New Pack Architecture that is Likely Used in P100D and New TE Products

[hickin]

I had the same question about the 18650's... it almost feels odd to change them at this point given how close we (assume) we are to the 2170's coming online.

I wonder if this implies either: the P100D's have secretly had 2170's all along, or that Tesla expects 18650's to be used for the foreseeable future in some applications.

Is it wrong to hope somebody wrecks one so we can get a salvage teardown soon?

Yes, it is wrong to hope someone gets in a car accident so your curiosity about a car battery can be satisfied.

 

[sandpiper]

Probably we all agree that the topic of this thread, the new pack architecture, thanks to vgrinsphun, is a major advance in practicality and cost effectiveness, not to mention both charging and discharging velocities. Now we wait to find out all the other nice advances we'll soon hear about.

And production cost/efficiency. There's likely a lot of hand labour in the production of the old modules. This design is well optimized for automated production.

 

[vgrinshpun]

My knowledge of this field of electronics is experiential only; not academic. With that, I would suggest that the "circuit breaker" function of wire welding (prior) or spot welding (as Vlad's assumption) is absolutely suboptimal* and could more elegantly, effectively and cheaply be done through pre-formed breakers - such as they are - for every single cell, within the flexible printed board.

*suboptimal is the polite word. Insert your own alternative

I am not sure I follow this. The fuse is inherently cheaper than a breaker as it is disposable, i.e. is not capable of being reset. The cell protection application does not require a reset, as defective cell need to be permanently removed from the circuit. So use of circuit breaker is not needed. If they found a way of precisely calibrating the spot weld to serve as a fuse (and presumably they did), it is hard to imagine a more elegant and inexpensive solution (weld needs to be there anyways).

 

[LargeHamCollider]

The bottom line to me, that all of this boils down to the "velocity of innovation".

I like this term "velocity of innovation" I've been using "rate of improvement" to describe to friends what is, for me at least, a primary reason for maintaining my stake in TSLA. It seems quite clear at this time that Tesla is improving their products far faster than any competitor.

And diameter.

Increasing diameter will have a very limited, if any, impact on pack capacity. Max circle packing density doesn't change with increasing cell diameter, in fact the voids at the edges of the pack will increase slightly in size as diameter increases so increasing diameter may actually reduce pack density slightly. The only guaranteed capacity improvements going to 2170s comes from increased cell height. We're hoping for improved chemistry but that is not guaranteed.

The evidence of this is circumstantial, but I think that the secret of the lower interconnection resistance is due to welding of the terminals to the conductive layer (plate) in the flexible printed circuit, rather than spot welding individual wires to the terminals and to the current collecting busses inside the pack.

I was also wondering how they got rid of the individual wires if they were providing the individual cell protection. My assumption that this role is now played by spot welds between the conducting layer of the printed circuit and cell terminals.

I've been wondering about this too, do you think it's possible that Tesla has had such low rates of cell failure that they're simply not worried about individual cell failures at this time?

 

[JRP3]

The evidence of this is circumstantial, but I think that the secret of the lower interconnection resistance is due to welding of the terminals to the conductive layer (plate) in the flexible printed circuit, rather than spot welding individual wires to the terminals and to the current collecting busses inside the pack.

The wires were sized so that their resistance value worked as a fuse. Lowering the resistance, or the resistance of any other component working as a fuse, means they would be a higher current fuse.

I am not sure I follow this. The fuse is inherently cheaper than a breaker as it is disposable, i.e. is not capable of being reset. The cell protection application does not require a reset, as defective cell need to be permanently removed from the circuit. So use of circuit breaker is not needed. If they found a way of precisely calibrating the spot weld to serve as a fuse (and presumably they did), it is hard to imagine a more elegant and inexpensive solution (weld needs to be there anyways).

I'm guessing Audubon feels this to be unlikely, and I'm inclined to agree. I think a board trace can be more accurately and consistently calibrated as a fuse. I'm not sure Audubon means an actual resettable breaker.

 

[JRP3]

Increasing diameter will have a very limited, if any, impact on pack capacity. Max circle packing density doesn't change with increasing cell diameter, in fact the voids at the edges of the pack will increase slightly in size as diameter increases so increasing diameter may actually reduce pack density slightly.

Only if the cell edges are in contact, which they are not in the existing packs because of the cooling tubes. But yes you are technically correct.

*Actually if we assume this new pack architecture is being used in the 100 packs with the 18650 cells then my statement is incorrect.

 

[Vitold]

I am not sure I follow this. The fuse is inherently cheaper than a breaker as it is disposable, i.e. is not capable of being reset. The cell protection application does not require a reset, as defective cell need to be permanently removed from the circuit. So use of circuit breaker is not needed. If they found a way of precisely calibrating the spot weld to serve as a fuse (and presumably they did), it is hard to imagine a more elegant and inexpensive solution (weld needs to be there anyways).

I think what he means is that for weld being a fuse is too much to ask as it's opposite to what the weld supposed to do (provide mechanical and electrical connection).

 

[vgrinshpun]

I like this term "velocity of innovation" I've been using "rate of improvement" to describe to friends what is, for me at least, a primary reason for maintaining my stake in TSLA. It seems quite clear at this time that Tesla is improving their products far faster than any competitor.

No wonder -it was coined by Elon.

I've been wondering about this too, do you think it's possible that Tesla has had such low rates of cell failure that they're simply not worried about individual cell failures at this time?

I personally think that it would be unwise - with the amount of energy stored and a threat of heat runaway, I do not think they would skip on ability to remove shorted cell before it causes bigger trouble.

 

[MitchJi]

*Actually if we assume this new pack architecture is being used in the 100 packs with the 18650 cells then my statement is incorrect.

No. The increased capacity due to the increased diameter of the individual cells is exactly matched by the decrease in the number of cells that will fit in a given area.

 

[vgrinshpun]

The wires were sized so that their resistance value worked as a fuse. Lowering the resistance, or the resistance of any other component working as a fuse, means they would be a higher current fuse..

Sure, but my assumption that improvement comes from the lower overall resistance of the current collecting infrastructure, not cell connections to it - it is easier spatially to do with the printed circuit than busses/cables

I'm guessing Audubon feels this to be unlikely, and I'm inclined to agree. I think a board trace can be more accurately and consistently calibrated as a fuse. I'm not sure Audubon means an actual resettable breaker.

Ah, that makes sense now. My electrical engineering background is in power as in auxiliary power systems in power plants (mostly), so breaker for me is protective device that is able to be reset.

 

[MitchJi]

An finally forth, the new architecture requires new suppliers, bot for heat pipes and flexible printed circuit. Once again it is beneficial to work out these new relationships on a lower volume platform before the mass produced M3.

Tesla might manufacture them.

170s comes from increased cell height. We're hoping for improved chemistry but that is not guaranteed

Elon said that the cells produced at the GF would have not big, but not small improvements due to cell chemistry changes.

 

[AudubonB]

I misused the word breaker....or rather, should have written "single use breaker". I.e., a fuse. But as JRP3 more elegantly wrote, it ought to be able to be more accurate and precise within the board.

 

[JRP3]

No. The increased capacity due to the increased diameter of the individual cells is exactly matched by the decrease in the number of cells that will fit in a given area.

Right, which is why I said my statement was incorrect, i.e. that since, (presumably), the original cooling tubes are not used in the 100 packs then my statement that the cell edges were not in contact is wrong, which would make LargeHam correct.

 

[ggr]

And diameter.

The diameter is bigger, but doesn't help you get noticeably more capacity, since the packing loss for cylindrical cells is a constant percentage independent of that size. They do gain a bit by not having the cooling ribbons, but that too doesn't depend on the diameter.

 

[zdriver]

That looks similar to what a bare cell looks to me (below is an unwrapped Panasonic NCR18650B). I don't think that is necessarily the top terminal version (or at least a special version; you can somewhat use existing cells as "top terminal" given the body is already negative, while the middle button on top is positive).

Correct - all 18650's I've ever encountered are made this way, and always have been. As someone who used to take apart laptop batteries for fun and to salvage the 18650's for projects, you learn pretty quickly to tape/cover/rewrap a cell with a cut in the wrapper on the positive end...

 

[RichardL]

One thought that occurs to me - currently the cooling tubing in the older packs is hand assembled after machine places the cells in the pack. Using this new layout would remove that manual step during pack production.

 

[LargeHamCollider]

Elon said that the cells produced at the GF would have not big, but not small improvements due to cell chemistry changes.

All these little changes are really adding up, assuming a 5% chemistry improvement in the 2170s puts an MS/X 2170 pack at about 140% the capacity of the original MS pack.

 

[FlatSix911]

Very interesting!

 

[jbcarioca]

...
I've been wondering about this too, do you think it's possible that Tesla has had such low rates of cell failure that they're simply not worried about individual cell failures at this time?

Definitely NOT! Despite the various techniques Tesla uses to isolate a failed cell and defend against thermal runaway propagation, they adopted an obsessive approach to test every single cell in production, after production completed, prior to installation in packs, and after installation in packs. Complete historical documentation of every single cell performance is maintained. Following pack installation performance monitoring is different.
source: 2013 testimony of Ms. Celina Mikolajcak, Seniot Manager, Cell Quality and Battery Technology, Tesla Motors (then and now)before the NTSB hearing on li-ion Batteries in Transportation. (The testimony was summarized publicly but I made detailed notes during sessions. This information was in my notes.)
At the time Tesla was the only manufacturer/OEM user that had adopted such exotic approaches, including the BMS and continuous pack/subpack performance monitoring. Theoretically somebody else might have done that but there was no indication of such during the sessions which included several major li-ion manufacturers and technical experts.
Also at the time Tesla was the only OEM that had never had an in-field thermal runaway that propagated beyond physically ruptured cells. Tesla had managed to induce thermal runaway of a non-ruptured cell in test conditions by purposely defeating internal cell protections.
Since that 2013 testimony Tesla has had a handful of fires, all very well covered. Because of the inherent instability of li-ion the Tesla quality, BMS and monitoring obsession continues. Ms. Mikolajcak continues in her role.

This thread is further clear evidence that Tesla continues to advance beyond other automotive competitors. Use of heat pipes is well established, to be sure, but apparently not on anything like the scale Tesla has deployed.
The 'virtuous cycle' continues, as each innovation sparks others, now at an accelerating pace.

 

[-=buzz=-]

All these little changes are really adding up, assuming a 5% chemistry improvement in the 2170s puts an MS/X 2170 pack at about 140% the capacity of the original MS pack.

Are you comparing to the original 85KWh-pack? For that I get ~133% from 17.6% (85->100)+7.7% (height)+5%(chemistry)