[TowerTalk] Fw: Prop Pitch Motor Power Supply

Gene Fuller w2lu at rochester.rr.com
Mon Apr 12 07:03:40 PDT 2010

Thanks Jim, it sounds like you have a really nice setup.  I've gotten to the 
point where I should be looking at something more like that. I have moved 
the power supply to the base of the tower, but a 100 foot pipe mast still 
seems a bit daunting. There would still be te problem of the big LP up on 
top. I wasn't looking far enough ahead when I designed my system. e.g. the 
ppm is mounted on the top side of it's mounting platethus making it almost 
impossible to change it out without bringing the whole carriage assembly 

I'm beginning to wish I had left my system on AC.  Have you ever replaced 
the brushes and/or had the commutator turned down?  I didn't know any better 
than to fill the gat case with oil wo there's the possibility that the lower 
seal finally gave up and the rushes/commutator are all burned up from oil 
seepage. Someone did suggest to me that I drill a hole in the bottom of the 
motor can to drain any oil that made it that far. Fortunately I have an 
extra motor. Now if I could just find/teach someone who could climb the 
tower and replace the motor (and a few other little odds and ends). In the 
meantime I have a TH-6 on a side gate a 45 feet that does supprising well.


Gene / W2LU

----- Original Message ----- 
From: "Jim Hargrave" <w5ifp at gvtc.com>
To: "Tower and HF antenna construction topics." <towertalk at contesting.com>
Sent: Monday, April 12, 2010 9:13 AM
Subject: Re: [TowerTalk] Fw: Prop Pitch Motor Power Supply

> Gene,
> 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 
> 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: towertalk-bounces at contesting.com
>> [mailto:towertalk-bounces at contesting.com]On Behalf Of Gene Fuller
>> Sent: Monday, April 12, 2010 12:18 AM
>> To: towertalk at contesting.com
>> Subject: [TowerTalk] Fw: Prop Pitch Motor Power Supply
>> ----- Original Message -----
>> From: Gene Fuller
>> To: tips at contesting.com
>> 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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