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Battery internal resistance. Its truthful science knowledge


What is it all about on NiCd recharge battery internal resistance (BIR), as its knowledge on

roughly tell this mind-confusing one which has at least 7.7 ohm BIR due to MM tested it 1.53 V  0.17 A
how to reduce or "dissolve" this BIR

I can't understand the Quora post.

For equivalent DC resistance, "dynamic resistance" is easiest to measure, and offers useful real-life number which you can then use to estimate voltage drop with given current, and heat dissipation in the cell.

Use two dummy loads of different resistances, which are significantly different. For example, if you have a cell with maximum rated discharge current of, say, 1A, you could use dummy loads of around 0.1A and 0.5A.

Connecting the first dummy load, keep it connected for at least 10-20 seconds, then read test current I1 and cell voltage V1.

Repeat for another test load.

Rdc = dV / dI = (V2 - V1) / (I2 - I1)

If the loads are connected for too long, the cell discharges during test, causing an error. You can significantly reduce this error by measuring the first dummy load again (i.e.: sequence of loads: 1 - 2 - 1), and use the averages of the two measurements for V1, I1.

Here is a good report of hands on impedance test back in their day.

I recall that one reservation about the new NiCd and also the merging Lead Acid variants at the time, was that UPS would
"lay down" in voltage during a sudden utility trip. But I don't know if that was true.

I expect the subject of battery impedance will be topical as transient storage becomes more common.

was studying these graphs of 18650 DCIR vs number of cycles and apparently LG last a lot longer despite having higher DCIR. https://endless-sphere.com/forums/viewtopic.php?f=14&t=114473&p=1694384#p1694384


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