Battery Module Welding

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The electrical team finished welding nickel plates to our battery modules last week. The battery modules are blocks of 13 3.7V lithium-ion battery cells connected in parallel, and the parallel connection is achieved using the nickel plates. Each size 18650 battery cell was individually spot-welded to nickel plates at both terminal ends (positive and negative, just like on a standard AA battery).

The next step is to punch holes in the nickel so the individual battery modules can be bolted together in series to form the car’s battery pack. The battery pack will use about 32 of these battery modules, which adds up to over 400 battery cells, weighing over 40 pounds, sitting in the battery box at the front of the car. By the way, these cells are very similar to the cells used in laptop computer batteries, but laptop computers generally only have 6 to 9 of them in their battery packs. In fact, when laptop manufacturers market their batteries as “6-cell” or “9-cell”, this is what they are referring to–the number of 18650 battery cells they use in their battery pack. Our battery pack’s output voltage would damage a laptop computer, but if it was wired for a different voltage, it could theoretically power a typical laptop for over a week, nonstop!

Bare 18650 Li-ion battery cells - these cells are similar to the model used in our battery modules. Source:
A battery module being worked on with the spot welder.
A finished battery module, showing the location of a battery cell hidden behind the nickel.

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