Start/Stop switch wiring for 240v electric motor

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  #1  
Old 11-04-15, 02:03 PM
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Start/Stop switch wiring for 240v electric motor

Hi All.
I have three nice 3HP motors salvaged from a Robland X31 combination woodworking machine. Unfortunately I do not have any of the wiring or switches from the machine. I am finally contemplating using these motors in a project or two. First up is a cyclone dust collector project. The project calls for a 5HP motor in a direct drive configuration so I may end up using two motors in a pulley/belt configuration since my motors are 3HP. Anyway, that's where I'm looking to get to way out yonder there ...

The Robland had two start capacitors and utilized a dial type spring loaded switch: you rotated the switch all the way and held it against the far spring-loaded position for a couple of moments until the motor was up to speed, then released it and it returned while the motor kept going. I THINK but can't recall exactly (was last used 13 yrs ago) that the switch was two position. I think this is called a momentary switch. The Robland also had a red mushroom button on two sides to turn off the machine.

My goal is to learn how to wire the motor in a similar configuration: push/hold start switch in one convenient location and one or more mushroom stop switches as deemed beneficial.

The motors do not have capacitors integral to them on the housing.

I have run them by initiating rotation by hand. I have listened for the tell-tale "click" indicating that the start winding switch has closed as the motor stops, and there is none. So, I think this has to be handled some other way. I've read that some solid state switch may be doing the same job internally, but so far haven't figured out how to test for that. (motors date from early 90's)

I have not figured out how to set up the start capacitor into the wiring.

I have been surfing the web for days now trying to get familiar with the terminology and various wiring diagrams.

I was hoping to get some direction from the experts here. Maybe a reference to a good book that covers the material, or maybe even someone interested in doing some coaching if they like this sort of stuff.

BTW my background is technical and DIY practical with 30 yrs of basic home & shop wiring, but I'm not a EE or electrician, and this project is something I need some more education to get done safely.
 
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Old 11-04-15, 02:24 PM
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Welcome to the forums.

Using two motors to run one machine is not going to work too effectively.

Do you have any information at all on those motors. It's pretty hard to guess what you have there. A few pictures would be a help too. http://www.doityourself.com/forum/el...-pictures.html
 
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Old 11-05-15, 02:23 PM
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Thank you for your reply.
Here are a couple of pictures

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I should have taken one of the whole body but I was concentrating on the wiring. I'll upload another asap.
 
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Old 11-05-15, 07:37 PM
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So far.... I haven't found one hit on that motor model number.
 
  #5  
Old 11-06-15, 12:10 PM
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Here's a pic of the motor and my wiring plan for hooking up a start capacitor to get it to start without the hand turn.

This is just a bench test setup. I plan to monitor the current on the cap circuit after starting to see if it cuts out on its own. The switch is to cut it manually if necessary.

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Can anyone comment on the cap wiring?
 
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Old 11-06-15, 05:35 PM
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How can we comment.... there is no wiring diagram.... nothing. It would just be a guess on our part.

The diagram is basically correct but you'll need to ID the windings.
 
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Old 11-07-15, 04:22 AM
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Two of the four wires of the cord going into the terminal box are heavier, so I have made the assumption (tested with ohmeter) that they are the mains, while the other two are the start winding. I have run the motor with a hand start using the mains.

Without finding a wiring diagram for the motor I guess it's a matter of experimentation, and I wanted to run the plan by someone as a sanity check.
Searching the web it seems this motor has been produced in versions using a start cap only and also with a run and start cap.
 

Last edited by RJamieson; 11-07-15 at 06:05 AM. Reason: Add to a sentence
  #8  
Old 11-07-15, 04:32 PM
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You need to use a magnetic starter for those motors. This will give you overload protection as well as allowing for multiple start/stop pushbutton stations. I would rather that you have a starting relay to remove the starting capacitor from the circuit but you can do it manually with the pushbutton start switch by adding another relay or a second set of contacts on the pushbutton.
 
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Old 11-08-15, 05:27 AM
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Ok, a magnetic starter with a relay! Thanks.
I will use those terms to see if I can find the products and wiring schemas. If you have any pointers in that direction that would be great.

I used the setup below with a start cap, and boy did it start! It was evident the cap was far larger than needed. I used the switch to cut it out immediately. However I wanted to get a current reading in the start winding and in the second it took to move my clamp over the wire the cap blew.

Next I hooked up a 55 uf combo start/run cap (the fan side) I had as a spare for my previous 5T heat pump unit. (Motor label says 40uf which I took to be a run cap rating not a start cap but turns out not necess. so)
Interesting thing happened: WITHOUT the cap in the circuit the motor self started! After that the motor would not self start with or without this cap in the circuit.
Also interesting (at least to me) is that with this start cap in the circuit the motor will only run in ONE direction. Even if I hand start it CW it reverses and spins up CCW. If hand start CCW it takes off. This just confirms current flow through the cap but not enough to initiate rotation, I think.

I do recall that the Robland had two black cylindrical caps. Perhaps they were 40uf wired in parallel? Or would it be series? I will try to find the machine wiring diagram and post it here. It's still a mystery whether the 40uf shown on the label is for start, run, or both. I also recall from using the Robland that the motors spun up nice and smooth while the switch was held engaged, not with a jerk.
 
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Old 11-08-15, 06:33 AM
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It takes very little capacitance to start an unloaded motor, it is when you add the load that you require a larger capacitor. I am going to make an educated guess that you will need between 100 and 200 mfd to start under full load. If you wanted to add a running capacitor I would start with about 20 mfd and not go over 40 mfd. You need to use capacitors with an AC voltage rating of at least 330 volts and 450 volts is better.

To change the rotation you need to swap the starting winding leads where the connect to the running winding.

For automatic starting you need to use a special motor starting relay, These operate by either a current signal or a "back emf" signal to remove the starting capacitor once the motor comes up to speed. Here is a short article on their application. Know Your Potential Starting Relays

You could, use an additional contact on the starting button to manually connect/disconnect the starting capacitor and eliminate the relay. You would simply hold the start button in until the motor came up to speed and then release the button. Best would be to do it with an additional general purpose control relay but the additional relay is not absolutely necessary.
 
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Old 11-08-15, 10:46 AM
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Thanks so much for the link. I understand the wiring.
Is this an example of what I need besides the caps?
http://www.amazon.com/Supco-Potentia...starting+relay

One thing I'm a little confused by with that product is that there are no choices to select NC or NO.
Also, this is the relay, but what is the role of the magnetic switch?


As I understand it normally open is what I'm looking for.

Question about multiple push-to-stop buttons: does this just entail running NC mushroom head push buttons in series with L1?
 

Last edited by RJamieson; 11-08-15 at 10:54 AM. Reason: Add question
  #12  
Old 11-09-15, 01:26 AM
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Yes, that is the proper type of relay. You need to measure the voltage across the starting winding when the motor is running to determine the coil voltage for the relay.

A magnetic starter is a special relay for motor operation. It has contacts that can handle the starting current of the motor as well as "overload" switches that are sized to the motor running amperage that will open the relay if a prolonged overload exists. https://www.youtube.com/watch?v=8Hez8qiELpU They are kind of expensive so you might want to check ebay and see what they have. Some have adjustable overload switches and others require changing "heaters" for different motor amperages.
 
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