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brette avatar image
brette asked

Brand New Victron LiFePO4 battery - cell imbalance

Gday,


We purchased 2 x Victron LiFePO4 battery 25,6V/200Ah Smart BAT52412041 for a customer install

Upon the first charge 1 battery had 2 cells go over-voltage (BMS cutout) well before full charge state. the other battery is in perfect balance.

Question: what is the factory balancing tolerance?

There seems to be 2 scenarios here;

1. If the cells WERE balanced in the factory and they went out of spec on the first charge then this indicates a capacity defect (ie 20% below) - they should be replaced


2. If the cells WEREN’T balanced in the factory then we also have a defect that cannot be rectified on our end (sealed cells). And this would have reputations implications for Victron. Although we could attempt it, we wouldn’t be prepared to undertake surgery to parallel and balance the cells as this would void any future warranty. Also doesn’t guarantee solving the problem.


I can see that Victron publish a method to bring them back into balance (without opening) however this is supposed to only be needed for batteries that have gone flat or have done thousands of cycles. Note these batteries were sitting at healthy voltages when delivered.


Good battery cell voltages 3.41, 3.40 , 3.40 , 3.40, 3.40 , 3.41 , 3.41, 3.41

"Bad" battery cell voltages 3.71, 3.37, 3.37, 3.37, 3.37, 3.37, 3.37, 3.53


The wholesaler is enquiring with victron but i'd like a second opinion.


Thank you

Brett

battery chargingBMSbattery manufature
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2 Answers
klim8skeptic avatar image
klim8skeptic answered ·

Can one assume you have read the manual?

Charge the errant battery at 1-2a overnight to let the BMS/cell balancers do their job.

Make sure the batts are running the latest firmware...

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brette avatar image brette commented ·

gday,

yes indeed the literature and manual was reviewed.

commissioning of a new battery does not involve any checking of the cell balance or undertaking balancing activity (which can take several hours). https://www.victronenergy.com/media/pg/Lithium_Battery_Smart/en/commissioning.html

if you read the literature (below) from the troubleshoot section, the only applicable cause for a new battery would be a defective cell.

No manufacturer in the world would assemble several cells into a battery pack and not balance them prior. Why would anyone pay the premium victron price ??


What causes cell imbalance or a variation in cell voltages:

  • The battery has not spent enough time in the absorption charge stage.

    This can, for example, happen in a system where there is not enough solar power to fully charge the battery, or in systems where the generator is not running long or often enough. During normal operation of a lithium battery, small difference between cell voltages occur all the time. These are caused by slight differences between the internal resistance and self-discharge rates of each cell. The absorption charge stage fixes these small differences. We recommend a minimum absorption time of 2 hours per month for lightly operated systems, such as backup or UPS applications and 4 to 8 hours per month for heavy used (off-grid type) systems.

  • The battery charger never reaches the storage (or float) stage.

    The storage (or float) stage follows the absorption stage. During this stage, the charge voltage drops to 13.5V and the battery can be considered full. If the charger never enters this stage, it might be a sign that the absorption stage has not been completed (see previous point). The charger should be allowed to reach this stage at least once a month. This is also needed for battery monitor SoC (state of charge) synchronization.

  • The battery has been too deeply discharged.

    During a very deep discharge, one or more cells in the battery can drop well below their low voltage thresholds. The battery might be recoverable by rebalancing, but there is also a realistic chance that one or more cells are defective, and that rebalancing will not be successful. Consider the cell to be defective. This not covered by warranty.

  • The battery is old and is near to its maximum cycle life.

    When the battery is close to its maximum cycle life, one or more battery cells will start to deteriorate, and the cell voltage will be lower than the other cell voltages. This is not imbalance, although it might look like it is. This cannot be fixed by rebalancing. Consider the cell defective. This not covered by warranty.

  • The battery has a defective battery cell.

    A cell can become defective after a very deep discharge, when it is at the end of its cycle life or because of a manufacturing fault. A defective cell is not unbalance (although it might look like it is). It cannot be fixed by rebalancing. Consider the cell defective. Very deep discharge and end of cycle life are not covered by warranty.

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renrgize answered ·

I just purchased 4 200AH batteries and they all have the same problem. All 4 landed imbalanced. Had to buy a smart charger to try to get them balanced. Definitely wasn't expecting this poor experience. Seems like the charging is going to be a nightmare in waiting time.

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