[amsat-bb] Re: G-5500 stuck problem
wa6fwf at sbcglobal.net
Thu Jan 1 20:51:47 PST 2009
these transformers and motors are rated for intermittent duty so getting them stuck and left that way kills them, if memory serves
they pull about 1.7 amps running, and drop to about 1.2 amps stalled, 1.2amps x 25v = 30 watts and over time that heat builds up and
fries the windings.
It's just a oddity of this particular type of ac motor that it behaves this way, if it was another type or a dc motor you would see
the current rise that you expected and fuses would pop.
I found this out when I was making a add on card to my LVB tracker to replace the G-5500 control box, I thought I would be slick
and add one of the PPTC resettable fuses on the motors, so I needed to know the running current and locked current so I could pick
the right one, I was also surprised when the current dropped a little instead of going up, and then doing some reading on the web
about dual winding AC motors that use a capacitor to phase shift the other winding explained why this happens.
----- Original Message -----
From: "Greg D." <ko6th_greg at hotmail.com>
To: <wa6fwf at sbcglobal.net>; <amsat-bb at amsat.org>
Sent: Thursday, January 01, 2009 7:04 PM
Subject: RE: [amsat-bb] Re: G-5500 stuck problem
Ha, really... Thanks, I was "sure" it was the other way around.
So, if the current drops a little on a jam, why would it burn up either the transformer or motor?
> From: wa6fwf at sbcglobal.net
> To: amsat-bb at amsat.org
> Date: Thu, 1 Jan 2009 18:42:15 -0800
> Subject: [amsat-bb] Re: G-5500 stuck problem
> Hi Greg,
> Actually you need to measure the current while it is moving, then if it drops a little then its a jam, if it goes to zero then
> its the limit switch.
> I know this goes against reasoning, you expect a locked motor to pull more current, but these are split winding AC motors with a
> capacitor and they act differently.
> This is also why when you get a cable snag you burn up the motor or the transformer or both before you blow the fuse, that fuse I
> think just saves you from a mis-wired or shorted cable.
> Kevin WA6FWF
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