7. Testing and connecting
Check that the PMG has no faults before it is put into use. It will be much easier to
correct the faults now, than to return the unit to the workshop later.
Mechanical testing
Mount the spine vertically in a vice. The magnet rotors are free to move. The shaft
is horizontal, as it will be in a wind generator. Check that the wires are not
touching each other, creating a short circuit which makes the PMG harder to turn.
Check that the rotor will spin freely.
Spin the rotor and listen for sounds. There should not be any scuffing or brushing of
the rotor, as it turns. It should spin freely for several seconds and gradually come
to a halt. If it slows down rapidly then there may be an electrical fault, or the
bearings may be over-tightened.
Grasp the stator with both hands. Push one side backward while pulling the other
side forward, while the rotor is spinning. It must not touch the rotor. If there is a
rubbing sound, then it may be necessary to disassemble the PMG and assemble it
more carefully, with more space between the rotor and the stator. Or it may be
possible to correct the problem by making minor adjustments to the stator mounting
studs.
Stop the rotor with one of the studs in the 3 o'clock position (diagram 43). Hang an
object weighing 100 grams on this stud. The rotor should begin to turn clockwise.
If it will not turn, then the bearings may be over-greased or too tight.
43. HANG A WEIGHT ON ONE OF THE STUDS
SPINE
STATOR
ROTOR
100g WEIGHT
Checking the balance
The rotors have already been balanced in section 6. The wind turbine blades must
also be balanced in the same way. When the unit is assembled, you should check the
balance again using the new procedure below. This is necessary because the rotor
disk may not be perfectly central on the PMG shaft.
PMG manual
page 41
June 2001