FSAE HV Pre-charge and Discharge Board

About Arjuna EV UGM:

Arjuna EV UGM is a Formula SAE from the Gadjah Mada University planning to compete in Formula SAE Japan in the 2022 competition season. Formula SAE is an international competition for university students to develop a formula racecar and improve their engineer talents and skills. Arjuna EV UGM is a team of young and talented students building an electric vehicle racecar.

Pre-charge Discharge Board:

Based on FSAE Rules, FSAE electric vehicle Race Cars must have both a precharge resistor to charge the battery’s power to a certain percentage when it is connected to the motor controller and a discharge resistor to slowly reduce the power within the motor controller when the tractive system has been shut down. The precharge and discharge resistors are parts of the electric vehicle’s tractive system. The precharge resistor is used to slowly decrease the current flowing from the battery while increasing its power until the power reaches a certain percentage before being directly connected to the motor controller through the accumulator isolation relays, while the discharge resistor is used to slowly reduce the power of the electrical current within the motor controller when the tractive system is being shut down so that the motor controller, the boards within the tractive system, and the people near the tractive system don’t experience any damage.

We realized that the previous generations of the Arjuna EV Team placed the precharge resistor and the discharge resistor on different boards. This year, our team has managed to design a new board containing a resistor that serves the function of both a precharge resistor and a discharge resistor. For the precharge mechanism, we use a Comparator (LM321) which is connected to an RC circuit and a MOSFET (IR9540N) to serve as a timer for the accumulator isolation relay (AIR+) so that the AIR would only connect the battery and the motor controller (emDrive 500) after the voltage and current of the electrical current reach the percentage that our team has decided upon, while the AIR is open the current from the battery will flow into the resistor and will begin to charge up, therefore making the resistor serve the function of a precharge resistor. For the discharge mechanism, we use two relays (G2RL-2-DC12) to disconnect the motor controller from the battery and connect the motor controller only to the resistor, this is done so that the resistor will begin to serve as a discharge resistor to slowly reduce the current and voltage of the electrical current flowing within the motor controller with the help of the capacitor placed within the motor controller.