[TowerTalk] Prop Pitch motor power

[NPAlex at aol.com]

There were several good responses to the question below - I have been using 
 a prop pitch motor rotator for nearly 40 years with great  success.  Most 
power supplies are located in the shack and feed cable wire  size is a key 
part of the supply voltage equation.  My power supply  delivers about 30 
volts at the source and drops to 22-23 volts at the  motor.   I now use a Green 
Heron/ K7NV controller and with the pulse  width ramp up and down of source 
voltage solves the inertia problem of large  arrays.  
 
There is a trick of wiring that can reduce the voltage drop to the motor  
for tower base mounted power supplies, and also works for shack located  
supplies.  The prop pitch motor is a three wire device, common lead with a  
forward and reverse set of leads.  The common lead can be grounded to the  tower 
at the PPM end and the power supply end as well.  If you ground the  coax 
shields at the top of the tower and again at the base of the tower (good  
practice for lightning protection) they two will form a parallel conductive 
path  along with the tower itself to the common wire lead.  This can  
significantly reduce the voltage drop of the total feed line.  If the power  supply 
is in the shack, connect the common to your coax grounds. 
 
Norm W4QN
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In a  message dated 3/14/2010 9:58:38 P.M. Central Daylight Time,   
w2lu at rochester.rr.com writes:

What is  the maximum DC voltage  used successfully/recommended for one of 
the  "small"  PPM's  ?  What speed was accomplished and how was the brush  
life 
at  that voltage ?
I 'm building a power supply to put at the base of  the  tower and can 
change the voltage from about 30 to 48 volts in 6 volt   steps. Cable to 
PPM will 
be 100 feet of 3-#12's. I'm figuring about 0.5  ohms  and about a ten amp 
demand  i.e. a 5 volt drop.
Any  suggestions will  be greatly appreciated.
Thanks,
Gene /   W2LU
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