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Re: Dead G-5400B




>>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.
>


It will certainly take several minutes for the heat to melt the enamel
coating
on the wire.  So, the timer has to not only time-out, but it should remain
off
until sufficient time has passed to let the windings cool.  If not, then you
could
create a collective heat build-up issue over time that could eventially lead
to
the dimise of the field coil windings.


>>  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.
>


The hardware timer would not prevent damage if the external switching
control
(i.e. relay or TRIAC) encountered a stuck or engaged condition.  The
hardware
timer assumes the external control devices are operating properly.  The
limit
switches in the rotor overcome this assumption in case the external high
voltage
controls fail in the engaged position.  When I say external, I mean external
to the
KCT.


>
>>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.
>


A few seconds should be adequate to detect a delta change in voltage with
the
Analog to Digital converters.  We have the same goal in mind and that is to
prevent an equipment (hardware or software) failure in destroying the field
coils
in a rotor.

Limit switches in the rotor protect itself from a controller failure whether
it is
hardware or software failure.

Software or hardware timers help protect the field coils in case the rotor
gets
hung between the end limits, but they assume the control mechanism external
to the KCT are working.  Since heat is the end factor that causes the
damage,
it would be wise to have a resettable thermal switch that opens at a
specified
temperature and resets when sufficient cooling has been detected.  The
thermal
switches should be placed in both the control box transformer and each of
the
rotor motor field coil windings.  The current Yaesu schematic drawings show
that a thermal switch is tied to the common leads of the field coils.  This
suggests
that it is inadequate with the number of motors I have lost to thermal melt
down.

I have never lost an elevation motor due to thermal melt down and it is
interesting
to note that none of the KenPro or Yaesu (5400 or 5600) elevation rotors
have
any thermal protecting.  They only have limit switches with the exception of
the
KenPro KR-400 elevation motor and it had no limit switches.

If a reliable resettable thermal switch were used along with the limit
switches,
then rotor failures due to hardware or software faults would be greatly
reduced.
It is my belief that all circuits and devices should have sufficient
protection to
protect themselves from each other to create a more fail safe condition, but
you should expect to pay slightly more for this redundancy.


73's,

Tim - N8DEU
Huntsville, Alabama



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