Model 3 pack configurgtion speculation

[scaesare]

So THIS ARTICLE makes a few interesting claims:

-60kWk base pack, 75kWh upgrade capacity
-Only 4 modules (assumed 60, implies 5 modules for a 75kWh pack?)
-Modules made up of 7 sections

So a few assumptions for the sake of this speculation:

-The model 3 packs of this size will operate at similar max voltage as their model S counterparts (~350V), meaning existing superchargers, etc... will remain compatible...
-The "section" in a module is also a set of parallel cells in series with other sections
-Cell voltage is max 4.2v

So, if that article is taken at face value, that would be 4 modules of 7 sections, for a total series pack voltage of only 118V. Seems unlikely.

If it were 8 modules as per the original presentation renderings, with 7 sections per module that would still only be 235v. Still seems low.

It would take 12 modules of 7 sections to hit 353 volts.

A 10 module/7 section pack would be 294v. That might be reasonable, but 10 modules matches neither rendering nor that article description.

I have to question the validity of that article, or my assumptions are way off...

 

[JeffK]

AFAIK voltage in the higher end Model S models is 400 V the lower end ones were 350 Volts if I'm not mistaken.

 

[scaesare]

I believe the 60 and 75kW packs both have only 14 out of 16 possible modules in the pack, hence they are 350v packs. That's why I'm using that as an assumption here.

the 85/90/100 packs are 16 module 400v packs... but those size options are not believed to be available for the Model 3.

 

[JeffK]

It's also strange that it says four modules because both prior speculation and the graphic during launch showed eight modules...

 

[Zaphod]

It's also strange that it says four modules because both prior speculation and the graphic during launch showed eight modules...

Depends on how modules are defined. The two cell groups could be considered a module, hence 4 not 8.

 

[Bokonon]

It's also strange that it says four modules because both prior speculation and the graphic during launch showed eight modules...

... unless each "module" is actually a "strip" of two blocks in the diagram behind Elon. That would match up with the four blocks shown in the S-versus-3 comparison.

Given that we've already identified some mathematical strangeness and inconsistency in the assembly-process numbers from that same article (likely because they are being conveyed second-, third- or fourth-hand), it wouldn't shock me if the number of modules was lost in transaction as well. My guess, though, is that the arrangement of the cells isn't as simple as @scaesare's assumptions suggest.

Or at least that's my hope... I sure as heck don't want to supercharge at 118v/235v.

 

[scaesare]

Thanks for posting the rendering @JeffK ... I couldn't locate it in the limited time I had to look a bit earlier.

The issue of assuming that 2 of the "blocks" (or cell groups) in the rendering comprises one module is the description in the article that a module has 7 sections. That odd number can't be split across blocks easily.

If you assume each block has 7 sections of it's own, then we are back to the "8 sets of 7 sections = 235v" scenario. Not to mention there would seem to be no distinction between a "block" in that rendering and a "module" from the article that I could see. In which case the article and rendering are again at odds.

The other thought I had is that there also could be an as-of-yet unannounced chemistry change that implies higher cell voltages.

A cell voltage of 5v would render an 8-module / 7-section pack voltage of 280v. If you moved to 6v cells, it's 336v. I don't know of any chemistries in that range that would meet the rest of the automotive usage criteria...

The other issue is that 60 and 75 packs for the Model S had the same # of modules, and hence voltage. They just had fewer cells in parallel per section. It will be interesting to see how they accomplish it on the Model 3...

 

[GregRF]

I believe the model S modules are 6s/72p, 16 modules making a complete pack of 96s/72p.

If they are reducing the module count, I'm guessing they will up the series count to compensate. For 4 modules they would need 24 in series (but that is not divisible by 7), so perhaps 21 in series per module and 3s per section? That would get you a 350V pack.

 

[scaesare]

The 350v Model S packs are actually 14 modules, making them 84s packs.

The idea that a "section" in that article is actually some group of a 3-series-cell arrangement, and hence "7 sections" equates to a 21s module. That would give you an 84s arrangement from 4 such modules. Interesting thought @GregRF

It still doesn't explain the different layout we see in the render... but it's the one explanation for 4 modules of 7 sections that makes sense. It's odd that they would define a "section" as being some arbitrary 3 cell-goups in series though. Unless it's a manufacturing/packaging thing, rather than an electrical design consideration.

 

[GregRF]

Further baseless speculation:

What if the modules are no longer in series, but now in parallel? Each module may be ~400V, which would make it much easier to have different pack configurations, 4 modules vs 5 would be as easy as bolting an extra one into the busbar, none of this missing cells nonsense.

In that case each module may have 7 parallel sections of 96 cells in series. Four module pack would have 96s/28p, five module 96s/35p. (2688 cells for 4 module, 3360 for 5 module).

Cell count sounds a little small for the 46% in cell volume over the 18650s, but perhaps new chemistry makes up the rest of the gap.

 

[Lysol]

Further baseless speculation:

What if the modules are no longer in series, but now in parallel? Each module may be ~400V, which would make it much easier to have different pack configurations, 4 modules vs 5 would be as easy as bolting an extra one into the busbar, none of this missing cells nonsense.

In that case each module may have 7 parallel sections of 96 cells in series. Four module pack would have 96s/28p, five module 96s/35p. (2688 cells for 4 module, 3360 for 5 module).

Cell count sounds a little small for the 46% in cell volume over the 18650s, but perhaps new chemistry makes up the rest of the gap.

The nice thing about getting the modules up in voltage separately would be the wiring that interconnects them can be smaller.