Battery Management System - What I Learned At Tesla Service Center

[navguy12]

ok here goes... let’s just look at the raven X with 5,000 miles even though I think it’s an important detail that I also own a model S.... with 40,000 because anecdotal scenarios aren’t all that helpful, BUT Bjorn’s videos and my experience at the same time means I am seeing something... and yes.... it’s super stupid by tesla either way.

If you own a 5000 mile Raven model x and have 325 mile range at 100% soc, then two updates and one month later, you can’t go higher than 312 EVER for the next 10 months.... that is super stupid lack of foresight on Tesla’s side. Particularly because it only affected perceived max range, which is really only useful for psychological purposes when the car can run similar stats on 311 mile trip pre and post knee capping. Ask yourself how many owners call and bug the service center claiming loss of range.... not understanding the issue as you (or I) do? That’s dumb.... perception of full range absolutely matters, just as suddenly capping your newish car at
13 miles fewer range overnight is really dumb. At least give the owner a heads up on why and how... they can live with the answer. Same thing with my model S happened... used to have 318 mile range max then over 40,000 it goes down to 311 max range before knee capping update, one day later whammy! 311 to no more than 294!!!! It’s never gone back to normal, which is why I appreciate the sheer brilliance of the OP at least asking the questions and getting an answer that is not totally clueless from service center.
I did the super long trip anyway and verified what Bjorn found, that the range is being hidden somehow based on algo. Though it s possible perhaps likely that it’s not at all on purpose, it was still made with minimal thought into ripple effect of owners thinking their tesla battery loses chunk of range early. It’s not smart decision to keep reasoning quiet but I guess that’s what happens when people do stupid class action lawsuits on autopilot technology not being delivered as hoped....

I see the argument you are making...one of many reasons why I have kept my display in "%" since day one of ownership 2.5 years ago.

 

[AlanSubie4Life]

I see the argument you are making...one of many reasons why I have kept my display in "%" since day one of ownership 2.5 years ago.

Obviously, this discussion has been had many times...so nothing new here. But I can't resist! There's nothing wrong with %, of course, as long as you're using the Tesla navigation (or live data for ABRP) for trips, etc. Personally, I just like to see how much energy I have left. So I use rated miles. And I still get to enjoy the % on the navigation interface!

I do find it a bit ironic that Tesla labels these two displays "Energy" and "Distance," but when you have it set to "Energy," you can't actually see how much energy you have left - you can only see the ratio of your current energy to the maximum your car can retain!

 

[navguy12]

Obviously, this discussion has been had many times...so nothing new here. But I can't resist! There's nothing wrong with %, of course, as long as you're using the Tesla navigation (or live data for ABRP) for trips, etc. Personally, I just like to see how much energy I have left. So I use rated miles. And I still get to enjoy the % on the navigation interface!

I do find it a bit ironic that Tesla labels these two displays "Energy" and "Distance," but when you have it set to "Energy," you can't actually see how much energy you have left - you can only see the ratio of your current energy to the maximum your car can retain!

Yep, leave it in %, set my destination (home, supercharger, the inlaws, whatever) and drive to arrive with 10%...

 

[buttershrimp]

Yep, leave it in %, set my destination (home, supercharger, the inlaws, whatever) and drive to arrive with 10%...

Totally and thanks for seeing my point!

For those of us that like rated mile consistency and losing our perceived max range in predictable ways... this issue feels as though we’ve been assigned 95% as the max SOC. You’d be able to live with that if it happened over 50,000 miles perhaps but lose it suddenly!? Hell no!

 

[Charliek]

hi I thought id chime in on my observations and agree with many of the that percent however flawed does allow you to not get into too much trouble with either short drives and mid level number of cycles and not getting too low or too high SOC for long periods.

In My 4 years of having a MS with only a 90K pack ( thank goodness it is a version 3, that's another story). I have had a couple of times when BMS and my charging were definitely adjusting range numbers/ capacity.

one time I had to leave the car at 15 percent for a day till I could get around to charging it ( id did go into sleep) and when I did that I got 83 Percent charge ( which translated to a range change ) from where I has set it at 80%. one other time just before trip I set it for 100% and I came back and it was charged to 103% ?( another range adjustment) .

don't worry I quickly used it up so not to stay at high or low SOCS for too long. another time on distance was "hot footing" it and lost a ton of miles ( this was when SC were farther apart) . that convinced me to go to percentage, not miles.

The only way to know with any more certainly for those " detailed" types is what the posters have said about measureing pack average voltages, discharge cycles ( from when you got the car , or you will be off) and BMS information but that is probably pretty obsessive as you cannot realy control all the variables to optimize things.

To follow battery university's information which I find to be spot on for my phone as well as my car, id like to know what 75% SOC really " is" and what is 20% real "is" relative to the real capacity of all the pack is after BMS has gotten to a regular " adjustment" . so is 80% charging is really 75% of real SOC? so then you could match maximum charge cycles with out limiting Max capacity as the BMS adjusts?

then I go and drive a long distance and use super chargers and mess everything up ? See I can be obsessive too! . I think from what I hear is don't go down to <5 % where it turns to red (unless you have to - yes I have seen it do that) , don't over super charge (that's hard cause for me its free!), don't charge a lot of cycles, but don't go full charge to discharge more than one in a while. eat your vegetables, lose some weight so the car doesn't have to carry it long term.

don't carry passengers they add to capacity reduction ( family will be not be happy) and move to a place where the climate is always 60 degrees F ( has to be on the cool but not cold side) and doesn't vary more than 10 degrees ( even San Diego doesn't count, but Ireland might ). anything less will not optimize resale. all things in moderation. including moderation ( that why we have a 0-60 number, personally I like what it does 30-90 Mph)

(moderator note: added spaces to improve readability. no other changes made)

 

[AAKEE]

So if you simply drive 40%-60% the car will not readjust. So when for some reason the BMS was off by 5% by the time you started doing that, it will remain at that 5% error the whole time.

The only way to retest it and give it more calculating space is to charge it to nearly full and drive down to nearly 0 on one go. You will see that the used kWh will be closer to what the BMS predicted when you were charging 10-90.

Old post, but I didnt see this thread until now.

I charge to 55% daily, and use 20 to 35% each day. 20%, in summer and top note is very cold days about 35%( -30C or so).

My daily 55% is only used when going to work or at weekends, I of course charge more for longer trips and use SuC when needed.

A single 100% charge between my regular 55% most often push the NFP up by 0.3 or 0,5 or so. Multiple big cycles during long trips seems to lower the NFP, specially during the hot days of the year.

Coming from a series of big cycles and a tad lower NFP and going back to 55%, the NFP initially stays at the lower value for a while. After that it starts climbing, and as far as I can estimate the real probable capacity, the NFP climbs above the real capacity after some weeks of 55%.
This maybe only be the case in colder climate, I didnt have very many 55% days in a row during the hot days this summer.
But last winter/earky spring and this fall/autumn and winter so far, the BMS seem to drift up during series of low SOC cycling.
My 82.1kWh (2170L) showed 81.4kWh for most of the late winter/spring, about 80kWh during the hot summer days and is back at about 81.4 since a few weeks.

The car is two weeks from 1 year and 30K km, so the calendar aging itself should have taken a 2 % or so bite of my battery by now( average resting SOC is 30-35%) and the cycle aging should be some 0.5-1%.
The real capacity should probably be in the 79.5-80kWh.

So my conclusion is in par the spanish guys finding. Constant low cycling -> BMS starts overestimating the capacity.