I have an old sears craftsman 1/2 hp split phase induction motor (model 12120, cat # 1212) but can't find any info for wiring it so it can run both forward & reverse via a switch. I was looking to use a dpdt switch with center off to do that but cannot figure out how to wire it properly and am wondering if it's possible. The motor has a yellow wire and blue wire with lugs that can be placed on either of 2 tabs. The cover plate says 'to reverse rotation interchange blue and yellow leads'. There's also two other threaded posts that the ac (110V) wires connect to. Can anyone point me in the right direction or provide a link if the solution has been posted already? Thanks.
When you are swapping 2 wires with a DPDT switch it works just like a "4 way".
The problem is your idea of also using this for the on off switch. You are dealing with 2 windings and they need to both be switched. The way I see it you need at least one more pole and then it still won't really be "off" in the sense of a disconnect. This is typically done with a drum switch. That actually functions more like a 4p dt
Look at the diagrams at the end of this catalog page for some ideas.
You're correct - the motor didn't really seem to be off in the OFF position. I'm also a little unclear with your drawing. What are you considering L1 & L2 to be as well as the 2 wires connected to the center of the dpdt switch? Is L1 & L2 the blue and yellow wires or my black & white AC in line? I tried this type of wiring setup and got forward and reverse to work, but the motor hummed and seemed to experience a magnetic field when in the OFF position. Thanks
#207297 - 10/14/1202:58 PMRe: Wiring a Split Phase Motor for Forward & Reverse
OK L1 L2 are the AC inputs, either 120 or 240 depending on the motor.
Black and orange are the 2 you swap to change direction and the other winding is not shown. You need another switch pole for a 120 or 2 for a 240.
The easiest way to handle this is still going to be one of those drum switches. That will switch on the main winding and select the start winding polarity to establish direction. Look again at those diagrams to see how this works. There are a few ways you will see used to do this but they all end up working basically the same way.
#207301 - 10/14/1209:50 PMRe: Wiring a Split Phase Motor for Forward & Reverse
Thanks Greg. I'm using 115V for the motor. On the motor (peckerhead) I got there are numbers 1 and 4 stamped next to the tabs that the yellow and blue wires attach to. I tried several different ways to wire it, but the one that I tried before posting my question was similar to your first drawing, but I had the blue & yellow where you had L1 & L2 and I had L1 & L2 tied to the center posts and jumpered from there back to the 2 threaded lugs on motor. That seems to be very similar to the 2nd drawing you posted. However, I am confused by the 2 arrows by L1 & L2 and am wondering where they are going. Are they tied to the center posts (like I tried) and then going back to the motor? It seems so and that's what I did and seemed to be why I got the hum when I had the dpdt switch in the OFF position. My next iteration was to tie the white wire to one center post on the switch and then bring that back to the motor while the black wire just goes to the other center post. I was thinking that would provide the break/disconnect needed to prevent the motor hum when the switch was OFF. I haven't tried that, but that was going to be my next attempt.
#207304 - 10/15/1204:07 AMRe: Wiring a Split Phase Motor for Forward & Reverse
In the second picture the arrows refer to the contact points that flip back and forth (center terminals on the switch).
That is a 240v trick that I found in a boat lift controller where they were doing the switching with 2 pole relays (represented logically with a DPDT switch)
I got into this a while ago when I was called to replace a motor where the colors did not match the new one and I drew this to sort out how it worked so I could make the new motor work. In the normal configuration you have one winding that is always connected the same to L1 L2 and the other will swap depending on direction desired. It is really just the relationship between windings that establishes direction so you could swap either winding.
I tried wiring the motor similar to what was shown in the 2nd diagram even though it's basically a 4-wire motor instead of 6 (2 posts for the blue & yellow wires and 2 posts for the black & white wires).
Since I don't have the dpdt switch mounted in an electrical box yet due to trying different wiring schemes, I would first position the dpdt switch to one of the 3 positions and then plug it in. The motor did seem truly off in the center position (no humming), and reversed direction when the switch was in the other 2 positions. However, the motor did not consistently spin in the same direction each time it was plugged in with the switch in a particular position. Sometimes the up position was forward and other times it was reverse. Occasionally it would not turn at all and just hum. The motor also seemed to get very warm rather quickly.
Not sure what's going on at this point or why. It does seem that the dpdt switch cannot provide the directional switching and off options for the lathe like I was hoping and a drum switch is needed to do the job.
#207403 - 10/24/1210:26 PMRe: Wiring a Split Phase Motor for Forward & Reverse
Have you ever seen this work? How was it wired then?
I don't understand everything I know about motors but there is one configuration where the 2 windings and the capacitor are wired in a delta configuration. You connect the neutral to the center point of the 2 windings and which ever end of the capacitor you connect the hot to, determines the rotation. Both windings will ohm out identically.
I think I would google every number I could find on that motor and see if you can find some application notes.
The motor works fine when the yellow & blue wires are connected to the .25" faston tabs marked 1 & 4 on the peckerhead and the black & white wires are connected to the 2 threaded lugs. It runs fine and cool like this. I'll also mention that the threaded lugs and faston tabs that the blue & yellow wires attach to seem to be connected together electrically. That is the left threaded lug seems tied to the left tab (1) and the right threaded lug seems tied to the right tab (4). If the yellow & blue wires are reversed on 1 & 4, the motor spins in the opposite direction.
It is only when I try using the dpdt switch I got from Grainger that I have problems getting the motor to run properly or reverse itself. I don't think the switch is bad since I can wire it as a single pole to turn the motor on/off, but without any reversing capabilities.
There does not seem to be a capacitor on this motor (start or run). It seems most like the resistance start induction motor that Scott35 posted in 2003 (figs 1.1 & 1.2) in the link I had on my first post. I can hear the centrifugal start switch open & close when the motor starts & stops so that seems to be working fine.