How to connect unlabeled prop-pitch motor wiring

Source: K1TTT and the ARRL Contest Rate Sheet (July 14, 2004)


Prop-pitch motor for rotating tower at VE7SV

In trying to find out how to connect unlabeled prop-pitch motor wiring, Dave, K1TTT contributed the following useful procedure. The prop pitch consists of a large motor and a three-phase synchro position sensor with an excitation coil. By exciting the synchro coils, a companion indicator in the shack will rotate to match the orientation of the three coils in the motor. I'll let Dave tell it...

"For normal wiring you should see two fat wires which are power to the motor and five other wires for the synchro and excitation coil. First, apply power to the fat wires and see which way the motor rotates, reverse if needed. For the remaining five wires, measure resistance from each wire to every other wire. You should find two of them with continuity to each other and none of the other three - this is the excitation coil. The other three should have continuity to each other. Connect the indicator to these three wires in any combination and apply voltage to the excitation coil. Rotate the antenna, and if the indicator turns the wrong way, reverse any two of the three wires. If the indicator is 120 degrees off, shift all three indicator connections to the adjacent terminal and try again."

Got it? It's easier than disassembling the prop pitch, that's for sure!


One additional note, according to the
Ken, K0PP, the Selsyn position sensors are not part of the motor itself and can be mounted externally in a number of ways. They're not inside the motor housing. Also, the motors have three wires - two for the motor and one for ground - not two, although it's common practice to either tie the ground wire to one of the motor leads or rely on the mounting hardware to provide a ground. 



 Last modified August 15, 2004 by Paul B. Peters, Show contact information
Copyright 2000 -2004 Paul B. Peters, VE7AVV. All rights reserved.