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[Towertalk] Motor Start Capacitors

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Subject: [Towertalk] Motor Start Capacitors
From: (Joe)
Date: Thu, 8 Aug 2002 15:22:17 -0500
While this is nothing new to many of you, there are a number of real
advantages in putting the motor start capacator on the tower at the rotator.

First of all, that's where it ought to be.  Check most any industrial
electric motor installation and you will find the motor start capacitor on
or near the motor itself.  Putting it several hundred feet away is hard to
justifiy in so far as good engineering practice goes.

Second, many users think that the "black and white" wires (Terminals 1 & 2)
are the primary motor current carrying wires ... otherwise why  would they
be of a heavier gage.  Wrong ... these two wires simply provide currrent to
the brake solenoid.  The current to the motor windings uses only one of
these wires along with two of the other smaller gage wires.  By freeing up
two of the wires in the normal 8-conduction rotor cable by putting the motor
start capacitor on the tower, it allows the two extra wires to be paralleled
with the "return" leads from the two motor windings, which reduces power
loss and assists the motor in turning more reliably.

Finally, capacitors designed for use with industrial motors are very rugged.
The ones that  come from a source like Gainger are expected to live in the
cruel, harsh external world.  (Go look at you outside A/C unit's fan motor
cap.) If properly installed, they will outlast most amateur antennas.  We've
had them on towers for over 15 years with no failures.

We took care to use quality stranded electrical wire and to ":pot" the
connections with electrical quality RTV. They are mounted with the
connections down and placed just beneath the rotor plate.  It's worked for

Joe, W5ASP

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