because your displayed miles are the BMS guessing at your pack capacity. All it's doing it taking voltage readings at different SOC. It can't really tell how much capacity the battery has unless it's full. The more areas you let it take measurements the more accurate it's guessing is. With the 3 and Y it's 3 hours of sleep before it takes these measurements.
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No battery degradation??
- Thread starter Kaz93
- Start date
re: BMS and range
Bjorn calls it the GOM (Guess-O-Meter) and I agree. You'll get some indications coming from your BMS, both positive and negative.
Bjorn calls it the GOM (Guess-O-Meter) and I agree. You'll get some indications coming from your BMS, both positive and negative.
Yup, agreed. While using the Open Circuit Voltage can help the BMS with maintaining calibration of the SoC value, it says nothing about how much capacity has been lost from degradation. Using voltage to understand capacity is highly inaccurate, it is nothing more than a guess.
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If anyone is not familiar with who Bjorn is, you should take a second to watch some of his videos on YouTube. He does a great job evaluating various EV‘s from all manufacturers and he is not shy about getting into the details. He has multiple videos that go over degradation tests, the process, and the results. Very eye opening.
pmont1
Member
you like that shiiiiieet? You like that?
BrianBigNFun
Giver of snark
me: 3 months MY LR 3100 miles charge at home almost every day to 90% with Gen 3 wall charger and no degradation at all as of yet
Um...eh.....
Yeah, and that is why amp hours by itself is NOT a measure of an amount of energy. It leaves out the voltage, which changes the answer drastically. You could have two batteries of vastly different sizes with extremely different amounts of energy with the same amount of amp hours if one is a 5V battery and the other is a 500V battery. Or doesn't even have to be that drastically different. If you don't realize that one battery is a 350V and the other is 400V, then the amp hours numbers are mismatched and don't reflect the capacity, depending on which voltage someone is assuming.
I do get what you are saying, but kWh is not a measure of power and amp hours is not a measure of energy unless you also have the unspoken and assumed voltage amount listed and included in there elsewhere. And I get the usage difference where those two types of units are used in different types of circumstances as far as pre-use and post-use kind of thing. Amp hours being used as if it were a measurement of an amount of energy (without listing what voltage it is) has always gotten on my nerves.
Agreed. Each unit of measurement is intended for different types of circumstances/applications. Voltage is obviously important to know in order to have a holistic understanding of a battery or power system. The confusion begins by not recognizing when it's appropriate, and when it isn't, to use each unit of measurement, in combination with what the BMS is reporting, when trying to develop an understanding of something like battery capacity or degradation.
Well, Joules per time multiplied by time is Joules. 1 kWh is 3,600,000 Joules. So I'm always going to disagree with people who say that's not a unit for an amount of energy.
I’m not disagreeing at all with that. I guess you’re not understanding how I choose to explain it. From my perspective, you’re basically repeating/reinforcing what I already said about voltage.
Feel free to try and explain it better if you get what I’m saying.
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FloridaSun
Member
Mine actually shows 330 miles for a full charge.. I wonder if this is normal.. VIN 1868xx. I have not charged to 100% yet, so I don't know for a fact if it will really show 330 miles if I charge 100% but right now, if slide the charging limit to 100%, it shows 330 miles range. Just under 600 miles on the car..
AlanSubie4Life
Efficiency Obsessed Member
You can't extrapolate from this low an SoC. There is too much rounding error - do the math on the the rounding error on 45.5% to 46.5% extrapolating to 100% (answer is that it can extrapolate anywhere between 323 and 331 rated miles - why you're seeing 333 I'm not sure, but there are a lot of rounding errors that may add up, and of course the range calculated here depends on whether your car can display higher than 327 rated miles (my assumption)). In any case, to see a better approximation of your range at 100%, do this same thing from an SoC of 90%.
It's too early. Tesla hides it by inflating the energy content of displayed rated miles when your battery capacity exceeds 77.8kWh (this has been confirmed by observations from in the car and from SMT concurrently). Also, at 2500 miles, with very little time passing, you probably have very little capacity loss, anyway (but it's not knowable unless you have been tracking with SMT or similar).
This may be part of it, yes. For example, if you do happen to have one of these, the battery may have a capacity of 79.5kWh (for some reason they don't make the 82.1kWh fully available in LRs). That battery would have to lose 1.7kWh of capacity (actually more like 1.8 or 1.9kWh) before you would see it in a reduction in your rated miles at 100%. This is more energy to lose before hitting the threshold, than we typically saw for the prior packs (though data is sparse).
I do need to update that post in the Model 3 thread, but just for reference here, this method establishes the lower bound for the energy content. If you are above the degradation threshold, it will just give you (roughly) the degradation threshold for your capacity. If you look at SMT and your energy is 79kWh (would have to be a new vehicle of course), you'd still get 77.8kWh from the energy screen method. FWIW.
It's also unknown at this time - if you do have one of the 2170L packs - whether they have address some of the capacity loss issues with the older 2170 cells. They may well have different capacity loss characteristics - it's too early to know.
I hesitate to reignite this debate, lol, but here goes:
The CAC is used as an input to the BMS display of kWh.
The voltage matters a lot. You need that to know anything about the battery energy content.
No.
In the end, what matters is the integrated area (integral over time) under the curve of amps*volts supplied by the battery. That will give you the kWh capacity of the battery. The voltage of the battery is not constant, even as it is being discharged at a constant rate (constant current). So you must integrate power (V*I) over time to give you actual energy. Often this is APPROXIMATED by using an "average voltage" for the battery and multiplying by Ah capacity. However, this is not what the BMS does. Integrals FTW.
Anyway the original point you were making is that the BMS answer is just an estimate. This is true, and it does make errors. However, they tend not to be too large. It's rare to see corrections or metered trips (use trip meter to see what the pack contained) where you see more than about 2% discrepancy in the pack estimates, when using SMT or other methods to track your pack energy and comparing to the trip meter (after accounting for the 1% fairly consistent loss factor when viewing the trip meter).
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