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Re: [TCML] How To Turn A Vacuum Cleaner Motor Into A Synchronous Motor
I did some experiments modifying a 120VAC universal motor (series wound)
from a vacuum cleaner. The motor current and HP ratings are unknown.
The commutator has 22 segments in total.
First I shorted 4 adjacent segments, and connected these to 4 more adjacent
segments on the opposite side of the commutator. So the 4 segments on
one side were shorted to the other 4 segments on the other side of the commutator
of the armature. I didn't use any diodes. With this setup, it was impossible to
obtain synchronous operation. I forget if the motor was always self-starting
with this arrangement.
Next I left the 4 segments shorted on opposite sides of the commutator, but
I cut out the short between the 2 groups of 4 segments. So 4 segments were
still shorted together on each side, but were no longer connected to the
segments on the opposite side. Again no diodes were used. This arrangement
gave synchronous operation between 24V at 4.5A, and 42V at 10.5A.
A reasonable amount of phase shift was obtained as the voltage was varied
between 24V and 42 volts. It was much easier to pull the motor out of sync
by loading it at the lower voltage than at the higher voltage as would be
expected. The sync-torque was good overall, but it didn't seem that
different than an induction sync-modified motor. I don't know if using
diodes helps the torque. The motor self-started at times, but not at other
times, depending on the armature rotational position at start-up. The higher
the voltage, the more likely the motor was to self-start. At 40 volts, the
motor always self-started. If the voltage was over 35 volts, any sudden
loading of the motor would cause the motor to speed up and lose sync.
Sudden loads would not tend to occur however in normal SRSG operation.
I confirmed sync operation, and phase shifting by observing a black line
drawn on a cardboard disc, attached to the motor shaft, under ballast-type
fluorescent lighting. I'm experienced at doing this and I have no trouble
telling if a motor is in sync or not.
These results show that sync operation can be obtained without using
diodes, however the diodes may perhaps improve the self-starting, and
reduce the current draw some? I didn't try shorting fewer than 4 segments
on each side. I have no photos or videos available for these tests.
In no cases did I encounter the "crazy mode" of operation. However
there were some hunting sounds just before the voltage was raised
enough to sync-lock the motor. In no cases did I see any arcing
at the brushes. I assume the motor was running at 3600 RPM (not
1800 RPM) because the motor has two poles, but I had no easy way
to verify that. Actually, by looking at the light pattern on the disc, it
looked like a 3600 RPM pattern, not an 1800 RPM pattern.
> On Fri, Dec 17, 2010 at 12:15 PM, Futuret <futuret@xxxxxxx> wrote:
>> It would still be interesting to see what happens if the opposing 180
>> segments are merely shorted (no diode). Maybe Clive tried that
>> and it didn't work??
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