EVE 304 Cells from 18650batterystore & zke-40 testing.

Sam Cho TX

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Well after seeing a slew of videos it seems to me that there is not much difference between grade A and B, so why not try some from 18650batterystore. Anyway I previously tested some of the EV grade from Sunfunktis and was pretty happy with the results, but they have raised the price a bit since then, here is that thread: https://diysolarforum.com/threads/new-toys-arrived-zke-40-tester-sun-fun-kits-eve-lf304-cells.56015/

I could use a few batts so when the 304 came back in stock I ordered 4.

Well... they are packaged Ok I would say, not as nice as Sun Fun Kits but no damage, however, I can already see some issues. I see 2 of my cells are 302AH and 303AH so this is already below the 304 18650store claims on there page... guaranteeing to pull 304 AH.

Also the welds on the terminals look pretty bad looks like they even burned the terminal plastic a bit.

Anyway my total cost was $149.33/cell shipped so lets see how they test. The Sun Fun Kits cells where $202/cell shipped so we are about $53.33 more per cell.
 

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Not sure I think I might have knocked off the v-sense wire, I'm currently charging the cell at 40 amps... assuming it arrived at 50% charge it will be a few hours to full charge.

Once done I'll discharge at 30 amps to 2.5v
 
Well I don't think I charged this cell up properly it only took like one and a half hours to charge. The test results are pretty terrible so I will recharge this cell and then do a full capacity test again this time with another cell as well.

But initial results are pretty bad 281.7 AH and 913.18 WH, however, I'm thinking its because of my error (I hope) and not the cell.

By going with the WH/3.2v method it comes out to about 285.3 AH. Still well short of the claimed guarantee to pull 304 AH. I'm attaching the zke report csv in zip format.
 

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Hrm, looking at your graph it seems ok you started at 3.54v / cell which is basically full. I would perform a charge test. See how many AH you put back into the cell. The cell said it tested to 302 AH?
 
Well I don't think I charged this cell up properly it only took like one and a half hours to charge. The test results are pretty terrible so I will recharge this cell and then do a full capacity test again this time with another cell as well.

But initial results are pretty bad 281.7 AH and 913.18 WH, however, I'm thinking its because of my error (I hope) and not the cell.

By going with the WH/3.2v method it comes out to about 285.3 AH. Still well short of the claimed guarantee to pull 304 AH. I'm attaching the zke report csv in zip format.

You didn't do anything wrong.

These cells are FULL at 3.65V and 15A per the datasheet. You more than met that requirement.

The datasheets detail the discharge test.
 
Well if you go by the 285 figure (yes I know controversial but whatever) you have 285 / 304 = 93.75% of rated capacity
If you go by 281.75 / 304 = 92.68% of rated.

I would test all of the cells you have.
 
So I fully charged the cell and it says it took in 295 AH and 986WH. Why such a big difference between discharge and charge? Guess I will run a discharge again, so this is how my weekend will be, cleaning attic and testing cells?
 

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So I fully charged the cell and it says it took in 295 AH and 966WH. Why such a big difference between discharge and charge? Guess I will run a discharge again, so this is how my weekend will be, cleaning attic and testing cells?

The datasheet indicates the discharge test may be run up to 3 times if it falls short, so that implies cycling may increase tested capacity.

And while near 100%, the charging efficiency isn't 100%.

EDIT: This is especially true when looking at it on a Wh basis. Discharging drops the voltage and results in less Wh drawn while charging increasing the voltage resulting in more Wh input.

Lastly, I would look for some other way to confirm that the current measurement on the tester is correct. if you have a shunt or a DC clamp ammeter, that's good validation of the two instruments read the same current. Otherwise, a very small current measurement error could make a noteworthy difference in the results.
 
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Ok So the 2nd test produced much better results, 297AH. Still short of the 304 but not too bad. I'm not sure what happened on the first test. Next I will test the 303 cell, I'm not sure why the first test was bad but I think it was because it did not charge fully.

Using the WH/3.2 Method it means I have 301.5 AH, very close to rated, not bad at all.
 

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Interesting, I have not seen this before, perhaps you have what is called a RUNNER cell something that jumps to full voltage when its not, these you usually have to keep the charge on a good bit longer to fully saturate.
 
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Ok So the 2nd test produced much better results, 297AH. Still short of the 304 but not too bad. I'm not sure what happened on the first test. Next I will test the 303 cell, I'm not sure why the first test was bad but I think it was because it did not charge fully.

Per my comments above, the datasheet strongly implies that subsequent discharges my be higher than the initial discharge. A test may be run 3 times to establish the capacity of the cell.

Your results assume that your equipment is accurate within 2.3%. Have you validated voltage and current readings with calibrated equipment?

Using the WH/3.2 Method it means I have 301.5 AH, very close to rated, not bad at all.

The Wh/3.2 calc is inaccurate. If a device measures and reports both Ah and Wh, those values are accurate.

Wh is an integration of the instantaneous Amps * Volts over time. The device is taking the average current and average votlage over a short period of time and adding it up over the entire course of the test.

Interesting, I have not seen this before, perhaps you have what is called a RUNNER cell something that jumps to full voltage when its not, these you usually have to keep the charge on a good bit longer to fully saturate.

This is incorrect. A RUNNER is a cell that is at higher state of charge than the other cells in the battery. It is not possible to identify a runner as an individual cell.
 
Did you use the remote voltage sensing directly on cell terminals? This is necessary to avoid high current lines voltage drop.

3.300v initial voltage slump for only 30A load says they are used cells. This assumes you used remote voltage sensing.

It is good to insert a 5 minute, zero discharge current rest period, at least at three points, approximately 75% SoC, 50% SoC, and 25% SoC. You can add more SoC points if you want more info, up to number of cycle sequences allowed by tester. The tester will still compute correct AH results with the no-load 5 minute rest periods.

Looking at the voltage slump after load picks up again gives good info on quality of cells. The less voltage slump the better. For 30A discharge on a 304 AH cell you should only have 50-60 mV max. slump from rested open circuit voltage. The 3.300v shown on first 25% discharge says you have about 100 mV of terminal voltage slump with 30 amp load. That is a high amount of slump voltage.

The voltage slump gives an indication of cell impedance which increases with aging/use of cell.

You should use 40 amp discharge to get a better test on cell quality. 40 amps is max of tester and still marginal on load test current. You would really like to have discharge current between 0.2 to 0.4 C(A), 60-120 amps for a 304 AH cell.

This curve is approximately what you should expect for terminal voltage slump for various amounts of discharge load current.

LF280 overpotiential curve.png
 
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