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No battery degradation??

SigNC

Active Member
Aug 23, 2017
1,519
1,358
NC
I consider it something and significant if it continues degrading at this rate. I’m just trying to understand the root cause of the sudden change because I expected degredation to be slow and steady.
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.
 

mark95476

Active Member
Jun 21, 2020
1,495
856
Bay Area CA
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.

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.
 
Oct 3, 2020
205
215
Seattle
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.

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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Oct 3, 2020
205
215
Seattle
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.

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.
 
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pmont1

Member
May 20, 2021
29
48
Knoxville, TN
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.
I agree, Bjorn's videos are enlightening.
 

Rocky_H

Well-Known Member
Feb 19, 2015
6,411
7,582
Boise, ID
To understand degradation, you must first recognize the difference between amp hours and kilowatt hours. Amp hours is a measurement of battery capacity, while kilowatt hours is a measurement of electrical power. Being that watts are used to describe the power that's involved to do work, and amps are used to describe electrical energy, it should become more clear as to why understanding battery capacity is not as easy as many appear to think.
Um...eh.....
As for why they’re rated in kWh, I would attribute that to the consumer and the need for there to be a universal figure to reference how big the battery is. If they were to rate them in Ah, they would also have to further complicate things by including the battery voltage.. Manufacturers would then have to rely on the consumers’ math skills when comparing to the competition.
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.
 
Oct 3, 2020
205
215
Seattle
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.
 
Oct 3, 2020
205
215
Seattle
Well, Joules per time multiplied by time is Joules. 1 kWh is 3,600,000 Joules.

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
Apr 19, 2021
431
738
Lakeland, Florida
I've had my MY long range for a couple months now and really enjoy the car. I keep hearing about battery degradation occurring within the first few months of ownership and then leveling off and not dropping as fast. I have over 2500 miles and am showing zero signs of degradation? I've attached picture to show that when sliding the charger line to 100% it shows over the rated range (327)? I attached a photo for others to see, my charging habits in case anybody is wondering is just keeping it plugged into a 120V outlet when not driving. I also have supercharged maybe 4 times. What are you guys seeing with degradation for your cars at or around this millage? Is my car still too new to show signs yet? Also i keep hearing that some of the model Y's have a 82kwh battery... maybe accounting for not showing signs of degradation? My vin is 157XXX
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..
 

jgris

Member
Feb 16, 2021
13
12
East Bay
VIN 138XXX, 03/2021 MY LR. Shows 333 miles for a full charge.

IMG_2266.jpeg
 

AlanSubie4Life

Efficiency Obsessed Member
Oct 22, 2018
10,016
12,068
San Diego
VIN 138XXX, 03/2021 MY LR. Shows 333 miles for a full charge.

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%.

st. I have over 2500 miles and am showing zero signs of degradation? I've attached picture to show that when sliding the charger line to 100% it shows over the rated range (327)?

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).

Also i keep hearing that some of the model Y's have a 82kwh battery... maybe accounting for not showing signs of degradation?

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).

and the kWh of the battery is easily seen via the energy screen calculation.

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:

CAC (calculated amp hour capacity
The CAC is used as an input to the BMS display of kWh.
If they were to rate them in Ah, they would also have to further complicate things by including the battery voltage..
The voltage matters a lot. You need that to know anything about the battery energy content.
Kilowatt hours is a measurement of the power

No.

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.

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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letswinit

Member
Mar 18, 2021
27
17
san jose
I have Teslafi when I purchased the car. Interesting to see charge capacity increasing.
 

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