For the Doka, we will be using 100 Thundersky lithium iron phosphate (lifepo) cells wired in series for a pack voltage of about 320 volts.
Lifepo chemistry has a long cycle life of 2,000 charge and discharge events. Pack capacity will linearly decay, and at the 2,000th cycle, capacity will be about 80% of the rated capacity. Other lithium chemistries get between 500 and 100 cycles. Ever wonder why your smart phone starts running out of charge before the end of the day after a couple years? The trade-off that the lifepo cells have for long cycle life is charge density – they weigh more and take up more volume than the other lithium ion chemistries.
The cells we are using have 100 Ah (amp-hour) capacity. They could deliver 100 amps for 1 hour, 1 amp for 100 hours, or any “reasonable” combination of current and time that multiply to 100 Ahr. Combining the volts and amp hours, we get the energy storage of the battery. 320 volts * 100 Ah = 32,000 watt hours.
So what do these numbers tell us about what we can expect in range? Just a bit more math is needed. We need to know how fast we are consuming the energy from the pack as the vehicle drives down the road.
A really rough estimate for energy consumption is to take the mass of the vehicle in pounds and divide by 10. The result is the amount of watt hours consumed to drive 1 mile. For metric calculations, take the mass of the vehicle in kg, and divide by 7.3 to get watt hours consumed per kilometer.
For the Doka, which weighs about 5,000 pounds (2400 kg) the energy consumption estimate comes out to about 500 watt hours per mile (325 watt hours per kilometer). The energy in the pack divided by the energy consumption gives the expected range of the vehicle per charge. 32,000 watt hours / (500 watt hours/mile) = 64 miles of range per charge. In metric, the range estimate is 32,000 watt hours/ (325 watt hours/kilometer) = 98 kilometers.
These are all just guesses. It will be a lot more fun to build the Doka and find out what it can do.
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