# Single phase 208v motor reversing



## Phillipd

We are doing motor labs at trade school. I’m using a Seimans mechanical interlocking contact and an o/l. I got it to work in a different way than our instructor suggested and he asked me to draw my circuit as it actually works. I have line one coming in and going to L1 and L2 on the fwd contractor than also to L1 and L2 on the reversing contractor. Line 2 is coming in going to L3 on the forward contractor and also the reversing. On the bottom T1 is going to 1 on the motor,T2 is going to 8 and T3 is going to 4. When I press reverse T1 and T3 reverse. It works .just wondering if it should have worked or was just a freak of nature? Thank you for any input. I’d post a diagram drawing but I’m not sure I can post pictures or not.


----------



## Phillipd

Contactor not contractor, also 2,3&5 are tied together.


----------



## dronai

Phillipd said:


> We are doing motor labs at trade school. I’m using a Seimans mechanical interlocking contact and an o/l. I got it to work in a different way than our instructor suggested and he asked me to draw my circuit as it actually works. I have line one coming in and going to L1 and L2 on the fwd contractor than also to L1 and L2 on the reversing contractor. Line 2 is coming in going to L3 on the forward contractor and also the reversing. On the bottom T1 is going to 1 on the motor,T2 is going to 8 and T3 is going to 4. When I press reverse T1 and T3 reverse. It works .just wondering if it should have worked or was just a freak of nature? Thank you for any input. I’d post a diagram drawing but I’m not sure I can post pictures or not.


Get your post count to 20 and you can post a diagram


----------



## Kevin

dronai said:


> Get your post count to 20 and you can post a diagram


Fastest way is to say hi in the new members section to all the new guys welcoming them to the forum...

Sent from my new phone. Autocorrect may have changed stuff.


----------



## Phillipd

That’s a great idea, thank you.


----------



## Phillipd

Pic attempt. 60515247048__F343C9C6-64EB-4809-A755-5296AB23E4FD.JPG


----------



## gpop

So you have wired the motor so A phase is 240 (2 coils joined) and B phase is only getting about 60-120 volts (parallel with one of A phases coils then series with the second). Not even going to try to figure the math's on that one.

It might start and run on the bench with no load but in real life that's not going to work as it wont have the balls to start. Also i guess thermal protection wasn't that important as a option. 

Will give you 9/10 for creativity i wonder what the teacher will give you


----------



## Phillipd

I drew out the circuit and my instructor looked it over and said ya I guess that works.kudos for figuring it out. I redid the wiring the same as was instructed also so I’d know how to do it. The trick was to remove the 1-2-3 to 1-2-3 jumper at the top of the forward reverse contacts, remove the 1-2-3 to 3-2-1 at the bottom and replace that with the 1-2-3 to 1-2-3. Then at the top of the forward we wired it L1-L2-L1 on the forward then wired it L1-L2-L2 on the reversing. On the bottom of the O/L we wired T1-1 T2-4 T3-8 and 3-5-6 tied together. I know you can’t really run a 240 single phase off 208 but it was just for simulation.


----------



## Phillipd

Here’s the drawings


----------



## Phillipd

Sorry 2-3-5 were tied together


----------



## gpop

Your drawing is about as much use as tits on a boar hog. (you could just list the connections as it doesn't tell you why it works)

Find the coil diagram for your motor (print screen then copy into paint)









now draw your connections onto this to see whats really going on inside the motor.

Why loose point with your instructor for doing it wrong when you can wire it wrong then show how it works and score bonus points


----------



## dronai

You have to switch 5, and 8 in the reverse contactor. Use a 4 pole contactor.


----------



## CMP

*1Φ motor reversing*

Your drawing will work, but I take it that you have no clue why.
You need to understand how the motor starts and runs, to be able to figure out why your connections work.


1Φ motors have basically 2 winding's, *run* and *start*. With dual voltage 1Φ motors, the *run* winding will consist of two coils. Wired in series for high volts and wired in parallel for low volts. 



The start winding is normally wound for the low voltage, so that it can be powered at the lower voltage. For the high voltage connection, one end of it is connected to the center of the run winding's common connections.


Both winding's need to be powered at first to get the motor started. Once the rotor gets up to speed. The centrifugal switch opens, and the start winding gets disconnected. The motor continues to run on just the run winding.


What causes it to start in one direction versus the other direction is, the phase relationship between the start and run winding's. If the phase relationship (polarity) between either start or run winding is changed, the motor will start in the opposite direction. One stays the same phase relationship, and the other winding changes polarity. If they both change, the the motor starts in the same direction, as before.


So looking at your drawing, what is happening to get the rotation to reverse?


Make a drawing of your motor internals, like suggested earlier, to see if you can understand why your connection reverse the motor.


Couple of sample 1Φ motor drawings to give you the idea.


----------



## Helmut

Why would you ever do this?

Your wiring a 3 phase motor to run on a 1ph input. It would be useless.


----------



## micromind

As noted, there are 2 - 115 volt run windings and 1 - 115 volt start winding. For 115 volts, all 3 windings are in parallel, for 208 - 230, the run windings are in series and the start winding is in parallel with one of them. Since the 2 run windings are on the same core there will always be roughly 115 volts on each of then even if there's different current on them.

Generally speaking, the start winding (5 & 8) will be in parallel with 3 &4, and to reverse rotation, you'd swap 5 & 8.

In your drawing, in forward, L1 goes to 1 & 8. L2 goes to 4 and 2,3 and 5 are tied together. The start winding is in parallel with 1 & 2. This will work, it doesn't matter if the start winding is in parallel with 1 & 2 or if it's 3 & 4. 

In reverse, 8 & 4 are connected together therefore the start winding is now in parallel with 3 & 4. This will result in opposite rotation. 

There's nothing wrong with it, it's simply not standard. 

P.S. Nice drawing, I like neat drawings but I can't draw very good.......lol.


----------



## Phillipd

Thank you very much, we’re barely scratching the surface on motors, it says in our motors book that besides changing 5&8 on the start windings that changing the leads on the run windings will also reverse the motor. By the drawing I had, 5&8 were unchanged but 1&4 were reversing. So I’m under the understanding that reversing the run windings leads will also determine a leading or lagging current as compared to the start capacitor in single phase? I’m assuming this only works for hv and in lv you must reverse 5&8?


----------



## gpop

CMP said:


> Your drawing will work, but I take it that you have no clue why.
> You need to understand how the motor starts and runs, to be able to figure out why your connections work.
> 
> 
> 1Φ motors have basically 2 winding's, *run* and *start*. With dual voltage 1Φ motors, the *run* winding will consist of two coils. Wired in series for high volts and wired in parallel for low volts.
> 
> 
> 
> The start winding is normally wound for the low voltage, so that it can be powered at the lower voltage. For the high voltage connection, one end of it is connected to the center of the run winding's common connections.
> 
> 
> Both winding's need to be powered at first to get the motor started. Once the rotor gets up to speed. The centrifugal switch opens, and the start winding gets disconnected. The motor continues to run on just the run winding.
> 
> 
> What causes it to start in one direction versus the other direction is, the phase relationship between the start and run winding's. If the phase relationship (polarity) between either start or run winding is changed, the motor will start in the opposite direction. One stays the same phase relationship, and the other winding changes polarity. If they both change, the the motor starts in the same direction, as before.
> 
> 
> So looking at your drawing, what is happening to get the rotation to reverse?
> 
> 
> Make a drawing of your motor internals, like suggested earlier, to see if you can understand why your connection reverse the motor.
> 
> 
> Couple of sample 1Φ motor drawings to give you the idea.
> 
> 
> View attachment 141204
> 
> 
> 
> View attachment 141206


Dam i wish you had been my teacher


----------



## dronai

gpop said:


> Dam i wish you had been my teacher


I'm with you, I know how to make things work, but this guy has a deep understanding about why 
Lucky we have guys like this dropping by.


----------



## CMP

Phillipd said:


> Thank you very much, we’re barely scratching the surface on motors, it says in our motors book that besides changing 5&8 on the start windings that changing the leads on the run windings will also reverse the motor. By the drawing I had, 5&8 were unchanged but 1&4 were reversing. So I’m under the understanding that reversing the run windings leads will also determine a leading or lagging current as compared to the start capacitor in single phase? I’m assuming this only works for hv and in lv you must reverse 5&8?



Nice work, your getting it. Reversing polarity of either the start or run winding's, but not both, will get the job done.


So now, can you answer your second question? How would you reverse the motor winding's if connected for low voltage...Can it be done with either winding as before? Can you make a drawing to show it?


----------



## Phillipd

It was for a lab at trade school,it was to simulate wiring a 240v single phase motor with a forward/reversing contractor. It was a 120/240 motor but supplied with 2 phases of 3 phase power


----------



## Phillipd

Far as I know the only way to reverse a lv 120 motor is to reverse 5&8 on the start windings because for lv your in parallel instead of in series?


----------



## CMP

It's the same deal, two winding's, run and start. Change the phase relationship between either one of them, with respect to the line and it will reverse.


Run winding would be T1 & T3 connected on one line, T2 & T4 connected on the other line.


Start winding would be T5 on one line, and T8 on the other line.


Change the polarity of either winding, with respect to the line and she will reverse. Same as before, in the high voltage connection.


In reality, not all motors 1Φ provide easy access to all of the terminal connections, externally. T5 & T8 are the standard leads used to change rotation, and are whats usually indicated on the connection label.


Was hoping you would make and post a drawing to further your knowledge.


----------



## Phillipd

Thank you very much! They’ve kept us pretty busy this last week. I had a lot of brain hurt on Thursday, one 3 labs required we use a HCR3 timer. One lab we were to set up a start time delay, press stop then the motor stops counts down again then restarts. That was easy enough because I just used the reset. Also we needed a pilot light indicating the motor was getting ready to start and go out when it started. Then my instructor said do you think you can set it up to delay on AND delay off? The timer I had only had A-D settings. C setting according to my interpretation of the spec sheet should have done this task. After a lot of wire tracing and trouble shooting I figured out I needed another timer that had G mode and then it worked perfectly. I have to redraw a couple labs but would be happy to post drawings if you don’t mind looking at them please? I spend most of the day Thursday on that one lab but I learned a lot about timers. As the last one before me left for the day I told them I’m staying and figuring it out if I have to spend the night there, luckily for me I was finished by 4.


----------



## Phillipd

Here’s a diagram of how I think I could reverse a 120V motor using a reversing contractor


----------



## Phillipd

Couple more labs


----------



## Phillipd

Last one


----------

