Re: not understand anemometer

From: Tim Wescott (tim_at_wescottnospamdesign.com)
Date: 01/20/05 

Date: Wed, 19 Jan 2005 22:25:45 -0800

developer wrote:

> http://www.otherpower.com/.html
>
> The internal circuitry of our brushless DC motor consists of 12 coils, and a
> permanent magnet ring that spins around them. These motors are NOT like a
> normal DC motor...they require a special driver circuit to make them spin.
> If you apply plain DC current to the motor, it will simply seek a point
> aligned with the coils, stop, and burn out. The motors have 3 leads...a
> common in the center and 2 outputs (well, actually inputs!). For connection
> to measuring equipment, you need only connect to the center common lead and
> one of the side ones. The output of the motor when spun as an anemometer can
> be measured with a multimeter set for AC volts, or by counting pulses with a
> frequency meter or BASIC stamp. We had the best results using a Fluke 87
> multimeter set for measuring Hz (cycles per second). There are 12 internal
> coils in the motor, but we only measured the output of half the coils (since
> we connected to only one power lead). Therefore, a meter reading of 6 Hz
> equals one revolution per second (60 rpm). Both frequency and voltage
> readings from the motor are quite linear, making for easy calibration. The
> other advantage of counting frequency over measuring voltage is that the
> length of the data cable would affect voltage readings; when counting
> frequency it can be any length and the calibration will stay the same.
>
> why you use the AC volts to measure a DC brushless motor?
> solar power arm board development team
>
>
> http://arm.web7days.com arm board
> http://www.web7days.com/led solar power control center
> http://www.web7days.com/farm farming
>
>
>
Because they shouldn't call them "DC Brushless Motors", they should call
them "permanent magnet synchronous motors". But nobody would understand
that, so they stick to the misnomer.

Inside of a "normal" DC motor you'll find a little gizmo called a
commutator. It's job is to take the DC from the power wires and switch
it around to the coils -- making it AC with just the right frequency to
drive the synchronous AC motor that's inside of nearly every DC motor*.
  A brushless "DC" motor takes the commutator out of the motor and puts
it into a circuit, eliminating one of the major wear points of a DC motor.

* except for the homopolar motors, but they're weird. 

-- 
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

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