EVE 280ah problem with 1 battery only?

Hello to everyone!

I have installed 16s lifepo4 eve prismatic grade B 280ah batteries (the old ones with the threaded stud) for about a year now with the old style JK BMS (2amp balancing current). Everything worked great until now.

To be more specific I have one specific cell ( cell 14) that when being discharged it goes to around 2,6v while the others are to 3,3v thus making the jk BMS disconnect the battery due to low voltage disconnect.

I have tried fully charging this cell and the whole pack and this happened again for the 3d time this week. I am convinced that cell14 might have gone bad (which is weird for solar use with low loads and only after LESS than 1 year)

I would like your thoughts on this. I have already ordered a new 280ah cell on the way and hopefully I will get it soon to test. However I am also thinking that it might be a BMS issue but I have never heard anyone else have a problem like this with a jk so I would like your opinion guys.

I have experienced this, it just gets worse and worse, you can try the little heltech active balancers and it will help but it will also lower down other cells as it uses energy from them to help the bad cell...

replacing it is a much better option.

Check all connections, crimps, etc.

Have you moved the cell to a different position to see if the problem moves with it?

Have you confirmed the BMS reading with a separate voltmeter?

"Grade B" cells may be classified as such for a multitude of reasons the consumer may never know. All you know is that they are defective according to the manufacturer's specification. This can very easily impact cycle/calendar life.

This forum and the proliferation of DIY LFP batteries is still in its relative infancy (<5 years). IMHO, insufficient time has elapsed to demonstrate that "grade B" cells have the longevity of cells fully conforming to the manufacturer's specification.

Yes I have checked all connections, no I have not changed the cell place I was thinking to do it but too much hassle I have already ordered a new one but I am trying to revive this battery for as long as the waiting time for the new one. Plus I am hoping it’s not a BMS problem. I will try to top balance them once more and see if it gets me through this week at least.

Yes I have tested with the multimeter every reading is exactly the same with BMS.

Should I change the balancing voltage to my JK to a lower value just to be a bit safer? I have Andy’s settings currently form the off grid garage

I have balance voltage at 3,45 should I try 3,3?

xristostsilis said:

Yes I have checked all connections, no I have not changed the cell place I was thinking to do it but too much hassle I have already ordered a new one but I am trying to revive this battery for as long as the waiting time for the new one. Plus I am hoping it’s not a BMS problem. I will try to top balance them once more and see if it gets me through this week at least.

Click to expand...

Even active balancers can't compensate for cells taking a crap. With #14 at 2.6V and the others at 3.3V, it's unlikely that you're going to be able to meaningfully increase the usability unless your draw is less than your balance current.

The 2.6V limits you to a certain capacity. For the time being, you should consider whatever that capacity is to be the actual capacity. Perhaps even reprogram the BMS to reflect that.

xristostsilis said:

Yes I have tested with the multimeter every reading is exactly the same with BMS.

Click to expand...

For me, this definitely points to the cell as the point of failure.

xristostsilis said:

Should I change the balancing voltage to my JK to a lower value just to be a bit safer? I have Andy’s settings currently form the off grid garage

Click to expand...

xristostsilis said:

I have balance voltage at 3,45 should I try 3,3?

Click to expand...

Generally, less than 3.40V may be counter-productive, but experimenting in the 3.35-3.39V range might have some very limited benefit.

xristostsilis said:

I have balance voltage at 3,45 should I try 3,3?

Click to expand...

No, That would be a lot of work for the same or worse outcome

On thank you guys. I will try to top balance them for one last time and hope for the best.

xristostsilis said:

On thank you guys. I will try to top balance them for one last time and hope for the best.

Click to expand...

If you're talking about disassembling and parallel top balancing, I wouldn't bother. You said you charged the cell to full individually. If so, parallel top balancing isn't going to benefit you.

No have let them charge fully via sollar and set my inverter to not discharge them for 3-4 days to leave the integrated JK balancer do its job. Then I use them. I know it’s stupid but it’s the only way with the equipment I have now

xristostsilis said:

No have let them charge fully via sollar and set my inverter to not discharge them for 3-4 days to leave the integrated JK balancer do its job. Then I use them. I know it’s stupid but it’s the only way with the equipment I have now

Click to expand...

If you still have a 30V/10A power supply from any parallel balance exercise, you can manually charge #14 without breaking down the battery or even taking the system offline.

If you need to balance as described, it sounds like the cell is losing its ability to retain a charge.

sunshine_eggo said:

If you still have a 30V/10A power supply from any parallel balance exercise, you can manually charge #14 without breaking down the battery or even taking the system offline.

If you need to balance as described, it sounds like the cell is losing its ability to retain a charge.

Click to expand...

Yes that’s what I was thinking. The cell might be so bad that it kinda self discharges or something

xristostsilis said:

self discharges

Click to expand...

Self discharges are INTERNAL shorts. They always convert your batteries energy into HEAT. Heat is bad mmmmK. If this were lithium cobalt chemistry I would tell you to get that cell out of your house.

Ok so here are now:

That's not quite as bad as you indicated earlier. Yes, one at 2.73 while the others are at 3.25V is not good, but it looks like you should still be able to use 50-60% of your 280Ah capacity.

If #14 is the first to fill, then the cell is just shot.

If it's first to drain and last to fill, it's almost certainly failed due to an internal short/self-discharge

sunshine_eggo said:

That's not quite as bad as you indicated earlier. Yes, one at 2.73 while the others are at 3.25V is not good, but it looks like you should still be able to use 50-60% of your 280Ah capacity.

If #14 is the first to fill, then the cell is just shot.

If it's first to drain and last to fill, it's almost certainly failed due to an internal short/self-discharge

Click to expand...

Please what do you mean that the cell is short?

Muzzammild36 said:

Please what do you mean that the cell is short?

Click to expand...

shot. not short.

"shot" = bad, failed, worn out, done.

So in any case I should replace the cell. I am hoping the new one will arrive as fast as possible

sunshine_eggo said:

That's not quite as bad as you indicated earlier. Yes, one at 2.73 while the others are at 3.25V is not good, but it looks like you should still be able to use 50-60% of your 280Ah capacity.

If #14 is the first to fill, then the cell is just shot.

If it's first to drain and last to fill, it's almost certainly failed due to an internal short/self-discharge

Click to expand...

If it's shot, there is no remedy but what is the remedy if it has internal short/self discharge?

Nothing its done you can not save it, it will just puff up and go to 0 volts like my grade B basen cells:

xristostsilis said:

Yes I have checked all connections, no I have not changed the cell place I was thinking to do it but too much hassle I have already ordered a new one but I am trying to revive this battery for as long as the waiting time for the new one. Plus I am hoping it’s not a BMS problem. I will try to top balance them once more and see if it gets me through this week at least.

Yes I have tested with the multimeter every reading is exactly the same with BMS.

Click to expand...

Did you measure the cell voltage on the bus bar or on the actual cell terminal or stud? It is very easy for a bus bar to make a bad connection to the aluminum terminals on these cells. You may need to sand the terminals and bus bars and reconnect it all with "No Al Ox" or come other aluminum corrosion inhibitor.

Adding to what @sunshine_eggo is saying, when you charge the battery back up, does the weak cell #14 charge up faster and hit high voltage sooner, or is it always low to the others? If the cell has low capacity, it will both charge and discharge faster. So if you top balance, the cells will still hit full together. The weak cell drops faster and becomes your usable capacity limit. But when you charge, it should then reach full along with the rest of the cells. But, if it charges slow, then the cell is either just way out of balance, or it has an internal short that is consuming power and making heat. A weak cell is less capacity, but still basically safe. A cell with an internal short is dangerous. Even LFP can over heat and blow it's vent if it is shorting inside.

A bad connection at the bus bar, would cause it to look like it is charging and discharging fast, just like high cell internal resistance. But the resistance is between the terminal and a bus bar. A bad connection can be fixed, a dying cell can only be replaced.

I also had a balance lead fail on my JK BMS. It caused it to report 2 cells as zero volts. I doubt this is your problem with the meter reading the same as the BMS, but it shows how a tiny bit of oxide can block current flow.

So I completely replaced the cell and my battery has been running well since then. It was definitely not loose connection or wrong measurement (terminal or bus bar). The cell was bad which is weird.

Its not weird when cells have some internal problem like a short they don't hold voltage, swell up, or other bad things. Not much you can do about it. Grade A a lot less likely to happen but still is susceptible to this.

Alkaline said:

Its not weird when cells have some internal problem like a short they don't hold voltage, swell up, or other bad things. Not much you can do about it. Grade A a lot less likely to happen but still is susceptible to this.

Click to expand...

yes mine were grade b from docan.. ughh its ok i just got a grade a cell from nkon and it now works like a charm