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As in using thousands of individual cells in stainless steel cans? That's all there was available in their beginning.
You are misinformed.
Wasn't it later that the individual fusible links were part of this design? What other 'fail-safe' do they have?-
I don't know the history of the fusible links. As I understand things, the primary fail safe was a heat absorbent between the cells.
 

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I was thinking about this notion that as Tesla goes to a larger form factor cell, it will have to come up with a new and better, or at least more advanced fail safe.

First things first -- what is the volume increase in the 4680 compared to the the 2170 ?
The radius is 46/21 = 2.19x so that adds 2.19*2.19 = 4.8x
The height is 80/70 = 1.432x
And together, 1.432*4.8 = 6.87x more volume and thus more energy per cell

Sounds like a big hurdle, but if I understand correctly current Tesla packs have six 2170 cells in parallel. If that parallelism is removed in packs with 4680 cells then the net increase in energy per node is 1.145x, or about 15%. That certainly sounds like only an incremental change in what they already have will suffice.
 

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-'engineered a fail safe'?
As in using thousands of individual cells in stainless steel cans? That's all there was available in their beginning.
Wasn't it later that the individual fusible links were part of this design? What other 'fail-safe' do they have?-

-But isn't there going to be pouch cells in some future Tesla?
No pouch cells in Tesla. The fail safe is the smaller cylindrical cells spaced just right assembled in fire retardant material. This prevents a chain reaction from one cell failure causing the entire car to be in flames.
 

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No pouch cells in Tesla.
I think NC was referring to this:

Did Tesla change their mind about that or was that report wrong?
 

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I think NC was referring to this:

Did Tesla change their mind about that or was that report wrong?
Thanks. I was not aware the the LFP batteries were pouch type. Tesla must feel the LFP chemistry is a lower risk of fire.
 

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Prismatic cells are NOT pouch cells. They are closer to a cylindrical cell, but in a rectangular packaging.
OK, rectangular cylinders. Got it... ;-) ;-) ;-)
Quick google search found this:

Sounds like prismatic are closer to pouch than cylindrical to me...
But I wouldn't listen to me... ;-)
 

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Prismatic cells are NOT pouch cells. They are closer to a cylindrical cell, but in a rectangular packaging.
Are the Bolt batteries Prismatic or pouch?
My point is that pouch or prismatic module construction does not include a fail safe construction where cells are spaced and insulated with fire retardant to prevent a chain reaction. One could probably do that with pouch and prismatic cells but the energy density of the battery pack would be reduced. Tesla and Rivian are building cylindrical cells into modules with adequate spacing and fire retardant “goo” that prevents one cell failure from creating a chain reaction.
 

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I think NC was referring to this:

Did Tesla change their mind about that or was that report wrong?
Apparently, LFP battery chemistry is an order of magnitude less likely to experience a cell failure than the NMC battery chemistry used in the Bolt cells. Tesla must have decided the risk was low enough to use prismatic/pouch construction. This is a significant shift from their past cylindrical cell construction.
 

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Tesla packs have six 2170 cells in parallel. If that parallelism is removed in packs with 4680 cells then the net increase in energy per node is 1.145x, or about 15%.
One would think that keeping parallelism is key to increased safety at the C rates of EVs for most of these cells. Decrease that and increase cell stress. Everyone’s going for cell density & cycle longevity because of the public’s (stupid) desire for crazy long ranges and the need for a “million mile” battery. Fun marketing, but silly in the real world for most.

I remember the excitement of A123’s C rate when they first came out. Holy crap could they kick out power. Too bad they screwed the pooch business-wise. Used to harvest DeWalt nano cells for my old ebike builds. Next favorite was Sony Konions from Makita packs… so stable you didn’t even need a BMS with those. They just stay balanced no matter what you threw at them. Anyways… parallel = good. :)
 

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I still think that they rushed the folding process in an attempt to increase production numbers. In theory, the folding process should be fine if the machines are aligned and they moving slowly enough.
So how often were they rushing? Would needing to replace 40,329,000 cells lead to conditions where rushing would occur? If related to running the machines too fast I think that this would happen more often (though we don't know how often it is actually occuring). We are not confident in LG providing us defect free cells told us a lot.
 

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Are the Bolt batteries Prismatic or pouch?
My point is that pouch or prismatic module construction does not include a fail safe construction where cells are spaced and insulated with fire retardant to prevent a chain reaction. One could probably do that with pouch and prismatic cells but the energy density of the battery pack would be reduced. Tesla and Rivian are building cylindrical cells into modules with adequate spacing and fire retardant “goo” that prevents one cell failure from creating a chain reaction.
They are pouch, which are soft covers and require compression but also movement for expansion. Prismatic, like cylindrical, don't have this requirement. Of course Tesla spaces the cells a bit for cooling and fire risk reduction. The same could be done for prismatic or pouches. Larger pouches with larger surface area are harder to mitigate the risks. Also, pouch cells swell when going bad so they press against adjacent cells, making the situation worse.
Tesla cells are lower energy density to begin with, due to being cylindricals. Yet they manage to do fire risk suppression too, despite lowering pack energy density even further. Maybe that shows where their priorities are?
 

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Tesla cells are lower energy density to begin with, due to being cylindricals. Yet they manage to do fire risk suppression too, despite lowering pack energy density even further. Maybe that shows where their priorities are?
What do you mean by 'low energy density' ? Measurement units would help here, along with some values. So far as I know, Tesla has the highest gravimetric energy density of all automakers; and in terms of volumetric energy density, the only time I have read of space restricting design was LFP in the Model 3/Y
 

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One would think that keeping parallelism is key to increased safety at the C rates of EVs for most of these cells.
Why ?

The only major advantage I know of (and I don't know much) for parallelism is reduced internal resistance, but the 4680 cell has made great strides in that area with their multi-tab design**, so perhaps they can get away with less parallelism.

** 4680 EVs are expected to charge some 20% faster than 2170 based models due to the reduced internal resistance.
 

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The only major advantage I know of (and I don't know much) for parallelism is reduced internal resistance, but the 4680 cell has made great strides in that area with their multi-tab design**, so perhaps they can get away with less parallelism.
Well... from what little I understand haha... volts = speed and amps = torque... more parallel = more torque with less stress on the cells... on the other hand more voltage = less amperage needed at speed once you're there so... anyways... in the Bolts (on my '17) the max C rate is 2.5C (150kW/60kWh). In normal everyday driving you're not sustaining 150kW discharge obviously so it's a non-issue. I'm quite sure they limited the 55kW charge rate to maintain a <1C charge rate. At speed you can regen in L with ROD paddle and sustain 70kW... for a few seconds until you're stopped, which is >1C, but not by much and not for long. Bolts are 96S3P obviously so that added parallelism reduces stress/adds capacity. Parallelism = good. The A123 cells I was mentioning could discharge like 30C sustained per cell without breaking a sweat, which was pretty amazing. I've actually always been a fan of more voltage vs more amperage because volts tickle and amps kill... I mean... you know... depending on a lot of things haha.

At the end of the day... don't listen to anything I'm saying as it's probably all incorrect anyways haha, but I'll stick by "parallelism = good" at least.
 

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Finally some good news - it looks like GM will be replacing all battery modules in higher risk Bolts starting in the next week or two.

Read on for full details:


What do you think? Is this enough? What else can GM do to make us whole? Let me know in the comments.
Have not heard that one yet. I have a 2020 Bolt EV Premium. Did receive an email with letter from VP of Chevy telling owners what they should do until a fix is in place:
1) Don't charge over 90% 2) Don't discharge to under 70 miles 3) After charging, park outside and do not charge overnight with vehicle parked inside.

I was a little confused about what they meant by parking outside after charge. In other words, always park outside or leave outside for a few hours after the charge. So I called the dealer and their interpretation was leave outside for a short period of time. I then called the BOLT EV Chevy Customer Service and he said they prefer the vehicle be parked outside all the time. So I requested a buy back and they have sent me an email to respond to with all the appropriate documents.

We really don't want to give up the car, but if it is not safe to leave it parked in the garage, then is it really safe to drive?

Am I over reacting? Is the 2020 Bolt that affected? Or is Chevy just covering their rear ends? Open to inputs.
 

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Have not heard that one yet.
That information was accurate when it was posted 24 days ago.
Unfortunately a lot happened since then...

Is there a risk of fire? Yes.
Is it very small? All signs point to yes.
There has been only one reported instance of a car having problems while driving and the driver had plenty of time to pull over and get safely out of the car...

So, it is much safer to drive than to have it sit, assuming you drive less than the car sits. ;-)
 

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Have not heard that one yet. I have a 2020 Bolt EV Premium. Did receive an email with letter from VP of Chevy telling owners what they should do until a fix is in place:
1) Don't charge over 90% 2) Don't discharge to under 70 miles 3) After charging, park outside and do not charge overnight with vehicle parked inside.

I was a little confused about what they meant by parking outside after charge. In other words, always park outside or leave outside for a few hours after the charge. So I called the dealer and their interpretation was leave outside for a short period of time. I then called the BOLT EV Chevy Customer Service and he said they prefer the vehicle be parked outside all the time. So I requested a buy back and they have sent me an email to respond to with all the appropriate documents.

We really don't want to give up the car, but if it is not safe to leave it parked in the garage, then is it really safe to drive?

Am I over reacting? Is the 2020 Bolt that affected? Or is Chevy just covering their rear ends? Open to inputs.
If my LT was a 2020 I don't think I'd be especially worried even though there have reportedly been a few fires and the LG factory in Michigan presumably uses the same technology that was in the Korean plant that produced most of the batteries that have caught fire. Unfortunately, my car is a "Korean" 2019 that was manufactured within a few weeks of a disproportionate number of the cars that have caught fire, and which was included in the priority "high risk" group that was prioritized for battery replacements before that program was suspended.
 
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