Bulges on side of cells during top balance

[Gurusi]

Hey, just in the process of a 16S. 280ah top balance. Using the ZKEEBCA 40 L. They are Configured in parallel and a under compression.

I had previously been using the cells with the inverters but found imbalance at the higher range of 3.4v when charging via the charge controllers

I noticed a spike in voltage on the test software at about 3.35 V. And when examining the cells I noticed bulges in the first two cells so have stopped the balance. I’m unsure what the cause is or how I should proceed….

Have I done something wrong in the process? Is it too much compression?

Edit added better cell bulge photos

 

[ArthurEld]

I would discharge them. Something might be wrong with your voltage setting.
How tight is the compression? It isn't supposed to be very tight

 

[Gurusi]

I would discharge them. Something might be wrong with your voltage setting.
How tight is the compression? It isn't supposed to be very tight

Underway discharging now. Charge settings were 3.65V C-CV, 40amps with a cutoff current of 1.amp.

I noticed the bulged end of the cells where my charger was hooked up was warm and noticeably cooler the other end.

Cells are compressed based on lots of reading on the forum and are variable for give (spring system). I can’t recall my spring in-lb settings right now!

I’m hoping I haven’t damaged them. but don’t know how to move forward. I could top balance each cell individually I guess

 

[toms]

Not much you can do to reverse the damage you have done. Sorry that you got caught in the parallel top balance farce.

Best thing to do now is to look for sources of information that aren’t going to encourage you to further damage your cells.

In your circumstance now I’d fully assemble your battery into its final configuration, run a charge/discharge cycle to determine usable capacity, ensure all working IR’s of the cells are within spec - then it depends on your system requirements what the next step is.

If the usable capacity is acceptable carry on - if not, adjust individual cell voltages (without dismantling the battery) until it is.

If you hadn’t tried to shorten the life of your cells by parallel top balancing, you’d be at this point already.

 

[Gurusi]

Not much you can do to reverse the damage you have done. Sorry that you got caught in the parallel top balance farce.

Best thing to do now is to look for sources of information that aren’t going to encourage you to further damage your cells.

In your circumstance now I’d fully assemble your battery into its final configuration, run a charge/discharge cycle to determine usable capacity, ensure all working IR’s of the cells are within spec - then it depends on your system requirements what the next step is.

If the usable capacity is acceptable carry on - if not, adjust individual cell voltages (without dismantling the battery) until it is.

If you hadn’t tried to shorten the life of your cells by parallel top balancing, you’d be at this point already.

I had been using the pack for the past 3-4 days successfully (but was looking for a better balanced pack).

Are the bulging cells safe to use?

How would you adjust individual voltages? Via bms balancer?

So sad after all the work I’ve put in.

 

[toms]

I had been using the pack for the past 3-4 days successfully (but was looking for a better balanced pack).

Are the bulging cells safe to use?

How would you adjust individual voltages? Via bms balancer?

So sad after all the work I’ve put in.

If the IR under load is not too high they will likely be OK to use. You can individually charge or drain cells to balance, easiest way is to use active balancer in conjunction with BMS.

 

[Gurusi]

Nothing I can do now but accept the current state of cells and use them as is.

Can anyone tell me what possibly went wrong or what I did wrong?

Cells were hooked up per resource guide and videos, compression is correct to minimize swelling. Charger settings I believe are correct. At time of swelling cells were 3.354v

 

[WindWizard]

I never have top balanced my cells to 3.65 volts. It seems to me to be a waste of time and also lots of potential to go wrong and possibly reducing my cell pack capacity.

I just hooked my 128 cells up to how I was going to use them and then hooked up my charge controllers and my inverters and they have worked. Sure, I had to balance them a bit at first but now they do not need any diddling.

You know what, I just don't care if my 280 ah cells produce 270 or 290. What does it really matter? I have my pack hooked up and it powers my house. I don't worry about compressing this or that. They have worked great for the last couple of years and they are powering my whole house off grid so isn't that what really counts?

I use an active capacitor balancer which works very well at keeping my cells balanced to less than 10mv. I turn on (automatic) the active balancer at 54.2 volts which is around 3.38 volts per cell. I only charge the pack to 55.6 volts which is around 3.48 volts per cell. I have never charged my cells to 3.65 volts. I want my cells to last as long as possible. I discharge the pack to 48 volts which is around 3 volts per cell.

I look at 3.65 volts and 2.6 volts as things to avoid at all costs. Yeah they are supposed to work at the extremes but why chance it?

Sure, I miss out on some of my potential pack capacity but to me having the pack last as long as possible is more important to me.

 

[Gurusi]

Noticed this on x2 cells. Should this be of concern?

 

[Gurusi]

Wasn’t sure whether to start a new post or not.

Completed a discharge down to 3.2 and started to charge at low amps but had issues with the compression requiring removal.

These are the cells as they stand now. Strangely cell 9 to 14 remain undamaged, cell 1 to 6 have even swelling and 7 8 15 and 16 are the worst.

I have attached multiple photos with reference to the gap to give an indication of swelling.

Am I still in a position where these can be used?

Edit:- I recall a video that Will uploaded with the cells being side to side to allow for swelling and contraction of bloated Cells. Is this something I could do?

So 8 and 16 look really bloated to me but I have no experience in assessing….

 

[GuyG]

Damn, that’s some serious bloating. What cells are they?

Whatever you do, DON’T try to compress them back into their original state.

 

[WindWizard]

I suspect that your cells got overcharged due to the damage displayed. If you insist on charging the cells up to 3.65 volts then you must have a voltmeter that measures the voltage accurately and not rely on the display of the charger.

LFP Cells have a very sharp voltage curve which starts at around 3.4 volts. At that point, they will run away if you do not monitor the voltage closely. They go to 3.65 volts and beyond very quickly.

The Cells have been damaged to the point where I would not use them myself. It just would not be worth the risk of a fire occurring. That is my opinion. If I examined my pack and found that one of the Cells was damaged, then I would replace it.

 

[Gurusi]

Damn, that’s some serious bloating. What cells are they?

Whatever you do, DON’T try to compress them back into their original state.

Eve 280ah

 

[Gurusi]

I suspect that your cells got overcharged due to the damage displayed. If you insist on charging the cells up to 3.65 volts then you must have a voltmeter that measures the voltage accurately and not rely on the display of the charger.

LFP Cells have a very sharp voltage curve which starts at around 3.4 volts. At that point, they will run away if you do not monitor the voltage closely. They go to 3.65 volts and beyond very quickly.

The Cells have been damaged to the point where I would not use them myself. It just would not be worth the risk of a fire occurring. That is my opinion. If I examined my pack and found that one of the Cells was damaged, then I would replace it.

Thanks for the opinion. I used the zke 40amp hooked up to the pc (has charging and sensing clips). The curve went slow and fine until a spike.

What’s done is done. I will charge cells individually in the future. No more top balancing for me.

 

[WindWizard]

I just use two Active Capacitive Balancers to keep the Cells balanced. The only time I use it is when the Cells start to approach full charge. LFP's voltage goes up very fast after 3.4 volts so I turn on my active balancer and it keeps the rogue Cells inline.

My understanding is that you were using your pack and then were having some balance issues with some of your Cells so you decided to take apart your pack and connect them all in parallel to top balance them.

I do not want to make you feel worse but in my opinion it would have been better to leave your pack connected in series and to analyze what the issue was and then deal with it. Again, the way I deal with my 128 Cell pack, is to setup an automatic system that takes care of the balancing. The Overkill BMS's just do not have the capacity to balance my pack. The Active Balancers are rated at 5 amps and do a very good job of balancing my pack.

I also have two Overkill BMS's which their whole purpose is to keep the Cells from damage. If one of the Cells approached 3.65 volts then the BMS would shut down the charge to the batteries to protect them.

 

[Gurusi]

I just use two Active Capacitive Balancers to keep the Cells balanced. The only time I use it is when the Cells start to approach full charge. LFP's voltage goes up very fast after 3.4 volts so I turn on my active balancer and it keeps the rogue Cells inline.

My understanding is that you were using your pack and then were having some balance issues with some of your Cells so you decided to take apart your pack and connect them all in parallel to top balance them.

I do not want to make you feel worse but in my opinion it would have been better to leave your pack connected in series and to analyze what the issue was and then deal with it. Again, the way I deal with my 128 Cell pack, is to setup an automatic system that takes care of the balancing. The Overkill BMS's just do not have the capacity to balance my pack. The Active Balancers are rated at 5 amps and do a very good job of balancing my pack.

I also have two Overkill BMS's which their whole purpose is to keep the Cells from damage. If one of the Cells approached 3.65 volts then the BMS would shut down the charge to the batteries to protect them.

Hey, no worries already feeling it! Yes I had considered I would have been better off leaving it and letting my bms do the work (has a 2amp balancer). But I can’t go back in time. The pack only had 3-4 cycles on it!

Luckily I have an identical pack next to it, but won’t be enough to take me off grid until I can afford replacements… I’m considering keeping the 6 flat cells

 

[toms]

The flat cells are likely still OK.

Unfortunately the top balancing guide on this site is not based on manufacturer information. It is never a good idea to place cells of different SOC in parallel.

LiFePO4 “charged” status is a combination of voltage and current. ie: if you reach 3.65V at 0.05C current the cell is 100% charged. If you approach 3.65V at a lower current, or hold a lower voltage for a longer time, you can overcharge the cell.

I have seen what you have experienced many times - the unfortunate thing is that even those that haven’t experienced excessive bulging have shortened the life of their cells through holding them at high voltage.

The main misunderstanding is that LiFePO4 cells in parallel can have different SOC but the same voltage.

Once you’ve seen a 75% SOC and s 50% SOC cell stay in parallel for a week, then still remain 20% or more different in SOC it makes more sense what is happening.

The higher SOC cells in your parallel pack are still subjected to the charge voltage, and will overcharge.

The only way to prevent this is to remove the charge voltage as soon as the cell is full which isn’t possible for two cells of different SOC in parallel.

To determine the usefulness/safety of your cells, you need to use a battery tester that measures the IR of the cell under load. Benchmark this off a known good cell or manufacturer specs.

 

[Aussieguy]

???? join the bus bars to increase the length and no bolts seams to be a bad idea
never saw that done before.????

 

[G00SE]

I wish I had a positive piece of advice but this is way beyond my knowledge. I do want to thank you for sharing this post as I have 32 cells in my garage that I am unboxing this weekend and I now have additional reading to do as my plan was to top balance as you did. Seems I will likely need to do different

 

[bestconcreteblock]

???? join the bus bars to increase the length and no bolts seams to be a bad idea
never saw that done before.????

This. How are these bus bars connected??? Looks like heat shrink is the only thing bonding them together???