[amsat-bb] Re: G-5500 stuck problem
wa6fwf at sbcglobal.net
Fri Jan 2 08:44:38 PST 2009
Yes these will burn up on their own, page 2 of the manual states that the maximum continuous run time is 5 mins, but when
normally tracking a sat were talking little movements of a couple of seconds.
I was measuring current with a standard VOM set for AC current and I had no way of measuring the PF so what you say could be
correct and I wasn't seeing the real current, and I'm not a motor guru but from what I understand the capacitor and the winding
90deg out of phase are only needed to get the motor spinning and turning in the direction that you want, that once the motor is up
to speed you could disconnect the capacitor and 90 deg winding and the motor would keep running, also the capacitor value needed to
start vs. the most efficient to run at "if you were going to leave the circuit engaged" are two completely different values, and
the current rise at run speed are caused by the mis-match.
So when you lock the rotor you are in start mode at x current and when your up to speed your seeing the mismatch/inefficiency and
the increased current flow.
Maybe there is someone on here that could do a better job of explaining why this motor works like this.
I don't remember the original sites I went to but a couple links that you might want to check out...
----- 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 11:08 PM
Subject: RE: [amsat-bb] Re: G-5500 stuck problem
So, my take-away here is that it's not the stall itself that is the problem; the motor is practically designed to self-destruct.
Simply running the rotor back and forth enough times will do the same thing. In fact, probably worse, given the higher draw.
One thing just occurred to me... AC current measurements assume a specific phase relationship between voltage and current - power
factor, I think they call it. This is a highly inductive load, and the phase-shift capacitor throws another unknown into the
puzzle. I wonder if the two measurements you took are real? It could be that you think that the running current is higher, when it
may just be a measurement error. How were they measured?
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