Cell imbalance during (slow) capacity test: not even near rated capacity

Martijn

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Yep pressure valve looks like CATL, terminals like ETC ... what is this ?



No QR code is a nono.
Hmhm, no method of checking anything like this. Don't know if these cells didn't pass QA, are damaged or whatever. I noticed some cells having a slight bulge.

Could these even be dangerous?
 

mrzed001

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Hmhm, no method of checking anything like this. Don't know if these cells didn't pass QA, are damaged or whatever. I noticed some cells having a slight bulge.
Amy and Dongguan and better sellers do a video where they test the V and internal resistance of all your cells one by one (before shipment).

Could these even be dangerous?

Do not know. Not puffy and not hot when under bigger load/charge that is good.
Can be low quality cells (low GRADE B). Meaning low capacity, low cycle count.
 

Martijn

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Do not know. Not puffy and not hot when under bigger load/charge that is good.
Can be low quality cells (low GRADE B). Meaning low capacity, low cycle count.
Well, the most I got from these was 233Ah, using a very slow discharge. Now I get between 205 and 227 with higher loads, depending on when to cut off charging/discharging.

That said, I was planning on using these in a camper with a 3000W inverter, so that would be about 125A current, a near .5C discharge, although not for hours at a time.

Will probably get under 200Ah then... :-(
 

mrzed001

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Well, the most I got from these was 233Ah, using a very slow discharge. Now I get between 205 and 227 with higher loads, depending on when to cut off charging/discharging.

That said, I was planning on using these in a camper with a 3000W inverter, so that would be about 125A current, a near .5C discharge, although not for hours at a time.

Will probably get under 200Ah then... :-(

Get a refund, send them back, and buy a good one ... that is what I would do.

@Will Prowse I would consider removing this seller's link from the video description (or a warning, not a quality supplier)
 

Martijn

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Get a refund, send them back, and buy a good one ... that is what I would do.

@Will Prowse I would consider removing this seller's link from the video description (or a warning, not a quality supplier)
"send them back", I think the shipping cost back to China would probably be on the high side, even if I, as a private person, can find a company to take them.

Personally, I would argue that it's their fault and they shouldn't bother me when shipping faulty/non-new/wrong/etc products, so they just have to refund me. But I'm not sure if this is the result.

From my end, I'm pretty sure I did my best to get decent capacity tests.

@Will Prowse did post an update to that video, saying they're new cells and " I used the barcode under the covers for verification. ", as said, mine have their QR codes scratched off. The "LiitokalaVariCoreFlagship Store" certainly is not a trustworthy supplier.
 
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mrzed001

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"send them back", I think the shipping cost back to China would probably be on the high side, even if I, as a private person, can find a company to take them.

Personally, I would argue that it's their fault and they shouldn't bother me when shipping faulty/non-new/wrong/etc products, so they just have to refund me. But I'm not sure if this is the result.

From my end, I'm pretty sure I did my best to get decent capacity tests.

@Will Prowse did post an update to that video, saying they're new cells and " I used the barcode under the covers for verification. ", as said, mine have their QR codes scratched off.

You can argue fraudulent behaviour. Item is not what they advertised. Not that brand, not that capacity, also damaged (QR code).
 

HighTechLab

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1629130660313.png

Here is a graph for a C/8 test (50a current on a 404ah pack). These are brand new A+ grade cells, and the actual capacity was 411.69ah on a pack that should only pull 404ah. Voltages at the end of the test are as follows:

Cell 12.542168
Cell 22.680206
Cell 32.575558
Cell 42.681001
Cell 52.633213
Cell 62.527864
Cell 72.559121
Cell 82.500182

Full capacity test data log attached, excel file.
 

Attachments

  • 2108-70017 through 2108-70032 Capacity Test Data.zip
    695.3 KB · Views: 4

HighTechLab

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Just was reading back and saw that the capacity was under advertised. I am mainly talking about the voltage points not so much an under-capacity issue. I don't think the voltage is telling you much, but obviously the under-capacity is a significant concern.
 

Martijn

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Just was reading back and saw that the capacity was under advertised. I am mainly talking about the voltage points not so much an under-capacity issue. I don't think the voltage is telling you much, but obviously the under-capacity is a significant concern.
Thanks, from reading your chart etc, it seems the voltage drop for load is less big than I was anticipating. But yeah, the capacity is way under what was advertised and given that I've top balanced (twice), using a Victron inverter/charger and shunt, and looking at the discharge curves for testing, I think what I've got here, doesn't work as expected.

Here's test 4, got 225Ah, low voltage disconnect at 22.0V. And the combined voltage on load at the beginning was < 26.0. So my test-results are consistent.
1629133340725.png

For another test, using an 80A load, voltage dropped to just over 25, pulled 205Ah in total. That test had a momentary BMS shutdown due to voltage difference in cells. So far: between 205 and 233, depending on discharge rate.
 

HighTechLab

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Discharge rate should NOT cause a difference of 28ah. This is suspicious.

I was testing some suspect 302ah cells a couple weeks ago and I got 289ah at a C/3 rate (100 amps), and 294ah at a 40a rate.
 

Martijn

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Discharge rate should NOT cause a difference of 28ah. This is suspicious.

I was testing some suspect 302ah cells a couple weeks ago and I got 289ah at a C/3 rate (100 amps), and 294ah at a 40a rate.
The first test I did was using a test device like the one in this picture, resulted in 233Ah, but it took days ;)

Second to fifth test was using the Victron inverter, so I could test with higher loads. Test 2 & 3 got 205-207Ah, test 4 and 5, for which I made sure the battery was full, did 225-227Ah. I think I perhaps didn't fully charge the battery for test 2 & 3.

Would you recommend a 6th test with, for example, an 100A load instead of 60?

Either way, I've put many hours in testing these cells now, and they're nowhere near 280Ah. Learned a few bits and got familiar with connecting everything :)
1629137507418.png
 
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Martijn

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While I continu to dispute the sale with AliExpress, I recorded a video of all 8 QRcodes. Made 2 photo's, see below. Look what I found, there's still some text left: 3.20V / 704Wh. Brand: REPT.

Well, 704 Wh would certainly explain why I can pull 227Ah max ;)

Also, is there a website or document that can be used to check that number of the left?

1629450285216.png1629450294240.png
 
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mrzed001

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While I continu to dispute the sale with AliExpress, I recorded a video of all 8 QRcodes. Made 2 photo's, see below. Look what I found, there's still some text left: 3.20V / 704Wh. Brand: REPT.

Well, 704 Wh would certainly explain why I can pull 227Ah max ;)

Also, is there a website or document that can be used to check that number of the left?

View attachment 60933View attachment 60934

Good catch. Do you have the user manual for the cell? There should be technical parameters like the cell dimensions and weight.
Not possible that a 220Ah cell has the same weight as a 280Ah cell.
Like 280Ah cell is 5,2kg and 310Ah cell is 5,5kg.
 

Just John

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I'm currently in a dispute, AliExpress stepped in and requires videos etc, that's why I'm redoing these tests.

Aliexpress is not on your side. I hope you used a credit card. There are a lot of vendors offering "grade A" cells that are actually end of life and pulled from electric vehicles.
 

Berseker

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While I continu to dispute the sale with AliExpress, I recorded a video of all 8 QRcodes. Made 2 photo's, see below. Look what I found, there's still some text left: 3.20V / 704Wh. Brand: REPT.

Well, 704 Wh would certainly explain why I can pull 227Ah max ;)

Also, is there a website or document that can be used to check that number of the left?

View attachment 60933View attachment 60934
Ahha, these are rept cells.
Likely 220ah and not 280ah. Some users here got decent ah from rept cells.
 

Martijn

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Aliexpress is not on your side. I hope you used a credit card. There are a lot of vendors offering "grade A" cells that are actually end of life and pulled from electric vehicles.
Well, there's the thing... I used to order by CC on Ali, but after a few CC-fraud instances, my bank actually told me to stop using it there. 😬
 

mmame

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Well, there's the thing... I used to order by CC on Ali, but after a few CC-fraud instances, my bank actually told me to stop using it there. 😬
Well in case of a chargeback, the bank will get back the money from Ali/it's Acquirer. But that means your bank has to do some work to get the money from them. And yes, banks usually don't want to do any work for earning money 🤭
 

Just John

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Well, there's the thing... I used to order by CC on Ali, but after a few CC-fraud instances, my bank actually told me to stop using it there. 😬
I use my Citibank, not because they are a good card or bank, but because they have an arrangement with Alibaba and I can create virtual numbers. Time and dollar limited one use numbers.
 

DJSmiley

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Well.. for 220Ah cells, getting 225-227 is good, even above specs.

If the seller listed them as 220Ah, everything was ok. It's just misleading to advertise and sell cells of 220Ah as 280Ah.

No way anyone can argue that's normal.

However, in my opinion, using local available payment methods (iDeal) doesn't have any form of insurance. That's why I prefer to use my CC. I only use iDeal for known sellers I trust. (Fees for using CC are higher). But with an unknown seller, it's better to spend 30 euro or so more to benefit from the additional insurances the CC provides.
 
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