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Re: [TowerTalk] Fw: Prop Pitch Motor Power Supply

To: "Tower and HF antenna construction topics." <>
Subject: Re: [TowerTalk] Fw: Prop Pitch Motor Power Supply
From: "Jim Hargrave" <>
Reply-to: "Tower and HF antenna construction topics." <>
Date: Mon, 12 Apr 2010 08:13:17 -0500
List-post: <">>

I'm no expert on motors, but will offer my experience.

The prop pitch motor is a AC/DC type motor, however it was designed to run
on 28 VDC.

I have used a small Prop Pitch motor since the 1960's and have always run it
on AC. I use a 24 volt battery charger transformer with a variac on the AC
power side. I use light weight lithium chassis grease in the gearbox, so it
slows down a little when the temp is below freezing. I make minor
adjustments of the variac to maintain a reasonable speed between
summer/winter operation.

The first twenty years I had it rotating a homebrew three element
tri-bander. Since that time it has rotated a HyGain TH6 Tri-bander and a 14
element 2M beam. I have had it at three QTH over the years and I serviced
the unit each time I moved. It has been operational for 13 years at this QTH
and has not needed servicing (yet--knock knock). You can minimize brush
arcing and prolong the life by making sure you clean out the spaces between
armature contacts.

I mounted the rotor at the top of the tower at the two previous QTH, but now
have it mounted about 4 ft of the ground and run a mast up the tower. Its a
50 ft tower and the mast is galvanized water pipe with a section of schedule
40 at the top where it goes thru the tower top section. I have a section of
automotive driveshaft at the bottom including the u-joint, so shaft
alignment is not a problem. The whole assembly is quiet heavy and is cable
suspended so there is no weight load on the rotor gearbox.

   73's  Jim - W5IFP

> -----Original Message-----
> From:
> []On Behalf Of Gene Fuller
> Sent: Monday, April 12, 2010 12:18 AM
> To:
> Subject: [TowerTalk] Fw: Prop Pitch Motor Power Supply
> ----- Original Message -----
> From: Gene Fuller
> To:
> Sent: Monday, April 12, 2010 12:48 AM
> Subject: Prop Pitch Motor Power Supply
> AC or DC is the question. I have heard from several sources that
> the PPM's should be run from DC or else the brushes would not
> last as long as they might. I had run one for 30-40 years on AC,
> with small to medium sized antennas, befor any sign s of a
> problem. In view of the recommendatioins I added a diode bridge
> to give me some DC. At the same time I had the commutator turned
> and put in new brushes. Much to my dissapointment it now appears
> that after only 6 or 7 years  (turning a fairly large, 7-60 MHz)
> LP) at least the brushes are gone.  Over a period of a few days
> the speed dropped to about 0.1 RPM and finally quit all together
> (same CW or CCW). I haven't had a chance to get the motor down
> off the tower yet.
> I was recently talking with an acquaintance who is an engineer
> and seems to be familiar with electric motors and he was quite
> emphatic that AC would generally be preferable. The reason is
> that with DC you tend to draw an arc from sector to sector of the
> commutator as the armateur rotates, whereas with AC the arc tends
> to be self-extingushing as the wave passes through zero. I didn't
> think to mention to him that the motor operates at about 9,000
> RPM. Perhaps he is right with motors that operate at lower speed
> relative to 60 Hz, but with the PPM running such high RPM's and
> drawing less current when operating on DC, DC really is the right
> way to go.
> Any comments would be appreciated.
> Gene's / W2LU
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