Download Appendix I - Harding University

Harding University
MAB-E
(Most Awesome Backpack - Ever)
Final Design Report
December 7, 2010
Eric Locke
Natalie Nill
Simon Reinhardt
0
Adrian Villalobos
Table of Contents
Requirements Specification ….…………………………………………………………………...3
Overview ……………………………………………………………………………….…4
Problem Statement ………………………………………………………………………..4
Operational Description …………………………………………………………………..4
Technical Requirements …………………………………………………………………..5
Deliverables ………………………………………………………………………………6
Preliminary Test Plan ……………………………………………………………………..6
System Design ……………………………………………………………………………………7
System Overview ……………………………………………………………..…………..8
Organization and Management ………………………………………………..…….........9
Block Diagram …………………………………………………………………………..10
Functional Decomposition of Blocks …………………………………………...……….11
Electrical Design ………………………………………………………………………………...12
User Interface ....…………………………………………………………………………13
Microcontroller ……………………………………………………………….…………15
Temperature Sensor ……………………………………………………………………..18
Car Cigarette Lighter Charging Circuit …………………………………………………20
DC to DC Converter …………………………………………………………………….21
DC to DC Converter for the LCD Screen ……………………………………………….23
DC to DC Converter for the Microprocessor ……………………………………………25
DC to DC Converter for the Temperature Sensor ………………………………………28
Solar Panels ……………………………………………………………………………...32
Battery………………………………………………………………………………......
Mechanical Design ………………………………………………………………………………35
Air-to-Air Thermoelectric Cooler Module Design ……………………………….........36
Thermoelectric Cooler Selection …………………………………………………..........36
Liquid Cooler Selection ………………………………………………….………….......37
Cold Side Fan ………………………………………………………………………........38
Chamber Material ……………………………………………………………………….38
Insulation ………………………………………………………………………………...39
Door Design ……………………………………………………………………………..39
SolidWorks Images .……………………………………………………………………..40
Calculations ……………………………………………………………………………...43
Budget ……………………………………………………………………………………….......46
Updated Prototype Budget ……………………………………………………………....47
Production Budget ……………………………………………………………………....48
Project Status ……………………………………………………………………………………49
Gantt Chart Fall 2010 …………………………………………………………………....50
Gantt Chart Spring 2011………………………………………………………………....51
1
Work Breakdown Structure Fall 2010 ………………………………………………..…52
Work Breakdown Structure Spring 2011 …………………………………………...…...53
Appendices …………………………………………………………………………………..…..54
Appendix A: Requirements Specifications Attachments …………………..………...….55
Appendix B: TPS40192 Datasheet……………………...……………………………….64
Appendix C: CSD16321Q5 Transitor Data Sheet…………………..…………………..65
Appendix D: Fan 3106kl ……………………………………………………..………….66
Appendix E: TEMP. SENSOR TD5A-Honeywell-datasheet-89078 ………………...…67
Appendix F: OP AMP LM741……………………...…………………………………...68
Appendix G: KEYPAD 96BB2-006-F-Grayhill-datasheet-71161………………………69
Appendix H: KP_ENCODER_EDE1144…………………………..…………………....70
Appendix I -Solar Panels Datasheet…………………………..……………………...….71
Appendix J -TEC - ZT5,16,F1,4040 Datasheet…………………………..……………...72
Appendix K -LCD Screen - RT204…………………………………………..………….73
Appendix L -Cooling - ECO A.L.C.…………………………..…………………...…….74
Appendix M -PIC24FJ256GB110.…………………………..…………………….…….75
2
Requirements Specification
Requirements Specification
Solar Powered Backpack Refrigeration Unit
Adrian Villalobos
Eric Locke
Natalie Nill
3
Simon Reinhardt
Overview
Vaccines have been one of the most beneficial healthcare discoveries of the past couple
centuries. Unfortunately, many people are unable to receive vaccines because, among other
reasons, health services are unable to reach them while keeping the vaccines cool enough.
According to the PATH organization, transporting vaccines in Africa can be extremely
challenging because regulating the temperatures of vaccines, while transporting them to rural
areas, is difficult and especially challenging in areas without constant power sources. In 2002,
over 84,000 people died from Hepatitis B (a vaccine that requires cooling) alone. Some of these
deaths are due to the inability of health organizations to transport vaccines to every place they
are needed. Many of these organizations are working to raise awareness about this issue and find
ways to reach more people. If more people could be reached, thousands of lives could be saved.
There are multiple ways of using alternate power to refrigerate vaccines currently being
used. The most predominant include nonelectric/uncontrolled cold packs, kerosene powered
refrigeration, and solar power. The cold packs have limited use because they have a maximum
cooling time of 48 hours. The kerosene refrigeration is impractical because it requires
continuous refueling and is potentially dangerous. Therefore, our team has decided to use solar
power because it is a portable, reliable, and an efficient way to solve this problem.
Problem Statement
There is a need for a better method for transferring vaccines into rural areas of
developing nations where power is not easily accessible for refrigeration. There is no developed
method that involves continuous refrigeration from a portable, consistent, and environmentally
friendly power source. By having a refrigeration system that can be powered during
transportation, the ability to distribute vaccines will be greatly increased and the chances of
ruining vaccines will be diminished.
Operational Description:
Before Transportation:
Before using the refrigeration backpack to transport vaccines any distance, the target
temperature must be met inside the refrigeration chamber. This can be achieved by one of four
ways:
1. External Power: The pack can be cooled by using external power from any outlet that
has an output standard to the US or African power grid.
2. Cooling Packs: The backpack can be cooled by placing cold packs, such as those used to
keep non-electric vaccine shipping boxes cool, inside the chamber.
3. Refrigerator: The backpack can be cooled by placing the chamber inside a larger
refrigerator or freezer until the target temperature is reached.
4
4. Solar Power: The backpack can be cooled beforehand using solar power. This method
may require time to charge the pack’s batteries and cool the chamber.
Also, the batteries must be charged before the vaccines are transported any distance. This
can be accomplished by either using an external power source and/or using solar power to charge
the batteries. For a faster charge time, the batteries can be charged while the cooling system is
off to send all power from the solar panels or external source to the batteries.
The user will be able to select the allowable temperature range via the user interface. First
select the mode for temperature selection, then type in the lowest allowable temperature and then
the highest allowable temperature in that order when prompted on the screen.
During Transportation:
IMPORTANT- avoid opening the refrigerator door until the destination has been reached
as this will compromise the environment of the vaccines and might deplete the backpack’s
energy supply prematurely.
The user will be able to monitor the current temperature inside the refrigerator via the
indicator mounted on the outside of the refrigeration chamber. They will also be able to read the
approximate battery life reading that will inform them as to the amount of energy currently in the
pack on the same screen.
The user should make sure that the solar panels are clear of anything that may block them
from the sun when possible.
After Transportation:
When the destination is reached the user should transfer the vaccines to a secure
environment to be used as needed. The backpack should remain in the refrigeration mode until
vaccines are no longer stored in the chamber.
Technical Requirements







The unit will cool a chamber within the backpack and maintain it at a temperature range
between 2℃ and 8℃ (35℉ and 46℉), for a minimum of 48 hours, at an average ambient
temperature up to 30°C (86°F), while stationary.
The temperature inside the refrigeration chamber will be read and relayed so it can be
displayed on the outside of the unit. The temperature sensor will have a maximum
resolution range of ± 1℃, and will cover a temperature range of at least 0°C to 30°C
(32°F to 86°F).
The entire unit will weigh less than 37 kg (≈ 82 lbs).
The backpack will not exceed a size of 60 cm x 100 cm x 60 cm.
The refrigeration system will be controlled to within the specified temperature range.
The unit will be able to measure the temperature inside the chamber to within ± 1℃.
The unit will be able to control the temperature inside the chamber to within± 3℃.
5



There will be a user interface used to control the refrigeration system. It will include: an
on/off switch, a digital temperature display, a temperature control interface, and battery
status indicators.
The unit will have a frame that can perform while being transported on foot and by
vehicle.
All systems will operate in a safe manner that will pose no threat of harm to the users.
Temperatures will not go above 50°C or below -30°C, voltages will not exceed 30 V DC,
and moving parts will be protected by a grill.
Deliverables
1. User’s Manual
2. Technical Drawings and Analysis of Hardware
3. Schematic of Circuit with Simulation Results
4. Code and Flowcharts
5. Report of Testing
6. Parts List with Budget
7. Final Technical Report
8. Solar Powered Refrigeration Backpack
Preliminary Test Plan




Four healthy individuals, with a minimum height of 1.6 m (≈ 63 inches) and weight of 54 kg
(≈ 120 lbs), will be able to pick up, put on, and take off the backpack with the assistance of
one other individual.
A performance test will be conducted. The backpack will be taken on a mile hike then will
immediately be put into a ventilation chamber for a 48 hour period. It will be tested at
temperatures between 22°C and 30°C (≈ 72°F and 86°F). The solar panels will be exposed
to two cycles of simulated sunlight for 12 hours then darkness for 12 hours. The maximum
and minimum temperatures will be recorded over that period. This test will be executed
three times.
Temperature gauge will be tested to ensure accurate (within ± 1°C) temperature readings
inside the chamber.
Backpack will be weighed to ensure it does not exceed the maximum weight.
6
System Design
System Overview
There is a need for a better method for transferring vaccines into rural areas of
developing nations where power is not easily accessible for refrigeration. There is no developed
method that involves continuous refrigeration from a portable, consistent, and environmentally
7
friendly power source. By having a refrigeration system that can be powered during
transportation, the ability to distribute vaccines will be greatly increased and the chances of
ruining vaccines will be diminished.
Our goal is to create a means of transporting vaccines to remote areas in rural parts of
developing countries. The design is a solar powered backpack refrigerator. The device will be
driven by a battery which can be recharged by either plugging it into a 110 V AC power outlet or
12 V DC car jack when available, or by a solar panel that is attached to the backpack when on
foot. A user interface will allow the user to set the temperature within the insulated chamber and
will inform him of the current temperature. It will also warn the user if the temperature ever gets
too high so that the ruining of vaccines can be prevented. A microcontroller continuously checks
the temperature within the insulated chamber and decides whether it needs to be cooled. The
device will weigh less than 37 kg (≈ 82 lbs) and will not exceed a size of 60 cm x 100 cm x 60
cm.
Organization and Management
Eric Locke – Eric is a senior level electrical engineering student, and was designated to be the
project leader for this design. He is primarily responsible for selecting and programming
the microcontroller that will control all of the functionality of the backpack. He will also
8
be responsible for designing and constructing the user interface that will allow the user to
control the backpack. Eric will assist Adrian with general circuit design and all other
team members in general project implementation. Finally, he will make sure that the
project is moving at the pace needed for its success as well as oversee each team
member’s work to ensure compatibility and communication between projects.
Adrian Villalobos – Adrian is a senior level electrical engineering student. He is primarily
responsible for the power and hardware circuits of the project. These include the battery
and battery charger, power control, and DC to DC converter circuits. Adrian will also be
responsible for any other circuitry that is needed for the backpack’s functionality. Adrian
will also assist other members in general device design.
Simon Reinhardt – Simon is a senior level mechanical engineering student. His primary
responsibility is to select and design the cooling system for the backpack. This will
include analyzing heat flow into and out of the chamber along with Natalie. Simon will
also assist Eric with selecting and mounting the temperature sensor. Lastly, he will assist
other team members in general project design and engineering decisions.
Natalie Nill – Natalie is a senior level mechanical engineering student. She is primarily
responsible for designing and constructing the cooling chamber of the backpack. This
will include selecting and applying the insulation that will line the chamber. Natalie will
also assist Simon in analyzing heat flow into and out of the chamber. She will assist other
team members with general project design and major engineering decisions.
The lists of tasks for each engineer are not all inclusive. Each team member is equipped
and able to assist one another in their respective tasks. Because of this, the schedule of tasks is
subject to change. Every member is responsible for consistent and thorough documentation of
their research, work, and progress. They are also responsible for presenting their data and
progress in each A3 status report.
9
Block Diagram
10
Functional Decomposition of Blocks
Solar Power: There will be solar panels attached to the unit that will output a minimum of
25W of power to the battery circuit.
Wall Outlet/ Car Outlet: The prototype will be able to run on power from a standard wall
outlet in a US home or business, and a standard vehicle dashboard power source.
Battery and Battery Charger: The battery will be able to hold enough energy to run the
backpack for 2 hours minimum, and be light enough to keep the backpack from
exceeding the weight limit of 37 kg. The battery charger circuit will allow the battery to
be charged from any power source connected at the time as well as ensuring that the
battery will not be discharged through undesirable sources.
User Interface: The user interface will be a panel on the outside of the unit that displays
the chamber temperature and the amount of battery power left. It will also allow the
user to input and change the desired temperature range.
Microprocessor: The microprocessor will have the following functions:
1) Read a user input from the user interface specifying a desired temperature range.
2) Read the current temperature inside the chamber and compare that temperature with the
user specified temperature. It will then be able to adjust the output from the power
control circuit to allow the chamber temperature to reach the user specified temperature
range, and then hold that temperature for a minimum of 48 hours.
3) Read an input from the battery circuit and analyze the battery life remaining. Once the
battery life is determined, it will output that value to the user interface screen.
4) Keep a time stamped record of the temperature during use and store the values in
memory to allow the user to trace the temperature history after use.
Power Control Circuit: The power control circuit will be controlled by the microprocessor
and will regulate the amount of power flowing from the battery to the cooling system.
DC to DC Converter: The DC to DC converter will take the power coming from the
battery and convert it to the desired input powers for the user interface, the
microprocessor, and the temperature sensor.
Temperature Sensor: The temperature sensor will be able to read the temperature inside
the cooling chamber to within ±1°C and relay that value to the microcontroller.
Cooling System and Chamber: The cooling chamber will have 35cm x 25cm x 20cm of
storage space as well as an insulation layer that will restrict heat flow into the chamber.
The cooling system will be permanently attached to the chamber and will consist of the
thermo-electric cooler, the heat sink, and the ventilation system to displace heat.
11
Electrical Design
12
User Interface
The user interface will be composed of three major parts. These are, the LCD screen, the
4x4 keypad, and the indicator LEDs.
LCD Screen:
Inputs: 5V dc (all components)
1.6 mA (operation)
145 mA (LED)
Outputs: ASCII characters on user
interface screen.
The LCD screen will be connected to power via the DC to DC converter and will have its
data lines connected directly to the microcontroller’s I/O pins. This configuration can be seen
below. Each switch in the circuit represents one I/O pin on the microcontroller. VCC will be
provided from the DC to DC converter and the circuit will be grounded to the same ground as the
battery. The values that are entered from switches 1-8 are recognized by the LCD screen as
ASCII values and interpreted in the internal circuitry of the screen. The pin marked A is the
enable pin and will be closed every time a character is written to the screen. The pin marked B is
the pin that controls whether the screen receives a control input or a data input. Finally, the pin
marked C controls whether the screen will read information from the microcontroller or write to
it. This pin will always be open, or grounded, because we will never need to write information
from the screen.
The eight switches
marked 1-8 represent the
leads coming from the
microcontroller’s I/O port
E. This port is composed
of 8 bits (RE0 – RE7)
which are listed as pins
1-3 and 60-64 on the
processor pin diagram on
page ##.
Switches A-C will
represent the leads coming
from I/O port G. The three
lines used (RG6 – RG8)
are located at pins 4-6 on
the processor pin diagram
on page ##.
Figure 1: LCD Screen
13
4x4 Keypad:
Inputs (rated): 12V dc
5 mA
Outputs (rated): 12V dc
5 mA
The keypad that will be used will be the Grayhill Standard Series 96BB2-056-F keypad.
Datasheet The 4x4 keypad has 16 buttons that allow current to pass through the keypad along a
certain path based on which key is pressed. These paths enter and exit the keypad through its
eight terminals located on the back side of the keypad.
The keypad’s eight terminals will be connected to a keypad encoder that will convert the
eight voltage signals from the terminals into a four bit binary input that will go to the
microcontroller. The encoder that will be used is the EDE1144 Keypad Encoder IC from eLab.
Datasheet This will reduce the amount of necessary I/O pins down to four and reduce the amount
of program calculation that will be needed to convert the keypad inputs into numerical inputs.
Figure 2 below is the circuit that will be used to connect the encoder to the keypad and send the
output to the microcontroller. The parallel outputs D0-D3 will be the outputs that are sent to the
microcontroller.
On the actual
keypad, the buttons
marked with the
numbers 1-9, * and
# will be used to
allow the user to
input the specified
temperature range
that the backpack
will operate within.
The buttons marked
A-D will be used to
allow the user to
control the mode in
which the backpack
is to run.
Figure 2: Keypad/encoder circuit
LED Indicators:
Inputs: 0 or 5 V dc
20 mA per LED (80mA total)
The LED indicators will be directly connected to the microcontroller I/O pins. There will
be a LED designated to display: Cooling system on, battery charging, low battery, and chamber
temperature out of range.
14
Microcontroller
The microcontroller that will be used is the PIC24FJ256GB106 microprocessor. The
decision between this processor and other TQFP 64 pin processors was made with the decision
matrix below.
Table 1: Microcontroller Decision Matrix
PIC24FJ192GB106 PIC24FJ256GB106 dsPIC30F6012A Weight
CPU Speed
2
2
4
0.1
Progammable Memory
3
4
2
0.2
RAM
4
4
2
0.16
USB Capable
2
2
0
0.04
A/D Converter Size
3
3
4
0.15
A/D Converter Speed
4
4
2
0.15
Price
3
3
1
0.2
Total
21
22
15
1.0
Weighted Total
3.17
3.37
1.86
These processors were considered because they were compatible with the MPLAB
module for programming and also because they have a sufficient number of I/O pins for our
applications. The PIC24FJ256GB106 was chosen primarily for its superior Programmable
Memory and RAM. These attributes make it preferable for embedded control and monitoring
applications.
The microcontroller will control all data flow between subsystems and signal analysis of
output signals that are needed in the backpack’s operation. The functions of the microprocessor
include:
 Temperature reading and control
 User input interpretation/User interface output control
 Battery status interpretation and display
 Controlling the operation mode of the backpack
The microcontroller will be able analyze the current temperature from the chamber by
receiving a voltage output from the temperature sensor. It will then convert that voltage into a
numerical temperature value using its A to D converter system. The microcontroller contains a
10-bit A to D converter that has 16 channels and can take 500k samples per second. Once the
temperature is found it will make a decision to turn the cooling system on, off or to have it
remain unchanged. These decisions will be based on the user specified temperature values that
will be entered via the user interface. The flow charts for these actions can be seen on the
following pages. The converted temperature values will constantly be sent to the LCD screen
during operation so little memory will be needed to record these values. These values will be
sent to the LCD screen continuously and will be recorded to memory every minute by using one
of the microcontroller’s five 16 bit timers.
15
Every minute the microcontroller will store a time stamped record of the temperature to
memory. These readings will contain an 8-bit temperature value and an 8-bit minute value that
will begin counting minutes when the backpack is turned on. The memory allotted for these
values will be enough to last the full 48 hour trip. That is 2880 slots of 16-bit records. That
comes out to 46 Kb of memory needed for these records. The microprocessor’s 256 Kb of
programmable flash memory will be able to hold this amount of data and have room for all other
functionality.
The microcontroller will also be able to read a voltage input from the battery and convert
that voltage into an estimation of the remaining battery life using the A to D converter. Because a
Lead Acid battery will be used in the project, there is no need to use any data besides the present
battery voltage to obtain an accurate battery life reading. To obtain the function for this reading,
the battery will be discharged over 12 hours over a constant load. The voltage will be read every
hour to obtain a curve that relates the voltage across the battery to the remaining run time. The
function of the runtime curve will then be mathematically entered into the microcontroller code
and used to convert the voltage into a numeric battery life result. The microcontroller will then
output that value to the LCD screen for the user to see.
Finally, the microprocessor will be able to control what mode the backpack is in by
controlling switches that connect and disconnect the different power source circuits and the
power control circuit. The flow charts for these actions can be seen on the pages below.
The flowcharts on the following pages have the conditions for the question blocks next to
the Yes or No condition indicators on the leads leading from the question block. If the condition
depends on whether a pin on the microprocessor is high or low, the values next to the yes/no
indicators is marked as a (1) for voltage high and a (0) for voltage low. If the conditions are
based on an analog value, the conditions for that are stated by the yes indicator.
Whenever a value is stored to memory it will be stored on the microprocessor’s general
flash memory. The bit by bit organization of this memory is not necessary because of the large
value of memory that is contained on the microprocessor. The C compiler will be used to assign
the specific spot in memory that the data and variables will be stored to.
16
Temperature Reading and Control
Read User Input
Start
Start
Load voltage from
temperature sensor to
memory
No(0)
Has Input
button(#) been
pressed?
Yes(1)
No
Convert voltage to a
temperature integer
value
Convert
temperature to
ASCII
Is
the temperature
above or
approaching the
upper limit?
Output present
temperature to
LCD Screen
Interrupt normal
processor operation
Ask for lower limit
temperature
Convert
hexadecimal input
from keypad into a
numerical string
Yes (temp_max –
temp) <= 2°C
Turn cooling
system on
No
Store value to
flash memory
Ask for upper limit
temperature
Is the temperature
approaching the
lower limit?
Yes(temp –
temp_min) <= 2°C
Turn cooling
system off
No
Is time elapsed
greater than one
minute?
Yes(# clock cycles >=
60*(cycles/sec)
Convert
hexadecimal input
from keypad into a
numerical string
Store value to
flash memory
Store temperature
to flash memory
No(0)
Is the cooling
system on?
Increment Total
time elapsed(min)
Output upper and
lower limit strings
to LCD screen
Yes(1)
Turn on cooling
system LED
No
Store total time
elapsed to flash
memory
end
Is the temperature
out of the specified
range?
Yes(temp >
temp_max // temp
< temp_min
Turn on
temperature out of
range LED
17
end
Reading Input from Battery
Controlling the Mode of the Backpack
Start
Start
Read input from battery
Read Input from
Keypad
Convert voltage into an
energy amount
estimation
Has
Button A been
pressed?
No(0)
Convert energy
estimation into a run
time remaining
estimation
Yes(button A
flag = 1)
Disconnect all
circuits and delay
Output runtime
estimation in hours and
minutes to LCD screen
No
Connect Solar
Panels
Is
the battery fully
charged?
Has
Button B been
pressed?
No(0)
Yes(Vbatt >= 14V)
Disconnect all
circuits and delay
Connect Wall
Circuit
Is
the battery low on
energy?
Yes(Vbatt <=11V)
Has
Circuit C been
pressed?
No(0)
Turn on low
battery LED
Yes(button C
flag = 1)
Disconnect all
circuits and delay
Is
the battery
charging?
Connect Car
Outlet Circtuit
Yes(1)
Turn on battery
charging LED
Yes(button D
flag = 1)
Disconnect all
circuits
Output current
mode to LCD
screen
End
Connect battery if
currently
disconnected
No(0)
Has
Button D been
pressed?
Yes(button B
flag = 1)
Disconnect the
battery from the
charge circuit
No
No(0)
End
18
Temperature Sensor
Outputs: 0 – 2.6V dc
0.1mA
Inputs: 3V dc
0.1 mA
Three different choices for the temperature sensor were considered and can be seen in the
decision matrix below.
Table 2: Temperature sensor decision matrix
A5003MA22P0
TMP122
TD5A Weight
Accuracy
4
2
3
0.2
Price
1
4
3
0.2
RTD Linearity
Easy Circuit
Application
Multisim Simulation
1
3
4
0.12
3
1
2
0.18
0
0
2
0.3
Total
9
10
14
1.0
Weighted Total
1.66
1.74
2.64
The temperature sensor chosen was the NIFE TD5A temperature sensor chip. Datasheet.
This temperature sensor was chosen because it was sufficiently accurate for our specifications, it
can be inserted into a circuit relatively easily, and is found in Multisim’s library. The sensor
basically works as a resistor that varies in its resistance as the temperature changes. This change
in resistance based on temperature is known as a resistance to temperature differential, or RTD.
The resistance to temperature change is very close to linear across the temperatures present in the
backpack (0-43°C) and can be represented precisely by the equation:
𝑅𝑇 = 𝑅0 ∗ (1 + 3.84𝑒 −3 ∗ 𝑇 + 4.94𝑒 −6 ∗ 𝑇 2 )
Where 𝑅𝑇 is the resistance at the temperature T
𝑅0 is the resistance at 0°C
𝑇 is the temperature in °C
The schematic for this device can be seen in Figure 3 below. As the resistance of
the sensor changes with temperature, the voltage Vout going to the microcontroller will also
change. The change in the voltage coming out of the temperature sensor only changes by 0.04
volts due to a temperature change of 0 – 65°C. This output needs to be amplified to use the full
range of the microcontrollers A to D converter system. Thus an op amp summer was used to
subtract the minimum voltage across the temperature range (2.8V) and then the voltage change
(0 – 0.04V) was amplified to make the change in voltage approximately 0V to 5V. This can be
seen in Figure 3. At 0°C the voltage should be at its maximum value for the temperature range,
the output voltage at that point is 5.112 V.
19
The high R1 value was selected to limit the current flowing through the circuit to below
100uA. This is done because any current beyond a value of 100uA will cause internal heating of
the temperature sensor and will cause the temperature reading to be less accurate. The voltage
value of 3V was chosen also to decrease the current going through the temperature sensor from
the normal 5V used in digital applications. This voltage value also allowed for a fairly simple
amplification to obtain an output voltage that uses the entire range of the microcontroller’s A to
D converter (0-5V). This amplification occurs across the op amp to the right of Figure 3 and the
gain is equal to the ratio of resistances R5 and R6.
Another consideration that must be addressed is the positive and negative voltages
required to power the op amps. To provide this from a battery it is required to use a separate
ground to reference the circuit. In Figure 4 the battery is represented by the 12V power supply
and the battery ground is seen at the bottom of the circuit. Voltage division is used to create a
node that is at 6V relative to battery ground. A voltage follower op amp is used to buffer that 6V
node to not allow the circuitry to the right of the op amp affect the 6V node. Thus the 6V output
can be used as a new ground and the 12Vsource and battery ground can be used as the 6V and 6Vseen in Figure 4.
Finally, the voltage that is to be subtracted from the circuit to obtain the correct output from the
summing amplifier (V4 in Figure 3) will need to be tested in circuit to obtain the exact value that
must be subtracted to have an output of 0V at around 50°C. A dc to dc converter will be used to
provide this voltage similar to the ones used to send power to the microcontroller. The actual
voltage that will be produced by this converter relative to the battery will be 6V minus the level
that needs to be subtracted because this will be negative relative to the new ground that will be
used in this circuit.
20
Figure 4: Temperature Sensor Circuit
Figure 3: Temperature sensor circuit
Figure 5: Op Amp Power Provision Circuit
Figure 3: Op amp power provision circuit
21
Car Cigarette Lighter Charging Circuit
Inputs: 12-14.5V dc
0-10A
Outputs: 12-14.5V dc
0-10A
The car connection circuit will be plugged into a cigarette lighter output on a car. The
standard output of these connections is rated at 12V and will output current up to their fuse rating
which is usually around 20-30A. When the car is off the input from the cigarette lighter will be
very close to 12V. When the car is turned on, however, the voltage will rise to anywhere from
13.5 to 14.5 V. Due to the durability of the lead acid battery no circuitry will be needed to protect
it from the higher voltage values. Thus the only circuitry needed is the car jack input and the
diodes to prevent discharge back into the car battery.
There will be a switch that the microcontroller will control that will connect and
disconnect the input from the car to the battery and the system. This switch will be closed if the
backpack is in the vehicle power mode and open otherwise. Also, diodes will be used to prevent
the battery from discharging if the voltage on the input drops below the voltage of the battery.
This is expected to happen when the car is first turned on and the engine is starting.
The lighter that will be used is the Digi-Key APP-001-20AMP-ND cigarette lighter plug.
Datasheet. This assembly contains a connection that will fit any standard car cigarette lighter
plug and is rated for 12V and up to 20A. This is well above the power requirements of our
system. The circuit can be seen in Figure 5. The 14.5V supply on the left is the car power supply
and the 12V supply on the right is the battery for the system.
Figure 4: Car Cigarette Lighter/Battery Circuit
22
DC to DC Converter
After researching about different circuit configurations for the design of the DC to DC
converter, we decided that we are going to use pulse switching regulators. This method is used to
transfer energy from the input to the output, converting one DC voltage level to another. It is
more efficient (power efficiency of 75-98%) than using a linear voltage regulator that would
dissipate unwanted power as heat. By using pulse-width modulation (PWM), the average value
of voltage (and current) fed to the load is controlled by turning the switch between supply and
load on and off at a fast pace. The longer the switch is on compared to the off periods, the higher
the power supplied to the load is. A LabVIEW file we found online demonstrates this, as shown
in Figure 6.
Figure 5: This LabVIEW simulation shows the longer the switch is on compared to the off
periods, the higher the power supplied to the load is.
23
According to the operating voltages and currents of the elements to be powered, the DC
to DC converter circuit needs to provide a power of about 0.8 W as shown in Table 1.
Table 3: Specifications for the DC to DC converter
Microprocessor
Temperature Sensor
Key Pad
LCD Screen
Total
Operating Voltage (V)
2
10
12
5
Operating Current (A)
0.001
0.0001
0.005
0.1465
0.1526
Operating Power (W)
0.002
0.001
0.06
0.7325
0.7955
The TPS40192 is an integrated circuit that is useful for this purpose. It has 4.5 V to 18 V
input voltage range and adjustable output voltage range of 0.59-15 V. The TPS40192 integrated
circuit is available in an 10-pin SOIC (Small outline integrated circuit) package which is a
convenient size for the design of the DC to DC converter circuits. This a very small integrated
circuit that may need to attached to the circuit board by using surface mount soldering. If the
budget allows us and we don’t have many further expenses, we can ask the company that will
make our printed boards to do this. The datasheet of the TPS40192 is available in Appendix C.
The TPS40192 integrated circuit is a cost-optimized synchronous buck controller. This
controller implements a voltage-mode control architecture with the switching frequency fixed at
600 kHz. The higher switching frequency facilitates the use of smaller inductor and output
capacitors, thereby providing a compact power-supply solution. The TPS40192 also has short
circuit detection, pulse by pulse limiting (to prevent current runaway) and provides limited
power dissipation in the event of a sustained fault.
Texas Instruments, on its website, provides software named SwitcherPro that can be used
to create circuits according to the specifications of the user. Using this software, the circuits for
the DC to DC converters were designed. These circuits use the TPS40192 integrated circuit
described previously.
24
Figure 6: DC to DC converter for the LCD screen
VinMin: 12.00V VinMax: 13.50V Vout: 5.00V Iout: 0.20A
25
Table 4 shows a list of the elements that the circuit for the LCD screen uses, along with
their values and manufacturer name.
Table 4: Elements of the DC to DC converter for the LCD screen
Name
C10
C11
C12
C2
C3
C6
C7
C8
C9
L1
Part Number
Standard
Standard
Standard
C3216X5R1C106KT
Standard
Standard
Standard
Standard
GRM32ER72A225KA35L
NPIS75T101MTRF
Description
Capacitor, Ceramic, 1uF, 6.3V, 10%
Capacitor, Ceramic, 1uF, 35V, 10%
Capacitor, Ceramic, 4.7uF, 10V, 10%
Capacitor, Ceramic, 10uF, 16V, 10%
Capacitor, Ceramic, 0.47uF, 16V, 10%
Capacitor, Ceramic, 8200pF, 10V, 20%
Capacitor, Ceramic, 330pF, 10V, 20%
Capacitor, Ceramic, 3300pF, 10V, 20%
Capacitor, Ceramic, 2.2uF, 100V, 10%
Inductor, 100uH, 0.5A, 360mΩ
Q1
CSD16321Q5
Transistor, NFET, 25V, 100A, 3mΩ
Q2
CSD16321Q5
R1
Standard
R10
Standard
R11
Standard
R2
Standard
R3
Standard
R5
Standard
Transistor, NFET, 25V, 100A, 3mΩ
Resistor, SurfaceMount, 10KΩ, 100mW,
1%
Resistor, SurfaceMount, 0.0Ω, 100mW,
1%
Resistor, SurfaceMount, 0.0Ω, 100mW,
1%
Resistor, SurfaceMount, 1.33KΩ,
100mW, 1%
Resistor, SurfaceMount, 4.22KΩ,
100mW, 1%
Resistor, SurfaceMount, 422Ω, 100mW,
1%
U1
TPS40192
IC, Controller, 10 pins
Manufacturer
Standard
Standard
Standard
TDK
Standard
Standard
Standard
Standard
muRata
Nic
Texas Instruments,
Inc.
Texas Instruments,
Inc.
Standard
Standard
Standard
Standard
Standard
Standard
Texas Instruments,
Inc.
The DC to DC converter for the LCD screen was designed for a minimum input voltage
of 12V, maximum input voltage of 13.5 V, output voltage of 5V and 0.2 A output current. This
circuit, compared to the DC to DC converters for the other elements has the best efficiency. Its
efficiency is displayed in Figure 8. The DC to DC converters for the microprocessor and
temperature sensor have the same configuration. Their only differences are the values of the
elements which provide the desired outputs.
26
Efficiency
80
Efficiency (%)
70
60
50
40
Efficiency For Vin Max
30
Efficiency For Vin Min
20
10
0
0
0.05
0.1
0.15
0.2
0.25
Current (A)
.
Figure 7: Efficieny of the DC to DC converter for the LCD screen
DC to DC converter for the Microprocessor
Figure 9 displays the circuit designed to provide the required energy for the
microprocessor. Table 5 shows an analysis for the outputs of this circuit.
Table 5: This analysis provided by SwitcherPro shows the desired outputs of 2V
Parameter
User
User
Default Default
Default
Calculated
Input
Input
Input
Input
Input
Minimum
Nominal Maximum Minimum Nominal Maximum
Calculated
Nominal
Calculated
Maximum
Units
Output Voltage 2.000
-
-
-
-
1.987
-
2.065
Volts
Output Ripple
-
-
-
-
40
-
-
1
mVp-p
Output Current
-
0.050
1.000
-
-
-
-
-
Amps
-
-
-
-
-
0.034
-
0.034
Amps
-
-
-
1.075
-
-
-
-
Amps
Gain Margin
-
-
-10
-
-
-
-19
-
dB
Phase Margin
-
-
45
-
-
-
48
-
Deg.
-
-
-
-
-
2
-
2
mOhms
-
-
-
-
-
2
-
2
mOhms
-
-
-
-
-
14.9
-
16.8
%
-
-
-
-
-
212.9
-
337.7
ns
-
-
-
-
-
-
24
-
KHz
Inductor Peak
to Peak
Current
Current Limit
Threshold
Upper FET
RDSon
Lower FET
RDSon
Duty Cycle
On Time
Min(switch)
Cross Over
Frequency
27
Figure 8: Circuit design of DC to DC converter for microprocessor
VinMin: 12.00V VinMax: 13.50V Vout: 2.00V Iout: 0.05A
28
Table 6: Values for the elements of the DC to DC converter for the microprocessor
Name
Part Number
Description
Manufacturer
Package
C10
Standard
Capacitor, Ceramic, 1uF, 2.5V, 10%
Standard
603
C11
Standard
Capacitor, Ceramic, 1uF, 35V, 10%
Standard
805
C12
Standard
Capacitor, Ceramic, 4.7uF, 10V, 10%
Standard
603
C2
C3216X5R1C106KT
Capacitor, Ceramic, 10uF, 16V, 10%
TDK
X5R
C3
Standard
Capacitor, Ceramic, 0.47uF, 16V, 10%
Standard
603
C6
Standard
Capacitor, Ceramic, 0.01uF, 4V, 20%
Standard
603
C7
Standard
Capacitor, Ceramic, 390pF, 4V, 20%
Standard
603
C8
Standard
Capacitor, Ceramic, 3300pF, 4V, 20%
Standard
603
C9
GRM32ER72A225KA35L
Capacitor, Ceramic, 2.2uF, 100V, 10%
muRata
1210
L1
NPIS75T101MTRF
Inductor, 100uH, 0.5A, 360mΩ
Nic
Shielded
Q1
CSD16321Q5
Transistor, NFET, 25V, 100A, 3mΩ
Texas Instruments, Inc.
QFN 5x6
Q2
CSD16321Q5
Transistor, NFET, 25V, 100A, 3mΩ
Texas Instruments, Inc.
QFN 5x6
R1
Standard
Resistor, SurfaceMount, 10KΩ, 100mW, 1%
Standard
603
R10
Standard
Resistor, SurfaceMount, 0.0Ω, 100mW, 1%
Standard
603
R11
Standard
Standard
603
R2
Standard
Standard
603
R3
Standard
Standard
603
R5
Standard
Resistor, SurfaceMount, 0.0Ω, 100mW, 1%
Resistor, SurfaceMount, 4.12KΩ, 100mW,
1%
Resistor, SurfaceMount, 3.74KΩ, 100mW,
1%
Resistor, SurfaceMount, 412Ω, 100mW, 1%
Standard
603
U1
TPS40192
IC, Controller, 10 pins
Texas Instruments, Inc.
SON
Table 7: Stress on the components of the DC to DC converter of the microprocessor
Device
Rated
Voltage
Calculated
Voltage
Rated
Current
(RMS)
Calculated
Current
(RMS)
Power
Calculated
Max.
Temp.
C9 (High Freq. Input Cap)
100V
13.6V
2.55A
19mA
731nW
-
C2 (Bulk Output Cap)
L1 (Output Inductor)
Q1 (Power Switch)
Q2 (Sync. Rectifier)
16V
25V
25V
2.01V
13.6V
13.6V
3.5A
0.5A
100A
100A
9.9mA
51mA
21mA
47mA
99nW
936uW
142mW
87mW
30˚C
28˚C
The DC to DC converters involve many elements, which imply lots of surface mount
parts. This is still more convenient than using voltage regulators that expel a lot of heat and are
less power efficient.
29
Figure 9: DC to DC converter for the temperature sensor
VinMin: 12.00V VinMax: 13.50V Vout: 10.00V Iout: 0.01A
30
Table 8: Main analysis for DC to DC converter for the Temperature Sensor
Parameter
User
Input
Minimum
User
Input
Maximum
Default
Input
Nominal
Default
Input
Maximum
Calculated
Nominal
Calculated
Maximum
Units
Input Voltage
12
13.5
-
-
-
-
Volts
Input Ripple
-
-
-
270
-
1.8
mVp-p
UVLO(Start)
-
-
-
-
4.2
-
Volts
UVLO(Stop)
Switching
Frequency
Slow Start
Estimated PCB
Area
Max Component
Height
-
-
-
-
3.4
-
Volts
-
-
600
-
-
-
KHz
-
-
1
-
-
-
ms
-
-
-
-
309
-
mm²
-
-
-
25
-
8
mm
Table 9: Output analysis for DC to DC converter for the Temperature Sensor
User Input User Input
Parameter
Nominal Maximum
Default
Default
Default Input Calculated Calculated Calculated
Input
Input
Maximum Minimum Nominal Maximum
Minimum Nominal
Units
Output
Voltage
10.000
-
-
-
-
9.900
-
10.383
Volts
Output Ripple
-
-
-
-
200
-
-
1
mVp-p
-
0.010
1.000
-
-
-
-
-
Amps
-
-
-
-
-
0.033
-
0.052
Amps
-
-
-
0.015
-
-
-
-
Amps
Gain Margin
-
-
-10
-
-
-
-18
-
dB
Phase Margin
-
-
45
-
-
-
48
-
Deg.
-
-
-
-
-
2
-
2
mΩ
-
-
-
-
-
2
-
2
mΩ
-
-
-
-
-
74.1
-
83.4
%
-
-
-
-
-
1055.6
-
1674.0
ns
-
-
-
-
-
-
22
-
kHz
Output
Current
Inductor Peak
to Peak
Current
Current Limit
Threshold
Upper FET
RDSon
Lower FET
RDSon
Duty Cycle
On Time
Min(switch)
Cross Over
Frequency
31
Table 10: List of elements used in circuit design
Name
Quantity
Part Number
Description
C10
1
Standard
C11
1
Standard
C12
1
Standard
C2
1
C3216X5R1C106KT
C3
1
Standard
C6
1
Standard
C7
1
Standard
C8
1
Standard
C9
1
GRM32ER72A225KA35L
L1
1
NPIS75T101MTRF
Q1
1
CSD16321Q5
Q2
1
CSD16321Q5
R1
1
Standard
R10
1
Standard
R11
1
Standard
R2
1
Standard
R3
1
Standard
R5
1
Standard
U1
1
TPS40192
Capacitor, Ceramic, 1uF,
16V, 10%
Capacitor, Ceramic, 1uF,
35V, 10%
Capacitor, Ceramic,
4.7uF, 10V, 10%
Capacitor, Ceramic,
10uF, 16V, 10%
Capacitor, Ceramic,
0.47uF, 16V, 10%
Capacitor, Ceramic,
0.015uF, 20V, 20%
Capacitor, Ceramic,
560pF, 20V, 20%
Capacitor, Ceramic,
3900pF, 20V, 20%
Capacitor, Ceramic,
2.2uF, 100V, 10%
Inductor, 100uH, 0.5A,
360mΩ
Transistor, NFET, 25V,
100A, 3mΩ
Transistor, NFET, 25V,
100A, 3mΩ
Resistor, SurfaceMount,
10KΩ, 100mW, 1%
Resistor, SurfaceMount,
0.0Ω, 100mW, 1%
Resistor, SurfaceMount,
0.0Ω, 100mW, 1%
Resistor, SurfaceMount,
619Ω, 100mW, 1%
Resistor, SurfaceMount,
2.87KΩ, 100mW, 1%
Resistor, SurfaceMount,
402Ω, 100mW, 1%
IC, Controller, 10 pins
32
Manufacturer
Standard
Standard
Standard
TDK
Standard
Standard
Standard
Standard
muRata
Nic
Texas Instruments,
Inc.
Texas Instruments,
Inc.
Standard
Standard
Standard
Standard
Standard
Standard
Texas Instruments,
Inc.
Table 11: Stress analysis for the components of the circuit
Device
C9 (High Freq.
Input Cap)
C2 (Bulk Output
Cap)
L1 (Output
Inductor)
Q1 (Power Switch)
Q2 (Sync.
Rectifier)
C9 (High Freq.
Input Cap)
C2 (Bulk Output
Cap)
L1 (Output
Inductor)
Q1 (Power Switch)
Q2 (Sync.
Rectifier)
Rated
Voltage
Calculated
Voltage
Rated
Current
(RMS)
Calculated
Current (RMS)
Power
Calculated
Max Temp
100V
13.6V
2.55A
13mA
363nW
-
16V
10V
3.5A
15mA
226nW
-
-
-
0.5A
18mA
117uW
-
25V
13.6V
100A
16mA
138mW
30˚C
25V
13.6V
100A
9.2mA
297mW
36˚C
100V
13.6V
2.55A
13mA
363nW
-
16V
10V
3.5A
15mA
226nW
-
-
-
0.5A
18mA
117uW
-
25V
13.6V
100A
16mA
138mW
30˚C
25V
13.6V
100A
9.2mA
297mW
36˚C
20
18
16
Efficiency (%)
14
12
Efficiency For Vin Max
10
Efficiency For Vin Min
8
6
4
2
0
0
0.002
0.004
0.006
0.008
0.01
0.012
Current (A)
Figure 10: Efficiency - this circuit is not as efficient as the other DC to DC converters,
although the overall power is very low.
33
Solar Panels
In order to choose the solar panels, 3 deciding factors were considered:
 The power draw during daytime use. (Governs the Solar Panel Wattage)
 The current draw during nighttime use. (Governs the Battery Size)
 The expected sunlight intensity during use.
For the system operation conditions during use it was assumed that there would be 12
hours of day and 12 hours of night for each day cycle. This means that there will be two days and
two nights in which the backpack must operate during the objective 48 hours of run time. During
the day the backpack will be charged by the solar panels if it is not being run by the wall outlet
or the car cigarette lighter. During the night, however, the backpack will be powered only by the
battery. Therefore it is necessary to obtain calculations on the power draw during the day to find
the amount of power that the solar panels must output to run the backpack along with the battery.
It is also necessary to find the current draw at night to find the amount of Amp-hours that the
battery must contain to provide energy through two night cycles.
To find the power draw during the day the heat gained through the insulation and the heat
expelled by the TEC are evaluated. The insulation is expected to have an average of 1.728W of
heat gain while the TEC is expected to expel heat from the pack by around 13W. These numbers
will be rounded, to account for inefficiencies and undesirable conditions, to 2W gained and 10W
expelled. Thus the cooling system will need to be turned on about one sixth of the total time to
expel the same amount of heat that was gained during the other five sixths. Or, the backpack will
be turned on 4 hours out of every day to expel the heat that was gained in the other 20 hours. The
amount of power draw taken by the system is now evaluated while the cooling system is on and
off. The values for this can be seen in Table 10 below.
Table 12: Full system (normal operation)
Microprocessor
Temperature Sensor
Key Pad
LCD Screen
Op Amps
DC to DC converter ICs
TEC
Cold Sink Fan
Heat Sink Fan
Total (Cooling system off)
Total
Operating
Voltage (V)
2
3
5
5
12
12
11.67
12
12
Operating
Current (A)
0.001
0.0001
0.0018
0.1465
0.0082
0.004
2.82
0.3
0.3
0.1616
3.5816
Operating
Wattage (W)
0.002
0.0003
0.009
0.7325
0.0984
0.048
32.9094
3.6
3.6
0.8902
40.9996
Now that the amount of time per day that the TEC will be turned on and the amount of
power in watts that the system draws are known, the power that the Solar panels must output per
34
day can be calculated. This was calculated using a 12 hour day and a 2 hour cooling system run
period. Increased values of for the power draw were used to compensate for undesirable
conditions.
𝑃(𝑊ℎ𝑟) = 𝑇𝑖𝑚𝑒(ℎ𝑟) ∗ 𝑃𝑜𝑤𝑒𝑟 𝑑𝑟𝑎𝑤(𝑊) = (2ℎ𝑟 ∗ 44𝑊) + (10ℎ𝑟 ∗ 1𝑊) = 98 𝑊ℎ𝑟
Thus the backpack will use 98 Watt-hours per day. A solar panel will need to output
more than this per day while being exposed to an average amount of sunlight.
Since the backpack will be operating solely on the battery during the 12 night hours per
day, the battery must provide most of the energy needed for the two night cycles that will occur
during the 48 hour period. The only energy that will be added to the battery for these times will
come from the recharge from the solar panels during the second day cycle. Thus the amount of
Amp-hours used during both night cycles must be evaluated to find how many Amp-hours the
battery must output for two nights before being fully discharged. The equation to find this, using
current values taken from Table 10, is as follows. The current values are also increased to
account for undesirable conditions.
# 𝑜𝑓 𝐴ℎ𝑟 = 𝑇𝑖𝑚𝑒(ℎ𝑟) ∗ 𝐶𝑢𝑟𝑟𝑒𝑛𝑡 𝑑𝑟𝑎𝑤(𝐴) = (4 ℎ𝑟 ∗ 3.8𝐴) + (20ℎ𝑟 ∗ 0.2𝐴) = 𝟏𝟗. 𝟐 𝑨𝒉𝒓
This shows that the backpack will draw 19.2 Ahr in the 24 hour period of two night
cycles. Thus the battery must be able to hold at least this much energy.
The wattage needed from the solar panel is governed by both the Watt-hours used by the
backpack during the day and the expected time of average sunlight per day. This can be found
many places and in many ways. A view of the solar Insolation or a measure of solar radiation
energy received on a given surface area in a given time (kWh/m2 /day) for each part of the world
can be seen in Figure 12.
Figure 11: Solar insolation in different parts of the world
35
From this map of sunlight intensity it can be deduced that the average amount of sunlight
for most target parts of the world (including most of Africa, South America, and Asia) is
somewhere around 4 kWhr/m2 /day. The areas that meet this sunlight intensity are shown in dark
orange, red, and dark red in Figure 12. The backpack will be designed assuming this amount of
sunlight intensity. 4 kWhr/m2 /day converts to about 165 Watts/m2 /day. The backpack’s power
requirement of 98 Whr/day is well below 4kWhr/day therefore the area of the solar panel can be
much less than 1 meter squared.
To obtain 98 Whr/day and charge the backpack’s battery, the solar panel’s wattage must
be high enough to absorb more than 98Whr of energy within the amount of time that the sunlight
intensity is high enough to provide power to the system. In an undesirable situation, the number
of hours of sunlight per day would be around 4 while in better cases the number would be around
10. The backpack will be designed for the worst case scenario of 4 hours. At 4 hours of sunlight
per day the backpack would need at least 25 Watts to provide the 98 Whr/day needed to run the
backpack. To partially charge the battery, the wattage would need to be higher than this. 30
Watts is a common output rating for solar panels and would be sufficient for this application.
Furthermore, 30W solar panels can be obtained within the budget requirements of the project.
Therefore 30W is the minimum wattage that will sufficiently power and charge the backpack
when the solar panel is exposed to 4 hrs of sunlight per day.
36
Battery
In order to choose the most convenient 12V battery, a decision matrix was made (Shown
in Table 11). The characteristics that were taken into consideration in this decision were: price,
amp hours, size, weight and energy density. For the batteries with less than 15Ahs, the
distribution of weights was given taking into consideration that 2 batteries would be used instead
of one in order to provide the required power.
Table 13: Decision matrix for choosing the battery
12 V Batteries:
B&B HR15-12
Shmarock
U1-12RTL
Batterygeek
2010wonder 15
2010wonder 9.8
UB121180
UB121181
SLA24-12
Price
$23.80
$214.11
$249.99
$27.24
$72.32
$40.00
$38.95
$38.95
$54.95
30%
10
4
4
10
6
8
9
9
9
Ah
14
10
24
10
15
9.8
18
18
26
20%
10
6
10
6
10
6
9
9
10
Size (in)
5.95x3.86x3.7
small
7.75x5.2x7.2
5.94x2.57x4.42
2.1x5.5mm
4.4x1.7x1.49
7.13x3.01x6.57
7.13x3.01x6.58
6.89x6.54x4.92
18%
7
10
6
7
10
9
5
5
6
Weight(lb)
9.26
1.32
9
7
1.27
0.94
11.9
11.9
19
22%
7
9
7
7
9
10
6
6
5
Energy
density
Lead Acid
Lithium Ion
Lithium Ion
Lead Acid
Lithium Ion
Lithium Ion
Lead Acid
Lead Acid
Lead Acid
According to the results of the matrix, it was decided that the B&B HR15-12 battery
would be used to provide energy to the system. The datasheet for this battery can be found in
Appendix X.
37
10%
8
10
10
8
10
10
8
8
8
Total
8.6
7.18
6.82
7.8
8.58
8.42
7.52
7.52
7.68
Mechanical Design
38
Air-to-Air Thermoelectric Cooler Module Design
An air-to-air thermoelectric cooler module was chosen for our cooling system.
Alternative solutions such as a free-piston Stirling cooler (FPSC) or a compressor proved to be
either unavailable or not suitable for our project due to cost, weight, and safety specifications.
The air-to-air thermoelectric cooler module consists of a thermoelectric cooler (TEC), a self
contained liquid cooler with radiator and fan to dissipate heat to the environment, and a cold sink
with fan to distribute the cold air within the insulated chamber.
Table 11: Decision matrix for cooler selection
Thermoelectric Cooler Selection
Laird Technologies, a manufacturer of TECs, offers free software called “AZTEC
Thermoelectric Design Guide” which lets the user enter certain parameters and then recommends
one or more TECs that are appropriate. The AZTEC software can be found at
http://www.lairdtech.com/Products/AZTec-Software-Download/. Using this software,
parameters for the ambient temperature, the cold surface temperature, and the required heat
pumping were entered. At an ambient temperature of 30℃, the TEC draws a current of 2.82 A at
an operating voltage of 11.67 V and is able to expel 13.10 W of heat. The liquid cooler and the
cold side fan draw an additional current of about 0.725 A. In order to account for inefficiencies,
it was assumed that the TEC expels 10 W of heat, and with a heat gain of 2 W, the TEC has to
run only 20% of the time, therefore justifying such high amperage for a portable backpack
refrigerator.
39
Liquid Cooler Selection
Figure 12: ECO Advanced Liquid Cooler
The “CoolIT ECO Advanced Liquid Cooler” (DATASHEET is found in Appendix __) is
a self contained, low profile liquid cooling system that was designed to cool a CPU of a desktop
computer. Liquid coolers are the next generation heatsink and have many advantages over
conventional extruded heatsinks. This cooler was chosen, because it is has a very low thermal
resistance and therefore is able to reject the heat from the TEC to the environment well, because
it is lightweight, and because it is reasonably priced (≈$60). Another reason why the ECO
A.L.C. is an attractive way to remove heat from the TEC is that the water block with the pump
and the radiator with the attached fan are two separate parts. This feature allows for more
options in the design of the air-to-air thermoelectric cooler module, because the radiator and the
fan can be attached below the insulated chamber rather than in its wall.
The pump that is attached to the water block uses only 1.5W, and the 120mm fan that
blows air through the radiator uses about 0.3A, which our system will be able to support.
Table 12: Decision matrix for heatsink selection
40
Cold Side Fan
For the cold side fan an 80 mm fan will be used, because the brackets of the ECO A.L.C.
are 80 mm apart and that way the TEC can be sandwiched between the water block and the cold
sink. Long screws will be used to attach the fan to the cold sink and to the water block.
The NMB-MAT 3106KL 80mm x 15mm fan (DATASHEET is found in Appendix__)
𝑚3
was chosen for the cold side fan. This fan is able to produce a maximum airflow of 0.93 𝑚𝑖𝑛
drawing a current of 0.3 A. Its low profile makes it ideal for this design, because the air-to-air
thermoelectric cooler module will be incorporated into the insulation of the inner chamber of the
backpack. It costs only $12 and its weight is negligible. Compared to other low profile 80 mm
fans, the 3106KL has the ability to produce a much larger airflow, which will increase
convection and therefore increase the efficiency of the cooling system. At its maximum speed of
3000 rpm, this fan is much louder (34 dB) than other fans of its size, but creating too much noise
is not an issue, so this property is totally acceptable. Overall, the Panaflo 80mm x 15mm fan has
everything that is needed for the cold side fan.
Chamber Material
The material chosen for the inner chamber and outer chamber is tempered hardboard.
The only types of materials practical for the chambers were hard plastics and metals. Most
metals were out of the question because the weight of the backpack must be minimized and they
would definitely be too heavy. The one metal considered was aluminum. It is a light enough
metal that it was a possibility, but it was more expensive than some of the other options we
considered. Injection molding was briefly considered because it would be the easiest way to
make it and because this is the usual way a chamber such as this would be made. But it is very
expensive and out of the range of our budget. Arcylic sheets were an option that we seriously
considered. They were very light and strongy, which were two very important qualities to us.
Their price was reasonable, but not the best. And while they were strong, they were also
flexible, which worried us. Tempered hardboard was a material we found based on a suggestion
by a Lowe’s employee. It is slightly heavier than the acrylic sheets, but it was still lighter than
aluminum. It is a very strong, non-flexible material and it has a very good price. These reasons
together contributed to it being chosen as the chamber material.
Table 13: Decision matrix for chamber material selection
Weight
Cost
Strength
Flexibility
2
2
3
2
Molded
Plastic
2
0
2
3
Total
9
Weighted Total
2.2
Aluminum
3
2
3
1
Tempered
Hardboard
2
3
3
3
7
9
11
1.3
2.4
2.7
Acrylic Sheets
41
Weight
0.3
0.4
0.2
0.1
1.0
Insulation
Polystyrene sheathing was chosen as the type of insulation for the unit. There were
multiple materials considered for the insulation. A vacuum was briefly considered because it is
the best insulator. But that would have presented problems in sealing it and if the box was
accidentally punctured the insulation would become completely void. Aerogel sheets were also
considered. They have very high R-values (insulation values), but they were very expensive and
out of the range of our budget. Fiberglass insulation was considered. It is commonly used as
housing insulation. Fiberglass also has a high R-value, but it greatly decreases when the
fiberglass is compressed (because its air pockets are what give it such a high R-value); which it
would be in our design. Also, fiberglass is not made to get wet, which it would from
condensation on the inner chamber, and it would not have provided a firm support for the inner
chamber, which was something we were looking for. Different types of spray foams were also
considered. Types of spray foam used in housing insulation were considered, but that could
only be gotten through a contractor, which would have been too expensive. Small bottles of
spray foam are sold at local hardware stores for home use, but these had a lower R-value than we
wanted. Also, they took several hours to cure and once cured become rigid. This would have
caused problems with holding the inner chamber in place while the foam cured and would not
have allowed for changing of the insulation if something unexpected happened. The material
that was then decided upon was rigid foam boards; more specifically, polystyrene sheathing
insulation. These had high R-values, provided protection/support for the inner chamber, are
relatively cheap, and locally available. Our team took a trip to Lowes and found a type of board
that fit our needs.
Table 14: Decision matrix for insulation selection
Vaccuum
Aerogel
Fiberglass
Sprayfoam
Rigid Board
Weight
R-Value
3
3
3
2
2
0.4
Durability
0
0
0
2
3
0.25
Cost
2
0
2
3
3
0.25
Ease of
Installation
1
2
1
1
3
0.1
Total
6
5
6
8
11
1.0
Weighted Total
1.8
1.4
1.8
2.15
2.6
Door Design
There were multiple way to design the door of the refrigeration unit. The door could
either be on one of the sides of the backpack or on the top. We decided to put it on the top of the
unit because it has less surface area and would therefore experience less heat loss when opened
as opposed to a side door. Another reason we choose to put it on the top was because there
42
would be less chance if it not being shut all the way or catching on something and being torn
open.
There will be one door on top that will open the outer chamber and have the insulation
below attached to it. Then the inner chamber will have its own door as well. Both of the doors
will be attached with hinges. Gasket seals will be applied around the edges of each door in order
to prevent heat loss. The rough cross sectional sketches below illustrated how these doors will
be designed.
SolidWorks Images
On the following pages are pictures of the model of our project in SolidWorks. The
model is built to the actual dimension and each part has its correct material properties applied to
it in order to allow future finite element analysis (FEA) studies. The outside box dimensions
(H×W×D) are 79.64cm x 59.48cm x 54.48cm.
43
Door
Hinges
Outer Shell
User
Interface
Figure 13: Backpack unit - front view
Outer Shell
Door
Hinges
User
Interface
Strap Attachments
Location
Figure 14: Backpack unit - back view
44
Door
Hinges
Insulation
Outer Shell
Inner Shell
Cool Pack
Vaccine Packages
Frame
User
Interface
Circuitry
Battery
Figure 15: Cross sectional front view of the backpack (note: vaccines are not packaged in a
standard way, this type of vaccine packaging is an example of one way to package them)
Door
Hinges
Outer Shell
Inner Shell
Cool Pack
Insulation
Vaccine Packages
Frame
Battery
Figure 16: Cross sectional side view of the backpack
45
LED Screen
Keypad
LED Screen
LED Lights
Figure 17: Model of user interface
Calculations
Heat Loss Through Insulation:
𝑓𝑡 2 ∙℉∙ℎ𝑟
The R-value of each sheet of our insulation is 𝑅 = 6.82 𝐵𝑡𝑢 .
Each sheet is 2.54 cm (1 in) thick. We will be using 12.7 cm (5 in), so our R-value of the
insulation on each side is:
𝑅5𝑖𝑛 = 5 (6.82
𝑓𝑡 2 ∙℉∙ℎ𝑟
𝐵𝑡𝑢
) = 34.10
𝑓𝑡 2 ∙℉∙ℎ𝑟
𝐵𝑡𝑢
.
Converting to metric units:
𝑅5𝑖𝑛 = (34.10
𝑓𝑡 2 ∙℉∙ℎ𝑟
𝐵𝑡𝑢
)(
𝑚2 ∙℃
𝑊
𝑓𝑡2 ∙℉∙ℎ𝑟
1
𝐵𝑡𝑢
0.17611
) = 6.005
𝑚2 ∙℃
𝑊
.
The surface area is:
𝐴 = 2(𝑡𝑜𝑝 𝑝𝑎𝑛𝑒𝑙) + 2(𝑠𝑖𝑑𝑒 𝑝𝑎𝑛𝑒𝑙) + 2(𝑓𝑟𝑜𝑛𝑡 𝑝𝑎𝑛𝑒𝑙)
𝐴 = 2(0.20𝑚 ∙ 0.25𝑚) + 2(0.25𝑚 ∙ 0.35𝑚) + 2(0.35𝑚 ∙ 0.20𝑚)
𝐴 = 0.415𝑚2
46
The average external temperature the backpack will operate at will be 30℃ (86℉) and the
maximum external temperature will be 43℃ (110℉). Our temperature changes then are:
∆𝑇𝑎𝑣𝑔 = 30℃ − 5℃ = 25℃
∆𝑇𝑚𝑎𝑥 = 43℃ − 2℃ = 41℃
Using these values, our heat loss is calculated to be:
∆𝑇𝑎𝑣𝑔 ∙ 𝐴 25℃ ∙ 0.415𝑚2
̇
𝑄𝑎𝑣𝑔 =
=
= 1.728 𝑊
𝑚2 ∙ ℃
𝑅4𝑖𝑛
6.005 𝑊
∆𝑇𝑎𝑣𝑔 ∙ 𝐴 41℃ ∙ 0.415𝑚2
𝑄̇𝑚𝑎𝑥 =
=
= 2.833 𝑊
𝑚2 ∙ ℃
𝑅4𝑖𝑛
6.005
𝑊
Box Dimensions
Top
Panel
Left
Panel
Back
Panel
Front
Panel
Right
Panel
Bottom
Panel
Figure 18: Outer chamber design
47
Figure 19 shows how all the panels will fit together. The calculations for the sizing of the
outer panels are shown below.
Height = top insulation height + inner top panel thickness + inner chamber height + inner bottom
panel thickness + bottom insulation height + error/uncertainty + bottom chamber height
Height = 2(insulation height) + 2(panel thickness) + inner chamber height + error/uncertainty +
bottom chamber height
Height = 2(12.7cm) + 2(1.27cm) + 35cm + 4cm + 12.7cm
Height = 79.64cm
Width = outer left panel thickness + left insulation width + inner left panel thickness + inner
chamber width + inner right panel thickness + right insulation width + outer right panel
thickness + error/uncertainty
Width = 2(insulation width) + 4(panel thickness) + inner chamber width + error/uncertainty
Width = 2(12.7cm) + 4(1.27cm) + 25cm + 4cm
Width = 59.48cm
Depth = outer front panel thickness + front insulation depth + inner front panel thickness + inner
chamber depth + inner back panel thickness + back insulation depth + outer back panel
thickness + error/uncertainty
Depth = 2(insulation depth) + 4(panel thickness) + inner chamber depth + error/uncertainty
Depth = 2(12.7cm) + 4(1.27cm) + 20cm + 4cm
Depth = 54.48cm
48
Budget
49
Updated Prototype Budget
Estimated Cost of Supplies(Prototype)
Item (Quantity)
Possible Vendor
Cost
Date of Estimate
Electrical
$215
7-Dec-10
$0
11-Oct-10
auspicious-e
$13
16-Nov-10
keypad/Encoder
Grayhill/
$25
7-Dec-10
Temperature Sensor(4)
NIFE
$13
7-Dec-10
Battery(2)
Battery Sharks
$65
7-Dec-10
Op amps(10)
bananza
$14
7-Dec-10
DC to DC Converter(8)
Texas Instruments
$16
7-Dec-10
Insulation
LOWES
$28
7-Dec-10
Casing
LOWES
$25
7-Dec-10
Frame
LOWES
$15
7-Dec-10
Thermoelectric cooler
Mouser
$50
16-Nov-10
Fan/Guard
Newark
$16
7-Dec-10
heat sink
Joorat
$61
11/16/2010
SUNSTONE
$40
11-Oct-10
$404
7-Dec-10
Solar Panel(2)
eBay
Microprocessor(6)
microchipDIRECT
LCD Screen
Mechanical
Misc.
Circuit Board
Miscellaneous
Total
$1,000
The budget above contains the rough costs for each of the components that were
purchased for the prototype. Shipping and handling has been incorporated into the prices that are
displayed. The solar panels, battery, and frame material all much less expensive than originally
expected. This will allow us to have sufficient miscellaneous funds for next semester if
difficulties are encountered. There were no real unpleasant surprises as far as pricing is
concerned. All parts can be found at reasonable prices and many decrease in price when
purchased in bulk.
50
Production Budget
Estimated Cost of Supplies(Production)
Item (Quantity)
Possible Vendor
Cost
Date of Estimate
Solar Panel
eBay
$175
7-Dec-10
Microprocessor
microchipDIRECT
$5
11-Oct-10
LCD Screen
auspicious-e
$9
7-Dec-10
keypad/Encoder
Grayhill/
$19
7-Dec-10
Temperature Sensor(4)
NIFE
$9
7-Dec-10
Battery
ATBATT
$52
7-Dec-10
Op amps(10)
bananza
$6
7-Dec-10
DC to DC Converter(8)
Texas Instruments
$9
7-Dec-10
Electrical
Mechanical
Insulation
LOWES
$11
7-Dec-10
Casing
LOWES
$10
7-Dec-10
Frame
LOWES
$6
7-Dec-10
Thermoelectric cooler
Mouser
$37
7-Dec-10
Fan/Guard
Newark
$7
7-Dec-10
heat sink
Joorat
$61
7-Dec-10
SUNSTONE
$40
11-Oct-10
Misc.
Circuit Board
Total
$456
The budget displayed here contains the estimations for the cost of the backpack if it were
to be sent into production and made in bulk. The key differences between this budget and the
prototype budget are: The microprocessor now has a $5 cost for purchasing the chips in bulk,
and the miscellaneous category has been taken out of this estimate. Some other component prices
have been dropped to account for the price drop when buying in large quantities. The circuit
board price under the miscellaneous category was kept the same as in the prototype budget
because the increase in number of circuits to be made is offset by the decrease in cost when made
in bulk. Many of the smaller electrical and mechanical parts are greatly reduced in price because
of the decrease in shipping costs per part ordered.
51
Project Status
52
Gantt Chart Fall 2010
53
Gantt Chart Spring 2011
54
Tasks
Activity
Work Breakdown Structure – Fall 2010
Description
Deliverables
Start/Stop
People
Resources
F1.0
Develop Requirements
Specification
Document stating the goals
of the project
8/30 –
9/28
ALL
Computer
F2.0
Overall Project Design
Develop block diagram,
design entire project layout
9/20 – 12/3
ALL
Computer
F2.1
Microcontroller Selection
Written document,
requirements list
Block Diagram,
major decisions on
parts and methods
Microcontroller/
Data sheets
10/04 –
10/12
Eric
Computer
F2.2
Cooling System Selection
Cooling System
method
10/4 –
10/29
Simon
Computer
F3.0
Device Design
9/28 –
11/19
ALL
Computer/
Mulisim/
Solidworks
F3.1
Cooling Chamber Design
9/28 –
11/19
Natalie
Computer
F3.2
Cooling System Design
Multisim schematic
10/12 –
11/19
Simon/
Eric
Computer/
Multisim
F3.3
Battery and Battery Charger
Circuit Design
Multisim schematic
11/15 –
12/3
Adrian
Computer/
Multisim
F3.4
Temperature Sensor Design
Multisim schematic/
Decision on
temperature sensor
11/8 –
11/19
Simon /
Adrian
Computer/
Multisim
F3.5
User Interface Design
Multisim schematic
11/8 – 12/3
Eric
Computer/
Multisim
F3.6
Power Control Circuit Design
Multisim schematic
11/15 –
11/30
Adrian
Computer/
Multisim
F3.7
DC to DC Converter
Design
Multisim schematic/
decision on DC to
DC converter
10/29 –
11/12
Adrian
Computer/
Multisim
F3.8
Program Microcontroller
Software on
Microcontroller
11/1 –
12/17
Eric
Computer
F4.0
System Compilation
Total System design
and all Simulations
11/29 –
12/10
ALL
Computer
F5.0
Final Design
Documentation,
presentation
12/6 –
12/17
ALL
Computer
A1.0
Project Management
Project progress
accounted for
8/30 –
12/17
Eric
Communica
tion
A2.0
Documentation
Documents, reports,
Engineering
Notebooks
8/30 –
12/17
ALL
Computer/
Engineering
Notebooks
Select a microcontroller that
will meet the project’s needs
Select the method of cooling
that is the most efficient
within budget constraints
Design sub-systems of
project. Specify inputs and
outputs.
Decide what material to use
and compute heat transfer
equations.
Define inputs and outputs of
cooling system. Develop a
multisim circuit of system
Define inputs and outputs of
battery and battery charger.
Simulate circuit in multisim
Decide what type of
temperature sensor to use
and design circuit for sensor
Design user interface and
indicators to be used in the
system.
Design circuit to control the
power into the cooling
system
Design circuit for the
converter that will control
power into system devices
Develop software for the
microcontroller to be able to
control the system
Make sure that Sub-systems
will be compatible with one
another. Find final parts to
order
Finalize design for entire
system and sub-systems
Make sure all projects are on
schedule and within budget
constraints.
Record design work and
progress. Record all research
and tests.
55
Schematics and
simulations for each
sub-system
Results of heat
transfer equations/
material choice
Tasks
Activity
S1.0
Parts Assembly and Testing
S1.1
Cooling Chamber
S1.2
Cooling System
S1.3
Battery and Battery Charger
Circuit
S1.4
Temperature Sensor
S1.5
S1.6
S1.7
User Interface
Power Control Circuit
DC to DC Converter
S1.8
Program Microcontroller
S2.0
Full Frame Assembly
S3.0
System Integration
S4.0
System Testing
S5.0
Project Finalization
S6.0
Prototype Presentation
A1.0
Project Management
A2.0
Documentation
Work Breakdown Structure – Spring 2010
Description
Deliverables
Start/Stop
Assemble Parts. Confirm
parts are operational
Build Cooling Chamber and
apply insulation. Test heat
resistance.
Assemble Cooling System,
heat sink, and ventilation
system.
Create circuit for the
battery and battery
charger. Test charger and
output from battery.
Create circuit for the
Temperature sensor. Test
for accuracy.
Assemble User Interface.
Test LED and screen
output. Test
communication with
microcontroller
Create Power Control
circuit. Test for output.
Test communication with
microcontroller
Create circuit for DC to DC
converter. Test outputs.
Develop software for the
microcontroller to be able
to control the system
Assemble frame that will
house all sub-systems
Compile all sub-systems
into system frame.
Test and verify
functionality and
compatibility of system as
a whole
Final testing and
troubleshooting
Present completed
prototype.
Make sure all projects are
on schedule and within
budget constraints.
Record all design work and
progress. Record all
research and tests.
56
People
Resources
1/18 – 3/11
ALL
Computer/ Test
equipment
1/18 – 2/10
Natalie
Work Shop
Compiled Cooling
System
1/25 – 2/21
Simon
Work Shop
Battery/Battery
Charger Circuit.
Test Results
2/2 – 2/15
Adrian
Work Shop
Temperature
Sensor Circuit. Test
Results
2/3 – 2/9
Eric/
Simon
Work Shop
User Interface
circuit and LEDs.
Proof of
communication
2/10 – 3/2
Eric
Work Shop
2/1 – 2/21
Adrian
Work Shop
2/1 – 2/9
Adrian
Work Shop
Software on
Microcontroller
1/18 – 2/21
Eric
Computer
Full System Frame
1/24 – 2/25
Natalie/
Simon
Work Shop
Full Frame with
Integrated SubSystems
2/21 – 4/25
ALL
Work Shop
Test Results
3/21 – 4/25
ALL
Work Shop/
Computer
Finished Prototype
4/26 – 5/9
ALL
Work Shop/
Computer
All test results,
models, simulation
data/ Prototype
5/9 – 5/13
ALL
Computer/
Documentation
Project progress
accounted for
1/18 – 5/13
Eric
Communication
Documents,
reports, Engr
Notebooks
1/18 – 5/13
ALL
Computer/
Engineering
Notebooks
Working Parts. Test
Results
Cooling Chamber
with insulation.
Test results
Power Control
Circuit/ Test Results
Proof of
Communication
DC to DC circuit.
Test results
Appendices
57
Appendix A
Requirements Specifications Attachments
58
Attachments
The following attachments come from the site:
“Centers for Disease Control and Prevention.” Web. 13 Sept 2010.
Guidelines for Maintaining and Managing the Vaccine Cold Chain:
In February 2002, the Advisory Committee on Immunization Practices (ACIP) and American
Academy of Family Physicians (AAFP) released their revised General Recommendations on
Immunization (1), which included recommendations on the storage and handling of
immunobiologics. Because of increased concern over the potential for errors with the vaccine
cold chain (i.e., maintaining proper vaccine temperatures during storage and handling to preserve
potency), this notice advises vaccine providers of the importance of proper cold chain
management practices. This report describes proper storage units and storage temperatures,
outlines appropriate temperature-monitoring practices, and recommends steps for evaluating a
temperature-monitoring program. The success of efforts against vaccine-preventable diseases is
attributable in part to proper storage and handling of vaccines. Exposure of vaccines to
temperatures outside the recommended ranges can affect potency adversely, thereby reducing
protection from vaccine-preventable diseases (1). Good practices to maintain proper vaccine
storage and handling can ensure that the full benefit of immunization is realized.
Recommended Storage Temperatures:
The majority of commonly recommended vaccines require storage temperatures of 35°F--46°F
(2°C--8°C) and must not be exposed to freezing temperatures. Introduction of varicella vaccine
in 1995 and of live attenuated influenza vaccine (LAIV) more recently increased the complexity
of vaccine storage. Both varicella vaccine and LAIV must be stored in a continuously frozen
state <5°F (-15°C) with no freeze-thaw cycles (Table 1). In recent years, instances of improper
vaccine storage have been reported. An estimated 17%--37% of providers expose vaccines to
improper storage temperatures, and refrigerator temperatures are more commonly kept too cold
than too warm (2,3).
Freezing temperatures can irreversibly reduce the potency of vaccines required to be stored at
35°F--46°F (2°C--8°C). Certain freeze-sensitive vaccines contain an aluminum adjuvant that
precipitates when exposed to freezing temperatures. This results in loss of the adjuvant effect and
vaccine potency (4). Physical changes are not always apparent after exposure to freezing
temperatures and visible signs of freezing are not necessary to result in a decrease in vaccine
potency.
Although the potency of the majority of vaccines can be affected adversely by storage
temperatures that are too warm, these effects are usually more gradual, predictable, and smaller
in magnitude than losses from temperatures that are too cold. In contrast, varicella vaccine and
LAIV are required to be stored in continuously frozen states and lose potency when stored above
the recommended temperature range.
59
Vaccine Storage Requirements:
Vaccine storage units must be selected carefully and used properly. A combination
refrigerator/freezer unit sold for home use is acceptable for vaccine storage if the refrigerator and
freezer compartments each have a separate door. However, vaccines should not be stored near
the cold air outlet from the freezer to the refrigerator. Many combination units cool the
refrigerator compartment by using air from the freezer compartment. In these units, the freezer
thermostat controls freezer temperature while the refrigerator thermostat controls the volume of
freezer temperature air entering the refrigerator. This can result in different temperature zones
within the refrigerator.
Refrigerators without freezers and stand-alone freezers usually perform better at maintaining the
precise temperatures required for vaccine storage, and such single-purpose units sold for home
use are less expensive alternatives to medical specialty equipment. Any refrigerator or freezer
used for vaccine storage must maintain the required temperature range year-round, be large
enough to hold the year's largest inventory, and be dedicated to storage of biologics (i.e., food or
beverages should not be stored in vaccine storage units). In addition, vaccines should be stored
centrally in the refrigerator or freezer, not in the door or on the bottom of the storage unit, and
sufficiently away from walls to allow air to circulate.
Temperature Monitoring:
Proper temperature monitoring is key to proper cold chain management. Thermometers should
be placed in a central location in the storage unit, adjacent to the vaccine. Temperatures should
be read and documented twice each day, once when the office or clinic opens and once at the end
of the day. Temperature logs should be kept on file for >3 years, unless state statutes or rules
require a longer period. Immediate action must be taken to correct storage temperatures that are
outside the recommended ranges. Mishandled vaccines should not be administered.
One person should be assigned primary responsibility for maintaining temperature logs, along
with one backup person. Temperature logs should be reviewed by the backup person at least
weekly. All staff members working with vaccines should be familiar with proper temperature
monitoring.
Different types of thermometers can be used, including standard fluid-filled, min-max, and
continuous chart recorder thermometers (Table 2). Standard fluid-filled thermometers are the
simplest and least expensive products, but some models might perform poorly. Product
temperature thermometers (i.e., those encased in biosafe liquids) might reflect vaccine
temperature more accurately. Min-max thermometers monitor the temperature range. Continuous
chart recorder thermometers monitor temperature range and duration and can be recalibrated at
specified intervals. All thermometers used for monitoring vaccine storage temperatures should be
calibrated and certified by an appropriate agency (e.g., National Institute of Standards and
Technology). In addition, temperature indicators (e.g., Freeze Watch™ [3M, St. Paul, Minnesota]
or ColdMark™ [Cold Ice, Inc., Oakland, California]) can be considered as a backup monitoring
system (5); however, such indicators should not be used as a substitute for twice daily
temperature readings and documentation.
60
All medical care providers who administer vaccines should evaluate their cold chain
maintenance and management to ensure that 1) designated personnel and backup personnel have
written duties and are trained in vaccine storage and handling; 2) accurate thermometers are
placed properly in all vaccine storage units and any limitations of the storage system are fully
known; 3) vaccines are placed properly within the refrigerator or freezer in which proper
temperatures are maintained; 4) temperature logs are reviewed for completeness and any
deviations from recommended temperature ranges; 5) any out-of-range temperatures prompt
immediate action to fix the problem, with results of these actions documented; 6) any vaccines
exposed to out-of-range temperatures are marked "do not use" and isolated physically; 7) when a
problem is discovered, the exposed vaccine is maintained at proper temperatures while state or
local health departments, or the vaccine manufacturers, are contacted for guidance; and 8)
written emergency retrieval and storage procedures are in place in case of equipment failures or
power outages. Around-the-clock monitoring systems might be considered to alert staff to afterhours emergencies, particularly if large vaccine inventories are maintained.
Additional information on vaccine storage and handling is available from the Immunization
Action Coalition at http://www.immunize.org/izpractices/index.htm. Links to state and local
health departments are available at http://www.cdc.gov/other.htm. Especially detailed guidelines
from the Commonwealth of Australia on vaccine storage and handling, vaccine storage units,
temperature monitoring, and stability of vaccines at different temperatures (6) are available at
http://immunise.health.gov.au/cool.pdf.
References:
1. CDC. General recommendations on immunization: recommendations of the Advisory
Committee on Immunization Practices (ACIP) and the American Academy of Family
Physicians (AAFP). MMWR 2002;51(No. RR-2).
2. Gazmararian JA, Oster NV, Green DC, et al. Vaccine storage practices in primary care
physician offices. Am J Prev Med 2002;23:246--53.
3. Bell KN, Hogue CJ, Manning C, Kendal AP. Risk factors for improper vaccine storage
and handling in private provider offices. Pediatrics 2001;107:E100.
4. World Health Organization. Thermostability of vaccines. Geneva, Switzerland: World
Health Organization, 1998; publication no. WHO/GPV/98.07. Available at
http://www.who.int/vaccines-documents/DocsPDF/www9661.pdf.
5. World Health Organization. Temperature monitors for vaccines and the cold chain.
Geneva, Switzerland: World Health Organization, 1999; publication no.
WHO/V&B/99.15. Available at http://www.who.int/vaccinesdocuments/DocsPDF/www9804.pdf.
6. Commonwealth Department of Health and Aged Care. Keep it cool: the vaccine cold
chain. Guidelines for immunisation providers on maintaining the cold chain, 2nd ed.
Canberra, Australia: Commonwealth of Australia, 2001.
61
TABLE 1. Vaccine storage temperature
requirements
35°F-46°F
(2°C-8°C)
Instructions
≤5°F
(-15°C)
Instructions
Do not freeze or
Vaccine
Instructions
Diphteria-, tetanus, or pertussis-containning
vaccines
expose the freezing
(DT, DTaP, Td)
frozen state with no freezethaw
cycles.
temperatures.
Haemophilus conjugate
vaccine (Hib)*
Hepatitis A (HepA) and hepatitis B
(HepB) vaccines
Inactivated polio vaccine
(IPV)
Measles, mumps, and rubella vaccine
(MMR) in the
lyophilized (freeze-dried)
state†
Maintain in continuosly
Vaccine
Live attenuated
influenza
vaccine
(LAIV)
Contact state or local health
department or manufacturer
for guidance on vaccines
exposed to temperatures
above the recommended
Meningoccoccal polysaccharide vaccine
Pneumococcal conjugate
vaccine (PVC)
Pneumococcal polysaccharide vaccine
(PPV)
Trivalent inactivated inflenza vaccine
(TIV)
range.
*ActHIB® (Aventis Pasteur, Lyon, France) in the lyophilized state is not expected to be affected detrimentally by freezing
temperatures, although nodata are
available.
†MMR in the lyophilized state is not affected detrimentally by freezing
temperatures.
TABLE 2. Comparison of thermometers used to monitor avccine temperatures
Thermometer type
Advantages
Disadvantages
Standard fluid-filled
Inexpensive and simple to use.
Thermometers encased in biosafe liquids can
reflect
Less accurate (+/-1°C).
vaccine temperatures more accurately.
No information on min/max temperatures.
No information on duration of out of specification exposure.
Cannot be recalibrated.
Inexpensive models might perform poorly.
Min-max
inexpensive
Less accurate (+/-1°C).
Monitors temperature range.
No information on duration of out of specification exposure.
Cannot be recalibrated.
Continuous chart recorder
Most accurate
Continuous 24-hour readings of temperature
range
and duration.
Can be recalibrated at regular intervals.
62
Most expensive.
Requires most training and maintenance.
Appendix B
TPS40192 DC to DC Converter Data Sheet
63
Appendix C
CSD16321Q5 Transistor Data Sheet
64
Appendix D
Solar Panel Fan 3106kl Data Sheet
65
Appendix E
Temperature Sensor Data Sheet
66
Appendix F
OP AMP LM741 Data Sheet
67
Appendix G
KEYPAD 96BB2-006-F-Grayhill
Data Sheet
68
Appendix H
Keypad Encoder Data Sheet
69
Appendix I
Solar Panels Data Sheet
70
Appendix J
Thermoelectric Cooler Data Sheet
71
Appendix K
LCD Screen Data Sheet
72
Appendix L
Cooling Data Sheet
73
Appendix M
Microprocessor Data Sheet
74