Mid Semester Presentation February 24, 2009

Team Members Chapman, Jonathan Duties: Recharging Major: Electrical Engineering Dang, Quoc Duties: Cell Monitoring Major: Computer Engineering Grice, Quintin Duties: Power Circuit Major: Electrical Engineering Teeple, Richard Duties: Communication Major: Computer Engineering Smith, David Duties: Fault Protection Major: Computer Engineering

Project Origin This project stemmed from the curiosity of Dr. Marshall Molen and the EcoCar competition. Eight lithium ion cells CAN-bus (Control Area Network)

Overview: Problem Solution Constraints Technical Practical Approach Progress

Problem When dealing with lithium ion battery systems, the following aspects must be taken into consideration: Safety Fire and Explosion Communication CAN-bus System Life Weakest Link (individual cell)

Solution A rechargeable battery system that offers the following: selective charging over-all current monitoring individual cell temperature and voltage monitoring CAN-bus communication

Technical Constraints: Name Description Battery TechnologyThe technology used to output voltage from the REBATEM must be lithium ion cells. AccuracyVoltage: 0 to 5 volts with a tolerance of ± 0.1 volts Current: 0 to 80 amperes with a tolerance of ± 10 milliamps Temperature: -30 to 200 degrees Fahrenheit with a tolerance of ± 2 degrees Cycle Life / Capacity The REBATEM must maintain at least an 80% state of charge for the individual cells and a minimum of a 400-cycle life.

Technical Constraints (cont.): Name Description Fault ProtectionDisconnect the cells from the system when temperature passes 175 degrees Fahrenheit or when current passes 80 amperes. Charge cells up to 80% capacity. OutputThe output voltage must be within 14 to 16 volts. Current hour rating must be between 3.4 and 3.8 amp hours. CommunicationThe battery management system must communicate cell voltages, temperatures and current to external devices.

Environmental Green energy Contains no toxic metals Cadmium Lead No toxic fumes released if improperly disposed (incineration)

Safety Unstable - needs to be monitored Sony battery recalls UL 1642 states that users must be protected from risk of explosion or fire due to any instability of the Li-ion cells [2]. [1]

Cell Geometry PrismaticCylindrical VS [3][4]

Advantages Disadvantages High energy density Good mechanical stability Can withstand high internal pressure Poor heat dissipation Packaging must be designed around available cell sizes Cylindrical

Advantages Disadvantages Can be shaped to fit packaging restrictions Better heat dissipation Lower energy density Higher manufacturing costs No venting system to release internal pressure Prismatic

Types of Lithium ion Cells Cobalt ChemistryNominal Voltage Maximum Voltage Energy density Wh/kg Life Cycle Cobalt3.6V4.20V Manganese V4.20V > 500 Polymer3.7V4.20V > 1000 Phosphate V3.6V >800 [5] Manganese Polymer Phosphate

Cell Configuration Series of eight Eight in parallel Two series of four in parallel Four series of two in parallel

Evaluation: Output Voltage Output Current Amp Hours Series of eight V A Ah Eight in parallel V A Ah Series of four in parallel V20 – 40 A3.8 – 4.2 Ah Series of two in parallel7 - 8 V40 – 80 A7.6 – 8.4 Ah

Temperature Sensing Thermocouples Resistance Temperature Detector (RTD) Thermistors Integrated Circuit (IC) Temperature RangeCost (each) Thermocouples 0° to 1250° C >$2 RTD-196° to 788° C> $2 Thermistors-45° to 260° C<$2 IC-45° to 150° C<$2

Voltage Sensing - BMS Chip DS2762 High-Precision Li+ Battery Monitor Pros Less control lines Measures temperature and current Cons Extra communication Single cell monitoring [6]

Charging Discrete Components Complex Potentially unsafe Already been done in a simpler format Integrated Circuit Independent voltage and current loops Stand alone or uses microcontroller Built-in linear regulator power microcontroller Monitors charge current

Summary BMS: DS2762 Charging Sensor: Max8677c Cells: PL603495K [8] [7] [6]

Timeline JanuaryFebruaryMarchApril Research Ordering Parts Hardware Design Constructing and test Prototype Working Prototype

References: [1] [Online] Available: [2] “Lithium Batteries.” [Online]. Available: [3] "Li - ion Battery." [Online] Available: network.com/b2b/88/89/445/page6/48031/li_ion_battery.html. [4] "INOVA T4 Tactical Flashlight." [Online] Available: [5] “The high-power lithium-ion.” [Online] Available: [6] “Hi-Power Polymer Li-Ion Cell.” [Online] Available: [7] [Online] Available: [8]

Any Questions?