2. WIND TURBINE
BLADES
TAIL
ALTERNATOR
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 (15A x 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
(170 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.
PMG manual
page 6
June 2001