I have 50 brand new batteries, how do I test them before assembly?

[mbgjt1]

Hello all,

I've recently purchased 50 x Molicel P42A batteries. I am getting ready to assemble them into a 16s3p pack for my eBike.

I have purchased them from a reliable source, and they have given me a certificate to show they are authorized distributors.

Before I assemble, what sort of tests do I have to do to make sure they are 100% functional and not fauly?

I will measure the voltage level to make sure they are all within 0.1V of each other.

Any other things to consider? IR test? Capacity test? etc.? I don't have access to much equipment, just a multimeter, and an oscilloscope.

I can do an internal resistance test by connecting it to a resistor. But I've also heard this isn't very accurate. Any advice?

 

[mbgjt1]

Hello all,

I've recently purchased 50 x Molicel P42A batteries. I am getting ready to assemble them into a 16s3p pack for my eBike.

I have purchased them from a reliable source, and they have given me a certificate to show they are authorized distributors.

Before I assemble, what sort of tests do I have to do to make sure they are 100% functional and not fauly?

I will measure the voltage level to make sure they are all within 0.1V of each other.

Any other things to consider? IR test? Capacity test? etc.? I don't have access to much equipment, just a multimeter, and an oscilloscope.

I can do an internal resistance test by connecting it to a resistor. But I've also heard this isn't very accurate. Any advice?

 

[jonyjoe303]

I would get a yr1030 internal resistance tester, its what I use, its in the 50 dollar range. I wouldnt build a pack unless I did an IR test, all the batteries got to be near the same IR, sometimes you might end up with one in the 100's milliohm, while all the rest are in the 40 milliohm.
Its a big purchase but its worth it if you plan on building packs. Without testing the IR you might get lucky and build a good pack, but from my experience all it takes is one high IR cell to give you balancing problems. And taking a battery pack apart is too much work.
You can also test for capacity with the opus btc3100 or similar but thats another 50 dollar investment. But since they are new you can probably skip it. As long as the IR is good and they don't self discharge they should be good.
The opus has its own IR testing but its unreliable, you test the same battery 5 times and you get a different reading everytime. The yr1030 you test the cell 5 times, and it reads the same every time.

 

[mbgjt1]

Thank you I managed to get one and it is measuring the IR for batteries between 17 and 18 milliohms is this normal for brand new batteries?

Molicel p42a

 

[pwd]

Make sure when you are measuring the IR of cells that they are all in the same state of charge (resting voltage) and that the temperature is a close as possible.

For the record when I measured my P42A cells @ 20 Celcius and ~3.525V per cell; I was getting an average of 10 milliohms - testing isn't so much about comparing different types of cells but to catch any outliers in your batch

 

[docw009]

Data sheet says AC IR of 10 milliohms, and DC IR of 16 milliohms. I believe the YR1035 uses AC

https://www.eremit.de/WebRoot/Store30/Shops/84214678/5F78/D052/445D/99D3/CDA6/0A0C/6D0B/EA3B/INR21700_P42A-V1-80092-datasheet.pdf

I was getting 16-18 milliohms out of new Lishen 21700 cells, 4.5aH, 13.5A, which seems compatible to your P42m. I've built two packs out of new cells, and I didn't bother checking them. I have a Liitokala 500I tester. It takes a day to run 4 cells thru a full test to get their maH rating. A 52 cell battery will take 13 days of testing. I also have the YR1035, and since that's quick, I'll check the IR, but didn't have one when I built my packs.

 

[mbgjt1]

Thank you both for your reply.

Yes, I've managed to check all batteries and they are all within 17 to 18milliohms which is good. Even though the method may be inaccurate at least there is consistency between all the cells. I have also made sure to measure them all at the same voltage level.

 

[eMark]

Can a cells' increase in IR near its EOL comparison be made between all Li-ion cyclindrical cells. For example Molicel P42A 21700 and Panasonic NCR18650B ??

Four identical 18650 3200mAh Panasonic NCR18650B li-ion cells were tested. Each cycle included a 1600mA charging rate (0.5C) and a 3200mA discharging rate (1.0C). Charging to 4.20V = 100% SOC and discharging to 2.50V = 0% SOC (typical industry standard).

One can see why many ebikers don't charge their pack more than 90% SOC to extend a packs' cycle life. One can also anticipate a decrease in cycle life with increasing discharge rates (2C - 3C) and increasing of IR ... https://www.mdpi.com/1996-1073/10/9/1284/htm

When this Panasonic B cell was first introduced Panasonic said an IR "less than 100mΩ" was OK. So this Panasonic B graph with IR in the mid-40s is AOK. Were pack builders to assume an IR less than 100mΩ was still viable as the cells neared EOL with an IR approaching 100mΩ ?

With an IR of 17 for Molicel P42A cells any guess as to the IR of these cells approaching EOL ? Can we draw any comparisons beween 36.5mΩ (blue line 85% SOC) and "less than 100mΩ" as usable IR range? Using a range of 2.6 times 36.5mΩ is 95mΩ ("less than 100mΩ"). P42A at 17mΩ (85% SOC) when new would still be usable at 44mΩ (2.6 x 17 = 44.2mΩ).

Is a Li-ion IR range of 2.6 reasonable for figuring when 18650 cells or 21700 cells are nearing EOL?

Data sheet says AC IR of 10 milliohms, and DC IRof 16 milliohms. I believe the YR1035 uses AC

Does the YR1035 (and SM8124A) measure AC or DC internal resistance?