Software Locked Batteries - Do they ever Balance their cell/module Voltages?

[KyleDay]

Hello friends-

I'm looking for someone who is technically versed in Tesla-land to answer a question I've had for some time (paging @wk057 and others alike):

Do software-locked batteries ever actually balance their cell/module voltages? I have some Lithium battery experience outside my car and understand well the need to maintain a battery's voltage evenly across cells/modules. I also know that my software-locked S60 is top-limited to stop charging at roughly 84% of full charge. So, how does my pack, if ever, actually get to go through a balance cycle? I'd imagine that if it doesn't, that will be very detrimental to the battery life.

I'm wondering if this scenario could play into why Tesla stopped selling software-locked batteries and reduced the unlock price significantly. I'm very likely going to unlock my battery eventually, but I'm mostly interested in the technical impacts of the balance or imbalance due to top-limited locking.

 

[Ande]

Yes, balancing is done internally, same for the charging parameters (max input current/voltage)

 

[pinball_player]

Tesla stopped selling software locked batteries because they did not want to have a 60 kWh battery anymore in their offerings. Having the battery software locked merely meant that it never could charge to 100%.

The charging parameters are the same for the locked and unlocked batteries though. It is just that the battery stops charging at less full.

 

[Rocky_H]

I'm wondering if this scenario could play into why Tesla stopped selling software-locked batteries and reduced the unlock price significantly.

I think you're asking the question backward. You shouldn't be asking why they stopped, but why they started. Remember that the first case was that they were selling 75 kWh batteries. Then, they created the situation of offering the 70 and 60 locked versions. Why? Well, they were getting overwhelmed with reservations for the Model 3 and wanted to lower the barrier to entry of the price level of the S and X to try to convert some of those sales out of the Model 3 reservation line. It wasn't something they wanted to keep doing long term.

 

[gregd]

But the base question is about balancing. Normally that only occurs when the cells are just about full, which doesn't happen if the pack is software locked. So, did they create a non-full balancing algorithm, or do they just not do (or not as well) the balancing?

 

[KyleDay]

But the base question is about balancing. Normally that only occurs when the cells are just about full, which doesn't happen if the pack is software locked. So, did they create a non-full balancing algorithm, or do they just not do (or not as well) the balancing?

Exactly. Thank you. I am under the impression that balancing is best done when cell voltage is at near maximum. Maybe I'm wrong.

I've also read several posts encouraging people to charge their tesla pack up to 100% at least once in a while as that also kicks in thr BMS' balancing procedures. Perhaps that's misguided, but those recommendations are the genesis of my question.

 

[Lasttoy]

Not to 100% if you are at home and just a daily driver.
But always plug it in as per manual.

 

[Moonwick]

Typically balancing is done at 100% but in theory I think it should be possible to balance the pack near the bottom end of SoC as well. The tricky thing about balancing at mid-SoC is that the SoC/voltage curve gets very shallow so it becomes very difficult to tell which groups of cells need balancing applied. The curve becomes steeper near 100%, where balancing normally takes place, but it also gets quite steep close to 0% and thus the voltage differences between cell groups become more apparent. Even if this isn't an ideal place to do the actual balancing (since it's done with resistors and it would take longer to burn off a watt-hour at a lower voltage) there's no reason the BMS couldn't observe which groups have the highest voltages near 0% SoC and then save that information for later once the pack has been charged to do the actual balancing.

I don't have any inside knowledge to say that's what Tesla is doing here, but in theory it could work this way.