Building the PMG

This manual describes how to build the PMG. Read right through it before starting.

Section 2. is a list of materials and tools for the job.

Section 3 explains how to build the special tools (called jigs) and the moulds which are needed. You can build more than one PMG with them. There are many possible ways to make these jigs and moulds, but there is only room in this manual to describe one way to do it.

Section 4 is about the stator. It describes how to wind the coils of enamelled copper wire, and cast them in resin, using the jigs and moulds.

Section 5 shows how to build the magnet rotors, using magnet blocks and steel disks, set in another resin casting.

Section 6 shows how to assemble the parts into a whole PMG. It explains how to build the mechanical parts, how to balance the rotors, and what is required to connect the wiring from the stator.

Section 7 is about testing the PMG. It contains procedures for checking that it is correctly balanced and ready to use. It describes the options for connecting up the electrical output. It also explains how to connect the PMGto the battery.

Section 8 contains additional information about the use of polyester resins, and about using the PMG for hydro power.

What this PMG can do

This PMG is made for small wind generators (see diagram 2). To build a complete wind generator, you also need

• a tower : perhaps a steel pipe, supported with guy ropes,

• a 'yaw head' swivelling on the tower top,

• a tail, to keep it facing towards the wind,

• a set of blades, to turn it.

The spine of the PMG bolts on to the yaw head. The blade assembly fits on to the front of the PMG. The yaw head and tail need to be so constructed that the wind generator will turn from strong winds, to protect itself. (This manual does not describe the blades, tower, or yaw head.)

 

TOWER

On test at Scoraig

The PMG works at low rotational speed. The chart shows the power output of the PMG, charging a 12 volt battery. At 420 rpm it generates 180 watts, which is 15 amps at 12 volts (15Ax 12V = 180W).

At higher speed, the PMG can generate more power. But high currents cause the coils to heat up, and so the efficiency gets worse as the output current gets higher. For higher speed it is better to change the stator coils, either by using different size wire, or by changing the way they are connected.

If the PMG is always used at higher speeds, it is better to use thicker wire, which can carry more current without getting so hot. Using thicker wire means there are fewer turns on the coils, which means that the PMG would not work at low speed.

To use the same PMG for both low and high speeds, it is possible to change the connections. There are two ways to connect the stator wires to the rectifier. They can be connected 'star' or 'delta'. See Section 7 for a detailed description of the star and delta connections.

See diagram 3 for the graph of power vs. speed. Star begins to work at low speed (1 70 rpm). Delta gives more power, but only at higher speed. Star is good in very low windspeeds, and delta is better in higher winds.

A bigger version of this PMG would be able to give higher power at lower speed.