Objective:
The performance of a battery is determined by its worst-performing cell.
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“A capacity drop in any one of our modules will affect the whole pack. If one cell in one module drops by 10% capacity due to an uncaught cell parameter outlier (IR or capacity), then we lose (3.5Ah * 10% * 3.7 * 36 = 47Wh) 47Wh of energy in our pack. That single cell will then also start to degrade quicker and the module will have to be replaced. Going by the efficiencies of other winning solar cars, 47Wh could add an additional 1-2 Km of range to the car (and avoid headaches from increases in variation after many cycles)”. [2]
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Pick up a cell from the packaging
Number it with Sharpie
Place in the Gamry cell holder with a Keysight 34410a
Measure the OCV (4-point) of the cell
Collect the AC impedance IR via the equipment Keysight 34410a
Add data to the designated row: MSXV_celltracking
Place the cell in a box labeled labelled ‘Tested’
Production (Capacity) [DRAFT]
Place cells into [parallel cell charger(s)]
Charge cells at 1.45A (well below the standard charge spec [5])
Observe the thermal performance of batteries via thermistors/heat gun [optional]
Once fully charged, allow the cells to rest for 10 mins (recommended per spec sheet [5])
Commence discharge on [parallel cell charger(s)] at 1.70A
Once fully discharged, record values in the following MSXV_celltracking
Allow the cells to rest for 20 mins
Charge cells at 1A (well below the standard charge spec [5])
Observe the thermal performance of batteries via thermistors/heat gun
Once fully charged, allow the cells to rest for 4+ hours for the temperature to normalize temperature
Place all batteries in a box until module/pack assembley - when placing them in your module, check ocv and make sure it hasn’t dropped to much (self-discharge check), if discrepancies: record in MSXV_celltracking
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