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Mid Range Battery Math
- Thread starter hugh_jassol
- Start date
TimothyHW3
Active Member
In his other video 15000 miles or so ago he had 518 I believe. But now it is around 0° C.
It is useful to see what the cell imbalance is and to fiddle with temperatures. It is also good to track the kWh without the need to fully charge. It is a powerful tool.
I wish he showed what happens with the stators in the back on RWD when you charge a cold battery. On AWD they go up to 3,5-4kW each, but you only have RWD 1 motor. I guess it will be 3.5kW, but who knows, might be 7kW at the back.
AlanSubie4Life
Efficiency Obsessed Member
Sure, that would be the “diagnosis” I referred to. With that information you could try things and see whether imbalance could be improved if it exists.
If you charge to 80-90%, you can just look at the rated miles, and if you are really careful about watching the % value change, you can derive your Full kWh with quite a bit less than 1% error.
Sure. Again, for figuring out what is going on with the car exactly, it provides info, if you want it. Just not needed for accurate assessment of available capacity.
Background: dec 2018 build mid range model 3. 12,000 miles on the odometer and pretty much used for local commuting where i charge at home nightly with full 32-amps to 70% and over the day use down to approximately 45%.
So I just recently took a long-ish trip in my mid range model 3 and tried to charge at home to 100% but the car stopped at 99% and notified me that it was “fully charged”. At 99% when I toggled to miles it said 257 miles.
what I surmise is that I have 1% real degradation and the Tesla mid range software equates 100% to 259.5 miles.
i think in an update Tesla software limited to battery down.
So I just recently took a long-ish trip in my mid range model 3 and tried to charge at home to 100% but the car stopped at 99% and notified me that it was “fully charged”. At 99% when I toggled to miles it said 257 miles.
what I surmise is that I have 1% real degradation and the Tesla mid range software equates 100% to 259.5 miles.
i think in an update Tesla software limited to battery down.
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AlanSubie4Life
Efficiency Obsessed Member
Full new is 264. That is 264rmi*237Wh/rmi = 62.5kWh
So you are at ~61.6kWh which is pretty good. Only 1.5% degradation after 12k miles and over a year. Awesome.
Stopping at 99% is just something that happens sometimes for whatever reason.
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On my mid-range, my NomFullPack is now 58.8 kWh (up from 57.6-ish when I first got my OBD dongle a couple of weeks ago). I also am seeing the ~4ish mi increase in my displayed range. It's been consistently that for over a week now.
That's the first time since I've owned the car the range estimate increased, albeit a small one. I was hoping the trend would continue, but seems to have leveled out.
That's the first time since I've owned the car the range estimate increased, albeit a small one. I was hoping the trend would continue, but seems to have leveled out.
TimothyHW3
Active Member
Definitely no temp increase. The only thing that was different is I had two weeks off over Christmas and New Year and so my car was above 80% for most of that time because I drove very little.
And of course the major software update on Christmas Eve...
TimothyHW3
Active Member
Hmmm, that is very interesting, do you know the EXACT % you left it at? This is rather important if you can find a screenshot!
There is an internal document that states that if you leave the car at 4.0V or more (AWD this is 85%, but is probably different on Mid range, could be around 80% - just check with SMT what % it says inside the car when you are at 4.0V) - then the car will balance itself roughly 1mV imbalance for each day. So for 14 days that is 14mV imbalance. So that might be it!
Do you have screenshots of your SMT before and after the drop, particularly nominal full and cell imbalance?
Edit:
I actually found a screenshot where your car is at 83% and is above 4.07V so this really could be it!
Batman and Robin (internal names of the chips) could have been working in your favour during christmas!
https://teslamotorsclub.com/tmc/attachments/screenshot_2019-12-28-18-55-39-png.494003/
The cell imbalance was at 2mV, but you had some bad readings so it might be just a default value. Try slow charging from 10-90% and see how that goes. If you can, try leaving the car at about 85% for a few days and see if it has positive effect again!
When I do the math, if we take 62 MAX kWh with 2.6 buffer. Your battery is still pretty good at 58.8kWh. You might be able to squeeze another 0.5kWh or so with the suggestion from above, but no worries your battery is still ok!
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AlanSubie4Life
Efficiency Obsessed Member
Based on our (I think?) current understanding, LEMR will start showing degradation below (237Wh/rmi*264rmi) 62.5kWh (compared to 76kWh on LR), but probably started in SMT between 63 and 63.5kWh (compare to 77-78kWh on LR AWD). (EPA document says 63.8kWh, compared to 79.2kWh for LR AWD.)
I assume no CAN bus readbacks were ever done for the LEMR when it was new...so perhaps we will never know for sure where it started.
But probably 58.8kWh represents 5-7% loss of available energy.
@TimothyHW3 - I have been charging to 90% since mid-November because i thought i might help... My charging settings are approximately like so:
0 - 2,000 mi - charged to 90% after every drive, every time I plugged in at home
2,000 - 9,000 mi - charged to 80%, set to charge after 8pm
Note: First range drop was at about 5,000 mi
9,000 - present (almost 11,000) - switched to 90%, scheduled departure set to 7am.
Notes:
- Dec 19-Jan5: was above 80% the entire time
I think I am going to set it start charging at 8p again - that will mean for most workdays, it will be at 90% from about 10p to 7am (9 hours).
This may all just be silly as there are many people who don’t do anything and have only lost a few miles. I’m starting to thing @AlanSubie4Life has the right theory of “luck of the draw”
Anyway I will continue to monitor and report
0 - 2,000 mi - charged to 90% after every drive, every time I plugged in at home
2,000 - 9,000 mi - charged to 80%, set to charge after 8pm
Note: First range drop was at about 5,000 mi
9,000 - present (almost 11,000) - switched to 90%, scheduled departure set to 7am.
Notes:
- Dec 19-Jan5: was above 80% the entire time
I think I am going to set it start charging at 8p again - that will mean for most workdays, it will be at 90% from about 10p to 7am (9 hours).
This may all just be silly as there are many people who don’t do anything and have only lost a few miles. I’m starting to thing @AlanSubie4Life has the right theory of “luck of the draw”
Anyway I will continue to monitor and report
AlanSubie4Life
Efficiency Obsessed Member
To be clear, I think there are certainly things you can do (like always charge to 50% or something and never discharge below 30%) which will presumably eventually confuse the BMS. And I also believe there are things you can do that are known to be abusive to the battery (nothing that you have described above would qualify). But I guess my claim is that I think that while the BMS confusion stuff could impact estimates temporarily, it seems to me there is no avoiding the overall capacity loss trend that corresponds to your battery, even if BMS confusion is layered on top. And my feeling is that specific behavior is somewhat "luck of the draw."
I'm really liking this theory about this "hidden degradation" initially, because it fits all the data:
1) BMS readbacks don't fit the expectation (charging constant * rated miles) when "full" energies (as per SMT, TM-Spy or whatever) would result in rated miles available higher than the EPA rating. (264rmi for the LEMR for example is 62.6kWh but that's not what the EPA document says, and probably the CAN bus would read a larger value on a brand-new LEMR car.)
2) The CAN bus readbacks on AWDs clearly show that energies start relatively close to Tesla's result from the EPA test.
3) Most people don't report degradation (at least on MR and LR AWD) right away. There is nearly invariably a delay before people see capacity loss.
4) Physically, we know that actually lithium ion batteries are expected to degrade fastest when they are new. Then the capacity loss slows down (a lot). This isn't what we're seeing, though, so I suspect this initial degradation is hidden.
So I think what happened to you in those first few thousand miles is that you lost ~1kWh of energy (went from 63.5kWh available to about 62.5kWh). It just didn't show up due to Tesla's manipulations of the numbers to make things look unchanged.
I still don't understand exactly how Tesla hides this extra degradation initially, but it would not be hard to do (there are several ways to manage it via modification of the constants, etc.). It could be detected, but would require careful trip meter tracking over time.
It doesn't matter though - I think the 30% warranty would apply to the energy relative to the EPA number (and your initial available energy) - not relative to initial rated miles. So in the case of the MR it would kick in around 63.5*0.7 = 44.45kWh. We know that would be at about 188 rated miles. (Not 0.7*264 = 185 rated miles). That would certainly be my argument anyway, in the unlikely event that you have to use that warranty.
My guess is this capacity loss is going to slow way down for most people once they reach 12-18 months of ownership, so warranty claims will be rare (I hope!).
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TimothyHW3
Active Member
If you continue to charge daily you will not see any improvement. It will get worse.
Like I said, you have to let the car go down below 20%.
How many % do you use daily? If you only use 20% of the range daily ,then only charge it on every 3-4 day or so.
Charge like that for at least a month or seetwo and how it goes.
That's about what I use - about 20% of the battery on my daily commute. I'd like to do the let-it-go-to-20 thing... but then it starts to be inconvenient
I did an experiment back in November when trying to figure out why I had a one-day loss of about 10-12 rated miles. So for three consecutive charge cycles, I let the battery drop to <10%, then charged to >90% (one time all the way to 100%, then left for work immediately). This took about 2-3 weeks. During those cycles, there was no change in rated miles @ 100% whatsoever. So, if I did that again (only plug in when below 20%) for a month, I would likely still only get 3-4 cycles. No so hopeful it will change anything...
TimothyHW3
Active Member
That's about what I use - about 20% of the battery on my daily commute. I'd like to do the let-it-go-to-20 thing... but then it starts to be inconvenient
I did an experiment back in November when trying to figure out why I had a one-day loss of about 10-12 rated miles. So for three consecutive charge cycles, I let the battery drop to <10%, then charged to >90% (one time all the way to 100%, then left for work immediately). This took about 2-3 weeks. During those cycles, there was no change in rated miles @ 100% whatsoever. So, if I did that again (only plug in when below 20%) for a month, I would likely still only get 3-4 cycles. No so hopeful it will change anything...
I am not quite following what you did. You did three consecutive charges from 10-90%? If you do 20% or so each day, that was one charge on monday and one on thursday and two charges the next week - so more like 1.5 weeks and not 3?
This is why I suggested to run it over a longer period of time, like 2 months at least - 3 cycles over 2 weeks will not do much.
If you do it consecutively over 2 months, once the weather gets nicer, I am sure you will get your range back.
There are far too many reports of people charging 20% daily in the top range 70-90% who end up with disbalanced BMS and lower range after each charge to be a coincidence.
And the 2 weeks above 85% standing and rebalancing thing you did over christmas without knowing was straight from the internal docs and a good indication that the car needs to rebalance itself.
I don't think you actually lost real capacity so it is worth a try.
But hey, if you don't wanna try it out and can live with deminishing range every time you charge...
Of course I am going to try... It’s just that I don’t use EXACTLY 20% every commute. IT’s like 18+/-2 depending on many things. If I charge to 90% when I leave the house on Monday morning, I can usually make it through Thursday, and if it’s a good week, through Friday (and I don’t drive much on a typically weekend). So essentially so to first order, I’ll get about 5 cycles a month. So not sure how rapidly I should see something.But hey, if you don't wanna try it out and can live with deminishing range every time you charge...
TimothyHW3
Active Member
Well, I didn't mean to say 20%!!! exactly, Of course there will be deviasions. 5%-10%-15%-20%-25% whatever works for you. I think the lower the better, maybe 10-15 is a good benchmark. 5 cycles a month, 10 cycles 2 months. I think this is a good reference. If you do this until April when the weather gets better above 20C and if nothing has changed - then you will know.
Would be great if you can report back after month to see the progress
@TimothyHW3 @AlanSubie4Life Well, it's not quite exactly a month, but thought I would report in. I have been running my mid-range down to between 5-20% and then charging to 90% all month. Through that time, the displayed range at 90% is 223-224 (estimated at 248 @100%). Throughout that time, my Nominal Full Pack in SMT was always 58.7-58.8 kWh.
It jus so happened I had time today and my car was < 20% so I decided to hit the local supercharger and charge to 100% - this is only the second time I have every used a supercharger. I recorded the session in SMT and here is the data:
You can see, I hit 100% SOC in a little over 60 min, but the supercharger was still charging, so I let it go until it stopped. At 61 min my displayed range was 250 mi and remained so for the rest of the session... however an interesting thing happened with the Nominal Full Pack number... over the first few min at 100%, it went from 58.8 - 59.1kWh and (not shown) the energy buffer went up by 0.1 kWh (from 2.6 to 2.7). But notice that if you look at the Charge Power curve, it was still dumping energy into the battery - I estimate between 1-2 kWh. So when it finally stopped at just over 100 min, I had the following:
displayed range: 250 mi (up from est. 248)
Nom_Full_pack: 59.1 kWh (up from 58.7)
Energy Buffer: 2.7 kWh (up from 2.6)
As I drive away from the supercharger, I drove 5.8 miles before the range display ticked down to 249 rmi. I am now down to 88% SoC with a displayed range of 221.
Not sure what this means, but I wonder if I should do the same next time I need to charge.
It jus so happened I had time today and my car was < 20% so I decided to hit the local supercharger and charge to 100% - this is only the second time I have every used a supercharger. I recorded the session in SMT and here is the data:
You can see, I hit 100% SOC in a little over 60 min, but the supercharger was still charging, so I let it go until it stopped. At 61 min my displayed range was 250 mi and remained so for the rest of the session... however an interesting thing happened with the Nominal Full Pack number... over the first few min at 100%, it went from 58.8 - 59.1kWh and (not shown) the energy buffer went up by 0.1 kWh (from 2.6 to 2.7). But notice that if you look at the Charge Power curve, it was still dumping energy into the battery - I estimate between 1-2 kWh. So when it finally stopped at just over 100 min, I had the following:
displayed range: 250 mi (up from est. 248)
Nom_Full_pack: 59.1 kWh (up from 58.7)
Energy Buffer: 2.7 kWh (up from 2.6)
As I drive away from the supercharger, I drove 5.8 miles before the range display ticked down to 249 rmi. I am now down to 88% SoC with a displayed range of 221.
Not sure what this means, but I wonder if I should do the same next time I need to charge.
TimothyHW3
Active Member
It seems like your battery recalibrated itself. So a good 20%-90% and then a 100% does indeed seem to recalibrate the battery.
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