Back of envelope 18650 cell battery pack

I started looking at LiFePO4, 18650, cells at: http://www.batteryspace.com/LiFePO4-Cylindrical-Single-Cells.aspx

• significant operating temperature range limitations - if going for air cooled, there would be challenges.
• max discharge amps, ~30A >> max charge amps, ~1.5A - the discharge is fine but a battery management system needs to clamp regeneration or do some sort of fancy pack, power switching. It may make more sense to use a smaller, max amp discharge battery, ~5A, and then use parallel modules to handle the regeneration and high-speed charging.

I have an electric bike that needs a better battery than the 48V, sealed lead acid pack. It has a ~400W motor, 400W / 48V = 9A. Minimum two cell, parallel modules. But I want faster charging, so six cells in parallel would give, 9A charging for the module, 6*1.5A. It is charging rate during regeneration that specifies the number of parallel cells.

Given the goal is 48V, I will need in series, 15 modules. This gives a total of 90 cells in 15s x 6p configuration. This will run about $338 plus shipping. Not great but not bad either. At 120VAC, it should draw about 4A during the initial charging.

It is charging rate that defines the battery pack architecture. The nature of the cells means there is excess power to drive the electric bike. A total of 135 Whr / ~75 W ~= 2 hours at 25 mph, about a 50 mile range minus the low and high voltage margin. Cell weight in the pack, 8.1 lbs, probably 10-12 lbs including case and charger.

Bob Wilson