Hi Electromagnaman,
THE ROTATIONAL EFFECT.
This is probably one of the more difficult aspects to grasp.
So i will try to explain it clearly.
(i have already re-written this quite a few times)
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In the picture you posted, the windings are shown at an angle, I would
expect them to be at 90 deg, although they needn't be, but 90 degrees
should give the best results.
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I am going to assume you have a working knowledge of magnets, and coils
and some understanding of how a winding behaves like a magnet, and that
reversing the current in a winding also reverses it's magnetic field.
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Allow me first to mention the type of motor that has two very similar
windings, one usually fed via a capacitor.
If the two windings were simply fed from the same source,
then they would both act in unison pulling and pushing together on the
rotor, but without any rotational effect, as from the same source the
rise and fall of the magnetism would be synchronised.
If they were both fed from the same source, the rise and fall of the
magnetism would be somewhere between the two windings, but it would
have no rotational effect.
This is why one of the windings is fed via a capacitor, as this will
introduce a change in the timing of the magnetism's 'rise and fall'.
This puts it 'out of step' with the magnetism in the other winding.
This gives a 'Rotational effect' to the magnetic fields around the
rotor, and sets it running up to the motor speed.
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Now the motor you have there has no capacitor, but it has a 'Start'
winding which again, has to be 'out of step' with the 'Run' winding.
With this type of motor that is done by having a distincly different
inductance, the start winding is typically a heavier winding taking a
little more current than the 'Run' winding.
The different inductance causes the current in that winding to rise
and fall at a slightly different time to the current in the 'Run'
winding.
Even though they are connected in parallel to the same source, the
currents inside the two windings are not 'in step' because they are
different inductances.
Once the rotor starts to spin up, the start winding drops out, and the
motor runs up to its running speed.
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I have tried to cover the how and why, if my explanation is incorrect
i feel sure someone will set it straight, i hope i have described it
well enough for you to grasp the principles.
If something wasn't clear just say so and myself or someone else will
try to clear it up.
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Regards, John