[amsat-bb] Re: Motor for Yaesu G5500 Azimuth Rotator?

[i8cvs]

----- Original Message -----
From: "Phil Karn" <karn at ka9q.net>
To: "Joe Fitzgerald" <jfitzgerald at alum.wpi.edu>
Cc: <amsat-bb at amsat.org>
Sent: Saturday, February 25, 2012 10:25 PM
Subject: [amsat-bb] Re: Motor for Yaesu G5500 Azimuth Rotator?


> On 2/25/12 6:46 AM, Joe Fitzgerald wrote:
> >
> > controller, but it was not particularly sophisticated.  They simply
> > pulsed 60Hz AC from a 24V transformer when they wanted to accelerate or
> > slow down.  I am not exactly sure how they generated torque since there
> > was no evidence that they did anything to shift the phase of the three
> > windings.
>
> If it really was a 3-phase induction motor then there *had* to be some
> sort of phase shift at least to start it. An induction motor connected
> to a single-phase supply has no starting torque, so it'll just sit there
> and burn out unless some sort of protection circuit kicks in first. If
> you give it a twist in one direction or the other, it'll start and
> continue to run in that direction.
>
> This suggests a possible failure mode for these Yaesu/Kenpro antenna
> rotors: if the run capacitor fails or the connection to one winding opens.
>
> Most induction motors designed for single-phase supplies (like these
> rotor motors) are actually 2-phase motors. The second winding connects
> to the supply through a phase shift capacitor either permanently
> ("capacitor run") or disconnected with a centrifugal switch once the
> motor starts ("capacitor start").
>
> People usually think of 3-phase induction motors as industrial-sized
> behemoths, but one especially common application is in the so-called
> "brushless DC motor". They're actually AC induction or permanent magnet
> motors with built in inverters producing 3-phase AC at a frequency set
> by a sensor (usually Hall effect) on the rotor.
>
> One could argue that there really is no such thing as a "DC motor"
> except for Faraday's homopolar motor that's still not much more than a
> curiosity. So-called "DC" motors are really AC motors with built-in
> DC-AC conversion.
>

Hi Phil, KA9Q

If you are interested in a very simple but effective "Single to 3-PHASE
Power Converter for azimuth and elevation motors currently used for
EME, look at this web page made by John Yurek, K3PGP

http://www.k3pgp.org/3phconv.htm

73" de

i8CVS Domenico