Rutgers University Retired Lithium Ion Electric Vehicle Batteries Making the Most Out of their Second Use Jarek Roszko, Mohammad Khan, Ammar Sal, and Nabil Ali ECE 332:418 Table of Contents Page # 1. Table of Contents 2 2. Introduction (Background and Contributions) 3 3. Technical Background (Hardware) 3 4. Schematic 7 5. Technical Background (Software) 8 6. Experimental Results 16 7. Project Enhancement and Future Work 18 8. Economic analysis and Impact 18 9. Conclusion 18 10. Acknowledgements 19 11. References 20 Introduction Lithium ion batteries are some of the most widely used rechargeable batteries in the world. They are present in portable devices such as cell phones, handheld video game consoles, mp3 players, laptops, cameras, etc. They are even used for some power tools. Virtually any device that relies on a rechargeable power source uses lithium ion batteries. It is daunting to imagine a society without lithium ion batteries. Purchasing traditional one time use batteries repeatedly in a vicious cycle both generates more waste and forces consumers to spend more on energy. Because of lithium ion, the practicality of electric cars such as Tesla and Chevy Volt was attractive. Electric vehicles (EV’s) and plug-in hybrid electric vehicles (PHEV’s) are gaining popularity in the US and around the world because they are promoted as environmentally friendly cars. Air pollution, record high gas prices, and dependence on foreign oil are pushing sales growth of the EV’s and PHEV’s. Advertisements assure us of “zero emission” and the question asked is no longer “why electric?”, but “why gasoline?” While most electric car owners consider themselves “green”, the process of mining for lithium and the production of these batteries in reality are actually not as green as they think. In addition, the recycling process is neither simple nor cheap. Our objective for this capstone design is to utilize retired lithium ion batteries from EV’s and PHEV’s as a reusable power source for residential applications. We have divided the project into 2 phases: hardware and software. In the first phase, Ammar Saleem and Jarek Roszko worked on the hardware layout of the project while in the second phase, Mohammad Khan and Nabil Ali measured and monitored the core component of the project: the battery bank. Dividing the workload and focus in this way was efficient. It will be efficient to work in group of two people and successfully complete the project on time. Also, it will be very helpful to troubleshoot if any error occurs while testing. Hardware The hardware phase consists of planning the layout of the physical electronic materials, testing and creating the lithium ion battery banks and the load circuit. We created our battery bank with a 12 V maximum output consisting of three lithium ion cells. Each cell current specification is at 2 Amps. Being wary of the dangerous volatility of lithium ion batteries, we are installing several safety parameters to our project. The most important safety device that we acquired was a battery charger. We had ordered the Intelligent Digital Balance Charger/Discharger for (NiMH/NiCD 1.2V-18V, Li-Ion 7.4V-22.2V, LFE 6.4V-19.2V, SLA 2V-20V) battery packs and found it to be the best way to safely charge the battery cells at the appropriate rates. Balanced charging was a crucial component in our project, and if we had been unable to obtain the battery charger, our project would have been much more difficult. We would have needed to find a way to keep the rate of charge appropriate for each rate simultaneously, a task that would have been beyond the scope of this 3 month semester project. Though the National Instruments myDAQ helped us take measurements from 4 ports, we would have needed double the amount to measure the voltages of each cell in unison. Regardless, the myDAQ did not have balancing capabilities and the need for safety parameters would have been significantly larger. This need for balancing was biggest obstacle we had throughout our project. Because of the battery charger, we were able to overcome our difficulties and land one step closer to our goal. As a failsafe, we installed a circuit breaker and temperature sensors with automatic cutoff options onto the battery cells. The temperature sensors were a remarkable addition in that they ceased the charger from supplying power to the cells if temperatures exceeded 60 degrees Celsius, a threshold which conveniently reflected the lithium ion battery operating parameters. This was a key piece of hardware that assured us that in the case of a power surge, where the battery charger would have overloaded and supercharged the batteries, the temperature sensors would have broken the wire connections from the charger and the bank. This is what would have prevented the lithium ion batteries from being overcharged and thus, self-incinerating. To emulate a residential home, we assembled a small scale load circuit to test the battery bank’s functionality. In the load circuit, we included three light bulbs and a small fan. We also included a fan to provide an additional source of cooling for the battery bank. Figure (1) The Battery Banks emulating a laptop charger Figure (2) The Load Circuit with lightbulbs and fan Though we did not use myDAQ to balance our battery bank, it was an essential tool for measuring the voltage and current of our battery bank. In addition, we constructed a small scale simple RC circuit to learn the proper experimental measurement procedure before testing the lithium ion battery cells. By testing for voltage and current on the RC circuit, we were able to better learn about the myDAQ and its LabView partner software. It was crucial for us to have a standardized testing procedure on the RC circuit that we could then carry over to the actual battery bank and load circuit. If we had not refined our testing procedure and jumped straight into measuring and experimenting on the actual project circuit, we would have been in trouble if we ran into unforseen complications. Because we are dealing with lithium ion batteries, it is much better to run into those “unforseen complications” on a simple RC circuit than on the real deal load circuit where in the latter, bulbs can burst and fires can occur. Figure (3a) Above, the RC Circuit with Resistor and Capacitor Figure (3b) Below, the myDAQ supplying power and taking measurements Figure (4) Schematic Software Throughout the Information age, the rise of software became more and more prominent. Today, many hardware systems have complementing software systems to guide them. In a way, a hardware and software system can be seen as a metaphor for the human body and brain. The brain is what guides the body, tells it what to do, etc. The body is heavily reliant on the brain’s health. Without the brain, the body is just a shell. Analogous to many systems, the hardware is heavily reliant on the software. Without a prominent software component, the hardware component cannot fulfill the same level of performance. Let’s take a vehicle manufacturing facility. The hardware is the mechanical arms that piece together a car from different parts. With a human operator, comes the concern over stamina, precision, and efficiency. But with a software component that takes the human operator’s role, you have unlimited stamina, maximum precision, low cost, and an overall efficient system. Though the hardware component of our project was very important, the complementing software side was equally as important. Due to the dangerous volatility of lithium ion batteries, it is important to be wary of the batteries’ voltages so that they are not overcharged or too discharged. To observe and maintain the batteries’ voltages we are using the National Instrument’s myDAQ. Connected with NI’s LabView software, we are able to observe and record data measurements ranging from current to voltage. Without LabView and the myDAQ, we would have been unable to take measurements and plot real time graphs to show the charge and discharge of the lithium ion battery bank. http://images.studica.com/images/product/ National-Instruments-Mini-Systems- Accessories/94myVTOL%20miniSystem%20 07161207.jpg Figure (5) The myDAQ Hardware and LabView Software We had several goals to accomplish from a software perspective. We first used myDAQ and LabView to measure and test the RC circuit board. It is important to emulate our procedure on a low risk circuit board so that we may perfect our testing procedure on the actual lithium ion board design. The RC circuit board provides room for errors that we can avoid for the dangerous lithium ion batteries. http://www.ni.com/cms/images/devzone/t ut/measure_battery.PNG Figure (6) Battery voltage measurement example We have successfully taken voltage and current measurements from the RC circuit using the myDAQ and plotted our data with LabView. We created a LabView program to automate the measurement process. To record documented data and efficient graphs, we learned how to export data to Microsoft excel. Figure (7) Our LabView program, with Excel charts and graphs Fortunately, LabView is a very in depth software that provides users with many options and tools for common experimental needs. However, one challenge that we were trying to overcome is being able to stop power from supplying into the RC circuit board. This is a very crucial ability that we as the software designers need to be able to take advantage of. The usefulness of this feature will be most noticeable when experimenting with the lithium ion battery circuit. If we notice that batteries approach the minimum discharge voltage, we want to cease the process. Alternatively, if we notice that the batteries approach the maximum charge level, we also want to maybe use the myDAQ to cease charging the batteries. This is important because lithium ion batteries can’t be too overcharged or too discharged. If we transgress beyond a certain threshold, cataclysmic damage can occur and the batteries will self-ignite. We found that the best way to tackle this dilemma was through the battery charger. Initially, we were very concerned with balancing the lithium ion cells. Each of the 6 battery cells had different voltages. If we were to charge them all at once at the same rate, some cells would have been overcharged, and this would have caused an ignition that would have caused a fire to spread to the other batteries and the whole design board. As our project progressed, we were able to get our hands on the battery charger that relieved us of having to worry about the balancing dilemma from a software and control point of view. Another challenge we faced was how to be able to use multiple myDAQs to take multiple voltage measurements. Fortunately, LabView is powerful software that can support multiple myDAQ utilizations from the same computer. Since we did not have to worry about the balancing of our battery bank, our main focus became measuring and logging in the voltage and current at the terminals of the bank(s) just after the fuse to the ground. Therefore, to measure voltage of the bank, we used the DMM ports of the myDAQ to measure the analog voltage with respect to time and simultaneously to log it into a technical data management system (TDMS) file or excel document. All the data acquisition was done in 500 milliseconds sampling rate through all the ports or channels. MyDAQ was perfect for data acquisition since our measurement needed a minute time scale instead of smaller time divisions such as nanoseconds or milliseconds. The MyDAQ can acquire data as fast as 200K samples per second as per the manufacturer’s rating. Since our main focus was to acquire current and voltage readings, we had two myDAQ assistants in our software. We needed to acquire this data for our