Thank you for the detailed information on battery management systems for electric vehicles. Let me know if you need any other assistance.

1. As presented to
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
http://www.trojanbattery.com/BatteryMaintenance/Testing.aspx
5.7
5.8
5.9
6
6.1
6.2
6.3
6.4
6.5
0
10
20
30
40
50
60
70
80
90
100
110
6V Lead Acid Battery Discharge Curve
Battery
Voltage
State of Charge

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
1. Must not Over-Charge an individual cell
2. Must not Over-Discharge an individual
cell
3. 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
Advantages: Does not need printed circuit boards connected to individual
cells.
Disadvantages: Master-Slave isolated communications can be challenging in
an EV.
 Several Slave
controllers
consolidate data
to a master

10. BMS Topology: Centralized
 Centralized
Master Control
Unit
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.
Central
Master
Control Unit
1

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
Company
(1)
Topology
(3)
No
of
cells
(4)
Balan.
(5)
Temper.
(6)
Display
Fuel
gauge
(8)
Over
Volt
Protection
Comm.
(9)
Case
(10)
Price,
48-cell
(11)
Agni
motors
Stybrook
Ltd
Distri
b.
1~200 ✓ - - - - Wire - ~$1000
Black
Sheep
Technolo
gy
Mod
ular
4~any ✓ ✓ - ✓ ✓ Seria
l
Plastic /
metal
~$2200
Elithion Distri
b.
1~255 ✓ ✓ ✓ ✓ ✓ Wire
CAN
RS23
2
- ~$2000 -
$4000
EV power Distri
b.
1~any ✓ - - - ✓ Wire Metal ~$1800*

13. Li-Ion BMS options (continued)
Company
(1)
Topology
(3)
No
of
cells
(4)
Balan.
(5)
Temper.
(6)
Display
Fuel
gauge
(8)
Over
Volt
Protection
Comm.
(9)
Case
(10)
Price,
48-cell
(11)
High Tech
Systems
(SSI?)
Distri
b.
1~any ✓ ✓ ? - ? Wire - ??
Ningbo
Yangming
Elite
Power
(BMS 50)
Mod
ular
Up to
50,
higher
available
✓ ✓ ✓ ✓ - ? Metal $1789
PackTrakr
from
KJHall
Motor Co
Mod
ular
6~40 - ✓ ✓ - - RS23
2
Plastic $710 (40
cells
only)
REAP
systems
Mod
ular
4~168 ✓ ✓ ✓ ✓ ✓ Bus - 697 x 4 =
$2788*
Volt
Blocher
Distri
b.
1~any ✓ - - - opt Opt
wire
- $864-
1008
assemble
d

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:
1. Company: A few other companies are getting ready to offer Li-Ion BMSs, but are not yet ready to be listed here.
2. 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
3. Topology: See previous slides
4. Number of cells: this is the acceptable range in the number of cells in series. The number of cells in parallel does
not matter.
5. 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.
6. Temperature: The BMS is able to measure and report individual cells' temperature.
7. 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.
8. "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.
9. 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.
10. 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.
11. Price: from manufacturers' websites or discussion with their clients.

16. 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
858-775-6275