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Top Balance Screw Up, How Bad?

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rcc

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May 31, 2020
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Greetings,

So I recently received 8, 280Ah cells from Basen and started the process of getting ready to assemble 2, 4s 12v batteries. I started the top balance process with 4 cells but the volt meter was set too high. The power supply I have has a free spinning volt dial and the display would not go above 3.5v at 10 amps while the batteries were at 3.3v. but it was apparent that the setting was higher than that because once the cells were charged the voltage jumped up. Anyway I was watching the process and checked and the cells were at 3.3v, I went away for about an hour and came back to cells at 4.4v., well above the 3.65 max recommended. I immediately disconnected the power supply and assembled the batteries in 4s and put a draw on them. The volts came back down to normal pretty quickly. here is shot of the BMS app:
BMS app.PNG

All seems good but all cells now have a bit of bloat to them, they were perfectly flat when arrived. not sure if you can tell but here is a top down shot:
Battery.jpg
You can see the gaps between the cells from the bloat.

So my question is: How bad did I screw up my cells??

Thanks,
RC
 
Bob B said:
The charge voltage should be adjusted while the battery is DISCONNECTED. Seems this is getting to be a common mistake.
Click to expand...

I pointed this out many times already. @Everyone reading this: you set the voltage with your supply disconnected, then you connect once you verify the voltage is correct. Once connected, the voltage might drop. This is normal. Do not adjust when you have the supply connected to your batteries - the power supply is doing what it is supposed to do.
 
You damaged them for sure, but not a total loss. You likely lost a bit of capacity and internal resistance is now higher, which means you can't put heavy loads on them anymore. But if your normal usage rate is low and you can live with lower capacity, then it's still perfectly usable battery.
 
Based on the pictures, it looks like they did get quite overcharged, but It's somewhat difficult to believe that 4 - 280ah cells in parallel (1120 ah) would have gone from 3.3V to 4.4V in one hour with a 10a charge current. Did you receive your cells fully charged?
 
electric said:
You damaged them for sure, but not a total loss. You likely lost a bit of capacity and internal resistance is now higher, which means you can't put heavy loads on them anymore. But if your normal usage rate is low and you can live with lower capacity, then it's still perfectly usable battery.
Click to expand...
Thanks for the constructive reply. The battery is not going to have heavy use or high demands, it will be one of 2 280 Ah batteries for a house bank for a sail boat. When I measured it out the typical peak draw may be less than 30 to 40 amps.
 
cwstnsko said:
Based on the pictures, it looks like they did get quite overcharged, but It's somewhat difficult to believe that 4 - 280ah cells in parallel (1120 ah) would have gone from 3.3V to 4.4V in one hour with a 10a charge current. Did you receive your cells fully charged?
Click to expand...
when I got the cells they were at 3.27v, the last time checked them before they went over, they were at 3.33.
 
To know for sure, you could do a capacity test on the battery. If you get within 90% of their rating, I would call it good.
 
rcc said:
Thanks for the constructive reply. The battery is not going to have heavy use or high demands, it will be one of 2 280 Ah batteries for a house bank for a sail boat. When I measured it out the typical peak draw may be less than 30 to 40 amps.
Click to expand...
When I first started with LFP cells in 2009 I made exactly the same mistake with exactly the same results. Those "puffy" cells still worked for 4 years in a very demanding job in my home made EV and then few more years in less demanding job for energy storage. Even when I finally recycled them after 7-8 years of operation they were still in working condition.
I think your battery will be fine and you learned a very good lesson on how to set the voltage, ALWAYS in open circuit, NEVER under load.
 
I have a similar-ish situation. I have 16 LiFePO4 176AH cells. I am starting out by doing a top balance following both Will's video and the Top Balancing Tutorial Since the cells were at a 3.26v (slight variation from cell to cell) when I got them, I tried to break them into groups of 4 12V batteries and bring up the charge a bit before balancing. I followed the proper steps in using the desktop charger (adjust voltage before attaching to load) and tried to charge to 14.2 (3.55 per cell). I monitored the individual cells using a (BattGo ISDT 8S) throughout the entire process. I kept seeing random cells jump to 3.7-4.1. I am sure the voltage didnt just jump so I assumed I had a bad cell. I would pull it out and add a different cell to the 12v setup but it kept happening. I finally gave up and went to the 16s setup and figured in a month I'll be done ?‍♂️
 
pangrande said:
I have a similar-ish situation. I have 16 LiFePO4 176AH cells. I am starting out by doing a top balance following both Will's video and the Top Balancing Tutorial Since the cells were at a 3.26v (slight variation from cell to cell) when I got them, I tried to break them into groups of 4 12V batteries and bring up the charge a bit before balancing. I followed the proper steps in using the desktop charger (adjust voltage before attaching to load) and tried to charge to 14.2 (3.55 per cell). I monitored the individual cells using a (BattGo ISDT 8S) throughout the entire process. I kept seeing random cells jump to 3.7-4.1. I am sure the voltage didnt just jump so I assumed I had a bad cell. I would pull it out and add a different cell to the 12v setup but it kept happening. I finally gave up and went to the 16s setup and figured in a month I'll be done ?‍♂️
Click to expand...

You're supposed to charge in series with a BMS in place for protection. Without a BMS, you have to sneak up on it. Start at something really low like 13.6V and inch up from there.

Or don't do it at all and charge in parallel.
 
I read the part about the BMS. I only have a 48v one so I just babysat the process and watched the monitor. I would imagine the BMS just would have cut off the charge as soon as the voltage spiked so I just did it manually. Unless we are talking about the BMS acting as a balancer?
Thanks.
 
The BMS does what it's supposed to do - protect the cells. It sees one spike to 3.75 - cut off. The voltage spike can happen very quickly. If you're not watching it constantly, it can get away from you.
 
Apparently. The interesting thing is that it was a battery in the middle of the pack. You figure it would have been one of the end cells (although I have no legitamate basis for that assumption). Maybe I should test my theories on something other than $2,000 worth of lithium cells. :cry:
 
Assuming they all have roughly the same capacity, the cell at the highest state of charge will peak first regardless of position. In series charging, each of the cells experience exactly the same current. The one that fills up first peaks first.
 
snoobler said:
Assuming they all have roughly the same capacity, the cell at the highest state of charge will peak first regardless of position. In series charging, each of the cells experience exactly the same current. The one that fills up first peaks first.
Click to expand...
Makes perfect sense. Thanks.
 
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