The First Battery Pack (Thundersky)

After deciding on a motor and inverter combination, the next challenge when planning an EV conversion is choosing the traction battery pack voltage, capacity and chemistry. Which impacts the motor performance, vehicle dynamics, high voltage cabling, pack size and battery mounting options.

There are many tools for sizing the battery pack for electric vehicle conversions and I investigated several, but in the end I was forced to use a pragmatic approach to battery selection. The criteria being:

• Minimum practical pack voltage (The TIM inverter can operate from 80 – 400 Volts).
• Packaging (I wanted the initial battery pack to be mounted in in the MR2 rear engine bay).
  
• Availability (There were not many suppliers of EV components at the time).
• Product reputation (There was a small selection of batteries commonly used by members of AEVA Sydney).
• Price (I wanted to purchase the minimum number of batteries practical to start and figured that I would purchase more latter). 
  

In the end I purchased sixty Thundersky 60ah prismatic lithium-ion batteries and braided links from EV Works in Perth.

I was pretty excited when they were delivered!

The battery box was fabricated by Geoff O’tool from GT Tooling and mounted in the rear engine bay.

Because the final dimensions of the battery box meant only 56 cells would fit, the final traction battery pack specifications were:

56 cells * 3.6Volts        = 201.6 Volts
2.5 kg * 56 cells           = 140 kg
60 * (56 * 3.6) / 1000  = 12.1 kilowatt/hour

This is a picture of the pack installed in the rear engine compartment. I drove MR02EV for about 3 years with this setup before embarking on a replacement, which I will describe in a future post.

You can also see the Batrium battery management cards mounted on the top of each cell. Its a great system and I will write more about that also.