Battery Pack Temperature Distribution - adjusting cell spacing

Owned by Micah Black
Last updated: Dec 31, 2019

Our prototype module has a problem:

This temperature distribution of the module is with a 100A discharge and the Noctua NF-F12 iPPC 3000 fan pulling air though it. It is evident that not much air is moving through the middle of the pack, which allows the interior cells to heat up significantly (10-15 degrees) more than the exterior cells. We want to bring this temperature distribution down as far as possible, in order to:

  1. Keep the pack as cool as possible, thus prolonging cycle life
  2. Minimize the variation between cells to prolong cycle life
  3. Keep all cells under the 45 degree limit as much as possible, in order to keep regen and solar on.

Given our limited resources in simulating the pack, and our timelines, we have chosen the following approach to remedy this situation:

  • Assume that the large difference in temperature distribution is indeed caused by a lack of air flowing over the cells
  • Move the cells  further apart in the middle in order to get more airflow through the module, essentially creating an airflow channel within the pack
    • This is similar to what MSXII did by removing rows of cells inside the module
  • Assume that making the cells as close together as possible (without touching - as we would run in to immediate thermal runaway propagation issues)
    • We will aim for 0.5mm spacing, similar to the NASA battery pack design slides I have seen
    • We must remember to leave room for thermistor and voltage taps to reach the hole in the top plate
      • Have a 2mm gap between the cells in the series groups.
  • We will put 2 channels through the module so that there are no more 'interior' cells, and that every cell has direct access to an airflow channel

The proposed new layout will be outlined below (once I get it done)