Miniature Wind Turbine

Introduction

The cellar at Oaken Clough has been set up as a workshop / lab with the purpose of building alternative energy projects.This project is for a small scale portable wind turbine suitable for charging AA sized batteries. This device provides an alternative energy source using free energy from the wind.

The range of devices which use power in this form is large and growing from mobile phones and digital cameras to remote controls and battery powered clocks.We discard millions of batteries every year and even when we use rechargeable cells charging them from the A.C. mains is a very inefficient way of using energy as much of it is lost in the transformer.

Materials

Any renewable energy device requires a certain amount of energy to manufacture it, so a key measure of such devices is the return on energy invested. The device has to generate the same amount of usable energy as was used to manufacture it before it starts paying for itself. By making use of recycled materials less energy has to be invested in constructing the device and this also gives a new lease of life to discarded materials which would otherwise end up in land fill.

Components

Dynamo

The dynamo was constructed from a motor recovered from a vacuum cleaner. This kind of motor has two sets of coils. The stator coils are fixed to the motor chassis and rotor coils are attached to an axle. In normal motor operation electrical power is supplied to the rotor coils through carbon brushes, when these burn out the motor fails and the device is discarded. By removing the rotor coils and replacing them with a set of permanent magnets mounted on a length of threaded rod the damaged motor can be recycled as a dynamo.

A motor with the rotor coils removed exposing the stator coils.

Housing

The housing for the dynamo is made from a standard sized food tin. Using a hole saw a perspex lid was made to fit the tin and this was drilled centrally for the axle and with fixing centres to bolt the dynamo to it. A small strip of sheet metal was used to make a bracket to secure the lid to the housing with two self tapping screws.

Magnets mounted on an axle.	Assembled dynamo being fitted in the housing.

Turbine blades

The blades are made from a length of plastic drainage pipe about 7cm in diameter and 30cm in length. The pipe is cut into three sections using diagonal cuts so that the section gets narrower and is offset at the narrow end. This creates a twist in the section which forms the aerofoil. If you print this template at A4 size and wrap it around the section of pipe it will show how to make the cuts.

Blade coupling

To couple the blades to the axle you need to make an equilateral triangle with sides 7cm out of light sheet metal (0.5mm steel).Drill this centrally to the same diameter as the axle and also drill two 5mm holes at each edge about 2cm apart. These will be used to bolt the blades to the triangle. Bend the edge of the triangle around the base of each blade and drill matching holes in the base of each blade using the triangle as a template. Bolt the blades to the triangle using some short M5 bolts. You will need to trim the corners off the base of each blade so that they will line up without overlapping. Finally the triangular piece is attached to the threaded rod which forms the axle using a locking nut and a wing nut. The photo shows the assembled blade coupling.

Pivot

We want the turbine to be able to pivot horizontally so it can turn into the wind. To achieve this the housing was mounted on a pivot made from a caster removed from a piece of old furniture. The wheel was removed and the can is fixed to the caster using a band of metal.

Tail Fin

A tail fin is made from a piece of sheet metal and attached to the back of the can to help the turbine turn into the wind. A small hole drilled in the side of the can where the caster attaches allows the wires attached to the stator coils to exit the housing.

Support

The caster is attached to a wooden support pole by means of a hole drilled vertically in the top of the pole.A cross piece provides a base for the support. Guy ropes are attached to the pole near the base using picture hooks. These should be low enough so that there is enough clearance for the rotating blades when the ropes are fully extended. When the turbine is deployed the ropes can be secured to the ground to provide stability.

Rectifier

The output from the dynamo is alternating current so a rectifier circuit is required to convert this to a direct current suitable for charging a battery.