ECE 441 Senior Design Preliminary Design Specification
Page 1 of 17
1 Revision History
Date
Description
Creator
Revision
10/29/2008
Initial Creation
Philip Hobbs, Adrian
Smith, and Nathen Perry
1
10/31/2008
11/01/2008
11/02/2008
11/03/2008
Edited sections 2 and 2.1,
Adrian Smith
Appendix A, Appendix B.
Edited sections 2.2
Philip Hobbs, Adrian
Creation section 2.2.1
Smith, and Nathen Perry
Edited sections 2.2.1,
2.3.1
Adrian Smith, Philip
Creation section 2.2.2,
Hobbs, and Nathen Perry
2.3.2
Adrian Smith, Philip
Creation section 3.1, 4.1
Hobbs, and Nathen Perry
1.1
1.2
1.3
1.4
Group # 23 - Charge Balancer for Solar Car Battery Pack
ECE 441 Senior Design Preliminary Design Specification
Page 2 of 17
2 Introduction
Is the future technology for automobiles going to revolve around solar energy? One
hopes so for economical reasons. Senior Design group 23 feels their solar project
provides a contribution to this field and a better future. The Senior Design group project
is the Charge Balancer for Solar Car Battery Pack. It is being sponsored by PacifiCorp
and mentored by James Johnson, an employee of PacifiCorp, and Hai-Yue Han, a
graduate student.
The purpose of this project is to design and develop a way to balance and equalize the
charge of the battery pack. This is going to be used in the Oregon State University (OSU)
Solar Powered Car for the 2010 North American Solar Challenge (NASC2010). Earlier
this year, 2008, the team used Lithium-Ion (Li-Ion) batteries and after finishing in last
place they decided to switch to a different type of Li-Ion batteries.
Specifically, the new cells the team is purchasing are the 18650’s produced by A123
Systems. One problem with Li-Ion batteries is that not every one is exactly the same, they
can have different capacities and discharge efficiency can vary. The Team plans on
balancing the charges using a capacitive method and limiting the transfer losses.
2.1 Customer Requirements & Project Background
Last year Oregon State University’s solar cell car participated in a national competition to
see who could build the most efficient and longest running solar cell car. OSU placed in
the middle of the group, which is not good enough. Last year the battery pack in the car
did not require a charge balancer because of the low energy density batteries that were
used. The plans for the 2010 solar cell car are to use a more sophisticated battery
configuration, which enables the car to run father on a single charge.
The change in the batteries require the implementation of a charge balancing system
(CBS) that can monitor the battery pack to ensure a full even charge [1]. The charge
balancer makes sure that all 670 Li-Ion batteries get charged to within 10mV of each
other. The cells are placed in a configuration to get the output voltage to 177 volts. To
achieve this, the cells are placed into groups called modules, which consist of 24
batteries. The cells placed within the modules are wired in a parallel configuration
making the modules self-balance. The trick comes when wiring 27 modules in a series
configuration, because they cannot balance. They charge unevenly thus creating the need
for the balancing system. The charge balancer ensures each module charges to its
maximum voltage and then stops charging. If a module charges slower than the rest the
balancer continues to charge it until the desired state is reached.
There are some specific requirements for the charge balancing system the Solar Cell Car
Team wants enforced. One of these needs is that everything on the car must communicate
to the main computer through a system called a control area network (CAN) bus. This
includes the feedback from the balancer. All data is real time and is constantly
communicating with the main computer. This allows the driver to have updated
Group # 23 - Charge Balancer for Solar Car Battery Pack
ECE 441 Senior Design Preliminary Design Specification
Page 3 of 17
information on where the current state-of-charge (SOC) is on the batteries. The
communication gives the driver the option to personally inspect the current charge and
change the charging scheme on all of the modules.
Li-Ion batteries ideally operate at a SOC from twenty to eighty percent of their fully rated
charge capacity [2]. To maintain this specification the CBS must equalize all the cells
within two watt-hours of charge in one hour. Another important specification requested is
the weight requirement placed on the CBS. It needs to be engineered to be as light as
possible, no heavier than 4 kg. This is complicated due to the number of components
required to ensure a safe and environmentally protected design. The weight requirement
is a trade off, because the more efficient the charger is the more it will weigh. The goal is
a happy medium between the weight and how efficient the balancer is.
2.2 Project Research
The following information contains decisions of components and designs needed for the
project.
2.2.1 Technology Review Analysis
Table 1. Competitive Analysis
Model No.
Vendor
Charge
Tolerance (%)
# series
cell
charging
LM3420
National
Semiconductor
1,0.5
>4
bq77PL900
bq24115
bq2954
Texas
Instruments
Texas
Instruments
Texas
Instruments
NA
NA
NA
5,6,7,8,9
,& 10
1, 2, &
3
1, 2, &
3
LTC6802-1
Linear
Technology
0.25
>12
AD7280
Analog
Devices
.1, .5
>6
ADP2291
Analog
Devices
1
1
ADP3820
Analog
Devices
1
1
MCP73861/2
/3/4
Microchip
0.5
2
Full
charge
Vmax
(V)
4.6, 8.2,
8.4,
12.6,
16.8
4.55, 5,
5.45
2.1, 4.2,
8.4
Max
input
Voltage
(V)
Control
Topology
cell over
temp
cutoff
Over
current
protection
over
voltage
Protection
under
voltage
protection
Reference
20
Linear,
Switch
mode
No
No
Yes
No
[3]
Yes
Yes
Yes
Yes
[4]
Yes
Yes
Yes
No
[5]
NA
7
Yes
Yes
Yes
No
[6]
2.3, 3.6,
4.2, 4.6
60
Yes
No
Yes
Yes
[7]
Yes
Yes
Yes
Yes
[8]
4, 5,
5.25
4.158,
4.2,
4.242
50
16
30
Switch
mode
Switch
mode
Switch
mode
Linear,
Switch
mode
Switch
mode
12
Linear
No
Yes
Yes
No
[9]
4.1, 4.2
15
Linear
No
Yes
Yes
No
[10]
variable
8.7
Linear
No
Yes
Yes
No
[9]
As seen in Table 1, National Semiconductor’s LM3420 is a nice compact charger that
allows for multiple cell charging and precision end-of-charge control. The LM3420 does
lack high temperature and over current protection, which endangers the cell’s life [3].
Texas Instruments (TI) makes several variations of chips that can be used for the CBS or
Charge Monitoring System (CMS). There are three best-fit models: the bq77PL900,
bq24115, and bq2954. Of the three there is one more suited to this project.
Group # 23 - Charge Balancer for Solar Car Battery Pack
ECE 441 Senior Design Preliminary Design Specification
Page 4 of 17
The bq77PL900 is one of the best systems TI has to offer and offers a great number of
options applicable to the charging process. This chip is designed to be a stand-alone
system and covers most situations that a battery experiences during charging [4].
On the other hand, the bq24115 chip offers much of what the bq77PL900 offers. The
difference being that it is not designed as a stand-alone system. The bq24115 also does
not contain an option for under voltage protection for the cell. This protects the cell from
completely draining itself [4, 5].
The bq2954 is the last of the TI chips analyzed. It has some small variations from the
bq24115. The option of great difference is the integrated switching controller [6].
Although there are differences, all three of the TI chips could work for the team’s
application with some modification.
Out of all the Linear Technology (LT) options analyzed the LTC6802-1 is the best fit.
This stand-alone system provides several options and application variations. It offers an
ability to monitor up to 12 cells at once, which none of the other systems in this analysis
do. Unfortunately, it is limited by its ability to protect the cells against over current [7].
Analog Devices makes two variations: a CMS and charge protection. Within the two
choices there are three other options. First is the AD7280, a CMS, which offers the
broadest options of the systems viewed in Table 1. There are very few circumstances that
this system does not cover. The only fault found is the minimal amount of cells that could
be monitored by the system [8].
The other two systems are oriented more toward the protection category. Both the
ADP2291 and the ADP3820 have very limited options. These limitations range from
their lack of cells they could charge to the cell protections that they offer, neither of these
would be an ideal choice for the project [9, 10].
MCP73864 produced by Microchip Technologies is the last possible chip reviewed for
the design. Like most of its competitors it offers many of the same options. The system
claims to be LI-ion and LI-Polymer ready, which none of the other system can claim
[11].
There are three full systems researched that could fit the application: the Texas
Instruments’ bq77PL900, Linear Technologies’ LTC6802-1, and Analog Devices’
AD7280. All three of these options are stand-alone and must be able to communicate to
the existing car system through the CAN.
Group # 23 - Charge Balancer for Solar Car Battery Pack
ECE 441 Senior Design Preliminary Design Specification
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Table 2. System Level Comparison
Vendor
Texas
Instruments
Linear
Technology
Analog
Devices
Model No.
# series cell
charging
Full charge
Vmax (V)
Max input
Voltage (V)
Control
Topology
Over voltage
Protection
Reference
bq77PL900
5,6,7,8,9,& 10
4.55, 5, 5.45
50
Switchmode
Yes
[4]
Yes
[7]
Yes
[8]
LTC6802-1
1-12
2.3, 3.6, 4.2, 4.6
60
Linear,
Switchmode
AD7280
1-6
4, 5, 5.25
30
Switchmode
The bq77PL900 is one option that TI offers for a CMS, shown in Table 2. This is an
individual chip designed to be a stand-alone system. It monitors the charging of up to 10
cells in series. There are features included that give the user the option to protect against
over voltage, over current, under voltage, cell temperature limits, and variable maximum
cell voltage [3].
LT offered very few CMS’s. One of them is the LTC6802-1. Another stand-alone system,
it provides several options and application variations. A noticeable benefit is the number
of cells monitored in series. This system offers an ability to monitor up to 12 cells at
once, which is the most optimal of the systems analyzed. Other beneficial features
included are over voltage protection, under voltage monitoring, temperature limiting of
the cells, and variable maximum voltage. Unfortunately, it is limited by its ability to
protect the cells against over current [7].
The most ideal Analog Device’s option for the CMS is the AD7280. It has a smaller
variable maximum voltage range and can only manage up to 6 cells in series. This
contributes to a decrease in the overall appeal of the chip for the project. The AD7280
has a feature that the others did not: the ability to daisy chained cells together. This
allows the user to increase the number of cells that can be monitored [5].
2.2.2 Technology Review Analysis – Blocks
Table 3. Microcontrollers
Ram Size
(Bytes)
Model Number
Manufacturer
Price
CPU Speed Packaging
AT90CAN32 [12]
Atmel
9.7$
2k x 8
16MHz
Tray
MB91210 [13]
Fujitsu
8.9$
288K
40MHz
LQFP-100
Core
Processor
AVR
FR60 Lite
CPU
Interface
Data Converters
CAN
A/D 8x10b
CAN
A/D
The microcontroller’s role in the charge balancing system is vital. The microcontroller is
responsible for all the electronic signals that go in and out of the balancing system. This
component directly controls the comparative analysis that is done on each of the modules
within the battery pack. All signal processing is done via a standard automotive
connection, the CAN bus.
Both of the microcontrollers listed in Table 3 communicate through this bus making them
both good candidates for the use of the project. The two biggest differences between the
chips is the core processor and clock speed. The balancing system does not require a fast
processor speed. Therefore nothing is affected by choosing the Fujitsu chip based on
speed. The deciding factor on the chip is the access to the software to program them. All
Group # 23 - Charge Balancer for Solar Car Battery Pack
ECE 441 Senior Design Preliminary Design Specification
Page 6 of 17
the resources needed to program the Atmel are attainable through the OSU engineering
accounts. The Atmel is thus a better fit for this system.
Table 4. Enclosures
Model Number
Manufacturer
Price
Dimensions (in)
Weight
Material
Latches
N4X-FG-100806RCHTL [14]
Adalet
62.98$
10x8x6
5 lbs
Fiberglass
Twist
1554VGY [15]
Hammond
19.03$
9.4x6.3x3.5
3 lbs
Hard Plastic
Screw on Lid
The balancing system is subjected to many different weather conditions and must be able
to withstand all of them. An enclosure assists in vibration reduction, water resistant, and
protects all the fragile circuitry from being crushed or shorted. The two enclosures, Table
4, compared are both very sturdy and protective against water damage. Both are made
from nonconductive materials, the Adalet of fiberglass and the Hammond of hard plastic.
The use of these materials means that a short from the case to the system is not possible
and vibrations are not passed along to the fragile components inside.
The main differences in the enclosures are the weight and the level of water resistance.
The Hammond easily defeats the Adalet in both of these categories. Due to the strict
weight requirements placed on the system this is a major advantage. The water resistance
varies due to the different latching systems. The Hammond has a rubber gasket under the
screw on lid and this makes it desirable for this application.
Table 5. Fuses
Rated
Amperage
Diameter
(in)
Terminal
Shape
Model Number
Manufacturer
Blow Speed
ROHS
Fuse Type
AGC-3 [16]
BUSSMAN
Fast
No
Electric Fuse
35A
0.25 Pin Wire
AGC-1-R [17]
BUSSMAN
Fast
Yes
Electric Fuse
35A
0.25 End Cap
Placing an in line fuse in the charge balancing system is not only a design requirement,
but also an essential aspect of designing a safe reliable system. The fuses in Table 5 share
the ability to be fast acting. This means there is no delay once the maximum current has
been reached. The protection of the fuse ensures that if one system in the solar car fails
then the others fail along with it.
Both of the reviewed fuses have every quality required for the project to be safe and
reliable. They vary slightly in two categories. One of these categories is the ROHS,
which is the restriction of the use of certain hazardous substances in electrical and
electronic equipment. This classification is not a deciding factor. The other difference is
the terminal shape, which changes the fuse holder that is required to hold each fuse in
place. Since this is just a preference the End Cap shaped fuse is chosen.
Table 6. Charge Balancer
Part Number
BQ24032A[5]
Battery
Charge (V)
Manufacturer
Texas Instruments
4.2 V
Optional Functions
Vout Regulated to 4.4V
LP3947 [3]
National
Semiconductor
Accepts either AC adapter or
USB power source
4.2 V
LiPolymer
Vin (max) (V) Li-Ion
USB
18
Yes
Yes
Yes
6
Yes
Yes
No
Group # 23 - Charge Balancer for Solar Car Battery Pack
Series Cells
3
1
ECE 441 Senior Design Preliminary Design Specification
Page 7 of 17
There are many charge balancing systems on the market, but the two listed in Table 6
meet the battery charge voltages needed to charge the cells. The ability to charge a cell to
a maximum of 4.2 V makes these balancers fit the power curve on the chosen cells
perfectly. The TI balancer has the ability to be retrofit to charge Li-Polymer cells, making
it a great choice if the type of cell were to be changed. The TI also has the ability to take
a larger input voltage, which allows the team to use the standard 12 V motherboard
power supply to run the electronics in the whole system. The most important feature the
TI has over the other is the ability to manage three cells as opposed to just one. Since the
pack being monitored is 27 cells in series the higher monitoring value it needed.
Choosing this feature for the final design requires fewer balancing systems. This results
in less heat and overall components on the circuit boards.
Table 7. Batteries
Typical
Model Number
Capacity Min Capacity
ICR18650NH [18] 2200mAh 2150mAh
LR18650 [19]
2200mAh 2150mAh
Nominal
Voltage
3.7
3.7
Discharge
Charge
Discharging
Current
max (V) Current (Std) Weight (Max)
4.3 .2 A
45 g
2 Amps
4.2 .2 A
47 g
2 Amps
Price
13.95$
8.25$
The batteries listed in Table 7 both have the same dimensions. They are both 18 mm in
diameter and 65.0 mm long, demonstrating the model number of 18650. The Solar Car
Team chose this battery dimension for use in the new pack.
The regulations of the solar car challenge state that if Li-Ion batteries are used then the
team is only allowed 30 kg of cells in the car. When the cells in Table 7 are compared
they are identical except for price and weight. The weight is the aspect that becomes
important because the more batteries you can fit in the pack the more power can be
stored. If the heavy cell is chosen then the team could only fit 638 cells into the car. If the
lighter one is used then the team can fit 648 cells into the car. The difference between the
two is 22.2 A-hr. This small weight difference makes the more expensive and lighter
weight cell the correct choice for this application.
Type
Level
C
General Purpose
Assembly Low
Table 8. Code
Used For
Debugger Portable Object Code
Programming
Software
Yes
Yes
No
Device Drivers Yes
No
Yes
Programs to use
Ease of Use
Flat assembler
Miracle
Moderate
Difficult
The microcontroller used in the charge balancing system comes without the operation
code installed. The chip has to be programmed to monitor the voltage differences in the
modules and decide to keep charging them or to stop when they become charged to the
programmed voltage. The options listed in Table 8 are to use a standard programming
language C or to use Assembly machine code language. Since the main computer uses C
code to do communication, the project must also be programmed in C to be capable of
exchanging data with it.
Group # 23 - Charge Balancer for Solar Car Battery Pack
ECE 441 Senior Design Preliminary Design Specification
Page 8 of 17
2.3 Feature Set
2.3.1 Absolute Minimum Requirements
The CBS must meet the following customer and instructor agreed upon requirements.
•
Use some form of resistive shunting or capacitive pumping
Grading Weight: 10/100
Engineering Requirements: Combination of capacitive pumping to charge
and/or resistive shunting to burn off excess charge going to the cells.
•
Able to equalize 2 watt-hours of charge in one hour
Grading Weight: 10/100
Engineering Requirements: Equalize 1 cell charged to 2 watt-hours and 1
uncharged cell in 1 hour.
•
Have protection circuitry to protect against accidental shorting
Grading Weight: 10/100
Engineering Requirements: Fuses will be placed in ideal locations on the
CBS to protect personal and individual systems in the chance of accidental
shorting.
•
Capable of balancing voltage on 2 or more cells in series
Grading Weight: 15/100
Engineering Requirements: Equalization of charge on as many cells in
series as possible.
•
Be water resistant
Grading Weight: 5/100
Engineering Requirements: Water resistant enclosure that protects the
circuitry against small sprays of moisture for 30 seconds.
•
Allow for manual override of balancing scheme from main computer
Grading Weight: 10/100
Engineering Requirements: Allows the charging scheme to be changed by
the driver or the cars main control system.
•
Must communicate to the main computer through the CAN bus
Grading Weight: 15/100
Engineering Requirements: The solar car main control system currently
uses a CAN bus, and the CBS will have to utilize the same system to
communicate with the current car controller.
•
Design weighs less than 4kg
Grading Weight: 10/100
Group # 23 - Charge Balancer for Solar Car Battery Pack
ECE 441 Senior Design Preliminary Design Specification
Page 9 of 17
Engineering Requirements: The CBS system design must weigh less then
4kg.
•
Operates through 20 minutes vibration test
Grading Weight: 5/100
Engineering Requirements: The CBS is placed in a vibrating environment
and required to operate during and after exposure to the vibration.
•
Be enclosed in a protective case
Grading Weight: 10/100
Engineering Requirements: Protective case will be used to ensure that the
circuitry will not be exposed to harmful elements that my damage it.
2.3.2 Desired Feature Set
•
Equalize cells voltages to < 10 mV
Grading Weight: 25/50
Engineering Requirements: 1 charge cell and 1 uncharged cell equalizes to
within 10mV of each other.
•
Equalization of more than 12 cells in series
Grading Weight: 25/50
Engineering Requirements: equalization of charge of more than 12 cells in
series.
Group # 23 - Charge Balancer for Solar Car Battery Pack
ECE 441 Senior Design Preliminary Design Specification
Page 10 of 17
3 Architectural Overview
3.1 Implementation Approaches
Approach 1.
The first option is a printed circuit board (PCB) that uses protection and balancing
schemes. This option requires the design of small PCB’s that employ balancing and/or
protection chips on it. These small PCB’s are applied to the individual cells. This
application works well typically, but the design requires at least 650 individual boards.
The production and application of so many boards is unacceptable due to the amount of
manpower and could exceed the budget. These issues, along with the fact that the
customer wants to avoid this scheme, are reason enough not to continue analyzing this
possibility.
Approach 2.
Another option is to use a configuration of power MOSFETs and comparators to control
voltages between the cells. It takes the application of hundred of MOSFETs, therefore
this option is not acceptable. Employing this alternative eliminates the ability for the
customer to control and observe the system. The option to override any charging scheme
is a key feature requested by the costumer.
Approach 3.
Finally the best-fit application determined is a system that is isolated from the battery
pack with its exclusive function balancing the cells. The CBS uses a possible
combination microprocessor for controlling the scheme of the charge, resistive shunting
to burn off any excess charge going to or on the cell, and capacitive pumping to increase
the charge rate of other cells. These choices, along with the ability to override the current
charging scheme of individual cells, meet most of the customers requested features.
Group # 23 - Charge Balancer for Solar Car Battery Pack
ECE 441 Senior Design Preliminary Design Specification
Page 11 of 17
4 Top Level Description
4.1 Top level block diagram
Figure 1.
4.1.1 Top level interface definition
Name
Power Supply
Type
Input
Table 9. Top level interface definition
Description
Power: 24 Pin Molex Connection
Pin 10,11 +12V
Pin 3,5,7,15 Ground
Pin 9 Standby +5V (10mA) Max
Micro Power
Input
Power: 2.7-5.5V Input, (400mA) Max
DC current per pin 40.0 mA
Balancer Power
Input
Power: +12V
DC Current: 2A (Max)
Group # 23 - Charge Balancer for Solar Car Battery Pack
ECE 441 Senior Design Preliminary Design Specification
Solar Power
Input
Power: Watts/Panel 305
Max Power: 187 kWs
Charge/Discharge
Input
Signal Type: Digital
Page 12 of 17
Output Power: Vcc = 5V, Min 4.2V,
DC Current Vcc and Gnd Pins 200mA
Signal Type: Digital C programmed Info.
Environment
Input
Protection: Water Resistance
Temperature: Heat Dissipation
Body Mount
Input
Mechanical: Mounting Hardware to car chassis
Mechanical; Vibration Reduction
Code
Input
Signal Type: Digital
Code Type: C
Balancer Mount
Input
Protection: Non conductive mounting Hardware
Mechanical; Vibration Reduction
Micro Mount
Input
Protection: Non conductive mounting Hardware
Mechanical; Vibration Reduction
Output Thermal Protection: Heat Grease
Power Bus
Input
Power: 4.2V (Max)
DC Current 2A (Max)
Motor Power
Output Power: 113.5 V (Max)
DC Current: 75A (Max)
Group # 23 - Charge Balancer for Solar Car Battery Pack
ECE 441 Senior Design Preliminary Design Specification
Name
CAN
Type
Input/Output Pin #
1
2
3
4
5
6
7
8
9
Page 13 of 17
Description
Signal Names
Reserved
Upgrade Path
CAN_L
Dominant Low
CAN_GND
Ground
Reserved
Upgrade Path
CAN_SHLD
Shield, Optional
GND
Ground, Optional
CAN_H
Dominant High
Reserved
Upgrade Path
CAN_V+
Power, Optional
Group # 23 - Charge Balancer for Solar Car Battery Pack
ECE 441 Senior Design Preliminary Design Specification
Page 14 of 17
Appendix A
References
[1] IEEE Xplore, "A PWM Controlled Simple and High
Performance Battery Balancing System" 2008. [Online]. Available:
http://ieeexplore.ieee.org/stamp/stamp, [Accessed: Oct. 15, 2008].
[2] Analog Zone, "Cell Balancing Maximizes The Capacity Of Multi-Cell Li-Ion Battery
Packs," [Online]. Available: http://www.analogzone.com/pwrt0207.pdf, [Accessed:
Oct. 20, 2008].
[3] National Semiconductor (July 2000), “LM3420 4.2, 8.2, 8.4, 12.6, 16.8 Lithium-Ion
Battery Charge Controller”, [Online], Available:
http://www.national.com/ds/LM/LM3420.pdf, [Accessed: Oct. 15, 2008]
[4] Texas Instruments (June 2008), bq77LP900, “Five to Ten Series Cell Lithium-Ion or
Lithium-Polymer Battery Protector and Analog Front End”, [Online], Available:
http://focus.ti.com/lit/ds/symlink/bq77pl900.pdf, [Accessed: Oct. 18, 2008]
[5] Texas Instruments (June 2004), bq24100, bq24103, bq24103A, bq24105, bq24108,
bq24109, bq24113, bq24113A, bq24115, “SYNCHRONOUS SWITCHMODE, LIION AND LI-POLYMER CHARGE-MANAGEMENTIC WITH INTEGRATED
POWER FETs (bqSWITCHER™)”, [Online], Available:
http://focus.ti.com/lit/ds/symlink/bq24105.pdf, [Accessed: Oct. 18, 2008]
[6] Texas Instruments (June 2008), bq2954, “Lithium Ion Charge Management IC with
Integrated Switching Controller”, [Online], Available:
http://focus.ti.com/lit/ds/symlink/bq2954.pdf, [Accessed: Oct. 18, 2008]
[7] Linear Technology (2008), LTC6802-1, “Multicell Battery Stack Monitor”, [Online],
Available:http://www.linear.com/pc/downloadDocument.do?navId=H0,C1,C1003,C1
037,C1134,P86662,D26880, [Accessed: Oct. 20, 2008]
[8] Analog Devices (2008), AD7280, “Lithium Ion Battery Monitoring System”
Available: http://www.analog.com/static/imported-files/data_sheets/AD7280.pdf,
[Online][Accessed: Oct. 19, 2008]
[9] Analog Devices (2008), ADP2291, “Compact, 1.5A Linear Charger Single-Cell
Li+Battery” [Online],
Available:http://www.analog.com/static/importedfiles/data_sheets/ADP2291.pdf,
[Accessed: Oct. 19, 2008]
[10] Analog Devices (2008), “AD3820, Lithium Ion Battery Charger” [Online],
Available: http://www.analog.com/static/imported-files/data_sheets/ADP3820.pdf,
[Accessed: Oct. 19, 2008]
Group # 23 - Charge Balancer for Solar Car Battery Pack
ECE 441 Senior Design Preliminary Design Specification
Page 15 of 17
[11] MICROCHIP (2008), MCP73861/2/3/4, “Advanced Single or Dual Cell, Fully
Integrated Li-Ion/ Li-Polymer Charge Management Controllers”, [Online],
Available: http://ww1.microchip.com/downloads/en/DeviceDoc/21893c.pdf,
[Accessed: Oct. 20, 2008]
[12] DigiKey, "AT90CAN32-16AU," 2008. [Online]. Available:
http://search.digikey.com/scripts/DkSearch/dksus.dll?lang=en&site=US&keywords
=AT90CAN32&x=0&y=0
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ECE 441 Senior Design Preliminary Design Specification
Page 16 of 17
Appendix B
Naming Conventions and Glossary
Block – A block is the basic element of a system. It is a standalone object that
performs some function in the system. A block should be ‘small’ enough that
everything contained inside of it can be fully understood as a whole, or the
contents can be purchased as a whole.
CAN – Control Area Network, type of bus permitting microcontrollers to
exchange data with other devices without requiring a host computer.
Cell – A single unit for electrolysis or conversion of chemical into electric energy,
usually consisting of a container with electrodes and an electrolyte; a battery.
CBS – Charge Balancing System, system that detects and equalizes the charge
level across several batteries.
CMS – Charge Monitoring System, system that detects and observes the amount
of charge in batteries.
Customer Requirement – A requirement that may or may not be able to be tested
as is. A requirement supplied by the customer, sponsor, or mentor.
Discipline Decomposition – The process of dividing a system into blocks based
on the primary knowledge used in defining each block. (e.g. computer science,
electrical, mechanical)
Engineering Requirements – A requirement that can be tested and evaluated
through a step by step process. Usually a numerical specification is included.
Environment – The set of influences that the system will be operating within.
These could include temperature, humidity, immersion, vacuum, etc…
Functional Decomposition – The process of dividing a system into blocks that
represent the required functions. See discipline decomposition, locality
decomposition.
Interface Characteristics – Every connection between blocks is defined by a
unique name and a list of interface characteristics. These characteristics define an
interface to the degree that a block can be built without knowledge of other blocks
in the system.
Li-Ion battery – Lithium-Ion battery, battery type that is capable of being
recharged.
Group # 23 - Charge Balancer for Solar Car Battery Pack
ECE 441 Senior Design Preliminary Design Specification
Page 17 of 17
Li-poly battery – Lithium Polymer battery, a more advanced type of Li-Ion
battery that is more robust and costs less to manufacture.
Locality Decomposition – The process of dividing a system into blocks based on
the similarity (locality) of blocks. (e.g. all inputs together, all outputs together)
Microcontroller – A working computer system on a chip that includes a processor
core (CPU), memory, and programmable input/output (I/O) peripherals.
Module – A separable component, frequently one that is interchangeable with
others, for assembly into units of differing size, complexity, or function.
SOC – State of Charge, the available capacity expressed as a percentage of its
rated capacity pertaining to batteries.
Sub-System – This is a grouping of one or more blocks that function together to
perform some task. (E.g. a motor and a motor controller perform the task of
motion.)
System – The complete system that you are designing. This includes all blocks in
your design.
Top-Level – This refers to the system block diagram containing all blocks in the
system.
Group # 23 - Charge Balancer for Solar Car Battery Pack