# Battery capacity calculation?

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carthikv12
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Joined: Saturday, August 1, 2009 - 07:30
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Battery capacity calculation?

Hi!

For a li-ion battery to be used in a car beyond the year 2020, in a car that weighs about a tonne with a 100kw motor... what would the power requirement be for a range of 150-200 miles?

I understand the KW-h rating would depend on the current drawn by the motor, so if this mini had the following spec -

572-pound lithium ion battery
150 miles range per 8-hour charge
Consumption 4.4 miles/kWh
204-hp & 162 lb-ft of torque
0-60 bit over 8 seconds
Top speed limited to 95mph
A bit over 3,200 pounds
Regenerative braking
More details:
Lithium pack maximum capacity 35kWh.
Nominal 380 Volts to motor.
Contains 5,088 cells grouped into 48 modules

From looking around 150 seems like a very optimistic figure, so lets assume it has a 100 mile range... so what battery capacity would a car weighing a tonne with a 100kw motor require for an approximate range of 150-200 miles?

Thanks!
Carthik

marylandbob
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Joined: Monday, June 22, 2009 - 12:24
Points: 524
Re: Battery capacity calculation?

when figuring RANGE, especially at highway speeds, weight is not anywhere as important as ROLLING RESISTANCE! Wing drag, and tire/drivetrain friction become very important, much more so than weight! weight is a big factor in figuring acelleration and braking, but a good regenerative system can minimize the ffects of weight in city type, stop-and-go driving. I would NOT consider a battery with "over 5,000 cells" as there are MANY more points of failure, and all those interconnections and cell cases add weight and size! A seemingly better solution would be a set of about 360 larger cells, wired to be 120 cells long, with 3 parrallel cells at each point. Such a 3 parrallel X 120 series battery could easily have its balance adjusted, if needed, by moving cells to optimize capacity of each set of 3 in parrallel with the other sets, and fewer connections would be required, along with easier monitoring and service.-Perhaps 360 cells, Li-FePo, of 60 Ah each? this would give 180 Ah, at about 380 volts d.c. (nominal)and 68.4 KWH. If your vehicle could cruise at 60 mph, while consuming an average of 566 watt-hours per mile, range would be 120 miles with this battery. (At 60 mph, my VECTRIX scooter takes about 200 watt-hours per mile, and it weighs 512 pounds, with me added, total weight is 712 pounds)-Bob Curry

Robert M. Curry

marylandbob
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Last seen: 5 years 6 months ago
Joined: Monday, June 22, 2009 - 12:24
Points: 524
Re: Battery capacity calculation?

To expand on my earlier post, a battery such as I described, 360 cells, at 60 ampere-hours each, Li-FePo, from "Thunder Sky", would weigh about 900 KG (One Ton) and cost about U.S. \$40,000.00---Bob Curry

Robert M. Curry

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