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Cell capacity at different temperatures
#1
I have been doing repeated capacity tests on 2 cells to look for loss of capacity over number of cycles the cells have done
This has been inspired by "generic" on here doing similar testing.
I am using a single tp4056 to charge and a single zb206 to test, so charging and testing should be as consistent as possible.
In Sydney at the momwnt emperatures get fairly cold during the night and warm during the day.
My testing is being done outside the house in an undercover area, so temperatures vary quite a bit depending on the time of day.
I have noticed that the capacity results seem to change with temperature. Tests started at night when it is colder seem to give lower capacity results and tests done during the day seem to give higher results.
Overnight temperatures probably get down to 5 degrees C.
Daytime temperatures are probably around 25 degrees C.
Today's forecast says 3 -19.
Overnight tests might give approximately 1950mah and daytime tests might give approximately 2050mah

My questions are.
Have other people noticed temperature affecting capacity results?
If so, do people try consider this and do testing in controlled conditions?
thunderheart and Generic like this post
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#2
It's sure related.
That's why in every data sheet is a nominal ma at approx 18 degrees Celsius.
When it is 25 degrees Celsius you will get a higher number.
Some sheets have even data on temperature
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#3
Of course. Thats why 100mah Range is Good enough to sort cells in for most People...
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#4
Chemical reactions generally slow down at lower temperatures, so performance of batteries that convert chemical potential energy to electrical energy degrades at lower temperatures, and it's particularly noticeable as it nears its empty state.
So while a warm battery at 20% State of Charge (SoC%) might be able to supply 1A, the same battery at 3degC might only be able to supply 0.2A, making the tester/device think the battery is already empty.

Not 100% sure about this, but if you can test at say 100mA, you'd probably get much closer results regardless of temperature.

Some extra interesting info:
(Tesla?) EV cars sometimes warm up the batteries to get better charging/driving performance.
You can squeeze out some more power from cold batteries by rubbing (friction heating) them.
Cold car batteries usually perform better at the 2nd cranking try, because the first failed attempt warmed up the battery.
Cold weather camera(wo)men keep batteries inside their jackets to get more filming time.
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#5
(07-20-2019, 09:34 AM)daromer Wrote: Of course. Thats why 100mah Range is Good enough to sort cells in for most People...

Putting cells into 100mah range bins can make sense as the actual values will average out because of the large number of cells.
Temperature changes affecting WHICH 100mah range the cells end up in could result in different capacity packs being made.
My repeated tests for the 2 cells appear to show about 1950mah when tested while it is cold (about 5 to 10 degrees C / 41 to 50 degrees F) and show about 2050mah when warmer (about 20 to 25 degrees C / 68 to 77 degrees F).
Without temperature being controlled (ie lots of peoples workshop/shed areas) If you make a pack in Winter and another pack in Summer or measure a large number of cells at night then a large number of cells in the day your pack capacities may vary (by 5% from the testing I have done) even when you use the same test result numbers.
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#6
(07-19-2019, 11:02 PM)Oz18650 Wrote: I am using a single tp4056 to charge and a single zb206 to test, so charging and testing should be as consistent as possible.

Have you tested that consistency you have assumed ?

Same cell, tested 10 times, same temperature .....
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#7
(07-21-2019, 04:37 PM)Sean Wrote:
(07-19-2019, 11:02 PM)Oz18650 Wrote: I am using a single tp4056 to charge and a single zb206 to test, so charging and testing should be as consistent as possible.

Have you tested that consistency you have assumed ?

Same cell, tested 10 times, same temperature .....

So far I have done 42 tests, so 21 on each cell.
Since I noticed that temperature seems to affect the results I have made a note of "cold" or "warm" at the start of the test being run and lower results are matching with "cold" and higher results are matching with "warm".
I might start recording temperature and time at tree start of a capacity test. A 9:00am test would mean that temperature is rising during the test while a 5pm yet would mean that temperature is dropping during the test.
I might also start a test with a another cell and try to test at consistent times/temperatures.
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#8
How is your test coming along?
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#9
(07-19-2019, 11:02 PM)Oz18650 Wrote: Overnight temperatures probably get down to 5 degrees C.
Daytime temperatures are probably around 25 degrees C.
Overnight tests might give approximately 1950mah and daytime tests might give approximately 2050mah

I'd expect more difference with such a loose temp range.
Ideal temperature for a Lithium cell is 23-27*C. Lower/higher temperatures assume lower capacity or reduced life and/or reduced charge/discharge current. That's all according to official datasheets.

Usually charging is allowed at 0-45*C and discharging at -20-60*C. For some high-drain cells there is an 80*C temperature cut requirement.

(07-19-2019, 11:02 PM)Oz18650 Wrote: My questions are.
Have other people noticed temperature affecting capacity results?
If so, do people try consider this and do testing in controlled conditions?

I have
I do
Smile

P.S. a screenshot from Panasonic NCR18500 datasheet:
   
LiFePO4: QB26650 2500mAh 50A vs A123 ANR26650M1B: https://youtu.be/GOSkte11lRc

Yinlong LTO Lithium Titanate safety tests: https://youtu.be/eAUYbSDEy6I
Toshiba SCiB LTO Lithium Titanate safety tests: https://youtu.be/XsrRDZxEFQE

XTAR DRAGON 4-slot battery tester review: https://youtu.be/S6yVMsIuauE
Miboxer C4-12 4 slot x 3.0A charger review: https://youtu.be/X-ww1YALjvU
Miboxer C2-4000 smart battery tester review: https://youtu.be/jrbJceNXv1g

Samsung 33J for TESLA: https://youtu.be/7FMxgMmPeh4
Samsung 40T - a high drain 35A 21700 cellhttps://youtu.be/lxgKWiQ9580
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#10
(08-11-2019, 04:11 AM)Generic Wrote: How is your test coming along?

I have started recording the time that each test starts as well as the temperature of the cell measured with a laser pointer themometer when the test starts.
I am at 100 tests now and while I still have to do some analysis of the data, capacity results look pretty closely linked to temperature.
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