Internal impedance/resistance of batteries

Nice to see this topic
I have a few questions.
My Liitokala gives a value in mR and I think this is the internal resistance of the cell

When I receive a cell I charge it, do discharge mAh test and connect/disconnect the cell in the charger to see what the lowest mR is (how a cell is placed affect the mR sometimes and I want to rule that out)
I then write the mAh and mR on a small piece of paper and stick it on the cell with tape.

I use my KeepPower 2200 measured 2300mAh for most testing and they got used the most of my cells.

They all three read 53mR when first tested.
Now the two most used (a lot of charge cycles went into the thorfire tests) now read 75mR and the third 61mR.
The two I always use together, if not in series then in a SRK never alone.

I have cheap rubbish cells that measure 125mR from the start and not getting used, and a 26650 Ultrafire that gives 35mR and 1646mAh that I use the first run of single 26650 flashlights since it is the only 26650 I currently own (2 good ones in transit)
Non of the cells become warm when charging or discharged.

When should I do a new mAh test on the KeepPowers? ( though at 100mR)

When used in serie I always put cells in the Liitokala and only use cells with same brand and mR even if the mAh is little (max 25) off, so if I have 4 Panasonic’s
1 3345mAh 61mR
2 3345mAh 70mR
3 3296mAh 65mR
4 3327mAh 61mR
I use cell 1 and 4 in series.
Not 1 and 2. Since mR is easy to measure and mAh takes a lot of time)
Is this good practice?

At what value is a cell considered written off?

the repeatability of the Liitokala test is poor.
anything over 150mohm is poor.decent laptop cells average 100.
i would keep the originally paired cells in service as they have in the past.its normal to see i.r rise with cycle count.1 and 4 are decently matched.

Ah OK 150mR means discard then for my future actions?

The cell data was made up
When I want to use a series light I grab the SRK with 4 panasonic cells in it ( use it as battery holder, place 4 fully charged cells then use it for 10 mins and put it away locked out)
And measure the mR and pick the two that are equal.
I measure all cells several times since how they are connecting makes a difference three times the same lowest mR is the one I think closest to reality.

very useful topic.
i am not an ee but use the LiitoKala chargers that offer a “similar” function.

i think we should press charger mfg to incorporate and improve this functionality.

peakelec ESR70 measuring battery internal resistance?

Hello I have peakelec ESR 70.

I ask if it’s true 100khz meter:

peakelec replies

1. I can confirm that the Atlas ESR (models ESR60 and ESR70) do measure the true ESR at 100kHz. It applies a test signal of exactly 100kHz and measures the true ESR and ignores the capacitor’s reactance (unlike many other ESR meters).

I ask if it’s possible to measure battery internal resistance

peakelec replies

2. It is possible to measure the ESR of batteries if a series capacitor is used. See attachment.

I have made the circuit to measure ers of batteries.
I’ve used 10uF 35V Rubycon cap (ESR 0.30), and 47K resistor 5%.

Questions:

1. How to zero out the wire resistance? The Atlas meter is zeroes out OK, but that can’t be done while meter is connected to this circuit. What am I doing wrong?

2. Is 5% resistor OK, do I need 1%?

3. The internal resistance of typical lead acid batteries is 4.22 milliohm, that’s 0.00422ohm
The ESR70 resolutions is only 0.01ohm so how can peakelec claim it can measure internal resistanceo of batteries

Why not use small non polarized cap? peakelec ESR70 can’t measure those the capacitance and resistance is too small i guess. This way nothing needs to be subtracted except the lead resistance. hmm.

ESR 70 measured internal resistance seems to be wrong:

0.06; 0.08ohm
60mili ohm; 80mili ohm;

When measured with proper battery tester it show
18mili ohm (manufacturer new battery is 16mili ohm)
http://www.yuasabatteries.com/pdfs/NP_12_12_DataSheet.pdf

That is huge difference. Any ideas?

There can be 2 factors:

  1. The circuit with a capacitor affecting the result
  2. The frequency. The standard battery IR test is at 1kHz, the ESR70 is probably more like 100kHz

I don’t know how capacitor (that alone gives stable results) in the circuit can have influence?
The frequency ESR70 is 100kHz, but how is this related to unstable measurements furthermore if the frequency is so critical then how ESR70 or Anatek Blue ESR meter can even claim they can measure battery resistance?

What do you know about YR1035 battery resistance meter, it’s quite well made? What is the com port for?
English manual would be nice. I did not find anything in this price range better then YR1035.

If you use a capacitor with very low impedance and ESR at 100kHz it will probably not affect the result much.
You can measure the battery impedance at any frequency you want, but do not expect the same result at different frequencies.
Sometimes scientists measure IR at many frequencies when testing batteries.

I do not know the YR1035 only the YR1030: Review of Vapcell Internal Resistance Meter YR1030

Thank you for the link, YR1035 is logically higher version of the same device the YR1030.
The YR1035 uses aviation connector vs. USB for YR1030.

How USB can be precise is beyond me, the worst connector you can get is USB, but it’s the cheapest and has 4 wires as required for this device. So the YR1035 is way better in this regard.

The YR1035 has also what looks like com port. I wonder for what, logging to PC?

I wonder who the manufacturer is of YR1035?

With 4 terminal connection you do not need a connector with low impedance, the usb will work perfectly.

Or for controlling a a sorting device, the YR1030 has functions to sort cells.

HKJ, maybe I just don't understand it well, but in this thread you mentioned that the health of a battery can be determined by monitoring internal impedance such as with a SM8124 meter, but in other threads, I thought you said that measuring internal impedance with a meter such as the SM8124A is only good when first receiving batteries and that only the DC method can measure the true IR as the battery ages? If I understood it correctly and the DC method that chargers use to measure IR are what we should be looking at, then what is the maximum recommended IR of a lithium battery with protection circuits before they would need to be recycled?

Maybe there is no correct answer to my question either as protection circuits add all that extra resistance and from the batteries I have with the same part #, IR has varied greatly as well and left me a little doubtful as to when I should not use them anymore. Right now, the only sane method I trust is if they heat too much whilst charging, then they go to the recycle bin and I'm done with them.

Henrik, do you think that impedance values from the SM8124A can be converted to approximate resistance values, e.g. by using a conversion factor?

The DC method is the best, the variation with AC is not as large.

The problem with chargers is that they all use different test parameters and the results is not completely comparable.

No.

Is there a reasonably priced DC IR meter that is available then?

I only know of hobby charges.

Thanks HKJ!

HKJ, thank you for this article! I now know much better how my SM8124A (pictured below) works.

I've used it extensively and am impressed with the way that IR reading are repeatable - unlike my analyzing chargers. I purchased mine on ebay for around $53 (including shipping), but it it can be found on Ali for about $10 less. See the Found a Quality Battery Resistance Tester thread for more discussion on the SM8124A impedance tester.