Troubleshooting JK BMS shutdown

Any thoughts on how to troubleshoot a JK BMS shutdown?


My BMS shut down while bulk charging. I was able to start it by pushing the button, but don’t know why it shut down.

The system log just shows
Before [5H27M36S] - [Boot]
Before [5H27M37S] - [Boot]

Detail log at assumed shutdown was
2024-06-09 01:15:11, Boot, CHG OFF, DSG OFF, BALANCE OFF, HEAT OFF, 0, 0, 0.0, 0.0, 0.0, 0.0, 293.6, 304.0, 0, 0, 0, 0.0
Numbers other than zero are: SOC Cap. Remain, SOC Full Charge Cap.

Some triggers that “might” have shut it down.

Battery avg 3.48
Cell OVP : 3.65
Cell UVP 2.6
Vol Smart Sleep 3.285
Charge OTP 70
Discharge OTP 70

But none should have been triggered.

Thanks!

Assuming battery avg 3.48V the average of all X cells, that's definitely a high state of charge. It's very likely that ONE cell hit 3.65V OVP.

IMHO, repeat the charge and observe the cell behavior.

What is your charge/absorption voltage?

sunshine_eggo said:

Assuming battery avg 3.48V the average of all X cells, that's definitely a high state of charge. It's very likely that ONE cell hit 3.65V OVP.

IMHO, repeat the charge and observe the cell behavior.

What is your charge/absorption voltage?

Click to expand...

They were all within .01 volts, so don’t think that was the cause, but am guessing. , but did a couple of adjustments down and drained today. So they’ll do a full charge again tonight.

I have 2 inverters and 2 batteries so they are drawing through a busbar and using whizbang jr for SOC.

Absorption: 56.8
Float: 55.6

So the batteries should never have gotten to 3.65V.

I might have a bad BMS, I did turn it off and on, and it appeared to reboot multiple times, which matches the log.

wsaharem said:

Absorption: 56.8
Float: 55.6

So the batteries cells should never have gotten to 3.65V.

Click to expand...

Except that they can, and they often do. Charging to 3.55V/cell means you're charging to peak SoC quickly, and it doesn't take much imbalance for a single cell to hit 3.65V fast.

Most, including me, will say your float voltage is way too high. Floating LFP above 3.375 can result in low current overcharging that very slowly causes lithium plating and reduced capacity over time. Float at 54V is recommended by the VAST majority.

wsaharem said:

I might have a bad BMS, I did turn it off and on, and it appeared to reboot multiple times, which matches the log.

Click to expand...

That is odd.

sunshine_eggo said:

Except that they can, and they often do. Charging to 3.55V/cell means you're charging to peak SoC quickly, and it doesn't take much imbalance for a single cell to hit 3.65V fast.

Most, including me, will say your float voltage is way too high. Floating LFP above 3.375 can result in low current overcharging that very slowly causes lithium plating and reduced capacity over time. Float at 54V is recommended by the VAST majority.



That is odd.

Click to expand...

Thanks. Will change float to 54V.

I ran it down to 48V last night then recharged again. I did notice that it was failing immediately when I was charging 1 battery at 156A. Well I had set max charge amp to 100. So I know it was protecting me . I upped it to 175A and it ran fine. I was hoping that fixed it, but it failed again.

I have both batteries at same config and same code level, but only 1 battery behaves this way.

Good news is everything else is working great! No significant heat when charging or discharging! (And this is during our Texas heat using 2 air cons.

Were you able to confirm that no cell hit 3.65V?

I wasn't able to confirm that no cell hit 3.65V, but today after recharging yesterday and resetting values in the inverter and the batteries, the 1 battery did not shutdown.

I changed the following:
Vol Cell RCV to 3.45
SOC-100% to 3.449 (apparently it needs to be below RCV)
Vol. Cel RFV to 3.350
And absorb on the inverter to 54V

Big win, but now I need to tweak it back up as the battery is showing 52V and the inverter showing 98% SOC. My guess is your call on the OVP is correct and I hit that with one cell at some point in time.

Thanks so much for your help!