Hello All: I am working on a project with a motor that originally came as an electric winch. The winch shipped from the factory with a tethered control box consisting of a DPDT spring loaded center off switch. Push up and the winch runs one direction. Push down and it runs the other direction. Release and the switch returns to center off and the winch stops.

We are going to use the motor in a system that will be controlled by some external equipment. I would like to simplify the current wiring diagram so that the motor direction can be controlled by a SPDT relay. There will be another relay that will turn the power on/off to the motor. So for the sake of (trying) to keep my question simple, lets just assume that I need to remove the factory DPDT switch and provide the exact same functionality with a SPDT center off switch.

Below is the wiring diagram of the winch motor and control switch as it shipped from the factory. My question is regarding the way they wired the starting cap through the switch. It doesn't seem to do anything at all except disconnect the cap when the power is off, which seems useless to me? Is there some reason to do this?


So here is a simplified version of the factory wiring when the switch is in the two possible operating positions:


And finally, my proposed wiring diagram to replace the factory DPDT switch with a SPDT switch. Can anyone tell me if this is OK or if I am missing something?


Thank you for sharing your expertise!

 

I have no idea why they chose to disconnect the cap when the motor is off. As you say, the cap is always connected between those two windings when the motor is on.

Sometimes they choose a wiring scheme like that to make it easier to connect, ie; there might be more room on that switch terminal and it might save a separate terminal block being needed (or additional BP connector). But that's just a guess.

Maybe they disconnect the cap so it doesn't get current through it when the motor is off, in motor overrun or freewheeling conditions? That's a long shot but might be plausible.

Assuming that it doesn't matter that the cap is always connected to those two windings, then your last circuit is fine and will give you the same reversible operation.

 

It would seem to me that you are reversing the cap but not engaging both windings, in the factory set up, they are reversing the windings WRT the capacitor.
Max.

 

Thank you both for reviewing. THE_RB I wondered about the same thing but just don't see where it would matter for the cap to be connected to the motor even when power was removed. It doesn't free wheel except for a very short amount of time when power is removed, maybe less than 1 second. I'm inclined to just go with it unless anyone else can answer our question about why the Cap might need to be disconnected from the winding when the power is removed?

MaxHeadRoom, I'm not sure I understand your comment. The side of the Cap that is connected to the Hot wire does get reversed on both the factory wiring and my proposed wiring. They are both exactly the same except in the factory wiring the Cap is disconnected from the windings through the second pole of the switch when the power is removed. Can you elaborate please?

I think my question boils down to what THE_RB said, can anyone tell us if there is any reason why the Cap should need to be disconnected from the windings for that instant when the power is disconnected and the motor stops turning?

Thanks again for helping me sanity check this.

 

The factory diag is correct, you cannot leave the cap connected when the power is off, in your scenario it looks like you are only energizing one winding, you require a main and split phase winding at all times when running.
Max.

 

Max, I am only energizing one winding at a time in my diagram. And so is the factory.

My diagram is exactly the same as the factory diagram except for one thing. The only difference between mine and the factory is that the factory is disconnecting one leg of the cap when the switch is OFF. Otherwise the circuits are identical, the exact same connections when the switch is ON in either direction.

My circuit at the bottom of the page and the factory circuit at the top of the page are EXACTLY the same when the motor is ON and running in either direction.

The only difference between the two diagrams is that when the motor is OFF and when there is NO POWER connected (switch is in the center) then the Cap is disconnected on the factory diagram by way of the second pole in the DPDT switch.

If anyone else has any input regarding whether or not it is necessary to actually disconnect this cap from the winding when the power is off (Maybe because of freewheeling as THE_RB wondered about) then please let me know.

Thanks,
--sam

 

Well they sure went to a lot of trouble to disconnect it, didn't they? Is the switch a toggle?

I'd say you need it wired that way. Perhaps it is just for plugging purposes. That way it is holding the opposite charge when you switch from one direction to the other instead of just centering it.

 

The factory diag is correct, you cannot leave the cap connected when the power is off, ...

My understanding from the diagrams is that he has duplicated the factory wiring in every way apart from disconnecting the cap in the "off" mode.

Can you clarify why you say the cap cannot be left connected? Why can't a cap remain connected across a winding of a non-running motor?

I was struggling to think of reasons why they would disconnect the cap.

 

I searched too, but did not find anything similar. But they sure went out of their way to design it that way. I'm sure they could have cut down manufacturing costs by using a lesser switch. So it must do something.

Disconnecting it would keep the charge in it a while where it would not if connected across the motor. Could it be a starter cap?

 

Max, I am only energizing one winding at a time in my diagram. And so is the factory.


--sam

You are not energizing one winding at a time, they have to both be connected at all times when in run, one is a main winding, the other a split phase winding, via the cap, both WRT neutral.
You cannot leave power on a cap when off otherwise current will flow in the the split phase winding all I see them doing is ensuring that there is not power to the cap when off, as it is always connected to a winding.
Max.

 

As this motor was probably made in China, the DPDT switch is probably to get it approved in NA. Here is a picture of a Chinese reversible motors wiring. But wouldn't the centrifugal switch remove the cap any way after starting?

 

You are not energizing one winding at a time, they have to both be connected at all times when in run, one is a main winding, the other a split phase winding, via the cap, both WRT neutral.
You cannot leave power on a cap when off otherwise current will flow in the the split phase winding all I see them doing is ensuring that there is not power to the cap when off, as it is always connected to a winding.
Max.

Max what I meant was I am only supplying HOT to one winding (primary), and the other winding (secondary) is connected to one side of the Cap. The remaining leg of the Cap is connected to HOT. This is how the factory diagram is, and also how my diagram is.

The winding that is the Primary or Secondary swaps depending on which direction you want the motor to run.

There is no power connected to the Cap when off. In both the factory diagram and in my diagram, the Hot wire stops at the switch, and therefore there is no power connected to the Cap or to anything else (when in center off position).

My question has to do only with the second set of contacts on the DPDT Switch. All I am asking is why in the world would they need to disconnect that leg of the cap when the power is already off. Remember, the HOT wire is not connected to ANYTHING when the switch is in Center Off position.

Today I wired it up with a SPDT switch, and it is working fine. Thanks everyone.

 

As this motor was probably made in China, the DPDT switch is probably to get it approved in NA. Here is a picture of a Chinese reversible motors wiring. But wouldn't the centrifugal switch remove the cap any way after starting?

Thank you, this is the exact same diagram that I came up with for use with a SPDT switch. I connected it up using this diagram and it is working fine. I appreciate the post.