Motor Pre-charge and Discharge Controller

Goals

• Safely pre-charge the motor controller by applying 12V to the pre-charge relay
• Discharge the motor controller to ground whenever 12V is not applied

Background and strategic fit

The pre-charge and discharge controllers will each be responsible for one motor controller. It's job is to safely charge the motor controller up to the same voltage as the battery before allowing the main relay to connect; and to discharge the motor controller to ground whenever power is not being applied. This allows the main relay to connect without arcing, and de-energize the motor controller when the vehicle is not running. 

Based on the requirements, it was determined that the high voltage from the battery would be reduced to 5-12V using two resistors in series, and an instrumentation amplifier would measure the difference in voltage across the pre-charge resistor. Once the differential is minimum, the main relay would then be closed with a MOSFET. The discharge portion of the circuit would simply be a normally closed relay that would open when the vehicle is in it's run state. 

Requirements

User interaction and design

Questions

Below is a list of questions to be addressed as a result of this requirements document:

Proposed Parts