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#### Yodastien

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So I am looking to build up an electric powered Beck Spyder I plan on using a all in one single speed power unit. I am leaning towards the bolt power unit. I was wondering what i should factor in to batteries I would like a 200 mile range but I do want to keep weight conscious because it is going to be a light sports car. Are there formulas I can use to determine how many amps i need where i can divide that into the number of cells?

#### brian_

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With typical recent EV drive units, such as the one in the Bolt, you need 360 volts (nominal) to produce the full rated power to the top of the speed range. You can run them on less, but the power will drop off at high speed.

As far as range is concerned, you need to think in terms of energy: assume some reasonable energy consumption per distance travelled (e.g. 300 Wh/mile), multiply that by the target range (200 miles in this case), and you get a required energy capacity (60 kWh in this example). It doesn't matter what combination of voltage and current capacity the battery has, as long as the product is enough energy.

The torque output of the motor depends on how much current it can be supplied with, but motor current is not the same as battery current. The controller takes current from the battery at whatever the battery voltage might be, and converts that to the current needed by the motor at the voltage needed to drive that current at whatever speed the motor is running. To size the battery, it needs to be capable of providing the required power: for the 150 kW Bolt drive unit at its full rated power, the battery needs to provide at least 150 kW (at 360 volts what would be about 420 amps). In general, in batteries more energy capacity means more power capability.

The energy capacity of a battery (in watt-hours) is the product (just multiply the values together) of the battery voltage and the amp-hour capacity. The amp-hour capacity of the battery is the cell capacity multiplied by the number of cells in parallel.

Unfortunately small and light are not compatible with high power in the battery world. You can find cells designed for particularly high power density, but to get the target range you'll need enough battery capacity that any battery that large should be able to handle enough to power to perform better than an original Porsche 550 Spyder.

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