Specuwaiting.....

[mwulff]

You've misunderstood how it works. The number of given cells dictates the capacity, regardless of how they are configured. Cells in parallel have their Ah added together, while cells in series adds the voltage together.

Say you have 10,000 cells with 4V and 2.5 Ah. You can configure them in one long series, giving you a pack with 40 kV and 2.5 Ah. Or a capacity of 2.5 Ah * 40 kV = 100 kWh. Or you can wire all the cells in parallell, giving you a pack with 4 V and 25 kAh. Or a capacity of 4V * 25 kAh = 100 kWh.

The voltage is selected not because the capacity or power is different, but because some voltages are easier to work with. Lower voltage is better because it's less dangerous and you need less insulation on the wires, higher voltage is better because the resistive losses will be less, and you need less copper to conduct a given power. 400-ish Volts is a good compromise.

I would expect the Model 3 to have a voltage similar to the Model S.

--- Authors note: I screwed up on the math. Yggdrasill is correct. I have left my post for completeness. ----

Actually I understand quite well how batteries work and how packs are designed. My point is that given a small volume of space (Model 3 is smaller than a Model S) it makes sense to drop the voltage to make room for more parallel cells to keep the capacity up.

So for any given volume of space you can have X cells. Now you must balance voltage or wH (serial vs parallel cells) when you design your pack. So given a space constraint in the model 3 Tesla might choose to lower their voltage for more parallel cells in the pack (which gives greater range). This will drop the performance of the car since the amount of work that can be extracted from the pack is Voltage*Amperage.

WRT to supercharging: As long as the supercharger can match the pack voltage then it can be charged at 1,5C. We don't know what the lower voltage limit is on a supercharger but it could be lower than what we have seen to date. Granted that is pure speculation.

You are right about less resistance with a higher voltage which may also contribute to their final choice. It will be fun to see what rolls of the line.

 

[coco81]

Battery size is not the problem. Model 3 will be only 20% smaller than model S. We are talking about around 4,7m long (BMW 3-series size more or less), there is only 10" less lenght.

Considering only using 20700 cells instead 18650 you have same energy storage with 30% less cells... I don't think space will be a problem... the problem is and will always be the cost.

 

[Yggdrasill]

Actually I understand quite well how batteries work and how packs are designed. My point is that given a small volume of space (Model 3 is smaller than a Model S) it makes sense to drop the voltage to make room for more parallel cells to keep the capacity up.

So for any given volume of space you can have X cells. Now you must balance voltage or wH (serial vs parallel cells) when you design your pack. So given a space constraint in the model 3 Tesla might choose to lower their voltage for more parallel cells in the pack (which gives greater range). This will drop the performance of the car since the amount of work that can be extracted from the pack is Voltage*Amperage.

You have to explain better what it is you actually think will help. How is a 70 kWh battery pack at 200V better for range than a 70 kWh pack at 400V? Remember the inverter converts this DC to the required AC, so this voltage is something only the inverter sees, and both battery packs require the same amount of cells.

From my point of view, the higher voltage battery pack will provide the best range, due to lower resistive losses.

WRT to supercharging: As long as the supercharger can match the pack voltage then it can be charged at 1,5C. We don't know what the lower voltage limit is on a supercharger but it could be lower than what we have seen to date. Granted that is pure speculation.

If I'm not mistaken, the superchargers are limited to 330A. With an empty pack voltage of 400V, that's 132 kW, while if the empty pack voltage is 200V, it's 66 kW. If the battery pack is 70 kWh, that means a max charge rate of 0.94C at 200V instead of 1.88C at 400V. A smaller pack can probably have a somewhat lower voltage than a Model S pack without being limited by the supercharger, but if the voltage gets too low, the superchargers just can't supply the required current for the best possible charging.

 

[mwulff]

You have to explain better what it is you actually think will help. How is a 70 kWh battery pack at 200V better for range than a 70 kWh pack at 400V? Remember the inverter converts this DC to the required AC, so this voltage is something only the inverter sees, and both battery packs require the same amount of cells.

From my point of view, the higher voltage battery pack will provide the best range, due to lower resistive losses.
If I'm not mistaken, the superchargers are limited to 330A. With an empty pack voltage of 400V, that's 132 kW, while if the empty pack voltage is 200V, it's 66 kW. If the battery pack is 70 kWh, that means a max charge rate of 0.94C at 200V instead of 1.88C at 400V. A smaller pack can probably have a somewhat lower voltage than a Model S pack without being limited by the supercharger, but if the voltage gets too low, the superchargers just can't supply the required current for the best possible charging.

You are correct, I just did the math again and somehow I got messed up on aH and kWh. Given X amount of cells you get Y kWh out of them no matter the configuration. My apologies, a lower voltage pack would have the same kWh as a higher voltage pack. The only thing you balance is how much current you need to draw for a given amount of work.

My apologies for muddying up the waters..

 

[Yggdrasill]

You are correct, I just did the math again and somehow I got messed up on aH and kWh. Given X amount of cells you get Y kWh out of them no matter the configuration. My apologies, a lower voltage pack would have the same kWh as a higher voltage pack. The only thing you balance is how much current you need to draw for a given amount of work.

My apologies for muddying up the waters..

No problem. We've all been there.

 

[Ingineer]

According to the labels on the modules used in the SuperChargers, they have an output range of 50-430VDC and 45A each. There are 12 of these in a gen 2 SC cabinet.

 

[Saghost]

According to the labels on the modules used in the SuperChargers, they have an output range of 50-430VDC and 45A each. There are 12 of these in a gen 2 SC cabinet.

If I remember right, the current limits on the connector and cabling is 330A? - though possibly a fancy liquid cooled connector like Elon mentioned in one of the interviews would have a higher limit.

Either way, the limiting factor on charge rate from the SpC side looks like it'll be a current limit, which means as long as the cells can take it, higher voltages = faster charging. The 430V max from each module means you can't go higher than the current 96 cell chains unless the SpC modules get connected in series instead - something I'm sure they aren't wired to do now, and doubt Tesla would do in the future.

Given all of that, my assumption would be that the larger battery will be a 96s design (assuming they keep the current Lithium chemistry or a similar one,) and the smaller battery might also be, or might be a lower voltage to let them use the same modules.


I don't think there's anything that would tie Tesla to the 16 modules of 6 series groups arranged in series approach, but I don't see an obvious reason to change it either, and it certainly seems to be working for them (and keeping those the same would let them use the same BMS hardware and programming they have now...)
Walter

 

[eliassorensen]

Do you guys think it will have a tow hitch? TMS will probably get an upgrade next year with that, so it would be nice if the whole lineup would get that too.

 

[MassModel3]

Do you guys think it will have a tow hitch? TMS will probably get an upgrade next year with that, so it would be nice if the whole lineup would get that too.

Why do you say that? Personally, I'd be surprised if the Model S got a tow hitch. But if you have reliable info, share the source, please.