Found my 280AH EVE LF280K LiFePo4 cells discharged really low

[robwolff3]

I have 8 EVE LF280K LiFePo4 cells configured in two packs of 4 cells to make 12v battery packs for my RV. They each also have a 150A JBD BMS protecting them. I left them in my RV after a trip hooked up with no large loads, just a few constantly running electronics in the RV that make up a low draw parasitic load. Today I went to put the charger on them to get them to a storage SOC and disconnect them. Both packs were at 5v ?. I am still trying to figure out how they were able to get so discharged. My best estimation is that they were at this voltage for a day or two. They look fine physically, no bloating.



Measuring the voltage manually with my volt meter, each cell was at:

1. 1.25
2. 1.09
3. 1.00
4. 1.87
5. 1.40
6. 1.28
7. 1.40
8. 1.24

In a rush to recover them I immediately put 10v @ 8a on them (1.25a per cell). They came up to 9-10v within seconds and dropped off the current in 10 minutes or so. Now I am trying to get them to 12v @ 0.5a.

As mentioned in other threads Im going to start reading up on LiFePO4 dendrite formation. Seems given the short circuit risk people wont put cells anywhere they dont want to risk getting burned down.

Not sure why they BMS didnt cut them off at 12v. The only thing I can think of, sometimes I will connect the bluetooth module to the serial connection, but in my RV I have a serial to USB adapter connected to the JBD bms to monitor them with a raspberrypi. Maybe the USB serial connection overrides the BMSs normal function or parameters? Here are the settings:



Here is them coming up to 10v:


Any advice on recovering them and using them in the future would be appreciated.

Thank you,
Rob

 

[time2roll]

No solar to keep these topped off?

Not sure what to say on recovery except to continue a very slow charge to at least 11 or 12 volts so all cells are above 2.7v.

 

[Steve_S]

The BMS Failed to Low Volt Disconnect, better go through your settings and get it to Disconnect @ 2.600 Volts per cell at the lowest. Something is definitely wrong. Recent days seems a few folks have had Over Discharge Fails that took cells below 2.000 which is not good at all.

Dendrite Formation is not a concern in such a situation unless it's frequent and then you have other issues like a bad BMS if it won't cut off.
Bring them back up "Gently & Patiently <5A) until all cells are at least 2.600 then apply the regular charge amperage you can and MONITOR closely for a potential runner.

 

[Sojourner1]

Do these bms's still draw power from the batteries once they disconnect the loads from batteries?

 

[Bud Martin]

I think the BMS did cutout the output voltage on the P- feeding the loads but the BMS circuits and Bluttooth are connected on the non-switched side B- of the BMS that is why you can still communicate with the battery. If you are not going to use the battery for a long long time the BMS and the Bluetooth circuit should be disconnected, but I do not know if that can be done on the off the shelf battery or not.

 

[RCinFLA]

Batteries should be fine. Not until you drop below 1.0v cell voltage do you run into lithium plating damage. The manufacturers 2.5v min discharge spec is to have some margin to the 1.0v hard limit as it does not take much additional discharge to quickly drop from 2.5v to 1.0v.

It is likely the 'just a few electronics' load dropping to BMS cutoff, followed by BMS idle draw taking it the rest of way down.

Lesson learned, with no real damage.

 

[time2roll]

Do these bms's still draw power from the batteries once they disconnect the loads from batteries?

Overkill FAQ:

Q: What is the quiescent current? What can I do for long-term storage?
A: The quiescent current is as follows: (this was measured on a 4 cell BMS)

• ● 5.5 milliamps with everything off, when the BMS is active, but no bluetooth.
• ● 15 milliamps with the bluetooth active (after about 10 seconds it drops to 0.8 milliamps.
  Reconnecting it wakes it up again).
• ● 0.8 milliamps when the BMS is inactive.
  So, assuming your battery setup is 100 amp hours, the BMS would run for 17 years. This proves that the BMS can be connected for long periods of time without any fear of it draining the battery.
  Unplugging the balance connector would ensure complete shutdown
  NOTE: The cell’s self-discharge rate will always cause the battery to drain over time, which may be several percent per month. This is simple chemistry and physics; there’s nothing that you or the BMS can do to avoid the battery cells from self-discharging over time, other than to occasionally top up the batteries.

 

[HRTKD]

Are you sure there isn't something connected directly to the battery that the BMS doesn't know about?

 

[robwolff3]

Thank you everyone for your input. Much appreciated!!!

Are you sure there isn't something connected directly to the battery that the BMS doesn't know about?

Yes, only the BMS is directly attached to the cells, nothing bypasses the BMS.

No solar to keep these topped off?

Its in my near term plan to get solar panels on my RV roof, for now I have two 100w panels I deploy on the ground next to my RV. In the process of putting the panels out is when I noticed them in this 5v state.

If you are not going to use the battery for a long long time the BMS and the Bluetooth circuit should be disconnected, but I do not know if that can be done on the off the shelf battery or not.

With these JBD BMSs I can disconnect the balance cable witch will cut power from the BMS and then not even the BMS would be creating a load on the pack. I have two other battery packs not in my RV, with the BMS w/ bluetooth continuously connected and they have had a healthy SOC sitting unused for months now.

The best theory I have so far is that the BMS did not trigger cell or pack under voltage and disconnect discharging. And electronics from the RV continued to discharge the batteries down to 5v.

I parked the RV after our last trip August 14th, I turned the main appliances off (mainly the electric fridge) and the battery bank was at around 30% SOC. My Victron shunt reports electronics loads as 11-13w. Yesterday August 21st is when I discovered them in the 5v state so they had only been sitting for 7 days.

Once the battery packs get up to a healthy SOC I will most certainly be testing both the cell and pack under voltage cutoff functionality. Further to prevent this in the future I will have permanently mounted solar panels on the roof (at the moment its not covered, obviously wont work for covered storage). Also the RV has a Intellitec Battery Guard 1000 that covers many loads but not all of them, not the co detector or the electronics ive installed. Thinking about moving it to cover all loads in the RV as a second line of defense.

 

[mikefitz]

Your screen shots show the BMS switched off the discharge path due to cell undervolts.
Do you have insulation between the cells and end plates?

 

[joltman]

Maybe consider a shore charging system as well (if the RV is near a power plug). I am curious if the serial connection you had plugged into the BMS caused the higher current pull. It's possible that a constant serial connection is not something that is tested during QA for the BMS since 99% of users with use bluetooth. If you get the battery pack back into a good SOC, you could test to see if the serial connection pulls a higher current.

 

[robwolff3]

Do you have insulation between the cells and end plates?

There is plastic insulation between each cell. The silver end plates are painted 3/4 plywood. No insulation is between the cells and wood end plates.

 

[rbanic]

Nothing related to the topic but I really like the pack build Did you do it by any guide?