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Totally dead cell

shavermcspud

Solar Enthusiast
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Mar 12, 2020
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I installed 16x Basen 280AH cells for a friend along with a seplos BMS a month ago.

All has been working well and has been through roughly 25 cycles top end 3.4v cut off bottom end 3v cut off

Yesterday I noticed the BMS showing a fault on cell 1, the lead positive to the BMS / Inverter and the pack voltage showing 49.7v

Taking cell 1 out of the group shows its totally dead, zero volts, measures absolutely nothing at all on a DVM or the BMS.

Its not bloated or vented, or overcharged its just gone "open circuit" but putting it back in the pack it passes voltage through from the rest of the cells and registers as 49.7v from cells 1 + to cell 16 -

Anyone experienced this?

Regards
 
may be internally shorted. Happens frequently to lead acid cells, I see no reason why it could not happen also on Lifepo
 
may be internally shorted. Happens frequently to lead acid cells, I see no reason why it could not happen also on Lifepo
I would have thought that internally shorted it would have bloated up and or vented.
 
Have you attempted to charge the single Cell with an external power supply ?
What is the IR of that cell ? do you have a tester ?
Apparently some models of the Seplos BMS had Diode Fault but that may be related to the balancing circuits I'm not sure. There is some discussion in a thread here, I saw it on a video and it was mentioned.

LFP won't just drop dead like that without a clear indicator like bloat or venting or something.

DO NOT Reinstall it into your pack till you've charged & tested the cell independently. Let us know what tests you've done and the results.
Do you have a "backup" BMS for testing or ? (Just in case).
 
It was me who found the Diode issue with the Seplos BMS as per my other thread but this is unrelated as the diode stops the BMS even turning on.

I put a spare cell in the pack and its working normally again.
The BMS logs data every second 24 hours a day and keeps that for a month , it shows at 12:45pm the cell went from 3.34v to 0v instantly then the BMS went in to fault mode.

The cell is 0.00V on my DVM as per the photos, no bloating, no vent ruptured.

To add, its on charge but taking zero current, dont have an IR tester unfortunately.

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The cell is 0.00V on my DVM as per the photos, no bloating, no vent ruptured.

To add, its on charge but taking zero current, dont have an IR tester unfortunately.
In post #1 was said the cell was passing current. Now it is not?

I assume voltage was also checked directly on the aluminum terminal pad.
 
In post #1 was said the cell was passing current. Now it is not?

I assume voltage was also checked directly on the aluminum terminal pad.
Nowhere did i mention passing current? re read the post. I said it passes voltage, two different things.

Yes checked on the pads, i Have built many of these pack so quite confident in measuring a cell.
 
might have shorted when mostly empty

That is the most likely explanation i can think of also. I have seen dendrite failures, and they end up short circuit.

My charger will blow a fuse if i connect the leads together though, which is what happens with a dendrite shorted cell.

Your charger might just check resistance first and refuse to charge.

Either way i think that cell is a goner.
 
I would say that the data from the BMS rules out an internal short. We know the cell voltage was at 3.34 and then one second later was at 0. Its reasonable to believe that the cell was at least 1/2 charged if the voltage was above 3.3. So 140ah would have had to discharge in one second. That would be a current of 504,000 amps, which should definitely leave a mark.

My best guess is that the weld of the foil in the jelly roll to one of the aluminum terminals was defective and it deteriorated through the first few cycles until it finally broke. I believe the electrolyte is conductive enough for the pack voltage to be read through that cell, even with the foil to terminal connection broken.

At any rate, it is worthy of a warranty claim. Please let us know how that process goes for you.
 
I would say that the data from the BMS rules out an internal short. We know the cell voltage was at 3.34 and then one second later was at 0. Its reasonable to believe that the cell was at least 1/2 charged if the voltage was above 3.3. So 140ah would have had to discharge in one second. That would be a current of 504,000 amps, which should definitely leave a mark.

My best guess is that the weld of the foil in the jelly roll to one of the aluminum terminals was defective and it deteriorated through the first few cycles until it finally broke. I believe the electrolyte is conductive enough for the pack voltage to be read through that cell, even with the foil to terminal connection broken.

At any rate, it is worthy of a warranty claim. Please let us know how that process goes for you.
Thats a good explanation, I will contact Basen today and see how it pans out. Like you say if it had shorted there would have been all manner of visible damage. it hasnt taken any charge since being left on, so I will take that as shot.
 
I would have thought the electrolyte would be relatively high (a few ohms?) resistance when measured with a meter across the terminals.

I understand you don’t have a battery IR meter, but what is the resistance across the terminals measured with a standard meter?
 
I would have thought the electrolyte would be relatively high (a few ohms?) resistance when measured with a meter across the terminals.

I understand you don’t have a battery IR meter, but what is the resistance across the terminals measured with a standard meter?
I will check and get back. On a side note the guy called me again today, a second cell has now shown exactly the same symptoms, i went over and this cell is exactly the same, zero voltage, not bloated or vented and this has a sequential QR code from the first cell although in a different place in the pack,if that makes any difference, starting think I now have a bad batch of cells.
 
If it was mine, especially with the second one having gone I would get a can opener out & and cut one side to open the cell to see wha't going on, even if that means loss of warranty.
 
If it was mine, especially with the second one having gone I would get a can opener out & and cut one side to open the cell to see wha't going on, even if that means loss of warranty.
I am tempted to be honest, I have resorted to buying two replacments here from a UK seller for an extortionate price of roughly $800 just to get the guy back up and running. it would probably cost more to send them back to China in the end.
 
I will check and get back. On a side note the guy called me again today, a second cell has now shown exactly the same symptoms, i went over and this cell is exactly the same, zero voltage, not bloated or vented and this has a sequential QR code from the first cell although in a different place in the pack,if that makes any difference, starting think I now have a bad batch of cells.

Did you get the chance to check the terminal resistance of the dead cell - i’m curious to see the result.
 
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