# Calculating Battery Module Requirements

1355 1
Hi, I am starting my own EV project and, as such, am scaling quite a steep learning curve right now!

Could anyone point me in the direction of a means of calculating how many of a particular battery module I'd require to power a Tesla Rear SDU? I know there are many variables to consider, but I'd be happy with very high-level estimates at this point.

It's been recommended to me that I use 12 x Tesla Model S battery modules to power said motor. However, I am keen to utilise the Nissan Leaf battery modules as they're smaller therefore more applicable to my tightly-packed vehicle layout. I therefore need to understand how many of these modules I'd require to get similar performance to the Tesla units...

Thanks in advance for any help!
1 - 2 of 2 Posts

#### brian_

·
##### Registered
Joined
·
8,305 Posts
The motor doesn't care what the battery is, but you need to provide the motor's controller with:
• enough voltage
• enough current, or enough power

12 Tesla modules is not a full set for any Tesla model, and would have a nominal pack voltage (assumed they are all connected in series as they are in a Tesla) of only 270 volts. That might be enough, and is the plan for some other projects, but would limit performance at high motor speed.

Tesla Model S/X modules have come in two different capacities, due to a different number of cells. The ones with 74 cells per group (from the 85 kWh packs) have a capacity of 5.4 kWh each, so a dozen of them have a capacity of 64 kWh, equivalent in energy capacity to 128 early Leaf modules (at 0.5 kWh each).

You can do the same thing with power output. It's not clear what the power limit of the Leaf modules is, but you could assume 80 kW for 48 modules, or 1.7 kW each; of course some people presumably run them much harder than that. You can estimate the power output capability of the Tesla modules by dividing the claimed total power of a given Tesla model and dividing by the number of modules (Wikipedia's Model S article has a nice table of the variants of the Model S), and multiply by the number of modules you are using. It's basically a matter of multiplying the power per module by the number of modules in each case.

The Leaf motor performance seems to have been limited by the controller in the stock Leaf to protect the battery. That was 80 kW in the first generation, 110 kW in the second generation with the base 40 kWh battery, and apparently higher in the big-battery version that has just come out. I don't know that this motor might be capable of with different controller programming and sufficient battery.
Smaller/earlier Tesla Model S variants had 14 modules, and larger/later variants have 16 modules... that's why 12 isn't a full set for any model, and will limit the performance of any Tesla motor.

Within variants having the same number of modules, the difference in capacity comes from a different number of cells in parallel, and changes in the cells; that doesn't change the voltage, since (as far as I know) they're still arranged as 6-in-series per module. That's (assuming 3.75 V nominal per cell)
• 12 x 6s = 72s or 270 V for a 12-module set (not used by Tesla)
• 14 x 6s = 84s or 315 V for a 14-module set such as in Model S "60" variant
• 16 x 6s = 96s or 360 V for a 16-module set such as in Model S "85" and "100" variants
Of course that's the nominal voltage. Actual voltage (per cell or for the pack) varies depending on the state of charge, so a nearly discharged 96s battery could be down under 300 volts.
Leaf modules have two cells in series, so they run at 7.5 volts per module. If 270 volts is enough, you would need 36 Leaf modules in series to reach that voltage.

1 - 2 of 2 Posts