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[TowerTalk] DC motors in rotators

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Subject: [TowerTalk] DC motors in rotators
From: (Pete Smith)
Date: Tue Mar 4 07:42:19 2003
I have a Yaesu G-800SA rotator turning a small tribander on a swinging gate 
sidemount.  The Yaesu has a locking rocker switch to control the direction 
of rotation.  On more occasions than I care to remember I've overlooked the 
fact that the switch had locked in one or the other direction, causing the 
sidemount to come up against the tower.  Minutes to hours later, I would 
notice where the antenna was pointing and unlocked the switch, sure that I 
had burned out the motor.  To my surprise, though, the rotator simply backs 
off the stop when asked and continues working as if nothing had happened.

I'm curious why this rotator seems so impervious to being run against an 
immovable stop.  Are DC motors inherently protected against overheating or 
damage when stalled (for example, does the current through the motor 
somehow drop to a low level), or is there some other explanation, perhaps 
in the design of the controller itself??

What would happen with an AC motor under similar circumstances?

73, Pete N4ZR
The World HF Contest Station Database was updated 23 Feb 03.
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