Shake Powered Flashlight Circuit

The post discusses a shake powered flashlight circuit using an simple copper coil and a magnet. The idea was requested by Mr. Dennis Bosco Demello

The Circuit Design

Electromagnetism was proved way back in 1873  my Maxwell, and later by Faraday, and amazingly the technology still forms the backbone of all the major electrical systems of today's modern world.

As the name suggest electromagnetism is a correlated phenomenon between electricity and magnetism, and appear to be the two sides of the same coin.

In an electrical system, when a magnet is moved close to a conductor, electricity is generated in the conductor due to the mobilization of the electrons in the conductor by the magnetic energy. Conversely when electricity is passed through a conductor, magnetic energy is induced around the same conductor.

In our present shake powered flashlight circuit we take the advantage of this unique electromagnetism phenomenon and implement this to generate electricity from the interaction between conductor and  magnet.

Materials Required

To build this interesting generator circuit we would require the following ordinary and inexpensive materials:

1) A cylindrical magnet

2) An appropriately dimensioned pipe whose internal diameter should be just slightly higher than the outside diameter of the magnet.

3) A few feet of magnet wire or super enamelled copper wire having a thickness of around 30SWG.

4) 4nos of 1N4007 rectifier diodes for making the bridge rectifier, and a 220uF 16V filter cpacitor which could be ideally a super capacitor

5) 1 LED rated at 1 watt, ultra bright, preferably an SMD type

The Circuit Layout

Building Procedure:

The procedure for completing this simple shake-a-gen or a shake powered flashlight circuit is very simple.

Wrap the wire around the pipe as shown in the following figure and secure the wire ends through the end pin holes appropriately drilled on the pipe.

You can wind multiple layers of wires one over the other for acquiring higher current from the unit.

Once the winding is done, slide the magnet inside the pipe, and seal the two ends of the pipe with epoxy glue, preferably do this with a piece of foam stuck at the inner side of the two ends of the pipe.

Let the unit dry until the epoxy has hardened fully.

Next, wire the ends of the coil with a bridge rectifier, a filter capacitor and an LED.

The set up is complete now, and the unit is ready for shaking.

Now it just require holding the pipe within your fingers and giving a quick to and fro shake.

As soon as this is done, the LED could be seen glowing brightly, and the illumination sustained even after the shaking is stopped.

Incorporating a Joule Thief Circuit for Maximum Brightness

The illumination period could be significantly increased by adding a "joule thief" converter with the bridge rectifier, as shown in the following figure, however when this concept is utilized, the number of turns must be reduced and instead more number of parallel turns must be added to the winding, because here the current needs to be relatively higher so that the Joule thief circuit is able to convert it into a sustained amount voltage for the LED

The number of turns in the above joule thief could be with a 20:20 ratio, or other proportions could also be tried for getting a preferred customized amplification.

Coil Specifications for the shake powered flashlight

The coil specifications for the first circuit is not critical, as a rule of thumb make the coil length 3 times the length of the magnet.

The number of turns in the coil determines the voltage level while the thickness decides the current magnitude. 

Preferably, instead of a single thick wire many thin wire strands must be used for acquiring proportionately higher level of current through the system. 

This could be possibly achieved by using a standard 14/36 flexible insulated wire and wrapping a single layer over the pipe, or a couple of layers could also be tried for boosting the voltage along with current.
As suggested earlier the diameter of the magnet must be just slightly lower than the inner diameter of the pipe so that the magnet is able slide effortlessly in response to the shakes, and additionally ensuring a minimum possible margin between the coil and the magnet. This gap decides the efficiency factor of the system, lower gap ensures higher efficiency and vice versa.

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