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Re: Dead G-5400B



At 10:27 AM 1/24/00 -0600, Tim Cunningham wrote:
>I lost a few motors in this fashion.  Then, I quickly learned how to rewind
>motor windings,
>which is not a fun project.  However, it is definitely cheaper than
>purchasing a new motor.

I'm impressed. I thought I was being crafty when I rebuilt the bearings (with factory-supplied parts), but I never would have undertaken to rebuild the motor.

>The preferred place to put the protection is in the rotor as limit switches.
>The software
>timer circuitry would be helpful, but it will still heat the field coils in
>the rotor if it is already
>stuck and you have to wait for the timer to expire. 

You make a valid point. The question is, how long does it take to damage the motor? I was presuming it would take minutes of stalled operation to cause a problem. If that's true, then the timer is fine. If damage starts in a few seconds, then the timer is insufficient.

>  I would prefer software that detects
>movement when the field coils are energized.  If the rotor has not been
>detected to
>be moving in a small time frame, then it should stop it's action.

You correctly point out that a control this complex would have to be in software. A software interlock like this would not have saved the original poster's motor, which was seemingly killed by a software crash. A timer could be in the hardware.

>In each of my rotor failures, I have found the relays to be sticking in the
>control box.  These relays will be replaced with TRIACS in the near future as the
>switching control.

As you say, this failure can't be solved by the rotor interface, whether in hardware or software. My installation uses "solid state relays" based on triacs.

>2) The KCT driver software or any other driver softwrae should check the
>rotor motion.  If the field coils have been energized, the software should
>insure that the rotor is moving in the desired diercetion within  a small time
>window.  if it is not moving, then the softwrae should detect this condition
>and not attempt to drive the rotor.

But the time window should not be too small. If it's shorter than a second or so, when the rotor's sense potentiometer develops small dead spots the rotor driver will declare failure too easily. It may also have problems with the ends of rotation, where there may be a few seconds worth of flat spot before the voltage starts to respond.

73  -Paul
kb5mu@amsat.org


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