Re: not understand anemometer
From: John Larkin (jjSNIPlarkin_at_highTHISlandPLEASEtechnology.XXX)
Date: 01/20/05
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Date: Thu, 20 Jan 2005 08:29:27 -0800
On Thu, 20 Jan 2005 13:32:43 +0800, "developer" <noemail@nowhere.net>
wrote:
>still do not understand
>
>
>
>>
>> The rotor spins. AC is just DC in motion.
>>
>> John
>>
>
Coils create magnetic fields and attract the magnets. If you apply DC
to a coil, the motor moves to some position and then stops; you noted
this yourself. To get the motor to spin, you have to keep changing the
current in the coils to keep the rotor moving; you have to keep
changing the "place where it would stop"
If you use the motor as a generator, by externally spinning the shaft,
the magnets move past the coils and generate voltage. As a magnet
approaches a coil, the voltage swings positive, and then as it moves
away, it swings negative. This happens over and over as the shaft
spins, so the average voltage induced into the coil is zero. So
there's no DC to measure.
Actually, as I said, AC is just moving DC. If you were to turn the
shaft very slowly and look at it with a sensitive DC voltmeter, you'd
see the slow positive and negative swings. But the voltage would be
very small. As the speed goes up, a DC voltmeter can't follow the
swings and reports the average value, 0. An AC voltmeter essentially
rectifies the voltage before measuring it, so you get a number.
John
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