[TowerTalk] prop pitch motor power

[Jim Thomson]

Date: Wed, 17 Mar 2010 00:02:23 EDT
From: NPAlex at aol.com
Subject: [TowerTalk] Prop Pitch motor power
 
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
=======================================

##  I was  going to proceed  to do exactly that, back in 1977,
but my no load V  was abt +34  to +36 vdc  on the HB Un-regulated
pwr supply.   I think the run to the PPM was 175' [350' total loop]
Somebody had given me some 3 x conductor stuff, forget what ga

##  The V drop was such, that it worked fine, as my V was on the 
high side anyway.  Just using the braid only of one coax run, would
also  do the trick.. like on a crank up tower.  That saves having to use
heavy ga wire on a long run... and up the side of a crank up tower. 

##  just cranking the V  up to compensate  for the drop will work too,
or a combo of all these idea's.... but maybe not these  days... with
PWM  being used.. like in the GH control box.  Dunno if the GH box's
PWM will handle the extra V... or if the extra v  would screw up the 
PWM operation ?? 

later..... . Jim   VE7RF