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The calculator below serves as an aid in designing an electric vehicle pre-charging circuit. It will calculate the pre-charge resistance required to achieve the desired percent charge of the system capacity in the desired time. Below is the circuit diagram with definitions. 
When the battery pack contactors are closed on the motor and inverter, there will be a current surge to the inverter capacitor. At the very least, this very high current poses a risk of aging the contactors and may permanently damage them.

Therefore, when closing the contactors on the battery, we do it in three steps:

Close the main negative contactor (S-)
Close the contactor with the resistor in series (S1)
Close the main positive contactor (S+)
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