Model S Battery internals question

[Trev Page]

HI folks, I'm new here. Big fan of Tesla and I wish I could afford a Model S but I'm waiting for the mass market car which I think will work for me.

I have a question about the battery pack for the Model S. I don't think anyone has actually seen in the internals yet but I've heard Elon state they use modified 18650 model Panasonic batteries. I'm just curious as to why they would chose batteries in a cylindrical form factor instead of a a newer flat-pack form factor. Seems to me that form factor has a lot of wasted space between the batteries. Or is this space used for the cooling system? Does anyone know how the cooling system works? Are the batteries bathed in an inert cooling fluid or are heat sinks involved?

I mention the flat-pack battery form factor because this is what Apple uses for their Lithium batteries in their MacBook laptops. See a video here how they are made and designed

 

[mnx]

It's all about cost IMO. 18650 are much cheaper at this point. I'll let others comment on how the pack is assembled.

HI folks, I'm new here. Big fan of Tesla and I wish I could afford a Model S but I'm waiting for the mass market car which I think will work for me.

I have a question about the battery pack for the Model S. I don't think anyone has actually seen in the internals yet but I've heard Elon state they use modified 18650 model Panasonic batteries. I'm just curious as to why they would chose batteries in a cylindrical form factor instead of a a newer flat-pack form factor. Seems to me that form factor has a lot of wasted space between the batteries. Or is this space used for the cooling system? Does anyone know how the cooling system works? Are the batteries bathed in an inert cooling fluid or are heat sinks involved?

I mention the flat-pack battery form factor because this is what Apple uses for their Lithium batteries in their MacBook laptops. See a video here how they are made and designed

 

[W.Petefish]

They use the extra space to allow for cooling and thermal management. The way I understand it, the batteries are inside aluminum tubes and there is some sort of thermal mitigation medium that enhances thermal transfer. The medium is then cooled by a liquid that is piped through the battery pack. The liquid is then cooled/heated by a heat exchanger.

Other space in the battery pack is taken up by sensors and safety equipment which is interconnected by a central CAN bus that links the battery to the VMS.

 

[vfx]

I like to point out Tesla is really downplaying the cells in the battery pack this time. I'm sure it's partly old news with the Roadster tech but I think Telsa is just going for the "It's a (regular) car" sales tactic.

Not any portable device talks about how many cells are in it's battery pack. It just works!

 

[ElSupreme]

Yeah cost and production capability and flexibility with chemistry without changing the external configuration. GM and Fisker both ended up putting their flat packs into a weird column through the center of the car also. With the small form factor Tesla can make the battery pack whatever size it wants.

 

[wycolo]

> I mention the flat-pack battery form factor because this is what Apple uses for their Lithium batteries in their MacBook laptops.[Trev Page]

'Flat' until they swell up like a dead pig in the hot sun. Both of my MBPs did this. "The replacement period ended 30 days ago". So mine were just slightly slower to go tits up than all the others? [@wycolo very sorry for attitude presented here & apologizes profusely].
--

 

[Todd Burch]

My understanding was that Apple batteries also use a different Lithium Ion battery chemistry (LiPo?) that allows for shaping the cells into just about any form factor. These batteries may have good characteristics for small devices, but they are clearly not preferable in the case of Tesla's drivetrain.

 

[bob_p]

Do we know how this battery system will degrade over time? Will the degradation be uniform? Or is it possible much of the degradation might be isolated to individual bricks (and possibly individual batteries)?

If the much of the degradation could be isolated to individual bricks or batteries - that could help to extend the life of the battery systems, and reduce the risk of getting a bad battery system if there is a possibility to do quick battery swaps.

Is there anything published so far about how the Model S battery system performs and degrades?

 

[Robert.Boston]

On the Roadster, Tesla sometimes replaces a "sheet" in the battery. Presumably the Model S uses a similar modular approach.

 

[iridium]

A few things I recall from chatting with a sales rep a while back. First, all of the battery packs weight the same, even if they have to add ballast. This is so the car weight is the same from crash testing. Second, the different between the 230 and 300 mile packs is chemistry... everything else is the same.

 

[tomanik]

A few things I recall from chatting with a sales rep a while back. First, all of the battery packs weight the same, even if they have to add ballast. This is so the car weight is the same from crash testing. Second, the different between the 230 and 300 mile packs is chemistry... everything else is the same.

I've seen this comment posted before and I find it hard to believe that they need to crash test the car because it weighs differently. Even if they did you would think dropping 10 to 15 percent in weight for the smaller pack vehicle would be worth the efficiency gain for Tesla. Guess we will se in a couple of months when the 60kwh and 40kwh versions come out.

 

[ckessel]

I've seen this comment posted before and I find it hard to believe that they need to crash test the car because it weighs differently. Even if they did you would think dropping 10 to 15 percent in weight for the smaller pack vehicle would be worth the efficiency gain for Tesla. Guess we will se in a couple of months when the 60kwh and 40kwh versions come out.

Since the battery is part of the structural integrity, I'm not surprised any change to its weight/structure would require retesting.

 

[jkirkebo]

Since the battery is part of the structural integrity, I'm not surprised any change to its weight/structure would require retesting.

So is the pano roof and that too have a different weight than the solid roof (pano weighs more).

 

[ckessel]

So is the pano roof and that too have a different weight than the solid roof (pano weighs more).

Well, one, they might have had it tested with both types of roofs. Second, the roof might not be part of the structural integrity, but rather the boron pillers and bits that protect on rollover.

 

[W.Petefish]

Well, one, they might have had it tested with both types of roofs. Second, the roof might not be part of the structural integrity, but rather the boron pillers and bits that protect on rollover.

I asked about that very thing at the Oct 2011 Fremont event (Beta reveal). I was told there is no difference in structural integrity.

 

[wycolo]

> the difference between the 230 and 300 mile packs is chemistry... everything else is the same. [iridium]

?? An 18650 is an 18650, at least from the same production era.
--

 

[W.Petefish]

> the difference between the 230 and 300 mile packs is chemistry... everything else is the same. [iridium]

?? An 18650 is an 18650, at least from the same production era.
--

No. The 18650 is a form factor. They can be made of different chemistries. The ones that I can buy are LiFePO4, the ones in the roadster are LiCo.

 

[Eberhard]

They are LiNiMgCo

 

[W.Petefish]

Thanks. :redface: