Cell and module balancing question

[Firn]

Anyone have detailed specs on how the BMS performs cell balancing? Current rates, etc.

Same for between modules, assuming it balances between modules. And detailed specs on currents, voltage tolerances, etc.

We have seen that the truck appears to do balancing between 99% and 100% based on variations in charging speed. I'm wondering if that is cell balancing, module balancing, or both.

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[Bearcats513]

If balancing happens between 99-100%, should we be charging to 100% occasionally?

 

[electricpig]

If balancing happens between 99-100%, should we be charging to 100% occasionally?

I am of the opinion, that charging to 100% occasionally is needed for BMS calibration and leveling. Question is, how often? Idk, but I would not do so more frequently than every 6-9 months in typical use. That typical use to me means level w charging to 80ost of the time, with occasional fast charging for a longer trip. JMO but hopefully someone will have some real data, and not just their perceptions.

 

[Adventureboy]

If balancing happens between 99-100%, should we be charging to 100% occasionally?

Yes. I charge to 100% SOC about once per month and SOH is 100% after 20 months and 25k mi. Just don't leave it at 100% for long. I do it just before a trip and adjust my charge rate (with my Emporia EVSE) to get to 100% SOC about an hour before leaving.

 

[Ry2023]

I’m not sure about the actual percentage where balances…. but once in a while at lower percentages … especially after charging (following the 20/90 rule ) I noticed it adjust itself and one or two percent up down… however I do charge you 100 once or twice a month….. For range purposes…. And never sits at 100 for more than an hour max

 

[Firn]

I believe that most BMS will balance cells continuously, in fact i think they have to.

On some systems you can find the specs and see how much current is available for cell balancing.

What i don't know is if when we see "balancing" at 100%, is it using off board energy to balance the cells more quickly, if we are seeing module balancing, some level of both, or just a weirdness not related to either.

 

[chl]

I believe that most BMS will balance cells continuously, in fact i think they have to.

On some systems you can find the specs and see how much current is available for cell balancing.

What i don't know is if when we see "balancing" at 100%, is it using off board energy to balance the cells more quickly, if we are seeing module balancing, some level of both, or just a weirdness not related to either.

Yes Li battery systems always have some cell balancing going on.
However, on large batteries like in the Lightning it can take considerable time.

BTW, balancing issues (unbalanced cells) can/could be a reason for some battery fires, and why they seem to occur during fast charging (DC) more often than otherwise - with multiple fast charging episodes, the cells may not (will not) have enough time to re-balance which can be problematic and possible unsafe:

"Possible causes of lithium-ion battery fires include: over charging or discharging, unbalanced cells, excessive current discharge, short circuits, physical damage, excessively hot storage and, for multiple cells in a pack, poor electrical connections."

Link to a pdf for futher reading: https://www.google.com/url?sa=t&sou...sQFnoECBQQAw&usg=AOvVaw10BrGgpi5H7HiqJoLgvoLt

There was some mention of the Lightning cell balancing system in a recall I saw last summer (not sure of the date-my vehicle a 2023 Pro was not apparently affected):
SSM 52039_Cell_Balancing (attached).

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