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.
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
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
