Reversing Rotation On AC Motor

[AndrewDouglasBird]

I have a capacitor start/capacitor run AC motor (two capacitors) that I am putting on my air compressor. Only problem is, it turns the wrong direction. From looking online, it seems all I need to do is reverse the starter circuit and it will reverse, but I tried and that didn't work. The motor acted like there was no starter cap at all and just hummed, but would start if rotated by hand, in either direction. So then I opened up the motor and found some odd wiring. Here is a diagram I drew up:

The starter coil is made of 3 wires. On one side of the coil, all the wires go to a single red wire, but on the other side, two wires go to one side of the caps and the other single wire goes to the other side of the caps. This seems odd to me. I' wondering if I can simplify this and hook it up like so:

that is how these style motors are normally wired based on this website.

Anyone see a problem with doing it like that?

 

[rkevins]

does your motor have a nameplate on it? there should be a diagram on it or it could be inside the connection cover. or can you post a picture of the nameplate of make and model number. some motors are not reversible. are the leads numbered ?

 

[AndrewDouglasBird]

It's a motor off of a Jet dust collector. There is a wiring diagram inside the cover, but it does not specify how to reverse it. My understanding though is that any AC motor, other than a shaded pole motor, can be reversed, it's just that some times you have to modify the wiring to the actual coils instead of just swapping wires around in the wiring box.

I went ahead and wired it up like my second diagram, and while I was able to wire for both CCW and CW rotation (switching the starter coil wiring around), it only runs at half speed. The motor is rated for 3450 RPM but is only running at 1725 RPM. That said, I didn't think about the centrifugal switch not disengaging at a slower speed and while running the motor, the starting capacitor blew (not made to be connected continuously). :-(

So, the second "run" capacitor must do something with the starter coil and double the RPM somehow. Anyone like to comment on this?

 

[AndrewDouglasBird]

So more reading tells me that the RPM of an AC motor is determined by the frequency of the AC supply and the number of poles that the motor has. 4 pole motors run at 1725 RPM and 2 pole motors run at double that speed of 3450 RPM. So it seems the run capacitor in my motor is basically turning a 4 pole motor into a 2 pole motor somehow. Lots of searching has gotten me know where. Any ideas?

 

[AndrewDouglasBird]

Talked with an electrical engineer friend of mine and while we both still don't understand exactly how the motor is working, we pretty much determined that the motor is wired in a way that it can't be reversed. The coils are wrapped in a particular way that it will only ever rotate one direction at full speed.

One thing I tried was connecting only the main coil and starting the motor by hand (with no capacitors or the starter coil). In the direction it was originally spinning (when not modified), it would spin at 1/4 the rated RPM. When spinning the opposite direction (the direction I'd like it to spin) it spins at 1/2 the rated RPM.

Anyways, unless someone else has some other idea, I'm just going to hook it back up the way it was.

 

[AndrewDouglasBird]

Ok, so more tinkering with it. I've for sure determined there are two main coils and a single smaller starter coil. I tried moving the run cap so it was on the other main coil, but it still spins the same direction, even without a starter cap hooked up.

 

[AndrewDouglasBird]

AH HA! Got it to reverse. When I switched the cap around, I also accidentally reversed the coil I switched it to. Once I switched the coil back, it ran in reverse. I also had to switch the black/red and grey/yellow wires to black/yellow and grey/red.

 

[6t7gto]

I knew you could do it!