Cell voltage difference 300ah pack

[xlvan]

I have two manufactured (won't disclose the manufacturer) 300ah LiFePo4 batteries. I am running them in parallel for a 12v 600ah system in my van conversion. I have been experiencing some issues with one of the batteries, and am hoping to gain some additional knowledge and insight here.

These batteries have only been charged to 100% three times in my ownership. They were purchased brand new.

The first charge was done individually, before I set them up in parallel in my van. Charging was done with a Victron IP65 Smart Charger. Everything went perfectly fine.

Second time, they were linked in parallel and charged to 100% while driving via my Orion 12/12-30. On this occasion, one of the batteries shut down charging for cell high voltage protect, while the other continued the charge cycle until complete.

Cells of the shutdown battery shortly after shutdown were:
1) 3.507
2) 3.363
3) 3.365
3) 3.514

Total pack voltage read 13.74v, max voltage reached 13.83. Total cell voltage discrepancy of 0.151.

I do not have cell voltages of the second battery (thought I did), but that battery reached max voltage of 14.19v before settling.

When the shutdown battery turned itself back on it took some voltage from the other battery before they leveled out.

I emailed the owner of the company who tried to assure me that everything was perfectly fine. I did continue to run the parallel pack for the rest of that weekend trip, and they performed fine.

Since then I have had the batteries out of the van, not paralleled. Yesterday, anticipating putting them back in the van, I charged each battery up individually, again with the IP65.

The battery that had previously shutdown for overvoltage did so again. Cell voltages were quite similar to last time:
1) 3.534
2) 3.348
3) 3.350
4) 3.516
These figures were recorded an hour after being taken off the charger, and amount to a cell voltage discrepancy of 0.186, total pack voltage 13.74v.

The second battery charged up perfectly fine, cell voltages:
1) 3.502
2) 3.564
3) 3.566
4) 3.559
Total pack voltage again of 14.19.

I again brought this to the attention of the company owner, who again told me everything was perfectly fine, the batteries are performing great. I am not so convinced. This battery continuing to shut itself down and have vastly different cell voltages does not seem great to me.

I am worried putting these back in parallel and continuing to run these two batteries together will degrade the lifespan of both. As everyone here know, these batteries are no small investment, and I did purchase them as an investment, not as a battery to throwaway and replace in a few years.

Please share your thoughts on if you agree with me or with the company owner. He touts a rock solid warranty, but he is not impressing me with his responses so far, so any additional knowledge you all can help me communicate is appreciated.

Thanks very much!

 

[sunshine_eggo]

Batteries go out of balance.

These batteries have only been charged to 100% three times in my ownership. They were purchased brand new.

3 full charges? Over how long a period?

Failure to regularly fully charge LFP runs the risk of cell imbalance depending on the BMS parameters. There is a recent example of a Battleborn battery that had about 50% rated capacity due to imbalance. The owner NEVER charged it above 14.2V... the minimum voltage the battery will begin balancing.

After keeping the battery at 14.2V for MANY days, the battery balanced and capacity was restored.

The first charge was done individually, before I set them up in parallel in my van. Charging was done with a Victron IP67 Smart Charger. Everything went perfectly fine.

Second time, they were linked in parallel and charged to 100% while driving via my Orion 12/12-30. On this occasion, one of the batteries shut down charging for cell high voltage protect, while the other continued the charge cycle until complete.

Time between first and second charges?

Cells of the shutdown battery shortly after shutdown were:
1) 3.507
2) 3.363
3) 3.365
3) 3.514

Total pack voltage read 13.74v, max voltage reached 13.83. Total cell voltage discrepancy of 0.151.

I do not have cell voltages of the second battery (thought I did), but that battery reached max voltage of 14.19v before settling.

When the shutdown battery turned itself back on it took some voltage from the other battery before they leveled out.

I emailed the owner of the company who tried to assure me that everything was perfectly fine. I did continue to run the parallel pack for the rest of that weekend trip, and they performed fine.

Since then I have had the batteries out of the van, not paralleled. Yesterday, anticipating putting them back in the van, I charged each battery up individually, again with the IP67.

The battery that had previously shutdown for overvoltage did so again. Cell voltages were quite similar to last time:
1) 3.534
2) 3.348
3) 3.350
4) 3.516
These figures were recorded an hour after being taken off the charger, and amount to a cell voltage discrepancy of 0.186, total pack voltage 13.74v.

Looks a little worse. how long since full charge #2?

I would use the charger in power supply mode and hold the battery at progressively higher voltages to see if balancing occurs. I would start at 13.8V, evaluate after 8 hours and work my way up 0.1V at a time until balanced.

If that doesn't work, AND one or more of the following is true:
1) You can't fully charge the battery per the manufacturer's charge voltage
2) You can't get rated capacity

Request warranty.

 

[time2roll]

What are the charging parameters?

For solar I recommend 13.80 volts or just low enough to avoid cell over volt protection. Absorption time 2 to 4 hours per day. Check for improvement (or getting worse) after 30 days. Post the results. If the results improve, boost the voltage to 13.90 and keep going.

 

[Samcat]

If you have Bluetooth access to the batteries you will need to record at what voltage battery cell is triggering bms. Also if you can get more information from unknown supplier on all parameters regarding bms that are set for this pack. If he is not willing to provide you with this information i would walk away and never purchase something without all parameters that are needed when using in parallel and needed information to setup charging profiles.

 

[toms]

Welcome to the joys of parallel packs - what you experienced is typical behaviour.

There are a few options, alter your charge profile - run the gauntlet of active balancers - periodically individually charge your batteries to the same SOC.

 

[mikefitz]

The cell Imbalance in low cost pre built batteries is a common issue.
I recommend you set your chargers to 13.8 volts and see how things turn out. If there are no issues with BMS shutdown perhaps increase to 13.9 then14.0 volts. There is no point having a charge voltage higher that 14.0 where the charge current is low compared to pack capacity.
Dont have a absorbtion longer than 30 minutes, better no absorbtion at all.

 

[Steve_S]

Set your Charger to Bulk/Absorb @ 13.7V (3.425Vpc) This is Constant Current.
Your EndAmps / TailCurrent should be set to 15A (300AH * 0.05)
Then set FLOAT to run at 13.6V (3.400Vpc) This is Variable Current. It will power your devices as required and gently feed the battery packs as they trickle up and balance out.

You appear to have a SmartBMS but you have not mentioned the Brand & Model. There are a LOT of them out there, and have a multitude of options.

To be perfectly clear... Balancing a pack is a bit of a tricky business.
Passive Balancing is not & never was intended for large capacity cells and most certainly not for paralleled cells within a battery "pack". It slowly bleeds off High Cells and lowers the overall pack voltage and it is Very Slow in doing so. Anything crossing 100AH will not benefit from Passive in any meaningful way.
Active Balancing works for Large Cell packs but the Amperage used is relative to the actual cell AH rating. Active Balancing "Transfers" energy from High Cells to Low cells in "pulse mode" which is much gentler on teh cells and quite efficient. For example 2A Active Balancing works for up to 250AH, 3A Balancing 350AH (This is per battery pack only). Active Balancing capabilities can go up to 10A.

Cells within the Pack should all match up but aside from the "cell itself" the busbar connections can have an effect that can cause such things. Everything has to be "clean & tight, even small things like Burrs or Ridges on a busbar can toss things for loop. Unless you can get inside the casing to verify that everything is tight you may never know. A Mobile System also has to contend with vibrations & temperature changes and some have discovered sadly that busbars on cells can get loose in such a situation IF there are no serrated/lock washers and this is a Real Bugger to track down and solve.

As for NOT Naming the Manufacturer, you are doing Noone but the vendor a Favour. The Membership here has come across pretty much everything and seen it all... There are many Known Good and even more Known Bad vendors/makers and sometimes the So/So Vendors are well known and their "quirks/foibles" and the solutions for those have been posted by others.

Hope it helps, Good Luck.