Senior Design II Midterm Presentation September 29, 2009

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

Overview : Problem Solution Constraints Technical Practical Progress in Design II Future Plans

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: Total output current monitoring Ambient temperature monitoring Individual cell voltage monitoring CAN-bus communication

Technical Constraints Name Description Battery Technology The technology used to output voltage from the REBATEM must be lithium ion cells. AccuracyVoltage: 0 to 5 volts with an accuracy of ± 0.1 volts Current: 0 to 20 amperes with an accuracy of ± 10 milliamps Temperature: -30 to 200 °F with an accuracy of ± 2 °F Capacity / Cycle Life 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 °F or when current passes 20 amps. OutputOutput voltage must be within 14 to 16 volts. Current hour rating must be between 1.7 and 1.8 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

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]

Summary of Design I SystemResults ChargingNon-operational Current SensingFully Operational Voltage SensingFully Operational Temperature SensingFully Operational Fault ProtectionOperational CAN-bus CommunicationOperational Complete System TestN/A

Modifications in Design II 4 Lithium Ion Polymer Cells in Series Addition of a CAN transceiver IC (MCP2551) Different Charge IC (MAX745) MAX1758 – Former Charging Chip: Unreliable

Schematic – Main Board

PCB Layout – Main Board

Schematic – Charge Board

PCB Layout – Charge Board

Final Design Test Plan Charging Current < 1.9 A Fault Protection Output current < 20 A Output Maximum and minimum current/voltage Communication CAN-bus signals

Future Plans CAN transceiver implementation and testing PCB ordered Populate and test PCB Design Packaging Final Testing

Any Questions?

References: [1] [Online] Available: [2] “Lithium Batteries.” [Online]. Available: