HV Battery Died with 7 miles range left showing on Range display

[LostVector]

Electrolyte oxidation happens at very high voltage - in general above the maximum voltage lithium ion batteries use.

4.20V/cell is the 100% that Tesla use. The examples in Jeffs presentation is above 4.20V.

Of course I do not know for a fact that this very particular mode of failure is what's going on in OP's battery, but it's called out in the presentation and clearly OP's battery is defective in some way. Averages and expected behaviors do not apply.

I havent studied the electrolyte oxidation specifically but I would guess that this is a non issue for EV users.

We do not use high voltage that often in general, as daily charging is ~80-90% (4.0-4.1V) or below. Most of us do not cycle the cells to 4.20V each time.

You're assuming the battery pack is degrading in a normal way. It clearly hasn't and so isn't there a different failure mode at play? Imagine something was out of tolerance on one or a few batteries in the pack and there's a faster than expected buildup on the electrodes causing a few cells to start losing capacity quickly. It does not have to be a high charging voltage causing the issue.

The point is I do not think you can look at studies designed to measure and predict the behavior of batteries within design spec when in all likelihood something is out of spec.

The failure mode described do not mean this. It means that the cell rapidly looses capacity in a low number of cycles, and then die - dead like in not possible to charge.

I'm a little unclear on what you are arguing relative to what I said about sudden drop in voltage and shutdown by the BMS.

When EV’s stops at whatever percentage above 0% displayed it do come from the fact that SOC can not be measured when driving (or charging).

Why do you think this is the case? I was under the impression that the BMS can get a more accurate reading when the battery has rested, but there are still certainly many data points that can be collected while the battery is under load to continue updating the SoC. Do you have a different understanding of this?

The State of charge is measured by measuring the resting voltage (OCV) of the battery (-cells).

Again, rested is the best way to measure it, but I don't understand it as the *only* way.

When driving (or charging) the BMS need to calculate the estimated SOC.
The calculation depends on the estimated capacity (and also the SOC). Any fault in estimated capacity or estimated SOC before the drive ends up in a error in the resulting estimated SOC we se on the display.

I agree? But also this seems a bit tautological?

 

[EVer Hopeful]

I'm curious what was going on as it shut down? Were you going uphill?

Funny you should say that (right at the beginning of this thread) but I have had that happen in an icemobile - but that was because the pickup must have been at the front of the tank causing it to cavitate when the fuel sloshed to the back

I've heard similar (but opposite) happens in a Cessna 182 and that a forced landing from fuel starvation can go awry in the flare as the nose comes up, fuel runs to the back of the fuel cell and the engine picks back up destroying all your careful calculations

Maybe the electrons are doing something similar

 

[AAKEE]

When EV’s stops at whatever percentage above 0% displayed it do come from the fact that SOC can not be measured when driving (or charging).

The State of charge is measured by measuring the resting voltage (OCV) of the battery (-cells).

Why do you think this is the case?

I would not call it *think*…

As you put a load on a battery, the voltage droops. The voltage droop vill vary with load, cell temp and SOC (internal resistance). It will also vary with the recent load history. There are too many variables to measure the drooped voltage and calculate the SOC from this.
If you are driving, and are stopping (at a red light for a minute, or something similar) and the battery voltage clearly shows that it is different than the estimate the BMS can adjust the SOC from this but this will be a rough adjustment.


The same is valid for charging - The SOC can not be measured in a reliable way during charging as we feed the batteryu with a higher voltage than the cell voltage to create the current. So, the BMS calculates the needed amount of energy to hit the set SOC level. Looking at the BMS values during a charging session we can see that there is a value “to charge comnplete”. This value is calculated before the charging commences and is calculated by “needed change in SOC x capacity”.
If the BMS overestimates the capacity, the end result SOC will overshoot the planned/requested SOC. This as the calculated amount of energey will be more than what was needed to hit the target SOC. This is quite common in threads for people to ask why it end up higher then the set level.
Seing a overshoot after a charge (need not to be a to small charge session) indicates that the BMS overestimates the capacity.

Same thing after a drive, but the other way around: If the SOC droops after a (longer) drive, it is most probably due to a BMS overestimating the capacity. If the SOC recovers after a (longer) drive, its probably a BMS underestimate. Using Scan my tesla or similar, so the SOC can be read in better resolution makes this very clear.

I never had any gross overestimate, but my M3P had a large underestimate. I developed a way of calculating the capacity during that time, and also drove a 100-0% drive to check the capacity.
During this underestimate any longer drive made it clear that the SOC recovered after a drive (see around 10 a clock).The 100-0 drive on the picture, and arrival after 240km with 52% SOC and after several hours of sleep it showed 54%. Same thing when arriving hime after the return drive, the SOC started to recover.

When I got my Plaid, the BMS hads the battery capacity at 96kWh, but the new capacity is aorund 99.4kWh when leaving the manufaqcturing line.

So, the same thing happened here. Every longer drive had a recovery afterwards. Every. Like this:

So, it was even possible to calculate the true capacity by using *Estimated used SOC/Real used SOC x BMS estimated capacity* to find the real battery capacity. This as the end SOC is a estimated value from the estimated capacity.
Also, the better way to calculate the capacity is *delivered energy/ delta SOC*. It will be very precise as long as the the power during the drive was not to high (speeds 90-100kph/55-60mph) as the specified capacity is at a certain battery load.

Well, the BMS adjusted slowly, and after one month the BMS came to the same capacity estimate that I had done ( = 98-98.3kWh). From that day, the SOC doesnt recover after a longer drive.
Scan my Tesla shows this very precise with SOC in one or two digits, but for the purpose of this forum, teslafi graphics show this better (but not as precise).

A full charge (100%) is not estimated, as in the end of the charge the supply voltage is held constant until the current has reduced below a (low) level. To think it in an easy way, the voltage is held at 100% SOC voltage until the battery stops receiving any more current.

 

[AAKEE]

Again, rested is the best way to measure it, but I don't understand it as the *only* way.

The “stop” above 0% is not extremely uncommon. And it doesnt need to be a battery failure, it just need to be a bad capacity estimate.

Think about how it can be possible for several cars to stop above 0% if the BMS could measure the SOC well during a drive.
Tesla use 4.5% of the total capacity below 0% displayed, so there should be a good margin before the car stops in the normal case.

 

[LostVector]

The “stop” above 0% is not extremely uncommon. And it doesnt need to be a battery failure, it just need to be a bad capacity estimate.

Think about how it can be possible for several cars to stop above 0% if the BMS could measure the SOC well during a drive.
Tesla use 4.5% of the total capacity below 0% displayed, so there should be a good margin before the car stops in the normal case.

If it were a bad capacity estimate on a pack with healthy cells, why would the pack go immediately into shutdown? Wouldn't you expect the remaining estimate to drop unusually quickly first as it enters the tail end of the discharge curve, not just enter a shutdown state (especially when there is supposed to be 4.5% buffer)?

On the other hand, consider a pack with some cells experiencing premature failure ... I believe the BMS would detect an unusual and unexpected voltage drop in either individual cells or the pack, then shutdown the car quickly to prevent serious damage to any cells from overdischarging. That looks to me like what's being experienced here. Do you have a different take?

I would not call it *think*…

As you put a load on a battery, the voltage droops. The voltage droop vill vary with load, cell temp and SOC (internal resistance). It will also vary with the recent load history. There are too many variables to measure the drooped voltage and calculate the SOC from this.
If you are driving, and are stopping (at a red light for a minute, or something similar) and the battery voltage clearly shows that it is different than the estimate the BMS can adjust the SOC from this but this will be a rough adjustment.


The same is valid for charging - The SOC can not be measured in a reliable way during charging as we feed the batteryu with a higher voltage than the cell voltage to create the current. So, the BMS calculates the needed amount of energy to hit the set SOC level. Looking at the BMS values during a charging session we can see that there is a value “to charge comnplete”. This value is calculated before the charging commences and is calculated by “needed change in SOC x capacity”.
If the BMS overestimates the capacity, the end result SOC will overshoot the planned/requested SOC. This as the calculated amount of energey will be more than what was needed to hit the target SOC. This is quite common in threads for people to ask why it end up higher then the set level.
Seing a overshoot after a charge (need not to be a to small charge session) indicates that the BMS overestimates the capacity.

Same thing after a drive, but the other way around: If the SOC droops after a (longer) drive, it is most probably due to a BMS overestimating the capacity. If the SOC recovers after a (longer) drive, its probably a BMS underestimate. Using Scan my tesla or similar, so the SOC can be read in better resolution makes this very clear.

I never had any gross overestimate, but my M3P had a large underestimate. I developed a way of calculating the capacity during that time, and also drove a 100-0% drive to check the capacity.
During this underestimate any longer drive made it clear that the SOC recovered after a drive (see around 10 a clock).The 100-0 drive on the picture, and arrival after 240km with 52% SOC and after several hours of sleep it showed 54%. Same thing when arriving hime after the return drive, the SOC started to recover.
View attachment 1040954


When I got my Plaid, the BMS hads the battery capacity at 96kWh, but the new capacity is aorund 99.4kWh when leaving the manufaqcturing line.

So, the same thing happened here. Every longer drive had a recovery afterwards. Every. Like this:
View attachment 1040969


So, it was even possible to calculate the true capacity by using *Estimated used SOC/Real used SOC x BMS estimated capacity* to find the real battery capacity. This as the end SOC is a estimated value from the estimated capacity.
Also, the better way to calculate the capacity is *delivered energy/ delta SOC*. It will be very precise as long as the the power during the drive was not to high (speeds 90-100kph/55-60mph) as the specified capacity is at a certain battery load.

Well, the BMS adjusted slowly, and after one month the BMS came to the same capacity estimate that I had done ( = 98-98.3kWh). From that day, the SOC doesnt recover after a longer drive.
Scan my Tesla shows this very precise with SOC in one or two digits, but for the purpose of this forum, teslafi graphics show this better (but not as precise).
View attachment 1040978



A full charge (100%) is not estimated, as in the end of the charge the supply voltage is held constant until the current has reduced below a (low) level. To think it in an easy way, the voltage is held at 100% SOC voltage until the battery stops receiving any more current.

I think we are talking a bit past each other because although what you say is true, the BMS is still estimating the SoC based on ongoing info available to it, both while driving or resting. Saying the SoC cannot be measured reliably while driving is a matter of degrees, not a binary yes it can or no it can't. I understand why you are saying it, but to me it's inaccurate to characterize the measurements and estimations taken while driving as completely useless.