Charging Your Mobile Phone on a Bike Ride

Rural India is slowly trying to come out of the darkness with initiatives like solar powered lamps and other such technologies. Most of the designs are simple and seem very very effective, both cost-wise and building-wise. This years IIT Bombay 2010 Techfest had some radical yet simplistic technology on display and here’s one that takes into account your health, the environment and you mobile phone is at the center of it all.

The one issue most users have with a mobile handset is battery life and in many places of rural India, electricity is sometimes scarce. Finding a suitable time and place to charge your mobile is not easy in this neck of the woods. It’s very difficult hence, for villages to keep this mode of communication alive. So as a solution, an entry at the 2010 IIT Bombay Techfest, for "Prayas-Utkarsh", saw an initiative called the Bicycle Mobile Charger. The project was co-created by Sujay Dilip Shet, (B. Tech Electrical) and Rahul Pradip Sakharkar (B. Tech EXTC) of Dr Babasaheb Ambedkar Technological University in Lonere, Maharashtra.

Charging Your Phone on the Go
One might argue that Solar energy can be used as a viable option to charge electrical gadgets sustainability, but their maintenance and upkeep can be cumbersome and expensive. Moreover, solar panels are rendered useless during heavy rain, cloud cover and in the night time.

So why pick a bicycle to create a changing device?
The mobile charger using a bicycle dynamo is simple in design, easy to implement and light in weight. It requires minimum components and these are cheap and readily available in the market, hence making the circuit a portable one. Such a charger has a long life and comes with almost negligible maintenance costs. The entire circuit can be easily mounted in a small place or carried away if required. The cost of such charger unit may range from Rs 50 to 100, which is affordable for anyone.

The charger is not only long lasting but also does not add to the carbon footprint. The dynamo charger uses an eco-friendly way of charging the mobile. It just converts the mechanical energy into electrical energy. The charging can be done any time and in any season. The mobile can even be charged while the user is on his way to work.

Understanding The Design
The device is made of a dynamo charger which is uncomplicated. The charger has a simple design and consists of a bridge rectifier with four diodes (1N4001GP). The frequency of input voltage required to charge the mobile is minimum 45 Hz and the input resistance of IC LM7806 is assumed to be 500 ohm. The expression for ripple factor using pi filter is given bellow:
1
r = ________________________
4*√2 * ω * ω * C1* C2* L*RL
Where, ω =2*pi*f
f =input frequency
C1, C2 =Capacitors used
L =inductor
RL =Load resistance= Input resistance of IC
To get 5% ripple we have from above formula
C1*C2*L=88.45 nano
If C1=C2=C=1000 micro farad
L=18 mH
Let us select 10 mH inductor.

Typical output current of IC LM7806 is 1 A, so to get 350 mA of current, for successful charging of mobile a 100 ohm resistor is placed across the input resistance of mobile which is approximately 180 ohm. The connection diagram is shown in Fig (1) and output in Fig (2) on the following page. As for the circuit configuration, the variable output up to 12V AC from the dynamo when cycle is in motion is given to bridge rectifier that converts AC input voltage into pulsating DC output voltage.

The AC voltage is filtered out from this output voltage through pi filter. This gives around 99% pure DC output voltage. This is not suitable to charge the mobile because as input AC voltage from the dynamo varies the output also varies. Stabilized voltage of 6 volts DC is obtained through a positive regulator IC LM7806. The output current of IC is typically 1A. Current divider circuit gives 350mA of current for successful charging of the mobile.

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Putting the Device Together
As simple as it seems, a lot of thought has gone into making the circuit safe. Care has been taken that the device can be used in an outdoor environment. The creators iterate, "This charger gives fixed output voltage and current hence manual control is not needed. The charger unit can be removed easily when not in use. The circuit consists of minimum number of components and hence it is easy to implement and can be manufactured without need of sophisticated instruments."

They further elaborate, "The dynamo gives varying AC Output up to 12V when the cycle is in motion. The output of the dynamo is given to the bridge rectifier. The bridge rectifier converts AC input voltage into pulsating DC output voltage. To get pure DC output, the output of the bridge rectifier is required to be filtered. To filter pulsating DC voltage, types of filters that can be used include capacitor filter, LC filter and a pi filter. Though the output of filter circuit is pure DC, it is varying according to the variation in the speed of cycle. The output of bridge rectifier is given to regulator IC LM7806, which gives regulated 6V DC output voltage and 1 A current. The current divider circuit gives 350 mA of current and the output of the circuit is used to charge the mobile successfully."

Components Used
_ Dynamo -1
_ Diodes (1N 4007) - 4
_ Capacitors (1000 μF) - 2
_ Inductor (10 mH) -1
_ Regulator IC (LM7806) -1
_ Resistor (100 Ω) -1

The Brilliant Minds Behind it All
Sujay Shet (B Tech, Electrical) and Rahul Sakharkar (B Tech, Electronics and Telecommunications) have been pursuing there respective Bachelor's degrees from Dr Babasaheb Ambedkar Technological University in Lonere, Raigad, Maharashtra. Sujay's interest lies in working in renewable energy technology towards which he has created projects like the "Wave Energy Conversion Technology Using Chain Drive Mechanism" apart from his "Bicycle Mobile Charger Application" project, which was a team entry along with Rahul for the Techfest 2010. Sujay has also attended various eco-seminars including one on "Efficient Utilization of Solar Energy for Home Based Application". He has also worked as the Secretary of Electrical Engineering Students Association for 2008-09.