Measuring cell resistance with an ESR meter

[wshyang]

Hi again :)

Well, I just remembered I have one of Bob Parker's Blue ESR meters, so I tried to get a measurement off one of my rather poor performing NiMH batteries.

Nothing exploded, but I didn't get a useful value either, the reading didn't remain stable as I was trying to get some fix on it. Was I doing something wrong? I actually got this idea while reading this post on the EEVBlog.

 

[SilverFox]

Hello Wshyang,

I think you proved to yourself why those cells are crap...

Try it with a cell that is in good condition and see what you get.

Tom

 

[Datman]

Hi,

you can't measure the internal resistance of a battery using a capacitor ESR meter! You have to measure the voltage difference when you apply two different loads, then calculate the differential resistance: (Va-Vb)/(Ia-Ib) or (Va-Vb)/(Va/R1 - Vb/R2)

Gianluca

 

[dragosios]

You can measure the internal impedance of a battery with an ESR meter. But you must add a capacitor between battery and ESR meter to pass just the AC pulses generated by the ESR meter.
I've used the method to pair cells.

Gialuca's method works as well and probably is more accurate than the reading of an ESR meter, but both are enough to give you a rough ideea about cells health.

 

[HKJ]

Internal resistance and internal impedance (DC and AC) is not the same for a battery.
I have written an article about how to measure them.

 

[dragosios]

HKJ, you are right in your tutorial. I've said that the internal impedance can be measured for matching purposes if no other method is used, even if it is different than internal resistance can give you a rough estimate about the cell.
Also, your Fluke 189 and 289 have a 100kHz bandwidth. I know that because i also have a 189 which can measure my ESR meter directly, even ripple in PC power supplies at around 42kHz.

 

[HKJ]

Also, your Fluke 189 and 289 have a 100kHz bandwidth. I know that because i also have a 189 which can measure my ESR meter directly, even ripple in PC power supplies at around 42kHz.

The high end Fluke DMM's do have good specifications, but some cheap DMM's have problems with 1kHz. Usual I prefer a oscilloscope to check ripple with.

 

[dragosios]

My 189 compared to oscilloscope differ at the 5th digit, which is inside calibration error specified by the manufacturer. It was verified with a calibrator at a local Fluke dealer and is still inside calibration error limits afther 10 years since production.

 

[HKJ]

My 189 compared to oscilloscope differ at the 5th digit, which is inside calibration error specified by the manufacturer. It was verified with a calibrator at a local Fluke dealer and is still inside calibration error limits afther 10 years since production.

A oscilloscope is usual less than 3 digits, but it shows the actual waveform and you can measure both peak and rms values and on some scopes you can also do a FFT and see the frequency contents (more or less).

 

[dragosios]

That is true. But the DMM is handheld and more practical to carry on.