EVAOSD

1. As presented to EVAOSD July 2009

2. Battery Management Systems for Electric Vehicles

3. Comparison:Lead vs. Lithium in EVs • Charging • Lead-acid batteries charges well in a long string • Over voltage in a cell is not good, but generally passes the current to the next cell in an equalization cycle with little damage. • Cell balancing can be done with a sophisticated charger (IUIa cycle) • Lithium batteries OK in a string, but over voltage on a individual cell can do serious cell damage. • Individual cell charging is solution, or • Balancing cells and charge in a string. • Discharging • Lead can tolerate discharging to 0% State of charge (SOC) with some cycle life damage. • Lithium will have serious damage when discharging below 2.0V, can be completely ruined.

4. Lead-Acid Discharge Curve 6V Lead Acid Battery Discharge Curve Battery Voltage State of Charge http://www.trojanbattery.com/BatteryMaintenance/Testing.aspx

5. Lithium Discharge Curves • Lithium Batteries have a fairly flat discharge curve with sharp shoulders http://enerdel.com/content/view/105/88/

6. Lithium BMS Challenges • Must not Over-Charge an individual cell • Must not Over-Discharge an individual cell • Must not let cells get too hot during charge or discharge

7. ENTER THE LITHIUM BMS • Many thoughts and discussions on what constitutes a Battery Management System (BMS): • Monitor and Detect Cell Over-Charge, and cut off charger • Monitor and Detect Cell Over-discharge and alert operator, or cut off system power. • Cell Balance for string charging • Temperature Monitoring • Remaining State of Charge determination • This is done in your cell phone & laptop, why not in your car? • High voltages and high currents make it difficult • Sparse BMS technology availability has held up Lithium conversion projects.

8. BMS Topology: Distributed • Put voltage monitor and discharge balancer on each cell, with digital communications for charger cutoff and status. Advantages: Simpler design and construction and its potential for higher reliability in an automotive environment. Disadvantages: Large number of mini-slave printed circuit boards which are needed and the difficulty of mounting them on some cell types.

9. BMS Topology: Modular • Several Slave controllers consolidate data to a master Advantages: Does not need printed circuit boards connected to individual cells. Disadvantages: Master-Slave isolated communications can be challenging in an EV.

10. Centralized Master Control Unit BMS Topology: Centralized Advantages: Single installation point. No complex inter-vehicle communications Disadvantages: Typical EV batteries are distributed in the vehicle, requiring wiring to a central location. Single source for balancer heat generation.

11. Li-Ion BMS Market options • Investigate BMS solution for highway capable EV conversion • Needs to support typical DC system: • 160 AH prismatic LiFeP04 (3.2V), • 250A + systems • 40-48 cells (128 to 153 volts) • Must monitor • Should manage, report and balance

12. Li-Ion BMS options

13. Li-Ion BMS options (continued)

14. BMS Honorable Mention • Lithium Balance – No published specs or pricing • Gary Goodrum – DIY BMS Ckt, 24 cell on Endless Sphere, Low current device for bikes • Metric Mind – Custom BMS, no pricing for BMS products • Boundless – creates custom battery packs. • Hot Juice Electric BEQ – Balance only • Manzanita Micro – Partial solution, 4 cells for $250 • Open Source BMS projects – no resolutions

15. Small Print: • Company: A few other companies are getting ready to offer Li-Ion BMSs, but are not yet ready to be listed here. • Class:• Simple: analog technology, just able to detect that some cell's voltage is too low or too high• Fancy: sophisticated digital technology, able to measure and report every cell voltage, and to calculate SOC • Topology: See previous slides • Number of cells: this is the acceptable range in the number of cells in series. The number of cells in parallel does not matter. • Balance: The BMS is able to remove energy just from the most charged cells, to allow the other cells to reach the same level of charge. • Temperature: The BMS is able to measure and report individual cells' temperature. • Current sense: The BMS includes a current sensor or at least an input for a current sensor, to measure battery current. This enables the BMS to react to excessive current, and to calculate the SOS or DOD. • "Fuel gauge": a.k.a.: "Gas Gauge". The BMS calculates the SOC (State Of Charge) or DOD (Depth Of Discharge), by integrating the battery current. • Communications: • Wire: separate wires are used, each with a single, specific function, such as to turn on the charger relay.• CAN: CAN bus, common in vehicles and European industrial equipment.• RS232: serial point-to-point communication, usually used only for initial set-up and testing, but some time also available for communication during operation. • Case: Whether the BMS controller is enclosed (metal or plastic case), or it is an open PCB assembly. Unless otherwise noted, any cell-mounted boards are assumed to be open PCB assemblies. • Price: from manufacturers' websites or discussion with their clients.

16. FLEX BMS-48 Hardy EV Flex BMS • Centralized BMS Architecture • Miniature In car display and operator alerts • Battery monitoring for over-voltage, under voltage • 3 versions in production • Up to 36 cells - For NEVs and small EVs • Up to 48 cells – For DC systems • Up to 84 cells – Prius plug-in conversions and AC systems • Temperature monitoring • Adjustable voltage and temperature thresholds • Cell balancing with built-in thermal management • Full diagnostic self test identifies faulty wiring • Internal Log allows identification of problem batteries • USB Log Option for detailed cell monitoring logs • Current monitor option for state of charge determination • Works with charger up to AC: 25A 240V • Priced for EV conversions: $891 for 48 cell system • Data logger option $50 • Current Monitor option $60 • www.ConvertTheFuture.com

17. Contact Information Mark Hardy Hardy EV, LLC Hardy.Mark@ConvertTheFuture.com ConvertTheFuture.com