Transcript Lithium Battery Management Systems

As presented to
July 2009
Battery Management
Systems for Electric
Vehicles
Comparison:
Lead vs. Lithium in EVs

Charging

Lead-acid batteries charges well in a long string



Lithium batteries OK in a string, but over voltage on a individual cell can
do serious cell damage.



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)
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.
Lead-Acid Discharge Curve
6V Lead Acid Battery Discharge Curve
6.5
6.4
6.3
6.2
Battery
Voltage
6.1
6
5.9
5.8
5.7
110
100
90
80
70
60
50
40
30
20
10
0
State of Charge
http://www.trojanbattery.com/BatteryMaintenance/Testing.aspx
Lithium Discharge Curves

Lithium Batteries have a fairly flat discharge curve with
sharp shoulders
http://enerdel.com/content/view/105/88/
Lithium BMS Challenges
1.
2.
3.
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
ENTER THE LITHIUM BMS

Many thoughts and discussions on what constitutes a
Battery Management System (BMS):






This is done in your cell phone & laptop, why not in your
car?


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
High voltages and high currents make it difficult
Sparse BMS technology availability has held up Lithium
conversion projects.
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.
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.
BMS Topology: Centralized

Centralized
Master Control
Unit
1
Central
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.
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
Case
(10)
✓
-
-
-
-
Wire
-
~$1000
Mod
ular
4~any
✓
✓
-
✓
✓
Seria
l
Plastic /
metal
~$2200
Distri
b.
1~255
✓
✓
✓
✓
✓
-
~$2000 $4000
EV power
Distri
b.
1~any
✓
-
-
-
✓
Wire
CAN
RS23
2
Wire
Metal
~$1800*
Price,
48-cell
(11)
Comm.
(9)
1~200
Fuel
gauge (8)
Distri
b.
Display
Over Volt
Protection
Temper. (6)
Topology
(3)
Agni
motors
Stybrook
Ltd
Black
Sheep
Technolo
gy
Elithion
Balan.
(5)
Company
(1)
No of cells
(4)
Li-Ion BMS options
Case
(10)
✓
✓
?
-
?
Wire
-
??
Ningbo
Yangming
Elite
Power
(BMS 50)
PackTrakr
from
KJHall
Motor Co
REAP
systems
Mod
ular
Up to
50,
higher
available
✓
✓
✓
✓
-
?
Metal
$1789
Mod
ular
6~40
-
✓
✓
-
-
RS23
2
Plastic
$710 (40
cells
only)
Mod
ular
4~168
✓
✓
✓
✓
✓
Bus
-
697 x 4 =
$2788*
Volt
Blocher
Distri
b.
1~any
✓
-
-
-
opt
Opt
wire
-
$8641008
assemble
d
Price,
48-cell
(11)
Comm.
(9)
1~any
Fuel
gauge (8)
Distri
b.
Display
Over Volt
Protection
Temper. (6)
Topology
(3)
High Tech
Systems
(SSI?)
Balan.
(5)
Company
(1)
No of cells
(4)
Li-Ion BMS options (continued)
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
Small Print:
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
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.
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











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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



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
Data logger option $50
Current Monitor option $60
www.ConvertTheFuture.com
Contact Information
Mark Hardy
Hardy EV, LLC
[email protected]
ConvertTheFuture.com