EVE 280A Load Capacity Testing Help Wanted

Stepandwolf

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Hi guys....rather than branch off an existing thread, I thought I would try and figure this out here. As some of you know, I received 8 EVE LF280 cells that were presumably made first half 2020 based on our interpretation of the date codes and the assumption they didn't put old codes on new cells.

In the spreadsheet provided by the vendor from EVE, it shows that 7 of the 8 tested at 291.XXXX and one tested at 289.XXXX. I charged the 289 to 3.65V and want to load capacity test it, something I have never done. I purchased Will's suggested load tester. If I remember right, will suggested setting the low battery cut off at 2.6V and said something about "all lithium". In earlier threads here, I have seen suggested values of 2.3 and 2.4V. The product sheet for the battery suggests 2.5v for testing to their specs. Presumably, the lower voltage you go to, the higher capacity result you will get? Can you guys help me determine the proper low voltage cutoff value.

Next, I connected the load tester to the battery I charged and tested to 3.65V, but the tester shows 3.47V? Will that error result in an incorrect capacity value?

You guys new I said I would likely blow something up, half in jest, but only half. Please help me do this correctly.

Thanks!
Low Voltage Lew
 
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Bob B

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What do you mean by "charged and tested"? Did you check the cell with a known accurate DVM while it was connected to the tester?
 

Stepandwolf

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Part Deux,

The product sheet refers to a sequence of 3 tests.

1. after standard charge and 1 h rest, discharge to 2.5v cutoff at .33C.
2. then at .5C
3. then at 1C

It says .33CA should equal 100%, .5CA should be 98%,a nd 1CA should equal .97.

My load tester won't go that high....I did a short test....it will only do about 12A...so....should I be doing all these capacity tests, or just the one test to 2.XX voltage?

I also read for measuring capacity they would do successive discharges, not like above, but doing the main discharge, measuring the value, then discharge further, let rest again, and continuing until you don't get more....I presume still down to the checkoff value, but doing successive tests?
 

Stepandwolf

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What do you mean by "charged and tested"? Did you check the cell with a known accurate DVM while it was connected to the tester?
Charged means I charged it, tested means I tested the battery to insure it matched the 3.65 I charged it to after resting.

I didn't check it when connected to the tester, I checked it after resting and before connecting to the tester. Then I connected it to the tester which displayed 3.47.

I am using a Fluke that has always been reliable.
 

Bob B

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The reason I'm asking is that if you charged to 3.65 .... and then rested the cell .... it could easily have settled to 3.47V

If you want to know if the load tester is accurate, verify its voltage reading with the DVM while it's connected to the tester and verify if the same or not.
 
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Bud Martin

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You need to test the Voltage at the battery terminals and at the tester input terminals, the Volt meter of these tester are not accurate and when you start drawing high current there will be more Voltage drops on the cables between battery and the tester which make the Voltage display on the tester show even less Voltage than at the battery terminals, I myself draw about 15A so the MOSFET of the tester will not blow up.
I set my tester cut off Voltage at 2.5V but the actual Voltage on the battery terminal is around 2.7V when test is finished which is close enough.
You should leave the Voltmeter attached to the battery sp you can monitor it
 

Steve_S

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BTW: Make sure you have a Proper Wire (thick enough gauge), I went too thin 1st time, skewed everything. and No Aligator Clips ! Those things are handy but evil too. I have the same tester but the 180W one. LFP will ALWAYS settle from 3.650V even if fully saturated till the cells take <0.5A they will settle to 3.550 +/- within one hour of charge stop. This is normal behaviour.
 

Stepandwolf

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The reason I'm asking is that if you charged to 3.65 .... and then rested the cell .... it could easily have settled to 3.47V

If you want to know if the load tester is accurate, verify its voltage reading with the DVM while it's connected to the tester and verify if the same or not.
Actually, the PS likes to overrun the votage, so actually when done charging, it was 3.71, and after resting, 3.65, and was still 3.65 when I connected to the load tester. I am just about done charging the battery back after my brief test yesterday. Then let it rest again, then start the load test.
 

Bud Martin

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Actually, the PS likes to overrun the votage, so actually when done charging, it was 3.71, and after resting, 3.65, and was still 3.65 when I connected to the load tester. I am just about done charging the battery back after my brief test yesterday. Then let it rest again, then start the load test.
Please clarify about "PS likes to overrun the votage, so actually when done charging, it was 3.71'.
Did you set the power supply to 3.65V before connecting it to the cell?
 

Bob B

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I would do as Bud Martin suggested earlier and keep a meter connected to your cell while testing .... that is almost .2V off.
If it remains off by that amount thru the whole range, the worst thing that would happen is that it would terminate the test too soon ..... but, I'm not sure I would trust it to measure current accurately either.
 

Bud Martin

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I verify the current meter by using DC clamp-on meter to verify my tester Amp meter accuracy, my is within 0.5A on 15A current draw.
BTW, using small wires will not effect Ampacity test result since we are performing current draw from the battery over time, but small wires and where the Voltage are measured at effect the Watt calculation since the power dissipate by the wires are not factor in if the Volt meter is not measuring at the battery terminal, that is why good tester has separate Voltage measurement wires for measuring Voltage right at the battery terminals. Less current draw will just take longer to empty out the battery.
 

Stepandwolf

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You need to test the Voltage at the battery terminals and at the tester input terminals, the Volt meter of these tester are not accurate and when you start drawing high current there will be more Voltage drops on the cables between battery and the tester which make the Voltage display on the tester show even less Voltage than at the battery terminals, I myself draw about 15A so the MOSFET of the tester will not blow up.
I set my tester cut off Voltage at 2.5V but the actual Voltage on the battery terminal is around 2.7V when test is finished which is close enough.
You should leave the Voltmeter attached to the battery sp you can monitor it
I think I measured at the battery before and after connecting the tester. I am just finishing the charge and after the rest stage, will connect it back up and test voltage. Thanks
 

Stepandwolf

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BTW: Make sure you have a Proper Wire (thick enough gauge), I went too thin 1st time, skewed everything. and No Aligator Clips ! Those things are handy but evil too. I have the same tester but the 180W one. LFP will ALWAYS settle from 3.650V even if fully saturated till the cells take <0.5A they will settle to 3.550 +/- within one hour of charge stop. This is normal behaviour.
Went through that with the PS. I grabbed some 10ga high quality wire and crimped a ring terminal for the battery and a fork terminal for the tester. I hope that is sufficient. I meant to get the 180w model and goofed when ordering. Thanks
 

Stepandwolf

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I would do as Bud Martin suggested earlier and keep a meter connected to your cell while testing .... that is almost .2V off.
If it remains off by that amount thru the whole range, the worst thing that would happen is that it would terminate the test too soon ..... but, I'm not sure I would trust it to measure current accurately either.
Before I assume there is a problem, I need to recheck the voltages which I will do soon. Thx
 

Stepandwolf

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Please clarify about "PS likes to overrun the votage, so actually when done charging, it was 3.71'.
Did you set the power supply to 3.65V before connecting it to the cell?
Yes...set to 3.65 at the PS before starting. I am probably minutes from that now....right at the end of charging again...was down to a watt when I came back to my computer.
 

Stepandwolf

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I verify the current meter by using DC clamp-on meter to verify my tester Amp meter accuracy, my is within 0.5A on 15A current draw.
BTW, using small wires will not effect Ampacity test result since we are performing current draw from the battery over time, but small wires and where the Voltage are measured at effect the Watt calculation since the power dissipate by the wires are not factor in if the Volt meter is not measuring at the battery terminal, that is why good tester has separate Voltage measurement wires for measuring Voltage right at the battery terminals. Less current draw will just take longer to empty out the battery.
I didn't test the amperage yet. As mentioned, I am using 10ga. Thanks...will see what happens.
 

Stepandwolf

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OK....I finally finished charging the cell to 3.65 and am in the resting stage. Will have to decide if I launch it before going to bed tonight, or wait until morning so I can monitor?

After charging the battery to 3.65, I connected it to the load tester. Once again, it is reporting 3.47v. The voltage at the battery is 3.65, at the leads on the tester, 3.545. Also, the meter always says .1A, even with nothing disconnected and won't clear? Is this normal?
 

Bud Martin

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OK....I finally finished charging the cell to 3.65 and am in the resting stage. Will have to decide if I launch it before going to bed tonight, or wait until morning so I can monitor?

After charging the battery to 3.65, I connected it to the load tester. Once again, it is reporting 3.47v. The voltage at the battery is 3.65, at the leads on the tester, 3.545. Also, the meter always says .1A, even with nothing disconnected and won't clear? Is this normal?
So 3.65V at the battery terminal, 3.545V at the terminal of the tester without current draw (Current pots set to Full CCW), that is about 3% tolerance.
I believe there is a away to Zero out the current reading, I do not remember how, it think it is in the in the user manual of the tester, 0.10A of offset is not that bad.
I monitor my Voltage at the cell terminals, especially when it gets close to the 2.5 ~ 2.6V, that is when I stop the test.
 

Stepandwolf

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I just realized I gave the wrong value....3.65v at the battery, 3.645 at the tester terminal, only a .005 loss

I chose every "clear" option in the instructions, i.e. single tap, double tap, triple tap, etc...nothing cleared that .1A value.
 

Bud Martin

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I just realized I gave the wrong value....3.65v at the battery, 3.645 at the tester terminal, only a .005 loss

I chose every "clear" option in the instructions, i.e. single tap, double tap, triple tap, etc...nothing cleared that .1A value.
The loss will become higher as you start drawing 15A, I run my at 15A to keep the MOSFET and the diode under the heatsink cool to touch.
 
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