Problem with 280Ah pack - did I toast these batteries?

[Corbury]

Hi - So last spring I built 2 x 12V batteries each with 4s 280Ah lifepo cells and 120A overkill solar BMS. I top balanced the cells and hooked everything up and it seemed to work great. Then I installed the pack in my van and discharged to around 50% - since it was going to be a few months until I finished the van. The overall system is victron multi-plus 3000 and victron solar charge controller (not configured yet). The guys at inverters R us configured the multi-plus for shore power charging with generic life4po batteries (this might be the issue). BTW - i torqued everything to spec (but maybe something is loose)?

Issue
I recently charged up the batteries with shore power and I saw a lot of cell over-current alarms on one of the batteries. The first charge showed the capacity at 271Ah - now they are showing at 243Ah and 100%. What happened here? I've posted some screenshots.

Thanks for any thoughts here,

Clyde

 

[NVS]

Since they set. I would re top balance them. Then retest capacity. Mine did the same thing when left setting. Making me think I need to add an active balancer that balances the cells full time. My Daly BMS will only balance on the charge cycle. I've been looking at a 5 amp active balancer for mine.

In an RV application where they set idle for months and not cycled daily i think they flot apart and mess up the top balance, especially if your cells are perfectly matched.

 

[Corbury]

Thank you - the 2 batteries seem to charge differently- which i was ascribing to slightly different cable lengths from the charger?

Also - can i top balance these in situ? Or do i need to disassemble the pack/ remove the bms?

Thanks!

 

[Fpoet]

I also had similar problems with the two 280Ah packs in my van during my first season. Everytime, the problem was with the busbar connections getting loose, and the busbars themselves (braided, with connecting ends not sufficiently compressed). This resulted in cell imbalance. I reworked my packs, replaced the busbars, and also added externally mounted active balancers, which I use to top balance the cells and disconnect when done.

 

[Corbury]

I also had similar problems with the two 280Ah packs in my van during my first season. Everytime, the problem was with the busbar connections getting loose, and the busbars themselves (braided, with connecting ends not sufficiently compressed). This resulted in cell imbalance. I reworked my packs, replaced the busbars, and also added externally mounted active balancers, which I use to top balance the cells and disconnect when done.

Thanks - What are you using for busbars and what active balancer are you using - i went looking and found like 100 different active balancers for 4s lifepo batteries!

 

[Corbury]

Thank you - the 2 batteries seem to charge differently- which i was ascribing to slightly different cable lengths from the charger?

Also - can i top balance these in situ? Or do i need to disassemble the pack/ remove the bms?

Thanks!

I figured out the top balance in situ thing.

 

[Fpoet]

Thanks - What are you using for busbars and what active balancer are you using - i went looking and found like 100 different active balancers for 4s lifepo batteries!

I am now using these busbars:

3.78US $ 3% OFF|LiFePO4 Lithium Battery Flexible Busbar Posts Straps Clips Contacts Tabs Connecting Bars For 280AH 320Ah 271Ah Battery Cell Bus|Battery Accessories| - AliExpress

Smarter Shopping, Better Living! Aliexpress.com

www.aliexpress.com

Flexible enough to allow some play, and the connecting "plates" allow for good tightening. I also used blue loctite in gel form on the grub screws to help prevent the serrated nuts from loosening (being very careful to avoid contaminate the contact area). So far so good...

As for the active balancers, I am using the Heltec 4S.

 

[HRTKD]

The Overkill Solar BMS is solid. It may be that your Multiplus is charging too aggressively for this situation, not giving the BMS enough time to do the cell balancing. Consider throttling back the charge amps on the Multiplus and go through a few charge/discharge cycles. The cells may come back into balance. Going through a complete top balancing may still be in order.

What happened between the 15th and the 19th to cause the battery to be so discharged?

When you left the system in storage, did you disconnect the battery from everything?

 

[Corbury]

The Overkill Solar BMS is solid. It may be that your Multiplus is charging too aggressively for this situation, not giving the BMS enough time to do the cell balancing. Consider throttling back the charge amps on the Multiplus and go through a few charge/discharge cycles. The cells may come back into balance. Going through a complete top balancing may still be in order.

What happened between the 15th and the 19th to cause the battery to be so discharged?

When you left the system in storage, did you disconnect the battery from everything?

Hi - i wanted to exercise the battery - so i left the inverter on - it slowly discharged the battery over a couple days. I totally agree the charging is too aggressive- i will reduce the charge settings. In storage - i fully disconnected the battery. Thank you!!

 

[Corbury]

I am now using these busbars:

3.78US $ 3% OFF|LiFePO4 Lithium Battery Flexible Busbar Posts Straps Clips Contacts Tabs Connecting Bars For 280AH 320Ah 271Ah Battery Cell Bus|Battery Accessories| - AliExpress

Smarter Shopping, Better Living! Aliexpress.com

www.aliexpress.com

Flexible enough to allow some play, and the connecting "plates" allow for good tightening. I also used blue loctite in gel form on the grub screws to help prevent the serrated nuts from loosening (being very careful to avoid contaminate the contact area). So far so good...

As for the active balancers, I am using the Heltec 4S.

I will try to buy a couple of those heltec 4s. Thank you!

 

[Corbury]

I will try to buy a couple of those heltec 4s. Thank you!

Is this the one?
Heltec 4S 5S 6S 5A Capacitor Active Equalizer Balancer Lifepo4 Lithium Lipo/Titanate LTO for Battery Car Audio Group Balancer https://www.amazon.com/dp/B08JCL4G2X/ref=cm_sw_r_cp_api_glt_i_MYN96KZTSF182BH2DJ72

 

[OTRwSolar]

We use a Heltec 4s 5a active balancer on our cells. Works relatively quickly to reduce imbalances.

Couple of questions:

If you leave a Heltec active balancer actively working on cells that are not fully charged, say 50%, will it undue a top-balance?

Is it better to only activate the Heltec when cell voltages are above a certain threshold (i.e., 3.4v)?

 

[time2roll]

We use a Heltec 4s 5a active balancer on our cells. Works relatively quickly to reduce imbalances.

Couple of questions:

If you leave a Heltec active balancer actively working on cells that are not fully charged, say 50%, will it undue a top-balance?

Is it better to only activate the Heltec when cell voltages are above a certain threshold (i.e., 3.4v)?

In my short experience there will be no balancing in the mid range of cell capacity due to the very flat voltage curve.
Balancing starts when there is a voltage issue to correct. This happens at the top or bottom depending on where the state of charge is hanging out.

 

[llubi]

I’m having the same problem after a year using the battery. Charged on Saturday at 30A with the multiplus (about 0.1C) and when finished one cell showed 3.97v while the other 3 stayed at 3,3x volts.
Take them to home, top balanced at 3,65v for 12 hours and disconnected to see what happens, now the 3 lowest cells are almost same at around 3,45v and the higher one is still at 3,62v.

Do I have 1 cell broken? Or this cell is the good one and the others are broken?

Thanks!

 

[Sojourner1]

I’m having the same problem after a year using the battery. Charged on Saturday at 30A with the multiplus (about 0.1C) and when finished one cell showed 3.97v while the other 3 stayed at 3,3x volts.
Take them to home, top balanced at 3,65v for 12 hours and disconnected to see what happens, now the 3 lowest cells are almost same at around 3,45v and the higher one is still at 3,62v.

Do I have 1 cell broken? Or this cell is the good one and the others are broken?

Thanks!

You put the cells in parallel and top balanced to 3.65v and then seperated the cells and 1 cell is still higher than the rest?

 

[time2roll]

I’m having the same problem after a year using the battery. Charged on Saturday at 30A with the multiplus (about 0.1C) and when finished one cell showed 3.97v while the other 3 stayed at 3,3x volts.
Take them to home, top balanced at 3,65v for 12 hours and disconnected to see what happens, now the 3 lowest cells are almost same at around 3,45v and the higher one is still at 3,62v.

Do I have 1 cell broken? Or this cell is the good one and the others are broken?

Thanks!

I don't think there is much that can be done except to replace cells. What happens at the low end when deeply discharged?
Consider an active balancer as these cells may need more balancing than the BMS can provide.

 

[Sojourner1]

Did he actually top balance or over charge and it appears maybe no bms. Cant really diagnose with so little info other than some cell voltages.

 

[jpimlott]

At that state of charge is only takes a few amp hours.
try using a resistor to lower the high cell to the same as others or if one is low use
a lap power supply to bring it up the others
When above 3.4 volts very small changes in charges make a large difference in voltage.
At 3.5 volts it is even smaller.
I get mine to be close at 3.45 and leave it be. The amount of amp hours difference is in the low single digits when about 3.45

 

[Corbury]

So I read some more on this and looked at some videos.

My batteries are tucked in to a bench in the van and not easy to get at for top balancing in situ.

Here is what I think I need to do (please correct me):
1. remove them from van
2. take them mostly apart (by removing the BMS)
3. remove all the bus bars
4. reattach a bunch of leads (to connect all the batteries in parallel).
5. attach DC charger and top balance to 3.65v
then (not sure here?)
6. deplete the batteries - to 3.XXv?
7. then charge again to 3.65v
8. then rebuild the pack by reversing steps 1-4

AND add an active balancer like heltec. So when I leave the van - all power off - the batteries don't drift out of sync.

Did I get this right?

Thanks,

C

 

[HRTKD]

Steps 6 and 7 are optional, in my opinion. You could do those steps to establish the Ah capacity, but that's not required.

For many installs, when the batteries won't be used for months at a time, everything gets disconnected from the battery. That would include both the BMS and any active balancer.