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UCEM High Voltage Battery Design for Electric Vehicle

Team 1822 Tejinder Jutla, Jason Clark and Sung-Lin Chen

April 27th, 2018

ECE 4902 – Senior Design II

Advisor: Sung Yeul Park Sponsor: UConn Electric Motorsports Club

Department of Electrical and Computer Engineering University of Connecticut

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Table of Contents Executive Summary……………………………………………………………………... 3

Background……………………………………………………….………………………3

Accumulator Cell Selection ………………………………………………………….......4

Battery Management System……………………………………………………….…….7

Charging……….……………………………………………………………………….....9

Accumulator Container……………………………………………………………….......9

Overcurrent Protection and Wiring…………………………………………………..…..10

Accumulator Integration and Testing…………………………………………………….10

Project Phases……………………………………………………………………….….....15

Project Budget……………………………………………………………………..……...17

Appendix A: Relevant FSAE Rules………………………………………………….…..18

Appendix B: Decision Matrices ……………………………………………….………...22

Appendix C: Part and Component Datasheets …………………..……………………....25

Appendix D: Test Procedure Documents ………………………………………………..28

Resources………………………………………………………………………………...41

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Executive Summary In the Spring of 2017 UConn formed a club: UConn Electric Motorsports (UCEM). UCEM will build a formula style electric racecar from the ground up and compete in an international level. UCEM is sponsoring four separate senior design teams, each tasked with building an integral component of a single-seat electrically powered formula-style racecar. From design to production 11 students have each brought together the best components sourced from around the world integrated into a single vehicle. North America’s first electrically powered aluminum honeycomb chassis is capable of accelerating from 0-60 mph in under three seconds. The electric racecar will be powered by a tractive accumulator system (the term tractive refers to high voltage system, and accumulator refers to battery), which includes a custom configured lithium ion battery pack, a battery management system (BMS), charger, and other necessary components. Since this is the first time the club is participating in this competition, most of the first semester was used on researching concepts and components to meet the power requirements from the electric motor. The second semester was spent on final design touches, assembly, and testing. Along with meeting the club’s requirements, design also had to satisfy Formula Student Automotive Engineering (FSAE) rules. This was accomplished by creating decision matrices, comparing all options that meet requirements of rules and performance. The accumulator design was changed numerous of times, as this system impacts other subsystems on the car. By the end of the first semester, the battery was selected and finalized, the battery management system was identified along with the charger. The accumulator container was designed, with accordance to FSAE rules and collaboration with the chassis team, however it is bound to change. The selected batteries arrived, and the high voltage battery pack was assembled. The BMS was configured to the battery, and tests were conducted to determine the BMS was working correctly. High current wiring was connecting the battery, and providing a main output line, also connected with relays for overcurrent protection. Background There are significant FSAE rules to follow. The maximum allowed voltage is 300 V along with a maximum power from the accumulator of 80 kW. The accumulator must be separated into segments with each segment having a maximum energy of 6 MJ and maximum voltage of 120 V. Each cell must be fuse protected. The maximum power required by the motor selected by the motor team is 80 kW. The team also requested a voltage above 200 V for the accumulator. This voltage is in direct relation to the torque and speed for the motor performance. UCEM, the motor team, and the battery team came to a conclusion for the kWh of the accumulator. The FSAE 2017 results were analyzed from the endurance event to see how much energy the teams used, the completion time, and weights of the vehicles. The conclusion was made that the accumulator needed to be 4-5 kWh for this design.

The accumulator must be designed to fit inside an accumulator container. The accumulator container must be removable from the vehicle, therefore must be placed in an accessible area. The accumulator needs to be transported on site to the charging station using a charging cart. A charger must be chosen to integrate into the system to meet the needs for the accumulator. A battery management system is required. All cell voltages must be monitored and at least 30% of their temperatures need to be monitored as well. A BMS must be chosen to communicate with the components of the tractive system and accurately meet the monitoring requirements.

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Accumulator Cell Selection Time and research was first spent on understanding the needs for the battery and making a proper selection of battery cells. It was discovered there were three realistic options to choose from: cylindrical cells, pouches, and modules. Batteries in the style of pouches offer a high-power output, and a simple way to connect them electrically. The problem arises with pressure. The pouches expand and must be pressurized by an outside component. Cylindrical cells are contained within the cylinder and are automatically pressurized by this design. This involves many connections because a single cell does not offer a high-power output. The third option is modules that contain cylindrical cells connected in parallel. This allows for easy electrical connections but comes at an expensive price.

The voltage and power requirements ultimately determine how the accumulator needs to be configured. Battery cell options were investigated comparing voltage, discharge current, capacity, weight, and cost. With these values, decision matrices were used to find the exact configuration to reach the desired power of 80 kW. Series connections add voltage, and parallel connections add current and capacity. The below equations were used for determining the configuration. Total Voltage (V) = Cell voltage (V) * # series connections (1) Total Current (A) = Cell discharge current (A) * parallel connections (2) Total Capacity (Ah) = Cell capacity (Ah) * parallel connections (3) Discharge Time = Capacity (Ah) / discharge current (A) (4) C-rate = Current (A) / Capacity (Ah) (5) Power = voltage(V) * current (A); P = VI (6) kWh = Accumulator voltage (V) * Accumulator capacity (Ah) (7) After these calculations, the number of batteries needed are known and calculations of total accumulator weight, volume, and price can be found. These are the ideal parameters to compare different cell types. A decision was made to use Samsung 18650 cells. These cells have a great discharge rate to capacity ratio, meaning they won’t be drained fast. They are also less expensive than comparable cells and weigh less. The Samsung batteries important parameters can be seen in Table 1. It was calculated roughly 500 cells were needed to meet the requirements given to us.

Table 1: Samsung 18650 relevant cell data.

Nominal voltage 3.6 V

Maximum Voltage 4.2 V

Max. cont. discharge current 20 A

Max. pulse current (< 1 sec) 100A

Capacity 2.5 Ah

Standard charge current 1.25 A

Max. charge current 4 A

Weight 44 g

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There were many concerns in the battery team, along with the advisor Professor Park, and the club members of UCEM. The rules require temperature monitoring and fuse protection for each cell, so additional components were needed to assemble the accumulator. With hundreds of cells, all parties realized much time was needed to physically assemble the accumulator with individual cells. There were also concerns for error, because this is a delicate component to the vehicle. Not much time would be left for integrating a battery management system, charger, or other components into the accumulator. After much consideration with UCEM, all parties came to an agreement on using prepackaged modules containing the cylindrical cells. The modules offer simple monitoring, and ease of assembly. Energus Power Solutions is a company that manufactures battery modules that many teams use for the FSAE competition. They even offer the Samsung cells the team chose as a choice for the cells inside the modules. They have different module types and another decision matrix was used to compare modules and their configuration. A decision was made on the Energus Li8PT modules which have 8 Samsung 18650 cells in parallel. The important parameters can be found in Table 3. The modules contain temperature sensors for each cell and 2 fuses for each cell, satisfying the FSAE rules. The temperature sensors and assembly of modules can be seen in Figure 1.

Table 2. Energus module comparison table, with 8 parallel modules chosen in green.

Table 3: Energus Li8PT relevant data

The accumulator is designed to contain 64 Energus Li8PT modules in series. The modules have 8 cells in parallel already, and offer a maximum current of 360 A, so no further parallel connections are needed as this aligns with the motor requirements. This offers a nominal voltage of 230 V, a maximum voltage of 268 V, a peak discharge current of 360 A, and a

Factors Li20pT Li8pT Li10pT Li6pT Voltage 3.6 V 3.6 V 3.6 V 3.6 V Capacity 50 Ah 20 Ah 25 Ah 15 Ah Max Current 750 360 375 270 Price $174 $89 $103 $75 Weight 1.05 kg 0.427 kg 0.505 kg 0.323 kg Wh 180 Wh 72 Wh 90 Wh 54 Wh

Nominal voltage 3.6 V

Maximum Voltage 4.2 V

Peak Current 360 A

Capacity 20 Ah

Max. charge current w/ cooling 40 A

Weight 427 g

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capacity of 20 Ah. These values can obtain the maximum power of 80 kW and give a 5.3 kWh accumulator. The configuration means the accumulator contains a total of 512 cells. The accumulator must be separated into segments with each segment having a maximum energy of 6 MJ and a maximum voltage of 120 V. The total energy of the accumulator can be found using equation (8). If the accumulator is separated into four segments, each segment has 16 modules. Each 16-module segment has 4.8 MJ and 67.2 V. Energy (J) = Voltage (V) * Capacity (Ah) *3600s (8)

Figure 1: Energus Li8PT module (left) showing temperature sensors (top) and assembled (right). Energus provides bus bars and bolts to connect the modules that match their M8 terminals sockets. Once the batteries arrived, the team individually tested each module’s voltage. Each module came charged and measured about 3.5V-3.6V. The assembly of the high voltage battery began the day the Energus modules arrived. Caution and care is needed when assembling a high voltage battery or whenever one works with high voltage. Proper safety gear needs to be worn by all persons working on the battery. Each 16-module segment was first assembled using bus bars and bolts provided by Energus. The segments are then connected using high current wiring and maintenance switches. The complete high voltage battery back can be seen in Figure 2.

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Table 4: quick non-quantitative comparison of BMS topology

Figure 2. Complete 268V battery using Energus modules, along with other components. Battery Management System A battery management system (BMS) is essential to the design and functionality of the tractive accumulator. Many hours of research went into this portion of the design, in simple terms, a battery management system is capable of monitoring/protecting the battery, balancing cells, estimate state of charge, maximize performance and be able to report to users and/or external devices. These are only basic requirements, BMS functions depends on manufacturer as well as customization. The BMS was selected based on three categories: analog versus digital, custom versus off-the-shelf and topology. Digital BMS is better, as it is capable of sensing each cell individually, this advantage allows the BMS to charge or discharge at cell level, as well as locate which cell might be at fault. A BMS off-the-shelf seemed like the only option, as the team does not possess the electrical experience one would need to carry out such an extensive task, several off-the-shelf BMS units are available within budget. Lastly, there are several different BMS topologies. Centralized is compact, least expensive option and easy to replace. Modular BMS are divided into multiple identical modules, one acts as the master, higher cost and more tap wires required. Master-Slave BMS are similar to modular, with the exception to slave prices which are lower. Lastly, distributed BMS have electronics contained on cell boards that are placed directly on the cells being measured, more points of error can occur which may be difficult to detect. The team decided on a centralized digital BMS, since all the voltage and thermistor tap wires are processed within a single BMS. This reduces error and eliminates the need to design individual circuit boards. Table 3 shows a comparison chart for different types of battery management systems.

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Figure 3: Orion BMS input/output interface

As seen in Table 4, a centralized BMS is the better candidate for the task at hand. A complete decision matrix can be found at the end of this document comparing different BMS units (BMS table). The BMS that was selected by our team and club was the Ewert Orion BMS 2 the 72-cell configuration, since the battery packs are configured in a 64-series connection (BMS data sheet).

The Orion BMS operates at 12v 250Ma, capable of measuring state of charge, discharge

current limit and charging current limit. This BMS has dual fully programmable CANBUS 2.0B, this is a high-speed Controller Area Network compared to many other options available. The CANBUS is a basic differential voltage, CAN-HI and CAN-LOW. This feature will be used to control the charger as well as the DC load (motor, inverter, etc.). The Orion BMS is made for electric vehicles, this means that it is of very high quality in both performance and functionality. It is capable of reading cell voltages from 0.5 to 5 volts, EMI resistance and functions between -40 to 80 degrees Celsius. The maximum and minimum open circuit voltage can be set within the BMS, if the voltages reach these set limits the BMS will open the Accumulator Isolation Relays (AIR). The temperature can also be set, so the BMS is again capable of opening the AIR if limit is met. The BMS is also equipped with Onboard Diagnostic (OBD), this will allow the team to read any error codes given by the BMS. The Orion BMS comes with a current sensor with an amperage rating of choice, which is 500A for this design. A temperature expansion module is needed alongside the BMS as the Orion is only capable of 8 thermistor inputs, and we need to be able to have 64 Zener diode inputs for all modules. Their company also offers a state of charge meter as a display module. It provides essential information on the accumulator as well as data logging for diagnostics and future testing.

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Charging The charger is also an important part to the accumulator design. The goal for our

charging research is to find one that is compatible with the battery, battery management system and has CAN communication protocol. Our battery pack contains 512 cells; therefore, the voltage and current are very high. All the power management work could be processed by the battery management system. The location of the race is in Canada which can only provide 120V AC voltage, so in the datasheet we can only view output current at 115V AC instead of 230V AC. We cannot just look at the peak power because of its output with 230V AC. In terms of the output power, higher output current gives us faster charging speed. But we also need to take into consideration that higher output power will generate more heat. If the charging environment is hot, it will reduce the performance of the charger. Initially we want to implement a fast charger to reduce charging time, so we chose Elcon PFC 5000 charger. However, charging time is not our priority since we have plenty of time during each event according to the club. We don’t need such a high output current charger. There are several chargers we found that have very high charging power output but it’s significantly more expensive. Our final decision is the Elcon PFC 2500 charger which delivers sufficient amount of charging current at 6A at half of the price of Elcon PFC 5000 charger. The Elcon charger is one of the few charger brands that is officially compatible with our Orion BMS. As a result, it is easier to implement. Using equation (9) we can find the charge time for our battery pack. Since the battery pack is 20Ah, and the charge current is 6A, the charge time is about 3 hours and 20 minutes.

(9)

Finally, according to the FSAE rules, if the battery needs to charge, the accumulator is required to be taken out of the car and transported to the charging station. This requirement will make the charger an external device which will reduce total weight of the vehicle. The battery must be transported with a hand cart equipped with a Deadman’s braking system. This is for safety reasons.

Accumulator Container An accumulator container is required to house the batteries and any other necessary components. This container must be easily removable from the vehicle in order to transport to the charging station at the competition. The tractive accumulator design and function is specified in the FSAE rule handbook (EV3.3). There are a number of requirements, such as grounding to chassis, removable from the chassis frame to be taken to the charging station. This translates into an efficient design which is both lightweight and robust to handle the track debris. The handbook also states that the battery pack has to be broken into segments for safety purposes, along with galvanic isolation requirements. Figure 4 is the final draft of design by this team, the accumulator container is subject to change as time progresses.

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Figure 4. Accumulator container design. Left showing back, openings for output connections. Right showing front opening with top shelf for components and bottom with walls to separate 4 segments. The thickness requirement is as follows: floor must be 3.2mm thick, vertical and the

segment separation walls must be 3.2mm thick, and the lid cover must be 2.3 mm thick. The material chosen for the container was aluminum, given its weight and strength properties. This material is also simple to construct out of and will save budget.

Overcurrent Protection and Wiring

Aside from the internal fuses of the Energus modules, there is one main fuse and two relays that protect the system. The relays are known as the Accumulator Isolation Relays (AIRs). According to the FSAE rules the main fuse must have a current rating that is lower than the continuous current of the component it is protecting, which in this case is the accumulator which has a constant current of 160 A. The fuse must also be rated for the maximum voltage of the system. Bussmann/Eaton FWH-150B is the decided fuse with a current rating of 150 A and maximum voltage of 500 VDC.

The rules also state the relays must have a switch off current that is higher than the fuse rating. The relays must be of a normally open type and open both poles of the accumulator meaning one on each side. Kilovac Lev200A4NAA are the decided relays with a switch off current of 500 A and maximum voltage of 900 VDC. The relays must also be supplied with a 12v power supply. The AIRs can be seen in Figure 5.

Figure 5. Both AIRs shown with high current wiring.

The battery segments must be electrically separated by maintenance plugs or contactors.

Maintenance switches from EVWest were found that were rated for 400 A. They have M8 bolts on the bottom that can be connected to ring terminals using wires, the same as the relays. There are 3 maintenance switches, each placed in between the segments of the battery. This offers a safe way to electrically separate the battery segments from one another.

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Figure 6. EVWest maintenance switches.

The Orion BMS ships with the necessary wires needed for the voltage taps, SOC meter,

and main wires. The main concern was finding wiring that was adequate for the high current path of the accumulator. A high current wire 2/0 AWG from EVwest can handle up to 390A which meets our requirements. This wiring can be used to connect the main fuse, the AIRs, the maintenance switches, and the high current path leading to the motor side of the vehicle. M8 ring terminals can be used to connect wires to the Energus modules because their electrical contacts are M8 bolt sockets.

Accumulator Integration and Testing This is a new club to UConn and there was lack of funding in the beginning. Since there was no money at first, the team was not able to get any batteries to do any testing on. With a finalized battery decision, the club ordered the batteries from Energus in late January. Energus had a 6-week lead time due to manufacturing, and the batteries did not arrive until late March. The assembly of the battery began immediately once they arrived. The BMS and charger arrived in mid-March and were set up and integrated with one another as much as possible before the batteries arrived. With the battery pack assembled, the BMS could now be configured with the battery. There are 64 series connections meaning the BMS has to measure 64 cell voltages (since all parallel connections have the same voltage). The Orion BMS 2 ordered is compatible for up to 72 cells, each separated into groups of 12. The voltage tap wires are provided with the Orion BMS 2, each numbered and must be connected in order. The voltage tap connections for one segment are shown in Figure 7. The end of the voltage tap wires were sent into ring terminals and then crimped. The ring terminals can connect to the M8 bolt terminals of the Energus modules. Starting with the most negative end of the complete battery, the ground cable for the first voltage tap group is connected. From here a cable is connected to each positive terminal of the Energus modules and must be in order. Once each group of 12 is complete, the ground for the next group can be connected to the next module, and the process can be repeated until all Energus modules are connected to the BMS through the voltage taps. If there are less then 12 cells in a group of voltage taps, the remaining tap wires must be connected to the positive most cell of the group.

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Figure 7. Voltage tap connections for one battery segment.

The Orion BMS software on a computer is able to connect to the BMS through a CAN to USB adapter. With all voltage taps connected correctly, the BMS software displays all cell voltages in real time. The software has a user interface that can allow the customization of settings. Balancing settings were set, along with charging settings. With the voltages being measured the SOC meter could now be tested. The SOC meter communicates with the BMS through CAN communication as well and displays the SOC of the battery in percentage form. As long as all voltage taps are connected correctly, and the battery profile is set up, the SOC meter should be reading correctly. The BMS data sheets state that the provided current sensor placement around the positive charging cable is necessary in order to read an accurate SOC. The Elcon PFC 2500 came equipped with CAN communication and must be placed on a 250 Kbps channel. Since the BMS has 2 CAN channels, one can be set to 250 Kbps while the other can be set to 500 Kbps for other devices. The Orion BMS software was picking up the charger once the charger was connected to the BMS through CAN. The charger turns on and has an indicator LED to signal what it is currently doing. 10 AWG cables are the output of the charger which are in an Anderson connector. The other Anderson connector was also equipped with 10 AWG wires and connected to the main positive and negative terminals of the battery. The Anderson connectors easily connect, allowing an easy way to charge the battery. The connection between the battery and the charger can be seen in Figure 8. The charger is connected to the Orion BMS through CAN and they can communicate with each other about the state of the batteries. The BMS can tell the charger when the batteries are full and can cut off power and prevent the batteries from becoming over charged. The team unfortunately ran out of time and could not test the charger actually charging the batteries.

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Figure 8. Complete battery pack and charger connected by grey Anderson connector.

The team wanted to perform discharge tests on the Energus batteries but were not able to do so because of the late arrival. Future testing needs to be conducted to shows temperature changes due to different discharge rates and charging time. The modules contain the Samsung cells and some temperature vs. discharge data was found as shown in Figure 9. The temperature in this graph increases over 60°C which is the maximum temperature rating for the Samsung cells and by FSAE. This testing data will directly lead to the future design of the cooling system. When batteries charge they start off with a fast current, and the current drops off to top off the charge on the battery. In the future testing phase, the Energus module should be drained to its shut off voltage of 2.5 V and then charged. From this charge time, it can be calculated how long the accumulator will need to charge once the whole system is operational and compared to the calculated charge time value of 3 hours and 20 minutes. The Energus temperature sensors measure the voltage across the sensor or circuit. This voltage corresponds to a certain temperature as seen in Table 5 and Figure 10. The temperature sensors are Zener diodes and the BMS is only compatible with thermistors therefore a custom temperature module is required. This involves multiplexer chips with ADCs taking in the measurement from the sensor and sent along a daisy chain. This can be done using LTC6803 chips. The LTC chips have SPI outputs for communication and can be sent into a microcontroller. The microcontroller must be programmed to read all the data from the LTC chips, and output signals using CAN. The TI TM4C123GXL is a great candidate and was chosen for this design. The MCU can communicate with the Orion BMS through CAN about any temperature readings it finds over the limit.

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Figure 9: Samsung 18650 discharge and temperature characteristics.

Table 5: Energus temperature sensors voltage to temperature conversions.

Figure 10: Energus voltage readings of sensors in relation to the temperature.

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The next step for future teams is the battery integration to the motor side of the vehicle. The first point of contact with the motor side to our accumulator system is the BMS and motor inverter. Through CAN communication the motor side and accumulator side can communicate on the required power draw and in turn the current draw. These systems can be programmed to not draw over a certain current, offering extra protection alongside the fuses and accumulator isolation relays. Once the motor and accumulator sides of the vehicle are integrated and working, all components need to fit inside the designed chassis. After everything is assembled into the vehicle the real testing of the vehicle can begin. UCEM will be performing driving tests before the competition to make sure the vehicle meets the standards of the events at the competition. During these driving tests, team members should be monitoring the BMS to make sure everything is working as it should. All testing documents can be found in Appendix D, these documents are subject to change. Although testing procedures are valid, the university does not have the resources to test the accumulator since it requires a maximum current of 360A. Next step would be to test the accumulator with the motor, since it will be able to provide the load needed to dissipate the power. Project Phases The first phase of the project was understanding the requirements, and also the rules given by FSAE. Much time was spent into cell research and selection type. At first, cylindrical cells were decided on and the Samsung 18650’s were chosen. After consideration about having to assemble these cells and not having time to complete the other aspects of the project, it was agreed on that the Energus modules would be used. After analyzing the decision matrix, the Li8PT modules were chosen, with a 64-series configuration to give optimal voltage and current. The next milestone was researching battery management systems and finally selecting a model. The Orion BMS 2 comes with multiple documents detailing how to use it and initialize the system. The unit also comes with software for monitoring the accumulator with a friendly user interface. This centralized unit is also less expensive and smaller than other units such as JTT electronics master/slave BMS. The accumulator container and charger have been undergoing research alongside one another. The dimensions have been received from the chassis team, and the container is designed from these dimensions. The types of chargers have been researched, and the team is confident on the type and model needed for this design. The Elcon PFC 2500 offers a maximum charging current for the accumulator and can provide fast charging. The temperature module was designed except for the coding of the MCU. All components were selected and received by the team, but the team did not have time to finish the coding portion of the temperature module. In the future it will be a good idea to have this custom component on a PCB. The testing and integration with the motor was also not complete because of the lack of time. The batteries arrived late in the school year and the teams did not want to rush the process. The battery must be assembled and tested delicately and cautiously because high voltage has potential to be dangerous. Proper safety protocols need to be in place in order to prevent injury to any student working on the high voltage battery. A safety protocol document was written by this team and will be accessible to any future UCEM members.

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With these final steps taken, the accumulator system is fully designed. The battery pack is assembled and is integrated with the BMS. The future work will be focused on testing components and integrating them into one another. With all integration and testing complete, there will be a fully functioning electric vehicle.

Table 6: Project timeline and phases

Figure 11: Gantt chart for project.

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Budget The total cost of this project was $9,410.15. The final cost breakdown of all the components for the accumulator can be seen in Table 7. The Energus modules were the most expensive part of the accumulator design followed by the Orion BMS 2 and Elcon PFC 2500. These are the 3 main components of the system, but many other products were researched, ordered, and integrated. UCEM did not give the team a definite budget for the accumulator system design. The club was waiting on responses from multiple teams working on the vehicle to determine a total price.

Components Cost 64 Energus Modules $5,980

Orion BMS 2 $1,601.60 SOC w/ data logging $235.00

Elcon PFC 2500 Charger $750 Relays $214.70

Main Fuse $56.95 2/0 AWG wire $58

Maintenance Switches 234 10 AWG wire $50

Ring Terminals $60.9 CANdapter $69

CAN Terminals $100 Total $9,410.15

Table 7. Final cost breakdown of accumulator design

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Appendix A: FSAE Relevant Rules

EV2.2 Power and Voltage Limitation EV2.2.1 The maximum power drawn from the battery must not exceed 80kW. This will be checked by evaluating the Energy Meter data. EV1.1 High-Voltage (HV) and Low-Voltage (LV) EV1.1.1 Whenever a circuit has a potential difference where the nominal operation voltage is greater than 60V DC or 25V AC RMS it is defined as part of the High Voltage or tractive system. EV1.1.2 The maximum permitted voltage that may occur between any two electrical connections is different between the competitions allowing electric vehicles. The following table lists the respective values:

Competition Voltage Level

Formula SAE Electric 300 VDC

Formula Student 600 VDC

EV1.1.4 The tractive system accumulator is defined as all the battery cells or super-capacitors that store the electrical energy to be used by the tractive system. EV1.1.5 Accumulator segments are sub-divisions of the accumulator and must respect either a maximum voltage or energy limit. Splitting the accumulator into its segments is intended to reduce the risks associated with working on the accumulator. EV1.2 Grounded Low Voltage and Tractive System EV1.2.1 The tractive system of the car is defined as every part that is electrically connected to the motor(s) and tractive system accumulators. EV1.2.3 The tractive system must be completely isolated from the chassis and any other conductive parts of the car. EV1.2.4 The tractive-system is a high-voltage system by definition, see EV1.1.1. EV1.2.7 The entire tractive and GLV system must be completely galvanically separated. The border between tractive and GLV system is the galvanic isolation between both systems. Therefore, some components, such as the motor controller, may be part of both systems. EV1.2.8 All components in the tractive system must be rated for the maximum tractive system voltage. EV3.2 Tractive System Accumulator Container – General Requirements EV3.2.1 All cells or super-capacitors which store the tractive system energy will be built into accumulator segments and must be enclosed in (an) accumulator container(s). EV3.3 Tractive System Accumulator Container - Electrical Configuration EV3.3.1 If the container is made from an electrically conductive material, then the poles of the accumulator segment(s) and/or cells must be isolated from the inner wall of the accumulator container with an insulating material that is rated for the maximum tractive system voltage. All conductive surfaces on the outside of the container must have a low-resistance connection to the GLV system ground, see EV4.3. Special care must be

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taken to ensure that conductive penetrations, such as mounting hardware, are adequately protected against puncturing the insulating barrier. EV3.3.2 Every accumulator container must contain at least one fuse and at least two accumulator isolation relays, see EV3.5 and EV6.1. EV3.3.3 Maintenance plugs, additional contactors or similar measures have to be taken to allow electrical separation of the internal cell segments such that the separated cell segments contain a maximum static voltage of less than 120VDC and a maximum energy of 6MJ. The separation must affect both poles of the segment. EV3.3.4 Each segment must be electrically insulated by the use of suitable material between the segments in the container and on top of the segment to prevent arc flashes caused by inter segment contact or by parts/tools accidentally falling into the container during maintenance for example. Air is not considered to be a suitable insulation material in this case. EV3.3.5 The Accumulator Isolation Relays (AIRs) and the main fuse must be separated with an electrically insulated and fireproof material to UL94-V0 from the rest of the accumulator. Air is not considered to be a suitable insulation material in this case. EV3.3.7 Contacting / interconnecting the single cells by soldering in the high current path is prohibited. Soldering wires to cells for the voltage monitoring input of the AMS is allowed, since these wires are not part of the high current path. EV3.3.8 Every wire used in an accumulator container, no matter whether it is part of the GLV or tractive system, must be rated to the maximum tractive system voltage. EV3.3.9 Each accumulator container must have a prominent indicator, such as an LED that will illuminate whenever a voltage greater than 60V DC is present at the vehicle side of the AIRs. EV3.5 Accumulator Isolation Relay(s) (AIR) EV3.5.1 In every accumulator container at least two isolation relays must be installed. EV3.5.2 The accumulator isolation relays must open both (!) poles of the accumulator. If these relays are open, no HV may be present outside of the accumulator container. EV3.5.3 The isolation relays must be of a “normally open” type. EV3.5.4 The fuse protecting the accumulator tractive system circuit must have a rating lower than the maximum switch off current of the isolation relays. EV3.6 Accumulator Management System (AMS) EV3.6.1 Each accumulator must be monitored by an accumulator management system whenever the tractive system is active or the accumulator is connected to a charger. For battery systems this is generally referred to as a battery management system (BMS) however alternative electrical energy storage systems are allowed and therefore AMS will be the terminology used in this document. EV3.6.2 The AMS must continuously measure the cell voltage of every cell, in order to keep the cells inside the allowed minimum and maximum cell voltage levels stated in the cell data sheet. If single cells are directly connected in parallel, only one voltage measurement is needed. EV3.6.3 The AMS must continuously measure the temperatures of critical points of the accumulator to keep the cells below the allowed maximum cell temperature limit stated

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in the cell data sheet or below 60°C, whichever is lower. Cell temperature must be measured at the negative terminal of the respective cell and the sensor used must be in direct contact with either the negative terminal or its busbar. If the sensor is on the busbar, it must be less than 10mm away from the cell terminal. EV3.6.4 For centralized AMS systems (two or more cells per AMS board), all voltage sense wires to the AMS must be protected by ‘fusible link wires’ or fuses so that any the sense wiring cannot exceed its current carrying capacity in the event of a short circuit. The fusing must occur in the conductor, wire or pcb trace which is directly connected to the cell tab. EV3.6.5 Any GLV connection to the AMS must be galvanically isolated from the tractive system. EV3.6.6 For lithium based cells the temperature of at least 30% of the cells must be monitored by the AMS. The monitored cells have to be equally distributed within the accumulator container(s). EV3.6.7 The AMS must shutdown the tractive system by opening the AIRs, if critical voltage or temperature values according to the cell manufacturer’s datasheet and taking into account the accuracy of the measurement system are detected. If the AMS does perform a shutdown, then a red LED marked AMS must light up in the cockpit to confirm this. EV6.1 Overcurrent Protection EV6.1.1 All electrical systems (both low and high voltage) must have appropriate overcurrent protection. EV6.1.4 If multiple parallel batteries, capacitors, strings of batteries or strings of capacitors are used then each string must have individual overcurrent protection to protect all the components on that string. Any conductors, for example wires, busbars, cells etc. conducting the entire pack current must be appropriately sized for the total current that the individual overcurrent protection devices could transmit or additional overcurrent protection must be used to protect the conductors. EV8.2 Charging EV8.2.1 There will be a separated charging area on the event site. Charging tractive system accumulators is only allowed inside this area. EV8.2.2 Accumulators must be removed from the car for charging within a removable accumulator container and placed on the accumulator container hand cart for charging. EV8.2.3 The accumulator containers must have a label with the following data during charging: Team name and Electrical System Officer phone number(s). EV8.3 Chargers EV8.3.1 Only chargers presented and sealed at Electrical Tech Inspection are allowed. All connections of the charger(s) must be isolated and covered. No open connections are allowed. EV8.3.2 All chargers must either be accredited to a recognized standard e.g. CE or where built by the team they must be built to high standards and conform with all electrical requirements for the vehicle tractive system, for example EV4.1, EV4.3 and EV4.6 as appropriate.

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EV8.3.3 The charger connector must incorporate an interlock such that neither side of the connector become live unless it is correctly connected to the accumulator. EV8.3.4 HV charging leads must be orange EV8.3.5 When charging, the AMS must be live and must be able to turn off the charger in the event that a fault is detected.

EV8.3.6 When charging the accumulator, the IMD must be active and must be able to shut down the charger. Either the charger must incorporate an active IMD or an active IMD must be within the accumulator.

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Appendix B: Decision Matrices

Table B.1: Energus modules comparison sheet.

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Table B.2: Cylindrical cell comparison sheet

Table B.3: BMS comparison sheet and selection.

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Table B.4: Charger Comparison

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Appendix C: Part and Component Datasheets

Table C.1: Energus Li8PT data table. Full Energus data sheet here.

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Table C.2: Samsung 18650 25R data table. Full Samsung data sheet here. Orion BMS documents found here

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ElCon PFC 2500 Battery Charger Technical Data

Full Elcon PFC 2500 data sheet here

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Appendix D: Test Procedure Documents

Charger Test Procedure 1. Purpose

The Charger is an important part of the accumulator system. The purpose to test a charger is to see whether it perform as expected so that it will not damage the battery pack. Also, to make sure it can charge our battery pack correctly.

2. Equipment Needed Part Name Nomenclature Elcon PFC 2500 216V 20A charger High Frequency industry charger Digital Multi Meter Test tool used to measure various value Timer To measure time Cable Cable that can handle up to 20A Input AC source Need to have 120V AC to 240V AC Max Load Can draw up to 20A Orion BMS Battery Management System

3. Test Procedure

3.1: General test

To test a charger, we need to first test the whether the actual output voltage and current of the charger is what it designed or programmed to be.

Action Results 3.1.1 Know the charger’s programmed

output voltage and current N/A

3.1.2 Prepare a Multi Meter switch Multi Meter to measure DC output voltage and current

DC output voltage should match expected value

3.1.3 Switch to DC output current DC output current should match expected value

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3.2: Charging time

Next, we need to test its charging time. The charging time equation is:

where time h is in hours.

Action Results 3.2.1 Make sure the output voltage from

the charger is larger than the overall voltage of the battery or battery pack. Otherwise it won’t charge.

N/A

3.2.2 Calculate the expected charging time using the equation above.

Get expected value to compare later

3.2.3 Charge the battery and start a timer to time the overall charge time.

N/A

3.2.4 When the battery is full, the charger will shut down.

N/A

3.2.5 Stop the timer. Compare the expected charge time and actual charge time. Charge time may not be exactly the same so few minutes off is acceptable.

3.3: Thermal testing

Next we test the thermal for the charger. Most charger come with over temperature protection. In our case, if the Elcon PFC 2500 charger’s internal temperature of the charger exceeds 75℃, the charging current will reduce automatically. If exceeds 85℃, the charger will shut down protectively. When the internal temperature drops, it will resume charging automatically.

To test this over temperature protection function:

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Action Results 3.3.1 Find a load, whether the battery or

machine load that can drain high current or near max charger design current.

3.3.2 Plug in the charger into Orion BMS system to use it measure temperature of the charger.

Charge indicator should be on. Observe whether BMS pick up charger temperature

3.3.3 Wait the charger’s temperature to go up. Monitor charger’s temperature using BMS. Measure the temperature.

Get charger temperature

3.3.4 Connect the output to a Multi meter and set it to DC current mode.

Get the output current from the charger

3.3.5 Observe the temperature and output current if temperature is over 75 degree C.

Output current should reduce if temperature is over 75 degree C.

3.3.6 Observe the temperature and output current if temperature is over 85 degree C.

Output current should be 0 if temperature of the charger is 85 degree C.

3.4: Short-circuit Protection

Short-circuit Protection: When the charger encounters unexpected short circuit across the output, charging will automatically stop. When fault removes, the charger will re-start in 10 seconds.

Action Results 3.4.1 Grab a wire that can handle up to 20A. N/A 3.4.2 Connect positive and negative terminal on

the charger Short-circuit detected, charger will shut down for 10 seconds

3.4.3 Disconnect positive and negative terminal Charger should restart

To test this function, we can simply use a wire to connect the positive terminal and negative terminal together to simulate a short circuit. And the we can observe whether the charger stop charger or not.

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3.5: Reverse Connection Protection:

When the battery is polarity reversed, the charger will disconnect the internal circuit and the battery, the charging will stop and avoid been damaged.

To test this protection function, connect the positive terminal of the charger to negative terminal of the load and negative terminal of the charger to positive terminal of the load. Plug in the charger and if charger is not charging then this function works.

3.6: Input Low-voltage Protection

When the input AC Voltage is lower than 85V, the charger will shut down protectively and automatically resume working after the voltage is normal again.

Action Results 3.6.1 Set the input AC voltage to 120V AC and

plug it into the charger N/A

3.6.2 Connect the charger to a random load that it can charge.

N/A

3.6.3 Next lower the input AC voltage to the charger under 85V.

The charger should shut down and stop charging

3.6.4 Crank up the AC input voltage to 120-240V, observe the charger.

The charger should resume charging.

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BMS TEST PROCEDURE

UConn Electric Motorsports

ACCEPTANCE TEST PROCEDURE NO. 01

DATE: 12/09/17

TITLE:

BMS Pre-integration Test Procedure

PREPARED BY: Tejinder Jutla

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CHECKED BY:

APPROVED BY:

Table of Contents

1.0 Purpose…………………………………………………………………..……34 2.0 Applicable Documents………………………………………………...34 3.0 Drawings……………………………………………………………….……..34 4.0 Test Equipment………………………………………………….………...34 5.0 WARNING…………………………………………………………………..…35 6.0 Test Procedure………………………………………………………………35 6.1 BMS SOC…………………………………………………………………….35 6.2 BMS Balance……………………………………………………………...35 6.3 BMS Charging…………………………………………………………….36 6.4 BMS Discharging…………………………………………………………36 7.0 Troubleshooting…………………………………………………………..37 7.1 Grounding…………………………………………………………………….37 7.2 Wire Shielding……………………………………………………………….37 7.3 Wire Routing…………………………………………………………………37

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1.0 Purpose

The Battery Management System basic functions will be tested in this Acceptance Test, main objective it to demonstrate satisfactory operation of the system installed on the FSAE racecar and compliance to the appropriate sections of the FSAE Rulebook 2017.

This Acceptance Test will confirm operation of the BMS at a component level, before integration to any other systems. This will mitigate risks of failure and promote safety of person working on the tractive accumulator.

2.0 Applicable Documents

1) OrionBMSOperationalManual2) OrionBMSTroubleshootingManual3) OrionBMSWiringManual4) OrionBMSSoftwareUtilityManual

3.0 Drawings

1) EnclosureAssembly,Std.Capacity,TechnicalOutline2) OrionBMSQuick-StartGuide

4.0 Test Equipment

PartNumber NomenclatureOrionBMS–StandardSize BatteryManagementSystem62Li2x4PT Li-ionbuildingblockwithtempsensor-3.6V/18CAeroVironmentABC-150 Testingofadvancedbatteries,fuelcells,capacitors,and

otheralternativeenergytechnologiesDigitalMultiMeter testtoolusedtomeasuretwoormoreelectricalvaluesPFC2500BatteryCharger Constantcurrentconstantvoltagecharger

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5.0 WARNING

This Test Procedure requires the use of high current and high voltage equipment(s). Safety is the highest priority. The rules of the lab and instructor of the lab must be respected and in compliance with the university’s safety rules. Verify all members of the team have the correct safety training to be working in such an environment.

At this stage, the BMS is deemed unreliable unless proven otherwise by completing this Test Procedure. If the test procedure fails, identify, and correct the problem using other documentation if available.

6.0 Test Procedure

6.1 BMS SOC

ACTION RESULTS6.1.1 Assumingthebatterypackisideal,

connecttoABC-150atthenegativeterminalanddischargepack

Voltageacrossterminalshouldresultinadecrease,confirmwithDDM

6.1.2 ConnectbatterypacktotheBMSandnotethereading

BMSshouldsignalandgiveanindicationoflowvoltage,chargershouldbeactivatedatthispointtobringvoltagebackup

6.1.3 ConfirmtheDMMreadingwiththatoftheBMS

ThiswillgiveyouaccuracyreadingpredictionfromtheBMS

6.2 BMS Balance

ACTION RESULTS6.2.1 Takeonepackfromthe62packs

connectedinmodule,usingtheABC-150,dischargethisonepackandconnectbacktothebattery

Theonepackthatwasdischargedwillbeoutofbalancecomparedtotherestofthepacks.Confirmandnotethevoltageofthispack

6.2.2 ConnectbatterypacktotheBMSandnoteanymessagesgiven

BMSshouldbeabletoreadthepackthatisoutofbalance,andpointoutexactlywhichoneistheculprit.

6.2.3 Atthispoint,allowBMStobalancethebatterypack

Batterypackshouldbebalancedouttooriginalvalues

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6.3 BMS Charging

ACTION RESULTS6.3.1 Turnonpowertothecharger BMSshouldappearoperational,sincetheBMSis

digital,notethecellvoltages,andcurrentisnowflowingintothepack

6.3.2 N/A BMSisawareofthecurrentflowingintothepack,theSOCvalueisincreasing

6.3.3 Verifycelltemperaturereadings,makingsuretheyarenotexcessive(60degreesC)

BMSshouldreadcorrectvalues,iftempreachesbeyond60Cthenbmsshouldshutoffcharging

6.3.4 N/A Notethatbalancingstartsoccurringonthemostchargedcellswhentheirvoltagesreachacertainthreshold

6.3.5 N/A Assoonasanycell’svoltagereachesthemaximumthreshold,chargingisinterrupted

6.3.6 Turnoffpowertothecharger Packisfullycharged6.4 BMS Discharging

ACTION RESULTS6.4.1 Turnontheload,inthiscase,thepack

shouldbeconnectedtotheABC-150whichwillactasthemotor

BMSshouldappearoperational,sincetheBMSisdigital,notethecellvoltages,andcurrentisnowflowingoutofthepack

6.4.2 N/A BMSisawareofthecurrentflowingoutofthepack,theSOCvalueisdecreasing

6.4.3 Verifycelltemperaturereadings,makingsuretheyarenotexcessive(60degreesC)

BMSshouldreadcorrectvalues

6.4.4 Dischargeat18C(360A)forfivesec.Repeatstepbutat8C(180A)constantcurrentuntilvoltagecutoffat60C

Assoonasanycell’svoltagereachestheminimumthreshold,batteriesshouldbedischarged

6.4.5 Turnoffload N/A

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7.0 Troubleshooting

Normal BMS functions can be verified through the Test Procedure section. However, there can be many issues of failure, this section outlines some general pointers. 7.1 Grounding be sure to use a short, low-inductance conductor between the BMS case to the chassis of the car if needed. 7.2 Shielding Make sure that for communication/sense wires, shielded cables and/or twisted pairs are used instead. This will greatly mitigate errors. 7.3 Wire Routing High-voltage cables should be routed along the power conductor and away from the chassis ground. Low-voltage communication wires should be routed away from power conductors and close to chassis ground.

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Resources

1. Davide Andrea 2011,” Battery Management Systems for Large Lithium

Battery Packs.”

2. September 13 2017, SAE International “2017-18 Formula SAE Rules.”

Retrieved from https://www.fsaeonline.com/content/2017-18-FSAE-Rules-

091317.pdf

3. Energus Power Solutions https://www.energusps.com/page/homepage

4. Orion Battery Management System

http://www.orionbms.com/?gclid=EAIaIQobChMIgv7Qq_Wi1wIVFQaGCh0C

vwzNEAAYASAAEgJxn_D_BwE

5. Elcon Charging http://www.elconchargers.com/index.html

6. 2013 Samsung “Introduction of INR18650-25R” retrieved from

https://www.powerstream.com/p/INR18650-25R-datasheet.pdf

7. Li-Ion BMS comparison http://liionbms.com/php/bms-selector.php