Updated 26 May, 2012, 4:18 pm IST

Charge Your Phone As You Walk

03 Sep, 2010, 11:31 am IST | by Gareth Mankoo

Students of Pune College of Engineering ensure that your cell phone never runs out of juice.

Angels whisper to a man when he goes for a walk”. This surely holds true for Tejas Narasimhan, the project team leader who came up with the idea to store the energy that is spent while walking. It may sound ridiculous to some, but a group of six students from College of Engineering, Pune (COEP) have developed a portable device called ‘Walk-N-Charge’ (WnC) that charges your mobile for the entire day in a 20 minute walk.

How does it work?
WnC is worn below the knee cap on one leg and a light string is attached to the other leg. The strides taken help in pulling and retracting the string, which is further attached to a dynamo that generates about 3.5 Watts; enough to charge low-powered devices like mobiles, MP3 players, GPS devices, etc.

What's so special about WNC?
A single pencil cell costs about Rs 7. Walk-N-Charge can generate as much energy as a AA battery in 21 minutes. If it is used for one hour daily, it would recover its cost in less than 12 days. A 20 minute walk charges your cell phone for a day’s usage. It can fit in your pocket and it costs you as much as it weighs, i.e. Rs 350 for 350 g.

Who are the product developers?
Aditya Nanavaty, Isha Nag, Rushikesh Pande, Shachi Pande, Sarvesh Patil, and Tejas Narasimhan teamed up for the venture and bagged the first prize� at Energise, Techfest at IIT Powai on 26th January, 2009.

The team (from left to right): Shachi Pande, Rushikesh Pande, Isha Nag, Tejas Narasimha, Aditya Nanavaty, Sarvesh Patil

Their Dream
Even if 0.1% of the Indian population uses this device, it can generate 1500 kW/h of energy and can help reduce carbon emission by 2.25 tonnes per day. Thus, Walk-N-Charge promises you a source of energy that is not only clean, portable and inexpensive, but also charges your mobile while you get charged up!

The idea
Walking doesn’t require considerable effort. However, when we hit an obstacle while walking, our legs are definitely hurt, thus, suggesting the immense untapped power that our legs hold.

The purpose behind its working
Walk-N-Charge is about converting a part of the bio-mechanical energy spent in our day-to-day lives (while walking) into a usable form and storing it to charge low-power battery-operated devices.

Technical specifications
Walking involves a change in relative displacement of around 35 cm between legs. This repeated linear motion could be converted to rotary motion with the help of a pulley and string. Thus, the bio-mechanical work is converted into mechanical form and eventually stored as chemical energy in batteries to store electric energy. The device is clamped on one leg using a Velcro strap and a hole lets out a Nylon string that is attached to the other leg that helps in the conversion of the displacement into rotary motion. Even a slight displacement pulls the string out, thereby rotating the pulley, which turns the central shaft. The shaft is common to the gearbox, the dynamo and the recoil mechanism. So, when the displacement reduces, there is a slack in the string, which is removed by the tension produced by the recoil system. Since the electricity produced is bi-directional and contains spikes, an electronic circuit encompassing a rectifier and a filter converts it into a unidirectional, spike-free wave and stores the energy produced in rechargeable batteries. This stored energy is used as an input supply to mobiles with the help of different adapters. The basic shape of the prototype is a cylinder 50 mm in diameter and 0 mm in height. It weighs around 200 g because of the combined use of low-weight and high strength material. If produced on a large scale, it might cost about Rs 300 only.