Wiki Sudden Loss Of Range With 2019.16.x Software

[David99]

Just to avoid any confusion, I didn't submit anything to the NHTSA. I just heard they are looking into the issue. I assume them and Tesla are talking right now. But I do not know for sure. I think this was discussed here months ago that a car manufacturer has to notify the NHTSA within a few days if they know of an issue. I believe Tesla didn't at the time but other has notified them. Long story short, I don't know what is going on with the NHTSA and Tesla.

 

[wk057]

The BMS's threshold for starting to freak out about things is > 20mV imbalance (over an extended period of time). A 40-50mV imbalance at the end of a charge, or at rest, is a pack with some problems.

Keep in mind the BMS calculates and models on-the-fly the SoC of each brick... and does so with incredible precision given the limited sensor information available.

So to me, the key words in that error screenshot are "Delta SOC", meaning there is a detected deviation in SOC for a brick (or bricks). There are multiple potential guesses at causes for the imbalance, in this case "weak short" would indicate that whatever brick has a SoC imbalance is consistently below the SoC of other bricks but not pushed above other bricks when charged. If it were pushed above other bricks when charged, that'd mean the brick in question was weak or had lost a full cell or otherwise had less capacity than the others. But the guess of "weak short" suggests that brick is being discharged in some way that is not being commanded.

 

[Battpower]

But the guess of "weak short" suggests that brick is being discharged in some way that is not being commanded.

That is what I thought too.

Which would permanently be working to create an imbalance? That would give BMS a hard time?

 

[CB198]

Does anyone have a hvil nodes set to 40?

 

[Battpower]

Does anyone have a hvil nodes set to 40?

Does that relate to this discussion?

 

[wk057]

Does anyone have a hvil nodes set to 40?

I don't think Tesla has made any quintrigint-motor cars as of yet...

 

[JustADude]

I don't think Tesla has made any quintrigint-motor cars as of yet...

I figured that number represents a config, not simply the amount of devices.

 

[wk057]

Last I saw it's just the number of resistors on the HVIL loop (generally number of HV devices, but for example, the A/C compressor, heater, and battery heater all count as one because of the junction box).

 

[Battpower]

But the guess of "weak short" suggests that brick is being discharged in some way that is not being commanded.

Sorry, an edit got lost.

Speculation:

Explanation for brick voltage reduction after charging.

Some cells take more charge than others.
Thermal image looks even, but we don't know state of those modules / bricks and any way, the materials are thermally conductive and had time to fully 'soak'.

If @wk057 happens to have video of thermal image from cold, might show something different. (or sequence of stills).

Once charging stops, cells with higher charge will balance with lower ones and the voltage would drop.

Also, as wk057 said:

"If it were pushed above other bricks when charged, that'd mean the brick in question was weak or had lost a full cell or otherwise had less capacity than the others."

I still think there are multiple ways that stresses could start to build internally to bricks. (may be heavy regen?) Anything that results in imbalance between bricks is going to give the BMS a harder time.

I guess the BMS will struggle more with elevated temperatures inside the pack potentially compromising its performance just when it needs to work harder to bring bricks back into balance.

IF charging goes ahead on the assumption that balance is being maintained, then this could be a problem if the BMS is already swamped. Only option would be to throttle charge rate to give BMS chance to catch up as well as keeping everything as cool as possible maybe helping BMS function.

This info is about resistor characteristics. Can't find exact graph I would like to see against ambient temp, but all looks like multiple factors potentially working in the wrong direction:

Resistors – Resistivity, Thermal Resistance and Temperature Coefficient

Are there paralleled FET's? I'll look at the photo again.

 

[Battpower]

> 20mV imbalance (over an extended period of time)

..... Makes life hard for BMS....

'extended period of time'

'progressive inability to address imbalance.'?

'prolonged stress on BMS components'?

 

[Battpower]

Just for reflection:

Especially:

"They're both just additional risk factors when looking at overall failure possibilities, neither of which will cause something catastrophic on its own and neither of which is any more of a problem than some aspects of general use (charging to 100%, supercharging, leaving the car in the sun, etc... or in an ICE vehicle, I'd say just pumping gasoline is riskier than all of the above).

There are a bunch of factors that increase the risk of fire in a battery. For example, I'd say just charging a car (one without any other issues, new, whatever) to 100% and letting the car sit without discharging soon can result in as much, or likely even more in many cases, risk of fire than any of the conditions mitigated by the range loss updates. Charging to 100% in direct sunlight is probably more risky than having condition Z."

This thread is pretty crazy, and I'll probably be stoned from multiple directions for posting here again.

I never said anyone's cars were going to burst into flames or anything. For that to happen, more failures than just condition X or Z would have to happen. They're both just additional risk factors when looking at overall failure possibilities, neither of which will cause something catastrophic on its own and neither of which is any more of a problem than some aspects of general use (charging to 100%, supercharging, leaving the car in the sun, etc... or in an ICE vehicle, I'd say just pumping gasoline is riskier than all of the above).

There are a bunch of factors that increase the risk of fire in a battery. For example, I'd say just charging a car (one without any other issues, new, whatever) to 100% and letting the car sit without discharging soon can result in as much, or likely even more in many cases, risk of fire than any of the conditions mitigated by the range loss updates. Charging to 100% in direct sunlight is probably more risky than having condition Z.

Heck, I'd say using Ludicrous+ battery heating is probably 5x riskier than any of the conditions relevant to this discussion.

So, let's not blow things out of proportion. There is acceptable risk involved with the operation of any automobile, ICE or EV. However, the more risk eliminated, the better.

The problem for me is that other conditions that would end up with condition X or Z as a catalyst for a disaster type failure are not really as easy to detect or prevent, so eliminating the risks you can eliminate (ie: update) is a positive thing in this case when you compound multiple problems.

I'm still not convinced Tesla is going to do the absolute right thing by owners as far as actually correcting the underlying issue (which requires a pack replacement to fix 100%, no way around it). I'm convinced they are working in the best interest of safety by pushing the updates they have pushed. I'm also convinced that they're really working pretty hard to mitigate as much as possible with as little adverse effect as possible.

I'm convinced no one involved on Tesla's side is sitting there thinking, "Well, we can just let cars have problems for the sake of our bottom line." As far as they're concerned, the update eliminates the risk factor entirely. By not applying the update, you're accepting that slightly elevated risk of failure... just like you would if you had an ICE vehicle and say, didn't replace a component you knew could fail.

From what I've gathered, the number of people who could possibly still be affected by conditions X or Z (ie, have not updated) is less than 100... out of tens of thousands. I'd say that's good enough.

Yes, it sucks that range loss could be involved, and I'm hoping they'll find a way to either mitigate it in a way that corrects that, or corrects the issue entirely by replacing packs for those who can not recover 100% of the range lost by software mitigation.

Commence the stoning...

 

[Battpower]

By complete coincidence, and just hours before I found the above post by @wk057, I had recently typed almost exactly the same as this from @wk057:

"..... I'd say just charging a car (one without any other issues, new, whatever) to 100% and letting the car sit without discharging soon can result in as much, or likely even more in many cases, risk of fire than any of the conditions mitigated by the range loss updates.......

(I added bold)

It seems to me that if you pushed the safety argument to the limit the end result would be a an additional sticker next to the CARB one something to the effect of:

'This vehicle is known to The State of California to contain components that can burst into flame'.

In fairness to the EV manufacturers, the same sticker should then probably be applied to gas cars too. A bunch of bureaucrats get work processing stickers and life goes back to normal.

Life is risky. Engineers try to mitigate risk. Not all engineers / designers adopt the same approach to solving a challenge, and neither should they imo. Some approaches may prove in time to offer more acceptable compromises than others in different applications.

That still leaves the question of owners losing range and charging performance. Even without conditions X & Y or anything else, lithium batteries age and deteriorate along with everything else around us. If we want to push the technology to the limits, then as the deterioration sets in (harder use = faster deterioration) in order to maintain a cushion for safety, you are likely to have to restrict stress on the battery.

How many Tesla owners have ever thought of owning a vehicle with such performance before? To get 0 - 60 in sub 4 seconds in a gas car is expensive and elite. Anything approaching 2 seconds is absolutely extreme. Owners of such gas cars would totally get that everything is a compromise. Nothing comes without a cost.

Now were you mis-sold?
Was documentation lacking?
Has your car degraded faster / failed outside of normal degradation with fair use?
Is there a clear, meaningful and enforceable warranty policy?

These strike me as the bigger issues.

 

[Battpower]

This thread is very hard to refer back through! Started to reavaluate when I first read this:

This thread is pretty crazy, and I'll probably be stoned.......

Hmm, hanging out with EM?!

Carried on reading and relaxed again.

Another post that seems to have some points worth reflecting on:

You have just shifted the issue to "other reasons." What if those reasons are simply because the battery has degraded due to usage and environmental factors?

See figures 1 and 2 in BU-1003a: Battery Aging in an Electric Vehicle (EV) – Battery University

This describes that as the battery ages (due to normal usage and environmental factors) the battery is more susceptible to stresses and adding grace capacity reduces the stress on the battery prolonging its life in the long run.

View attachment 468607

View attachment 468605

 

[Battpower]

More reflection.....

[post responding to Battery University being speculative] :

Of course — just like this forum.

But I thought that article had more interesting and informed hypotheses than most posts on this forum so thought it worthwhile to share it and point others to it.

I think it has a pretty interesting and plausible hypothesis that is directly on point.

And by the way, the website is sponsored by, probably run completely by, Our History | Cadex Electronics. Which seems to be a respectable organization in the industry. More information here: About Battery University

View attachment 468927

Here is my data charted with the charging voltage at each SOC on a 72kW urban charger.

 

[Battpower]

This thread is proof of monkeys, typewriters and Shakespeare!

The more I re-read all posts it feels like every possible point has been made over and over.

Somewhat obviously, as the recent thumb-twiddling post pointed out, is for Tesla to put an end to the speculation with externally verifiable facts to fill the remaining void that the thumb-twiddling is circling around.

Regulatory bodies need to wake up and instead of trying to deal with EV's as a varient of ICE vehicle, come up with specific standards, expertise and testing facilities specific to EV's.


[vaguely related issue about UK EV data reporting standards]

I've just seen this on Twitter and think it has some potential. Not sure if it's just an idea or if it's been passed yet?
https://twitter.com/goultralow/status/1288732498013429761?s=21

Until they do, then manufactures will likely continue unhindered to represent performance claims in ways that best suit them, and play warranty issues to minimize their costs.

Regardless of if any of us hit the nail exactly on the head with regards to X, Y and Z, I think if nothing else this thread does paint a reasonable halo around those areas if you can be bothered to do a lot of filtering, and the only reason to need to know more detail is if you plan on coming up with a fix or trying to argue a case against Tesla. I'm not personally planning on doing either but my Tesla Pride really needs them to put this to bed and directly effected owners surely deserve much better.

 

[Battpower]

A 40-50mV imbalance at the end of a charge, or at rest, is a pack with some problem

Unfortunately, I don't have access to such a car to test & measure, but I suspect it would be helpful to have clear guidelines for best approach to charging such a vehicle.

Given the huge amount of pseudo information that could imo have owners frantically running their batteries right down and recharging in endless effort to improve balance, what could actually be the best routine? Out of the malaise of anecdotes, what really could help?

A problem for some owners could be that their situation and use of the car would make it very difficult to follow an ideal routine, but no harm having guidelines.

Is there a SOC limit below which it is always 'safe' to charge consequence free?
Is there any benefit setting charge rate to some low level and leave the car on charge for extended periods? Would any such benefit be confined to certain SOC limits?
On a scale of 1 (pointless) to 5 (potentially very worthwhile in some cases) how beneficial could it be to leave a car with a problem battery regularly left plugged in on ac charge?
If / when fastest possible supercharging is not important, could it be beneficial (or detrimental in any way) to make a point of not allowing the battery to preheat before supercharging? Dependent on current battery temp?
Is there a 'sweet spot' combination of changing values / settings that would stand the best chance of bringing a problem battery back into balance?
Do we have values for the brick SOC delta after charging that flags concern?

 

[Battpower]

I couldn't find more plots like this:

(from @DJRas )

Comparison of this plot between different bricks, vehicles and different charge currents might be interesting.

 

[David99]

I think we have to keep different issues separate. The charge limit that Tesla has administered to an unknown number of cars is one issue. Battery packs going out of balance is a completely separate issue. Both issues happen to older battery pack so they show up at the same time but they are most likely not related to each other. I don't have official data, but from reading here over the years, packs that had bad imbalances are the ones that got swapped out under warranty. This has happened long before the batterygate issue. My range declining rapidly seems to be happening in the same way my imbalance increases. So my theory is that's the issue. Yesterday I actually saw an error message in my car that said "imbalance-something-something" so I know that's an issue. I guess the service technician that did a remote diagnostic on my car a few months ago was correct. I dismissed it back then but he probably saw it better than I could.

 

[Battpower]

My range declining rapidly seems to be happening in the same way my imbalance increases.

I think that is a key point in line with the discussion.

The charge limit that Tesla has administered to an unknown number of cars is one issue.

I think this is a necessary protection that could linked to the cause of the imbalance. I think the plot from @DJRas is relevant too.

 

[David99]

Imbalance causes capacity/range loss. The artificial voltage limit also causes capacity/range loss. The effects are the same but the causes and root issues are very different. The imbalance makes it impossible to fully charge the lower bricks. The 'weakest link' determines the entire pack's capacity as a result. It's not just a matter of equalizing the cells. The BMS would do that if it was possible. The pack goes out of balance if one cell/brick has degraded more than others. It cannot hold as much energy as the others, thus is will reach peak voltage sooner than the others. Even if it BMS is now indirectly charging the other cells/bricks to the same level, the weaker cells/brick would run out of energy faster than the others during discharge and the battery pack needs to cut off once the weakest cell/brick is at the cut off point, even if all the others still have energy left. No matter how you approach is, the pack is now limited by the weakest cell/brick in the entire pack.

The artificial limit by Tesla is a protective measure to prevent bad things from happening. It can be undone if Tesla decides to do so. When they find ways to better understand and deal with the underlying issue, they might and probably will. Cell imbalance due to degraded cells is irreversible.

That's why I'm saying these are different issues and need to be kept separate even if some packs have to deal with both at the same time (like my pack).