Recalibrating the battery

[Battpower]

Again the BMS manages all aspects of the battery and will balance all by itself with no additional input other than charging/discharging the battery.

And I have never seen written instructions from Tesla that you need to take charge above a certain level to maintain a healthy battery system.

The last little charging can be at extremely low current, taking near forever to top

I would certainly expect to see a prolonged period as low / decreasing current power as all cells reach the max voltage deemed to be fully charged (or user selected charge level)

Anyone disagree with the statement that in order for an unbalanced battery to balance, there will / should be an extended period during which the charge power reduces to allow cells to balance?

 

[Battpower]

or whatever harm it may cause) that would come from leaving a car charged for 100% for a month?

I doubt anyone can even guess an answer. It would depend on so many factors. Has the car regularly been supercharged at high power, is the temperature low (say sub 45f) with batt at 100%, is the car driven hard and to low SOC.

You could argue that battery gate cars are evidence of possible reduced range indirectly resulting from battery 'use' that could include any of the above. Best case you lose 20 or 30 miles. Worst case, your car deems the battery condition poor enough to need a new battery.

 

[Battpower]

I think the BMS estimate benefits from an occasional long trip where it can go limit to limit and actually measure what is coming and going in back to back continuous sessions.
I don't think it benefits the battery itself.

I have seen exactly this with a few different EVs. It's only when I give the car proof of what range it will get that the computer revises its range estimate. Not really a battery issue as the range estimation can and does change even without significant battery degredation. As ambient temps increase after winter months, the computer should adjust range accordingly.

If you fail to do this calibration does your battery pack actually lose range or does the computer that displays range become less accurate without in reality affecting the actual range of the battery?

There seems to be different views on this posted here, but in general I see no benefit to the battery in discharging to its absolute limits. In fact this could cause problems if done habitually. Charging to a high SOC may be needed for cells to fully balance, but I think what's more important is that you allow the car to compete the selected charge cycle to whatever level you set for the majority of charges, and don't regularly leave the battery sitting for weeks fully charged especially in cold weather.

 

[lencap]

I feel your pain - I posted this last week -- still active post. Feel free to contribute:

Battery Management System - What I Learned At Tesla Service Center

 

[Battpower]

I feel your pain - I posted this last week -- still active post. Feel free to contribute:

Battery Management System - What I Learned At Tesla Service Center

Looks like you have a lot of sensible posts there that make total sense.

Keeping your battery in good shape so it will give you good range and long service is not the same as your computer having an accurate idea of what that range is at any given time.

 

[rooter]

Alset4S added to Ignore. Thanks for letting me know.

 

[wildguess]

When I told the SC I still got 242miles at 100% they said I was very lucks as some were barely seeing 200miles.

My cousin owns a 2014 P85 Model S with 41K miles on odometer, and it charges to 258 miles at 100%.
The software version is 2020.4.1.

 

[SSedan]

My cousin owns a 2014 P85 Model S with 41K miles on odometer, and it charges to 258 miles at 100%.
The software version is 2020.4.1.

View attachment 512616

Mine was 257 ago till 2years ago with 70k on it, an update wacked it to 242, I did a few single digits to 100% cycles and saw 246-7 but it fell to 242 right away.
VIN is in the 42,xxx range and 94k miles now.

 

[wildguess]

Mine was 257 ago till 2years ago with 70k on it, an update wacked it to 242, I did a few single digits to 100% cycles and saw 246-7 but it fell to 242 right away.
VIN is in the 42,xxx range and 94k miles now.

Wow! His car's VIN is 30,xxx.

 

[Naekuh]

I dont think half you guys still understand how a BMS works...

Spoiler

There is a sensor on EACH cell, because if a cell in the middle dies, it causes the other cells in a series to try to charge that dead cell, which causes load on the pack, hence you get overcharging, and eventually fire.

You cant retrain a BMS, that's not what its built for.
The main reason for losing range, IMO, is probably the computer taking averages of each of your trip and then applying it.

For example, if you been riding your car hard with heater and all sorts of other stuff, it will recalibrate the range based on those numbers.
Its not a lets retrain a BMS, or lets recondition a Li-ion pack.

And you should never charge to 100% unless u intend to use it right away, because you basically eat a cycle on ALL your batteries effectively using them up quicker.

https://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries

Spoiler

You want to be on that BLACK (ideally) or RED line, and not ever on the green line which is 100%.

 

[ewoodrick]

I dont think half you guys still understand how a BMS works...



There is a sensor on EACH cell, because if a cell in the middle dies, it causes the other cells in a series to try to charge that dead cell, which causes load on the pack, hence you get overcharging, and eventually fire.

You cant retrain a BMS, that's not what its built for.
The main reason for losing range, IMO, is probably the computer taking averages of each of your trip and then applying it.

For example, if you been riding your car hard with heater and all sorts of other stuff, it will recalibrate the range based on those numbers.
Its not a lets retrain a BMS, or lets recondition a Li-ion pack.

And you should never charge to 100% unless u intend to use it right away, because you basically eat a cycle on ALL your batteries effectively using them up quicker.

https://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries

Spoiler

You want to be on that BLACK (ideally) or RED line, and not ever on the green line which is 100%.

Wait a second before you go there. Where do you get that the green line is 100% in a Tesla?

I'm pretty sure that Tesla has already taken those curves into consideration and has set 100% to be at a voltage that is suitable for providing the stated and required lifetime for the battery.

And if you took the time to understand the information provided, these numbers will vary based upon chemistry of the battery.

If you can tell me the number of cycles and the max charge voltage for the Model 3 batteries, I'd appreciate it.

But taking a graph completely out of context isn't a great thing to do.

Tesla has done it's homework to understand what expected life of the battery will be. Last I heard, Elon indicating that the Model 3 was trending to be well above 300,000 miles.

 

[Mediocrates]

The main reason for losing range, IMO, is probably the computer taking averages of each of your trip and then applying it.

For example, if you been riding your car hard with heater and all sorts of other stuff, it will recalibrate the range based on those numbers.

It is my understanding that the range value (rated miles) is a constant wH/mile value applied to the current state of charge. It is not something that adjusts over time based on driving conditions.

 

[FatherTo1]

I dont think half you guys still understand how a BMS works...

The main reason for losing range, IMO, is probably the computer taking averages of each of your trip and then applying it.

It is definitely not this.

In the last month I have lowered my lifetime average Wh/m by 7, yet my max range still dropped by five miles. According to the theory above, the BMS should be calculating more range based on my driving habits.

 

[Naekuh]

It is my understanding that the range value (rated miles) is a constant wH/mile value applied to the current state of charge. It is not something that adjusts over time based on driving conditions.

then i guess its reading the overall charge. (shrug)
Then that would mean you have dead cells, and the BMS is shutting those cells off, lowering the overall charge capacity on your pack.

To be honest i know a lot about Li-Ion's as i have played with a lot of them in DYI projects.
I do not fully understand how Tesla works there calculations with the BMS tho.
The BMS will tell the computer i am at 29.40V @ 100% using all 7 cells.
If the pack is slightly degraded, the BMS again will tell the computer i am at 28.4V @ 100 using all 7 cells.
If one cell dies, the BMS will tell the computer i am at 25.2V @ 100% with 6 cells.
There should be a way to read the voltage on the overall pack total, but Tesla wont give that to us.

f you can tell me the number of cycles and the max charge voltage for the Model 3 batteries, I'd appreciate it.

Its common knowledge that the Model S uses 18650 while the Model 3 uses 21700.
These are not special batteries like VW uses.

You can most likely find out from people who have done all the paper testing on the samsung 21700.

 

[aerodyne]

I have a 2015 85D. I stored it for months at 52-55%. It lost maybe 3 miles of rated range. Once I charged to 80% came back.

If you suddenly lost range it is batterygate.

 

[Cheburashka]

then i guess its reading the overall charge. (shrug)
Then that would mean you have dead cells, and the BMS is shutting those cells off, lowering the overall charge capacity on your pack.

To be honest i know a lot about Li-Ion's as i have played with a lot of them in DYI projects.
I do not fully understand how Tesla works there calculations with the BMS tho.
The BMS will tell the computer i am at 29.40V @ 100% using all 7 cells.
If the pack is slightly degraded, the BMS again will tell the computer i am at 28.4V @ 100 using all 7 cells.
If one cell dies, the BMS will tell the computer i am at 25.2V @ 100% with 6 cells.
There should be a way to read the voltage on the overall pack total, but Tesla wont give that to us.




Its common knowledge that the Model S uses 18650 while the Model 3 uses 21700.
These are not special batteries like VW uses.

You can most likely find out from people who have done all the paper testing on the samsung 21700.

The dimensions of the battery (eg 18650) have nothing to do with their chemistry.

 

[Naekuh]

The dimensions of the battery (eg 18650) have nothing to do with their chemistry.

Where in that post did i say it had anything to do with chemistry?

 

[Battpower]

then i guess its reading the overall charge. (shrug)
Then that would mean you have dead cells, and the BMS is shutting those cells off, lowering the overall charge capacity on your pack.

From pictures (MS battery) each individual cell has its own fuse. The cells are in parallel to form a supercell (brick) which behaves just like a cell, so talking cells is really talking bricks. In the bricks, each cell could fail and so has its individual fuse. Over time, some cells can therefore drop out of use. The BMS just keeps doing its thing and balancing brick voltage.

I'm not sure how Tesla makes its range prediction, but at least on the energy display it just extrapolates from whr / mile. But clearly the IC display / battery gauge shows either miles or percent charge, so to give a useful guess as to the miles you will get from 100% it must take into account the effects of temperature for example.

Where I see a noticeable difference between Tesla and other Ev's is how they update the indicated total range during long regen periods, say going down a long hill. My Raven S is very reluctant to show a increasing range on the battery indicator. Imagine driving down a 3 mile long hill. You have driven 3 miles, but your battery has gained energy. That information is clearly useless to base longrange prediction on. Assuming your route will return to your starting elevation then you could just ignore any short term effects but then you don't know the actual charge at a given time. Pilots are very familiar with this idea.

 

[rooter]

spdracer888 earns an Ignore.

Battery Management System - What I Learned At Tesla Service Center

This is what I've been saying for years, but it just doesn't stick.

 

[cousin_IT]

"See, this is what I get for trying to help ignorant people.

this seems like a good place to thank you for documenting your efforts. FWIW I enjoy your posts.