Starting up my Battery Finally ... Now hit Overvoltage Protection after charging for approx. half a day

[silverstone]

I finally started up my 2 first Batteries (2 x 16s x 280Ah cells) yesterday charging with one Inverter at around 3kW (approx 30A / battery).

Today Charging them with all Inverters at around 50-60 A / battery.

I read that the LiFePo4 Cells Voltage vs SOC is very flat in a wide SOC region. I also read that it got VERY steep near fully charged and approx. below 10% SOC.

I just didn't expect it to be *that* steep. In a matter of seconds at 60A, one cell went from 3.52V to 3.63V as if she was going to the moon . That triggered JK BMS High Voltage Disconnect.

Since then:
- I increased balance starting voltage to 3.42V (from Steve_S 3.36V) - Based on Andy's Offgridgarage, too low of a Balance Start Voltage could CREATE unbalance. This might be indeed the case here
- I reduced OVPR Overvoltage Protection Recovery Voltage to 3.42V (from Steve_S 3.525V) - I got something like 25 disconnect + 25 reconnect events within an hour or so, where i didn't supervise what was going on ... Simply because the JK BMS would allow charge again too early on.

I used mostly Steve_S configuration from

Steve_S-Tech: My Final Config for Midnite Classic SCC & JKBMS' w/ Large Bank (works amazingly well) Includes Charge Profile & BMS Config

INTRO: I have debated posting this for a while until I got everything tweaked in and working as best as possible. The End Result is Gobsmackingly Good ! I cannot speak for other SCC and such as each is different & unique in their own ways BUT this may likely be a Good Reference. Civility &...

diysolarforum.com

Inverter was set to 55.2V float and (initially) 56.4V absorbtion/equalization and 100A charge. Now set to 55.2V float, 56.0V absorbtion/equalization and 40A charge current.

I did NOT Top-balance the pack. This might well be the main issue. I completed the assembly and really, I didn't have much energy left to fiddle around with all the busbars.





The first cell in the second pack at 3.39V ... that's probably because it started at a lower SOC compared to the other 15 (3.23V vs 3.28V IIRC).

My plan would be to "top" balance the pack by charging with a small 5A source (possibly even set lower to 2A ?) and let it run overnight. That should (hopefully) be enough for the Active Balancer to manage to balance the pack during charge. Surely more manageable 5A than 50A ....

Any other ideas ? Originally I thought like I had a runaway cell but maybe it's just a lack of top balancing .

 

[Dinobot248]

There was a lot of reading and I'm not an expert here.

I thought over voltage would be around 3.7 or 3.8v considering max voltage per cell for lifepo4 is around 3.65 when charging them. I'm thinking of my 48v server rack battery which has a max of 58.4v or 3.65 per cell.

Also, I think your running too conservative. The EG4 Lifepower4 BMS is set to 58v when using closing loop for 100% SOC. That is 3.625 per cell. This battery is rated for 7000 cycles at some 80-90% DOD

You are correct that voltage is a poor indicator of SOC. I just recently manually top charged my 6 Lifepower4 rack of batteries. My gut feeling is you may need to top charged all cells (first preferred option) or replace the outlier cells (last option) to get your cells to behave/operate as intended

 

[Dinobot248]

Also, giving them a little more time (a week?) to adjust and passively balance and actively balance with your BMS running the show. Some cells may need a couple of charge and discharge cycles to wake up and operate at full capacity.

I'm kind of lazy and would not want to disassemble the battery pack. Just wait, increase your over voltage to be more aggressive (I don't know the recommended level though), and definitely cycle them a few times. Also check your connections and torque / tighten all connections.

 

[SeaGal]

Any other ideas ?

You can always bleed off some charge of a runner using a 12V car bulb and/or charge up a lagger using an isolated bench PSU without disassembling the whole pack. Just keep a constant eye on the cell voltages with a multimeter - they can change quickly, as you observed!

 

[silverstone]

Right now Battery 02 hit again overvoltage limit ... So I will just let the balancer work then charge with a 5A source.

Battery 01 is even more weird. When both batteries active, Battery 01 charge with 15A and Battery 02 charge with 35A. Don't know why and why the voltage seems so different between the 2. BUT if I disable Battery 02, then Battery 01 still charge with the same 15A. It doesn't "take over" from Battery 02. Any clue ? Battery 02 running in "Discharge" mode maybe (Discharge is still enabled for Battery 02) ? Not fully sure why though ... Maybe float / absorbtion voltage in Inverter are too low ? But Battery 02 reported "0 A" in the JK BMS app ...

 

[Zapper77]

Charge rate seems high for the top end assuming that your charger doesn't taper the rate when voltage climbs above 54.5v

 

[Dinobot248]

Check your connections considering those are your starting and ending cells.

Another option is to swap a middle cell say #8 with #1. Swap / switch cells to determine if the cell is grumpy or the connection needs reconnecting

Fixed numbers above

 

[Zapper77]

Give it a couple of days to passive balancing. Top off the batteries every 6 hours and let them rest (balance)

 

[WindWizard]

You can always bleed off some charge of a runner using a 12V car bulb and/or charge up a lagger using an isolated bench PSU without disassembling the whole pack. Just keep a constant eye on the cell voltages with a multimeter - they can change quickly, as you observed!

It is called wack a mole. Obviously, there is an imbalance in the Cell pack and it needs to be resolved.

 

[WindWizard]

I did NOT Top-balance the pack. This might well be the main issue. I completed the assembly and really, I didn't have much energy left to fiddle around with all the busbars.

I did the same with my Cell pack. I purchased an automotive light from Amazon and soldered some alligator clips to it and then once one of the Cells reached 3.4 Volts then I connected the light to discharge it. It takes a while of babysitting, but I think it is saves time in the long run. Eventually all of the Cells will be balanced. I also connected a power supply to the lowest Cell to charge it as @SeaGal mentioned.

https://www.amazon.com/gp/product/B076MKZS35/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1

 

[silverstone]

Check your connections considering those are your starting and ending cells.

Another option is to swap a middle cell say #8 with #1. Swap / switch cells to determine if the cell is grumpy or the connection needs reconnecting

Fixed numbers above

I'd say they should be fine ... Torqued to 6.0 Nm on the cell side. The fuse holder I couldn't manage 32 Nm (even bent the fuse holder terminal a bit) ... I think I managed 29 Nm.

I assume the current got so low because the Inverter entered "float" mode, so the current gradually decayed to zero.

But why the hell there was MORE current in the battery with a HIGHER voltage is still a mistery to me.

I was thinking more of a bad cell than a bad connection. This morning this very same battery was handling 50A fine. Usually internal resistance DECREASES when SOC/Voltage Increases.

 

[silverstone]

Check your connections considering those are your starting and ending cells.

Another option is to swap a middle cell say #8 with #1. Swap / switch cells to determine if the cell is grumpy or the connection needs reconnecting

Fixed numbers above

Swapping cells ... Nope. I don't want to do anything in this pack if I can help it at all. Believe me there is NO SPACE for anything. Plus just to re-arrange a couple of cells will involve dismantling the compression fixture (assuming I can get a wrench in there), undoing all of the connections, etc.

I guess I'll just have to settle to 10%-90% usage ... after top balancing properly.