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Wiki Sudden Loss Of Range With 2019.16.x Software
- Thread starter Dutchmeeuw
- Start date
islandbayy
Active Member
Usually, but lately they try to weasel their way out of it by saying it's just a estimate.
Ah. OK, that one we've seen several times on both forums. If the battery suddenly loses about 20-some rated miles, that is about the amount of one brick of cells inside the pack that has stopped working, and Tesla can diagnose that pretty easily.
Mucall
2013 Model S 85
The pack has a combination of series and parallel aspects to it. I forget the details of which sections are which, but I think it's like each brick is made up of a lot of individual cells wired up in series to make a higher voltage, so yes, one cell going out would stop that chain and mess up that brick. But then all of the bricks are connected in parallel, so one brick can stop, but the others will still be providing the same voltage level, but with less amp capacity. This aspect of series/parallel is a good method to leave some fault tolerance, so part of it can go out, while still leaving some basic reduced functionality, instead of the whole thing going out from one small failure.
You've got it backwards. Cells in a brick are wired in parallel, then the bricks are all wired in series. If an entire brick failed your pack would be completely dead. (Unless the brick somehow shorted out, which I don't think would be possible without then resulting in blowing all of the fusible links in that brick.)
Perhaps I did; I wasn't sure which way it was.
Except that's not what happens. I've seen this reported and fixed for several people. One brick dies, and the pack suddenly loses about 20-some rated miles, but the car still functions normally. So, I don't know how that is being handled. Maybe they have something that can bypass a dead brick if it goes out?
Not [realistically] possible imo. I suppose a pack left sitting near dead or with a very low brick voltage could theoretically end up with a dead brick, but since that brick would be in series with other bricks that would have suffered similar punishment, I doubt the pack would remain viable.
A whole brick can't 'die' and leave the pack useable except may be by failing to dead short. If it went open circuit (which would be an interesting / ?impossible? outcome) then the pack would be dead.
That leaves a question regarding why common 20 mile (ish) range loss, but that would need supporting evidence.
I don't specifically know or care how it is dealt with, but this is a fairly well known event, and it does happen this way.
What can happen is that a number of cells in a brick get weak, or internally short out. If they short out it could trigger the fusible link to disconnect them from the brick. Making that brick weak, and then it will discharge faster than the rest of the bricks reaching the minimum voltage first, making the remaining charge in the other bricks unusable.
So it isn't that a brick fails it is that a brick gets weak/loses some cells that causes the drop in available range.
Although, iirc, @wk057 said he had never seen those fuses blown. If an individual cell did go short, then it would certainly blow its individual fuse.
I expect uneven cell aging and increased mismatch would have same effect as dropping an individual cell.
Interesting if akind of gradual battery issue could cause a similar sudden range loss over a number of cars. (unlike software induced change).
well, the NHTSA are finally doing it. They are opening a PE, a Preliminary Evaluation into battery fires . .
. . for the Chevy Bolt.
2020 CHEVROLET BOLT EV 5 HB FWD
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In most cases, the range loss is a product of software manipulation. In other words, if you go back on older software, the pack charges to full range again. Now, there is a physical issue in those packs that may cause problems, but that is not where the initial range drop comes from.
No, you're not getting it. I am talking about something entirely different. This is not "initial range drop". I'm talking about cars that are years old, stable rated miles, and all of a sudden, one day out of nowhere, it's about 25 rated miles less instantly. And when taken to the service center, they test the battery and confirm that one of the bricks inside it has died, and the battery needs to be replaced while they send it in to California to get it fixed. This had happened several times, but I am talking about on the S and X, this is a possibility. With the redesigning of the packs for the 3 and Y, that may not even be applicable anymore--don't know.
As you said, the reason is secondary to the fact that it happens. Even so, it is useful to link together as many pieces as possible. Only explanation I can come up with atm is the software detects conditions in a battery such that they reduce the battery capacity pending investigation of the 'fault'.
I have seen no evidence nor can see a 'failure' such that one brick would (or could) just drop out of the battery completely. But no reason that software couldn't drop capacity by imposing limits in response to some condition or other .... that could well relate to 'sudden loss'.
The original 85kWh battery has 7104 cells, in 74p96s config (74 cells in parallel x 96 in series), in 16 modules. Each module is 74p6s, or ~ 22V, ~250Ah nominal. 16 modules are wired in series for 355V nominal (@ 3.7V/cell). It's all in wk057's teardown thread - Pics/Info: Inside the battery pack
If you lost a single cell in a parallel group (ie, fuse wire blew), you'd loose 1/74th of the groups capacity, and 1/74th of the module, and 1/74th of the whole pack, since Ah rating is determined by the weakest "virtual cell" (ie, 74p grouping). 1/74th is 1.4%, or around 3.6 miles. I'm not sure what sudden event could cause a 10% drop; you'd have to loose several cells at once. But I do have vague memories of this being discussed.
If you lost a single cell in a parallel group (ie, fuse wire blew), you'd loose 1/74th of the groups capacity, and 1/74th of the module, and 1/74th of the whole pack, since Ah rating is determined by the weakest "virtual cell" (ie, 74p grouping). 1/74th is 1.4%, or around 3.6 miles. I'm not sure what sudden event could cause a 10% drop; you'd have to loose several cells at once. But I do have vague memories of this being discussed.
I notice @Dave EV doesn't seem to like hearing about the brick failure for some reason. Why does this bother you, that you keep marking disagree on it?
Brass Guy
Active Member
Hmph - I just lost ~20 miles all of a sudden, and still on V8. So relevant to recent posts, but OT for this thread.
I would think it could be quite on topic. What would be clearer would be to know directly the loss of capacity and max cell voltage.
Probably just semantics. It is going to be a brick going bad / failing, in so much as its characteristics change, and then software makes a step change (likely to protect the weak brick) that gives the significant overall capacity drop.
Only difference being that the change isn't down to the brick ceasing to be part of the battery.
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