[TowerTalk] Figuring Out Prop Pitch Wiring

[Jim Smith]

The selsyns I used to have had 5 wires, 3 stator and 2 rotor.  The 
stator was a 3 phase winding and was not connected to the rotor.  I 
remember this clearly because once in the 60s at a UBC dance I drove the 
rotor of one from an audio amp, and connected each stator wire to its 
own audio amp and speaker.  The speakers were appropriately distributed 
around the periphery of the auditorium.  Don't remember how I dealt with 
the ground return.  Maybe I had 3 transformers, one across each stator 
winding.

Then I fed the Beatles' "Day In A Life" into the rotor while slowly 
turning the rotor by hand.  This caused a number of people to act very 
strangely indeed, especially when I sped it up and slowed it down.

So, if these selsyns are like mine, there will be 5 wires.  Find 2 which 
show some resistance between them but no connection to the other 3 
wires.  These are the rotor wires.  The other 3 are the stator wires.  
The resistance between any pair of them should be the same as between 
any of the other 2 pairs.

As I recall, the 2 rotors were connected in series with an ac voltage 
source, although I suppose parallel would work just as well.  Mine were 
60 Hz but I think 400 Hz is more common.  Don't remember the voltage.  
The stator wires for one were connected to the stator wires of the 
other.  Doesn't matter which goes to which except that if you get it 
wrong, the indicator will turn the wrong way when you turn the sensor.  
Just reverse any 2 stator wires.

Hope this helps.

73 de Jim Smith   VE7FO

Ward Silver wrote:

>Hi all,
>
>As you may have heard, John N7TT is the proud new owner of the W7RM QTH in
>southwestern WA.  John has a bit of a project on his hands, to say the
>least, as he restores the "infrastructure".  In the process of preparing the
>QTH for sale to what the family expected would be a "normal person" (to use
>John's words), all of the cabling was yanked from the radio area and into
>the yard, unlabeled, in preparation for a rapid takedown.
>
>John now has nearly a dozen prop-pitch motor/selsyn cables laying on the
>ground without any indication (so to speak) of what the connections are at
>the tower.  It would be really great if someone could suggest a method -
>such as an ohmmeter or DC measurement - that would allow him to figure out
>the connections without having to laboriously climb up and down the towers a
>million times.
>
>I've volunteered to help figure this out for John, but maybe this would be
>of help to others with "mystery wiring", too.  Such nfo might be of use for
>troubleshooting.  Suggestions?
>
>73, Ward N0AX
>
>
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>
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