Thread: Reversing a single phase motor

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I have a pulley driven extractor fan that was driven by a small 3Phase motor but I wanted to use it with a single phase (SP) GPO so I decided to swap the 3 phase motor out for a small SP motor from an old clothes dryer.

The SP motor turned out to have a number of problems and if I had stopped to carefully examine and test the motor I would have moved to another but I fixed each of the problems as they arose so once you invest some time into something the more you want to see it through to completion

The first problem was it did not seem to have sufficient cooling.
Unlike many extractor fans it will not be sitting in the air stream it generates so it needed some cooling.
Ss I made and added a fan.






Next the pressed galv metal pulley flange looked a bit flimsy so I replaced it with a beefier one


After doing all this, it turned out the wretched thing ran the wrong way. The way this is normally done is to reverse the connections for either the run coil OR the start coil but not both. To do either requires access to both of one of these coils but there were no accessible wiring connectors available outside the motor to do this.

Even when I opened up the motor and traced back along the connectors to find a junction, the one I needed to access turned out to be buried under two coils of wire squished together.
See next picture.
I prised the coils apart using a pair of small pliers with the jaws wrapped in cloth. the Green arrow in the picture shows the direction I had to pry that coil to get to the yellow wire buried underneath it.
The yellow wire was connected to two lacquered wires and I had to cut off one of these and then attached a new wire to the that I could take it outside the motor.



Here you can see the separated wires


Then silver brazed and new (tan coloured) wire, Squish everything back in place, stitch up the coils, cover in HT silicone and reassemble the motor.


Here is where the connections take place.
If it looks like a dogs breakfast - it is.


For anticlockwise direction, tan was originally connected to yellow inside the motor and yellow was connected to the brown (Active) on the AC mains cable
The blue wire near the green arrow was connected to the other blue (Neutral) wire from the supply.
Red is one end of the starter coil that is connected to neutral by the starter/centrifugal switch.

To reverse the motor simply entailed swapping the positions of the tan and blue wires (near the green arrow) coming out of the motor
Anyway it runs clockwise as required and I am finally happy with it.
Whew!