Best Charging Practice for Battery

[PremiumPackage]

Any tips for someone leaving the care in an unheated, detached garage in a cold climate? I've already set it to 70% charge, and I leave it plugged in whenever possible. I will note I've got time of day charging set as I get dirt cheap rates overnight, but I assume as long as it's plugged in it's managing the battery, even if it's not charging. Also - it's not infrequent that I go 2-3 days without driving it (I bike to work most days), and even when I do drive it, it's 15 miles round trip or less. I assume I should still plug it in after these trips, even if I'm only doing a bit of charging back to my baseline level.

 

[Kermee]

Any tips for someone leaving the care in an unheated, detached garage in a cold climate? I've already set it to 70% charge, and I leave it plugged in whenever possible. I will note I've got time of day charging set as I get dirt cheap rates overnight, but I assume as long as it's plugged in it's managing the battery, even if it's not charging. Also - it's not infrequent that I go 2-3 days without driving it (I bike to work most days), and even when I do drive it, it's 15 miles round trip or less. I assume I should still plug it in after these trips, even if I'm only doing a bit of charging back to my baseline level.

Pretty sure you're good to go setting to 70% and leaving it plugged in. The motor may run (stationary) to generate heat to keep the batteries warm though. You using a UMC2 or HPWC? If UMC2, what voltage and amperage?

 

[PremiumPackage]

240V NEMA 14-50 outlet in the garage. Set to charge at 9pm when the rates go to 4 cents.

 

[ninpb]

Any thoughts on charging right after an hour drive vs waiting say 1 or 2 hours to let the battery cool and then charge?

I have free charging at work and charge my current leaf lease right when I get in. Spots run out and it's 50/50 a charger will be available at lunch time.

I think I got this wait to charge strategy from leaf forums with our no bms and notorious degradation issues.

 

[Rocky_H]

Any thoughts on charging right after an hour drive vs waiting say 1 or 2 hours to let the battery cool and then charge?

That's not really a thing. Teslas can actively heat or cool their own batteries as needed.

I think I got this wait to charge strategy from leaf forums with our no bms and notorious degradation issues.

That explains it. Leafs don't have any active temperature control for their battery packs.

 

[Kermee]

240V NEMA 14-50 outlet in the garage. Set to charge at 9pm when the rates go to 4 cents.

Ah. That's plenty and you're ready to go. Was just worried you might be using 120V/12A which some people have some concerns may not be enough power, which would then use power from the batteries, to keep them warm in extreme cold temperatures.

 

[MikeBur]

Let’s just say I may know someone in the right place to see the right vehicle data from the right vehicles to know.

But, I also have experience as a battery test engineer for major OEMs. The strategy I mention also jives with my experience interfacing with BMSs. The BMS needs an opportunity to balance the cells to even out the voltages and keep them consistent and tightly grouped to each other. This allows for maximum usage of the energy out of the cells as a group and allows you to charge them at a higher rate as well. If you have cells that are out of balance, when a load is applied to battery pack, those out balance cells will likely move to a different voltages than the other cells that are in balance. As time goes on, that variance will increase and eventually, you start hitting lower voltage cutoffs early, reducing your range.

It is my understanding that the BMS on Teslas doesn’t read each individual cell, but several in parallel. So, those cells are constantly working to balance to each other naturally, but the BMS does not have individual control over any specific cell. This is one of the reasons why letting the pack sit for a bit after a full charge on a Tesla should help, because it gives the cells time to settle out and the BMS time to actively work the balancing circuits to keep everything even. The balancing circuits are likely active during charging, and will end up doing a lot of work towards the end of charge, but I'm assuming (based on some help from the right people) that the circuits are active even after charging has stopped. So, while letting a cell sit at high SOC for long periods of time degrades the cell more quickly, keeping the pack balanced is also very important from a practical perspective. If the battery spends 95% of its time at 80% SOC or less, and is allowed to balance at full SOC for the other 1 to 5%, its probably a lot better than never allowing the pack to spend some time balancing cell strings at 100% SOC.

Just to be clear, this strategy is predicated on the assumption that the balancing circuits are active even after charging has finished.

You might enjoy this post, even though a little older from my S: Chassis CAN Logging To ASCII Text Plus Graphing

Per module here’s a time lapse of per module charging voltage; with a keen eye you might note some balancing at charge completion, though this via Supercharger:

 

[MikeBur]

Any tips for someone leaving the care in an unheated, detached garage in a cold climate? I've already set it to 70% charge, and I leave it plugged in whenever possible. I will note I've got time of day charging set as I get dirt cheap rates overnight, but I assume as long as it's plugged in it's managing the battery, even if it's not charging. Also - it's not infrequent that I go 2-3 days without driving it (I bike to work most days), and even when I do drive it, it's 15 miles round trip or less. I assume I should still plug it in after these trips, even if I'm only doing a bit of charging back to my baseline level.

Agree with everything @Kermee says, indeed a plugged in Tesla is the happiest Tesla. It will done everything to ensure car is looked after.
You should also consider warming the car longer than needed to just raise the cabin temp. As mentioned, the 3 is different to the S in the ability to generate heat from the drive motor more efficiently, though also when not moving when plugged in. This will help warm the battery too and minimize the time spent with limited regen. Not needed, though a nicer experience.

 

[moridin2002]

You might enjoy this post, even though a little older from my S: Chassis CAN Logging To ASCII Text Plus Graphing

Per module here’s a time lapse of per module charging voltage; with a keen eye you might note some balancing at charge completion, though this via Supercharger:
View attachment 342442

Interesting... I like it. Thanks for posting. I'd like to figure out how to get in to the 3's BMS output and start pulling data on cell voltages and if there are any estimated health metrics. I imagine it would have to be an inline CAN bus splice of some kind to get at it.