller the number the closer it is to an ideal capacitor.

[w2aew]

I have a 0.1uF electrolytic cap which
my tester measures as 107nF
but it cant get a ESR reading from the cap.

Is this normal on caps this small ?

That's a pretty small value cap to measure ESR on.  Many ESR meters use something on the order of 100kHz as a test frequency.  This cap will have 16 ohms of capacitive reactance at that frequency, which many ESR meter designs will incorrectly interpret as ESR.

[AQUAMAN]

U need to either buy a proper LCR meter

Or u need a pulse generator and u can build a peak detector circuit to measure the peak current into the capacitor, from this u should be able to tell its ESR in some level roughly

I have built many circuits that approximately measure the ESR of gate capacitances in IGBTs or MOSFETs which are in the range of 50-100nF. They can be built very cheaply and easily.

What I do is I measure the peak current flowing through the charging resistor.

For my applications I only measure the CHANGE in the ESR during operation (and I measure this change in 1mOhm/C sensitivity), so actually I have no idea what the absolute value of it is and it does not matter to me either. But in theory you could probably work it out, even if I dont bother to do this.

Using a pulsed ESR detection will never give u the true ESR as the peak current/instant voltage is dependent on the capacitor size, the inductance and also the resistance (search Peak Inflow Current into capacitors)

[Flump]

Thanks Alan

Aquaman how will a LCR Meter helm me measure ESR ?

[AQUAMAN]

Because thats what it measures?

U can tell them to measure Cs-Rs

Rseries is the ESR of the cap right?