Final Year Project
Project Progress
Presentation
Title: Energy Conversion
for low voltage values.
Supervisor: Dr.Maeve Duffy
Aim of Project
The aim of this project is to develop circuits to
demonstrate the performance of bio fuel cells
which are being developed by the Energy
research centre in NUI Galway.
The ideal end goal would be where a microbial
fuel cell arrangement has the ability to charge
a mobile phone battery.
Outline of Presentation
This presentation will deal with the following topics:
1.
2.
3.
4.
5.
Overview of Project
Progress to date
Project Plan
Time Management
Questions
1) Overview of project:
2) Progress To Date:
•
•
•
•
Thévenin equivalent circuit
LED Demonstration
Low power devices identified
Demonstration of fuel cell powering low
power devices
• Research of charging algorithms
Thévenin Equivalent circuit:
0.6
1200
0.5
1000
0.4
800
0.3
600
0.2
400
0.1
200
0
0.05
0
0.1
0.15
0.2
0.25
0.3
Current density (mA/cm2)
0.35
0.4
Power density (mW/m2)
Voltage (V)
Power Density curve:
Blue line represents the power density Vs current density.
White line represents Voltage Vs current density .
Area across which power density is measured is 5.4cm^2.
1cm^2 = 0.0001m^2
The point at which we have maximum power output is the
second from right so we take this point.
When worked out the following outputs result:
Power ~ 0.486 milli-Watts
Voltage ~ 0.42 volts
Current ~ 1.215 milli-Amps
Internal Resistance of Fuel Cell ~ 345 ohms
Thévenin Equivalent circuit:
LED Demonstration:
On testing the LED’s found in the electronics labs it was found
that the lowest power LED needed a minimum of 3.8 milliAmps and a minimum of 1.83 volts to light.
This meant the voltage & current output from the fuel cell
needed to be stepped up.
There is three solutions to this problem:
1) Cascade a number of fuel cells in parallel, this way increasing
the current output and then use a DC-DC boost converter to
step up the voltage.
2) Use an RC circuit to boost the current using a mosfet to sfor
switching and then use a DC-DC boost converter to step the
voltage up.
3) Order a low power LED (1 milli-Amp LED can be obtained)
Low power devices identified:
Voltage needed:
1.5 Volts DC
Power needed:
0.0001 Watts
Current needed:
66.66 microAmps
Voltage needed:
5 volts DC
Power needed:
0.9 Watts
Current needed:
0.18 Amps
Voltage needed: ~5
volts DC
Power needed:
unknown
Current needed:
unknown
Demonstration of fuel cell powering low power
devices:
To demonstrate these devices a DC-DC boost converter needed
to be designed.
This caused problems as most common DC-DC boost converters
use either diodes or BJT’s which have a diode between the
base and emitter. The BJT is used due to its fast switching
speeds. The diodes cause a minimum of 0.3 voltage drop. As
the output voltage from the fuel cell is so low already we can
not afford to use BJT’s.
Demonstration of fuel cell powering low power
devices:
Using a boost converter obtained from Texas instruments called
the TPS61200 I am currently trying to boost the output
voltage of the fuel cell enough to allow me to power one of
the low power devices mentioned above.
This converter gets around the problem of using BJT’s by using
MOSFET’s instead.
The TPS61200 can needs 0.8 volts to startup, after which it can
operate at a voltage as low as 0.3 volts.
As the TPS61200 was to small to fit on a board I needed to order
the evaluation module.
Demonstration of fuel cell powering low power
devices:
Demonstration of fuel cell powering low power
devices:
Demonstration of fuel cell powering low power
devices:
Demonstration of fuel cell powering low power
devices:
From using the formula to work out the minimum inductance
needed (Vin = L * DI/DT) ,I found that the minimum
inductance required was 2.1333 micro-Henry’s.
So the 2.2 micro-Henry should be satisfactory to induct the
input current from the fuel cell.
Research of battery chemistries, charging
algorithms:
Example of type of voltage and current used to charge a phone:
My phone (Sony Ericsson) is a lithium-polymer battery which
supplies 3.6 volts to the phone. And has 780 milli-Amp hours.
The charger for the phone supplies 5 volts and a current of
1Amp. This is probably implementing a charging algorithm
known as constant charge where a constant charge is applied
to the battery.
The type of charging algorithm I will most likely have to
implement is trickle charging as it charges the battery with a
small current over a long period of time.
3) Project Plan:
As identifying a suitable DC-DC boost converter has slowed me
down I have revised my project plan as follows:
January 22nd: Configure the DC-DC boost converter to power a
low power device.
February 5th: More research on battery chargers. Design battery
charger needed to charge a typical phone battery.
February 19th: Either configure TPS61200 to output voltage
needed to power battery charger circuitry or identify a DC-DC
boost converter which can.
March 3rd: Identify a suitable microprocessor to read in voltage
across the battery and adjust the battery charger output
accordingly and Design a suitable Trickle Charge algorithm.
March 6th: Test the circuitry with different loads attached.
March 8th: Test the complete circuitry with a rechargeable
battery and determine overall efficiency.
March 16th: Draft Final Report.
March 24th: Submission of Final Report.
March 29th: Oral and practical presentation.
4) Time Management:
I feel that in the first semester time management also had a role
in slowing my progress on the project so this semester I aim to
improve on this.
This is a quiet tight schedule but I believe if I dedicate Tuesday
evenings and Fridays to practical work in the Laboratory as
well as any other free time and Saturdays to research I will be
able to get it done.
5) Questions!!