After 2 months and a 80A discharge momentum, 1/16 cell starts to "trip"

[Andre Magro]

Hello,

After the extraordinary help in this forum, with the top balance issue I had, I finally put my battery bank at work.
And after 2 months of great working, and right after a 80A discharge, one of the cells started presenting a strange behavior. Basically when the battery is charging/discharging, this cell is reaching very fast max and minimum voltages in an inconsistent way, and is causing the malfunction of all the battery bank, triggering the BMS consecutively to stop charge/discharge.

The bellow images show what happened before the 80A discharge.

Battery Cells voltages and current of last 7 days (cell 7 (purple) is the one)

In the day before of the 80A discharge I even thought the cell could recover, but in the next days the situation was getting worse, and at this moment the charge/discharge mode in the BMS of the battery bank was disabled, and I'm not using the battery at all until I can solve this issue.



After seeing this graphs I also found that this cell could not reach the 3.525 final voltage during the bulk charging procedure.


So, can I assume this is a faulty cell?
Is there any way that I can recover this cell?

16 cell (48V) 272Ah battery bank
JKBMS 24S 2A 200A BT
Inverter Voltronic Axpert MKS IV 5.6kW


Thanks

 

[mikefitz]

Check buss bar and BMS leads for poor connections.

 

[Hedges]

Check for warm busbars under heavy current.
Use volt meter to check mV drop between cell terminal and connected busbar.

Torqued?
Did you do anything about removing native aluminum oxide, and preventing further oxide growth?
I don't believe bare aluminum is proper for a bolted connection, should either be tin plated surfaces or a crimped terminal. But bare aluminum is what is being sold on these cells.

 

[Andre Magro]

Check buss bar and BMS leads for poor connections.

Hello @mikefitz,
Thanks for your reply.

Do you really think that a stationary battery bank after working well during 2 months could suffer from poor connections?
But still, I will double check.

Tks

 

[Andre Magro]

Check for warm busbars under heavy current.
Use volt meter to check mV drop between cell terminal and connected busbar.

Torqued?
Did you do anything about removing native aluminum oxide, and preventing further oxide growth?
I don't believe bare aluminum is proper for a bolted connection, should either be tin plated surfaces or a crimped terminal. But bare aluminum is what is being sold on these cells.

Hello @Hedges,
Also thanks for your reply.

Torqued was controlled by hand, so there is here a point of failure.
I think that the busbars that were sent to me are not in aluminum, but in zinc-plated copper, I did and extension busbar between cell 8 and 9 and the interior of the busbar was copper colored.

 

[Hedges]

Copper on aluminum may corrode more, in the presence of moisture.
Tin plate on copper more likely than zinc for electrical.

Did you buff off native oxide? Apply corrosion inhibitor? If you have experienced increased resistance, consider that.

First, test for high contact resistance. Pull a high current (e.g. plug space heater into inverter). If possible, use DMM probes to check how many mV drop from aluminum cell terminal to attached busbar. See if any differ from others, especially on the cells that show problems. Check for heating of connections.

 

[Andre Magro]

Hello @Hedges,
Yes it's probably tin plate on copper.

I applied on all cells terminals a fine sand paper and clean with isopropyl alcohol, on the busbars I only cleaned with alcohol, what your suggestion?

The BMS terminal cells are not crimped, but soldered, so I think the problem does not remain here.

Tks

 

[Andre Magro]

Copper on aluminum may corrode more, in the presence of moisture.
Tin plate on copper more likely than zinc for electrical.

Did you buff off native oxide? Apply corrosion inhibitor? If you have experienced increased resistance, consider that.

First, test for high contact resistance. Pull a high current (e.g. plug space heater into inverter). If possible, use DMM probes to check how many mV drop from aluminum cell terminal to attached busbar. See if any differ from others, especially on the cells that show problems. Check for heating of connections.

Even with low current the cells spikes a lot.


I will change the position on cell 7 on battery bank, to see if the problem remains with the cell.

 

[HRTKD]

The BMS terminal cells are not crimped, but soldered, so I think the problem does not remain here.

Very few of us (like < 1%) are soldering BMS balance leads. Ditch the soldered leads and put a solid crimp on them.

 

[Andre Magro]

Very few of us (like < 1%) are soldering BMS balance leads. Ditch the soldered leads and put a solid crimp on them.

Hello @HRTKD,
Thanks for your reply.

Let me ask you, what is the actual problem with soldered balance leads?

 

[HRTKD]

Hello @HRTKD,
Thanks for your reply.

Let me ask you, what is the actual problem with soldered balance leads?

I don't solder anything that I don't have to. My understanding is that a poorly soldered connection can add resistance. Your BMS results could very well be due to high resistance. Someone with more detailed knowledge on the effects of resistance will chime in I'm sure. I'm just providing a clue that what you've done is outside the norm. What do you have to lose by cutting off the soldered connection and replacing it with a crimped connection? If it works, you've eliminated a lot of time/effort/expense.

 

[Hedges]

Hello @Hedges,
Yes it's probably tin plate on copper.

I applied on all cells terminals a fine sand paper and clean with isopropyl alcohol, on the busbars I only cleaned with alcohol, what your suggestion?

The BMS terminal cells are not crimped, but soldered, so I think the problem does not remain here.

Tks

Very few of us (like < 1%) are soldering BMS balance leads. Ditch the soldered leads and put a solid crimp on them.

Balance leads carry so little current I'm not worried about them (although, people have reported contact problems in a connector between balance leads and BMS.)

Busbars or battery cable terminals of course need to go on cells first, balance leads after that. Can't have small ring terminals or washers under the high current connections.

Fine grit to clean aluminum sounds good. Some people then apply corrosion inhibitor, sand again, wipe off, reapply small amount of corrosion inhibitor. The idea was to remove oxide without allowing air to reach bare aluminum, don't know how well it works but couldn't hurt.

Resistive contact could develop later due to corrosion, loosening of bolted connection (especially if cable swings or expands/contracts with heat), compression of metal. It should be detectable by temperature rise or voltage drop between terminal and busbar.


By crimp, I didn't mean crimp of ring terminal to copper wire (which is fine). I meant if aluminum without tin plating is used (e.g. wire), bolted connections are a problem. Instructions call for scraping off oxide, separating strands, getting corrosion inhibitor between them. Then putting in screw terminal. But, when PG&E terminates aluminum power lines like when replacing transformer in a vault by my property, they just crimped on a terminal. The pressure apparently crushes oxide and flows bare aluminum together.

If cells had aluminum terminals hanging out which could be crimped, that could work. But they don't.
If they had tin-plated tabs standing up we could bolt through, that would be great (threads in a nut, not the soft aluminum.)
But all we get are flat aluminum terminals, with native oxide. Laser welding aluminum conductors to it is, I think, the only "right" way. If those were terminals with tin plating, we could go from there using conventional bolted connections. Not sure, but I think all that is done with available welded terminals is more robust aluminum threads, still have the native oxide problem.

 

[gabrielpc1190]

Today I'm noticiing a pretty similar problem on one of my cells.
I have 8 100Ah LIFEPO4 cells. The 6th on the group is behaving totally crazy.


I'm waiting for some additional charge on them to compare top charge voltage, but that 6th cell is going really high.
My BMS is JBD-SP10S009

 

[ChrisG]

Today I'm noticiing a pretty similar problem on one of my cells.
I have 8 100Ah LIFEPO4 cells. The 6th on the group is behaving totally crazy.
View attachment 105060

I'm waiting for some additional charge on them to compare top charge voltage, but that 6th cell is going really high.
My BMS is JBD-SP10S009

What software are you using for those graphs?

 

[gabrielpc1190]

What software are you using for those graphs?

Home assistant, that is feed by an MQTT broker, that receives the signal from jbdtool, that receives MODBUS to TCP adapter, that receives the signals from my BMS.

I just finish doing a manual balancing by using a light bulb.
Here's what I got.
Now time to wait and see what continues to happen



PD: If interested to copy my setup, I can share my files and tools I grab around internet and mostly Home Assistand and this forum.

 

[ChrisG]

Home assistant, that is feed by an MQTT broker, that receives the signal from jbdtool, that receives MODBUS to TCP adapter, that receives the signals from my BMS.

I just finish doing a manual balancing by using a light bulb.
Here's what I got.
Now time to wait and see what continues to happen

View attachment 105062

PD: If interested to copy my setup, I can share my files and tools I grab around internet and mostly Home Assistand and this forum.

That’s awesome. Didn’t know JBD tool can send to MQTT

 

[Andre Magro]

My setup is also through Home Assistant, but more simple, since there is an ESPhome code for JKBMS, I just flash an ESP32 and connect JKBMS directly to ESP and the data is automatically in HA. In HA I use Grafana for a better looking and more complex graphs.

At the moment the charge/discharge modes on BMS are disabled, only balance are activated, and the cell 7 is completely stable.
My question is, assuming that the problem is in the connections, shouldn't I see some activity by the cell 7?

 

[kuranaga]

If cells had aluminum terminals hanging out which could be crimped, that could work. But they don't.
If they had tin-plated tabs standing up we could bolt through, that would be great (threads in a nut, not the soft aluminum.)
But all we get are flat aluminum terminals, with native oxide. Laser welding aluminum conductors to it is, I think, the only "right" way. If those were terminals with tin plating, we could go from there using conventional bolted connections. Not sure, but I think all that is done with available welded terminals is more robust aluminum threads, still have the native oxide problem.

yeah what chinese factories deliver on terminals are absolutely DIY unfriendly