Procedure and Specifications

In order to effectively create a Power Management Subsystem (Battery Management System PCB and Battery Pack) that can be implemented in a FSAE vehicle, we would need to comply with the FSAE Rules EV3.3, EV3.4, EV3.6.2, and EV3.6.6 as listed in the student notes section at the end of this proposal. The Battery Management System must contain Current Protection, Temperature Monitoring, and Voltage Monitoring Circuits. We have made preliminary designs to our Power Management Subsystem of which we will explain further below:

1. Battery Management System Printed Circuit Board - We will follow the datasheets given by Texas Instruments to use as an aid for designing the Protection Circuit, Temperature Monitoring, and Voltage Monitoring to implement them onto our PCBs. We are planning on using Texas Instruments’ Power Management IC - bq76PL455A-Q1 - which allows us to use any type of battery chemistry.

I. Current Protection Circuit - The current protection circuit shown in Figure 2 will function as protection method for the Texas Instruments bq76PL455A-Q1 Integrated Circuit. This circuit will protect the IC from current inrush and over-voltage.

II. Temperature Monitoring - The ‘Ts’ inputs of the Texas Instruments bq76PL455A-Q1 utilizes the external thermistor and resistor circuits which is controlled by the output pin REG50 as shown below in Figure 3. The 47 nF capacitor functions as a method of noise reduction in the measurement system.

III. Voltage Monitoring - The bq76PL455A-Q1 IC has a built-in Analog-Digital Converter, allowing us to measure cell voltages. In order to obtain accurate voltage measurements, 1KΩ resistors and 0.1µF capacitors are used to build Nyquist Filters as shown in Figure 4.

IV. Cell Balancing – Cell balancing is critical for any battery pack as it will lower the degradation rate of the cells. The circuit shown in Figure 5 below will prevent self-discharge leakages of the cells and increase the longevity of our battery pack.

2. Battery Pack - We plan to design and assemble two battery packs, one pack placed on each side of our vehicle. Designing two battery packs gives us greater flexibility and increased safety when implementing the packs into accumulators and onto our chassis. The motor that we will be powering is the Motenergy ME1002 DC Series Wound Motor:

• Power: 26 KW (35 HP) continuous, 63 KW (85 HP) peak
• Voltage: 48 to 144 VDC

We plan to design a battery pack that will last at least 6-7 minutes with the motor running on peak power before recharging our accumulator packs again. Therefore, we would need to design a battery pack that has a minimum of 6.1 kilowatt-hours in order for our motor to run for 6 minutes continuously. The battery cells that we plan to use are Boston Power’s Swing 5300 cells and housings shown in Figure 6 below. Each cell contains 5300 milliamp-hours and 3.65 volts, giving us 19.3 watt-hours per cell. In order for us to create at least 6.1 kilowatt-hours of energy, we would need at least 318 cells. Each cell weighs approximately 93g, if we use 318 cells for our battery packs, the entire battery pack will weigh 29.574 kilograms (65.2 lbs). If we decide to split the battery packs (160 Cells on each side), the total area that we would need to allocate on each side of the vehicle is approximately 2.2 feet long, 0.50 feet wide, and 0.57 feet high. Furthermore, our team will be using Boston Power’s Cell Housing which will give our team the ability to easily modify the battery pack and add more cells for future designs.

3. Accumulator Container - We will design an effective housing that protects the battery packs and the PCB from outside elements, while also creating positive airflow for good ventilation for the battery packs in order to keep the cells below 60℃. We will be using materials with a honeycomb structure, which will reduce the weight of the accumulator while providing extra strength to protect the battery management modules. Building the accumulator onto each side as shown in Figure 7 allows our vehicle to have a lower center of gravity and will reduce risks associated with working on the accumulator and the battery backs. In addition, our team will be working with multiple Mechanical Engineers who will be guiding us through the accumulator designs.

Rule EV4.8 on the FSAE Handbook states that accumulator containers need to be monitored by an energy meter before connecting the containers to the motor controller as shown in Figure 8 above.

Figure 9 above shows a wiring method for our accumulator packs. Each accumulator container must have two accumulator isolation relays, one isolation relay for each pole. Furthermore, each accumulator must contain a main fuse as stated in EV3.3.2 in the Student Notes Section Below.