Measuring super capacitor ESR?

Darren2018

100 W
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Aug 18, 2018
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Does anyone know if it is possible to measure ESR with a ACIR 1khz meter? I got 3.44mOhm when charged to 2.75V. The capacitor is a Maxwell BCAP 1200 P270 which is supposed to have a DC ESR of 0.58mOhm. Does anyone have a conversion factor or a comparison with the same meter on the same series of capacitor? The capacity is so low that it makes it hard to measure the DCIR the old fashioned way.IMG_4553.JPG
 
Do you measure on charge or discharge?

You can slow the discharge ( old fashioned way) with a known load resistance if your meter is not fast enough or does not have a peak and hold function. Or datalogger. I have done that before. Should get a number. Use like a 10Kohm. I was figuring Vdrop through shunts yesterday on spreadsheets with a multimeter. .... . " oldFasionedway". Lol.
 
Darren2018 said:
Does anyone know if it is possible to measure ESR with a ACIR 1khz meter? I got 3.44mOhm when charged to 2.75V. The capacitor is a Maxwell BCAP 1200 P270 which is supposed to have a DC ESR of 0.58mOhm. Does anyone have a conversion factor or a comparison with the same meter on the same series of capacitor? The capacity is so low that it makes it hard to measure the DCIR the old fashioned way.
I have just got myself a Brymen BM867s, the last digit is a bit wild but I will give it ago. I guess that the timing would be crucial especially if you do it at 75A like the data sheet says. If I use 10k would it still be accurate to the data sheet?
 
why would you want to measure the IR of a supercap? its capacity is well outside the range of normal IR meters. the only hope you have is to fully charge the cap to its full rated voltage and have saturated it (so it does not draw ANY current anymore)
 
flippy said:
why would you want to measure the IR of a supercap? its capacity is well outside the range of normal IR meters. the only hope you have is to fully charge the cap to its full rated voltage and have saturated it (so it does not draw ANY current anymore)

This is the first batch of ultra capacitors I have had to work with so I wanted to test them before I use them. I noticed that on my bench PSU they remain in the CV phase for a while. I discharged them and they achieved over 850mAh so I am not too worried about their farad rating but I would like to know if the IR is good. I thought about using a resistor to get a DCIR reading but I was worried that the drift of the resistor and meter combined with the low capacity of the capacitor would give me poor quality results. I tried the DCIR function on my capacity tester but it gives me the same reading as my ACIR meter which is what it usually does when testing regular li-ion cells. I am certain that the IR of these capacitors is not 3.44mOhm because that would be way off. I am just wondering how other people are testing them because if you use the incorrect resistor to gain a time advantage you need a really accurate meter and if you use the correct resistor you need to be extremely accurate with your timing. I have 4 to test and compare.
 
fill them up. leave them at their rated voltage for a day or so to get fully saturated and then disconnect them and just leave them. measure after 12 hours what the voltage is. it does not tell you the IR but it does give an indication of self discharge wich is the best sign of a failing capacitor in that size range.
 
To anyone that is interested I found the answer in the datasheet. I misread it the first time :oops:. Sorry for the confusion.
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