Author Topic: single phase motors.  (Read 31050 times)

Offline DavidA

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single phase motors.
« on: May 30, 2013, 03:11:08 PM »
Is there anything on the site about how to fit a reversing switch to a single phase mains motor ?

I need to make my lathe go in reverse for screw cutting. I'm using a 1 HP motor as bought from Machine Mart.

Dave.

Offline doubleboost

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Re: single phase motors.
« Reply #1 on: May 30, 2013, 04:22:33 PM »

Offline BillTodd

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Re: single phase motors.
« Reply #2 on: May 30, 2013, 05:20:23 PM »
Essentially, the start/run capacitor is switched between the live and neutral - its other terminal is connected to the start winding.

On a motor with a start only capacitor (these usually have centrifugal switch to disengage the cap once the motor is spinning), it's usually necessary to stop the motor and restart in the reverse direction. Motors with continuous start/run caps, ( often small motors) the motor will reverse as the cap is switched.


Bill

Bill

Offline DavidA

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Re: single phase motors.
« Reply #3 on: May 30, 2013, 06:58:05 PM »
John,  Bill,

Thanks.
I'll be ordering one of those switches tomorrow.  It will certainly be better than moving the saddle back along the bed by hauling on the belt.

Dave.

Offline vtsteam

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Re: single phase motors.
« Reply #4 on: May 31, 2013, 08:48:32 AM »
I've always wondered about lathes that have a separate rack (as my Craftsman does) besides the lead screw and half nut and no tumbler reverse. Why the rack at all?

My Gingery lathe had no reverse, but it also had no rack so releasing the half nut released the slide to be positioned as easily as the tailstock is -- just slide it to where you want it. In fine adjustments or screw cutting without the indicator (not that I had made change gears yet) you could just release the motor drive and rotate the lead screw backwards with a ball handle at the end of the screw. It was very simple and very fast to work with.

I find the rack and wheel on the Craftsman clumsy -- fair amount of backlash -- very coarse adjustment virtually requiring a additional lathe stop or gauging setup to cut to a dimension, and slow to traverse the carriage compared to releasing it and sliding by hand. I can see the need for something like that on an industrial size lathe where the carriage is massive and needs a handwheel to budge it or the bed is very long. But on a small home workshop lathe? Perhaps it's just a bit of sales appeal to look like the big boys. Apologies if I'm missing something...
I love it when a Plan B comes together!
Steve
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Offline DavidA

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Re: single phase motors.
« Reply #5 on: May 31, 2013, 02:23:26 PM »
vtsteam,

... you could just release the motor drive and rotate the lead screw backwards ..

You can't do this when screw cutting unless you have an indexer to show you where to drop the half-nuts back into mesh with the leadscrew.

If you disengage the mandrel you will lose the synchronization and your thread will be,well, screwed up.

Dave.

Offline vtsteam

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Re: single phase motors.
« Reply #6 on: May 31, 2013, 02:44:38 PM »
Hi David, releasing the drive on the Gingery lathe means pulling the layshaft and motor assembly forward to slack the belt, not disengage the change gears.

Also, the Gingery change gear construction does include an indexer build.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline DavidA

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Re: single phase motors.
« Reply #7 on: June 01, 2013, 07:09:12 AM »
vtsteam,

Thanks for clearing that up.

If I cut small threads on my lathe (say 20 tpi) I leave the gear train in normal drive and then cut the thread by hand using the crank handle plugged into the end of the mandrel. This is ok for most modeling work.  But if I need to cut,say, 8 tpi it gets a bit tiring and I engage the back-gear and cut under power. The back gear and the lowest speed on the pulleys is about right for threading.
The problem is that it is almost impossible to wind the saddle back using the crank when the back-gear is engaged.

So I ordered the reversing switch and it arrived about an hour ago.
Now I just have to identify the wires on the motor.

Dave.

Offline DavidA

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Re: single phase motors.
« Reply #8 on: June 04, 2013, 06:58:04 PM »
Well, as I mentioned above,  I now have the switch.
The instructions are not quite as 'detailed' as doubleboost suggested but I am reasonably confident with the diagram

One point. Identifying the start windings.

The motor had two pairs of wires that disappear into the windings.  Both pairs consist of a red and a white wire.  I assume one pair is the start winding.

Question.
Is it the pair that has it's white wire connected via a condenser to the neutral supply (blue wire) ?

Dave.

Offline vtsteam

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Re: single phase motors.
« Reply #9 on: June 04, 2013, 09:57:33 PM »
Colors are often arbitrary --  one bit of the puzzle -- start windings have higher resistance and are thinner wire than run windings. Can you identify that much?
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline DavidA

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Re: single phase motors.
« Reply #10 on: June 05, 2013, 07:24:06 AM »
vtsteam,

I'm trying to add a sketch of the wiring to the post.

I've measured the windings and get 26 Ohm for the red winding and 21 Ohm for the white winding. So by your reckoning the red one should be the start winding.  But the capacitor is in series with the white winding.

The motor,  in case anyone has a similar set-up,  is a Clarke 800/4  1350 rpm  1HP .

I've managed to get the sketch as far as photobucket. just got to link to it.

Dave

Offline vtsteam

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Re: single phase motors.
« Reply #11 on: June 05, 2013, 07:41:37 AM »
There are run capacitors and start capacitors, also a throw out switch. Also sometimes there are wires for reversing and different speeds, and colors are almost never standardized. It's hard to tell just from a word description. For instance when you measured resistance was the throw out switch engaged? Were the two windings therefore paralleled? Or are the switch and leads brought out.? etc.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline DavidA

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Re: single phase motors.
« Reply #12 on: June 05, 2013, 07:45:58 AM »


Here's hoping this has worked.

Offline DavidA

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Re: single phase motors.
« Reply #13 on: June 05, 2013, 07:50:32 AM »
vtsteam,

Looks as if our posts crossed.

I don't hear any throw-out switch operating. So I don't think there is one.

I'll just have to try various connections and see what happens.

Unless,  as I mentioned above,  someone else has already done the same thing to hte same motor.

Dave.

Offline DavidA

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Re: single phase motors.
« Reply #14 on: June 05, 2013, 07:56:41 AM »
Bill,

...Essentially, the start/run capacitor is switched between the live and neutral - its other terminal is connected to the start winding.

This is starting to make more sense to me as I think about it. I am thinking that the winding with 21 Ohm reading (the white winding) is the start winding.  So I will have to keep the capacitor connected to that one.
The new switch will be switching the capacitor between the live and the neutral supply.

Dave.

Offline Pete.

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Re: single phase motors.
« Reply #15 on: June 05, 2013, 08:04:02 AM »
Some motors have no switch, they run on both windings permanently.

Offline Bluechip

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Re: single phase motors.
« Reply #16 on: June 05, 2013, 08:35:55 AM »
Is there anything on the site about how to fit a reversing switch to a single phase mains motor ?

I need to make my lathe go in reverse for screw cutting. I'm using a 1 HP motor as bought from Machine Mart.

Dave.

Is this a new motor ??
 
There should be a connection diagram with the motor, often inside the access cover.
 
Why not ask Machine Mart ???
 
Just guessing which winding is  which , is it cap start, cap start/run, split phase etc. etc. is nonsense.
 
Dave BC
I have a few modest talents. Knowing what I'm doing isn't one of them.

Offline DavidA

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Re: single phase motors.
« Reply #17 on: June 05, 2013, 09:49:53 AM »
Bluechip,

The motor was new about a year ago.  There was a instruction with it for how to change the direction of rotation if it was incorrect for your application ,  However, this has long ago disappeared.
I had to reverse the direction when I fit it to my lathe. But can't remember how I did it.  It has worked as it should for the last twelve month.

...Just guessing which winding is  which , is it cap start, cap start/run, split phase etc. etc. is nonsense...

Of course it is. It is also dangerous and can lead to damage,  My philosophy is never press a button unless you know what is going to happen. Or at least what should happen.

I am not intending to just connect random wires and hope for the best.  My first serious job was as an apprentice industrial electrician. Were this a three phase motor I would be completely at home.

The motor will start and run using only the red winding. It won't start using only the white winding.

I may indeed try asking Machine Mart about this.  But I was hoping that someone here may know. I suspect that MM will say 'we just sell them'.

I notice that Doubleboosts miller appears to have a similar motor attached. 

The only real concern I have is in positioning the capacitor.

I suspect that the changing of the capacitor from line to neutral alters the phase lead in the start winding which dictates the direction of rotation.

Dave.

Offline Bluechip

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Re: single phase motors.
« Reply #18 on: June 05, 2013, 10:01:46 AM »
David
 
MM do have a technical helpline number.
 
I have used them years ago for a pressure cut-out switch.
 
Very helpful and told me which one to get.
 
Not the one I thought was right ...  :scratch:  but one which was right.
 
If you don't ask, you won't know.
 
Not even premium rate.
 
http://www.machinemart.co.uk/pages/customer-service


Oooops now a 0871 used to be Nottm. Exchange
 
 
 
Dave BC
 
 
I have a few modest talents. Knowing what I'm doing isn't one of them.

Rob.Wilson

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Re: single phase motors.
« Reply #19 on: June 05, 2013, 12:51:40 PM »
Hi Dave

I am a bit late to the party  :Doh:




The dotted lines are link bars , If your fitting FW/REW switch you remove these completely . 

Rob

Offline DavidA

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Re: single phase motors.
« Reply #20 on: June 05, 2013, 03:44:20 PM »
Here is the supplied diagram and my proposed connection to motor.
The connection to the motor are exactly as Rob's picture shows.


Rob.Wilson

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Re: single phase motors.
« Reply #21 on: June 05, 2013, 03:51:11 PM »
Looks good to me Dave  :thumbup:


Rob  :zap:

Offline DavidA

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Re: single phase motors.
« Reply #22 on: June 05, 2013, 04:02:56 PM »
Rob,

Thanks.

Anyone find a problem with it before I wire it up,  switch it on ,  and shut down the national grid ?

Dave.

(Note to self: Wife needs to buy me a single to three phase converter this Christmas)

Offline DavidA

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Re: single phase motors.
« Reply #23 on: June 06, 2013, 05:02:27 PM »
As it turned out there was a problem.  Motor ran forward,  but not backward.
After a couple of checks of the wiring I striped off all the switching and re-assembled as a single direction motor just using the old start button.  It ran with no problem. Even in reverse when I had changed the straps around.

There was nothing wrong with the way I wired the switch.  double checked it.

So I have come to the conclusion there is an error in the supplied wiring diagram.

Anyway,  I know how it should be wired thanks to some of you guys. Earlier today I traced all the connections on the reverser switch and it is actually comprises of 16 single pole switches. Eight work for the forward motion and eight for reverse. Lots of links needed.

I'll let you know exactly where the problem was when I find it.

One chunky double pole double throw switch would do the same thing as this ghastly thing.  Cost me a fortune.

Dave.

Offline Bluechip

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Re: single phase motors.
« Reply #24 on: June 06, 2013, 05:37:25 PM »
As it turned out there was a problem.  Motor ran forward,  but not backward.
After a couple of checks of the wiring I striped off all the switching and re-assembled as a single direction motor just using the old start button.  It ran with no problem. Even in reverse when I had changed the straps around.

There was nothing wrong with the way I wired the switch.  double checked it.

So I have come to the conclusion there is an error in the supplied wiring diagram.

Anyway,  I know how it should be wired thanks to some of you guys. Earlier today I traced all the connections on the reverser switch and it is actually comprises of 16 single pole switches. Eight work for the forward motion and eight for reverse. Lots of links needed.

I'll let you know exactly where the problem was when I find it.

One chunky double pole double throw switch would do the same thing as this ghastly thing.  Cost me a fortune.

Dave.

Alas! Probably not  :(
 
If you reverse the connections to the start winding/capacitor while it is still running the chances are it will just slow down and growl at you without changing direction, unless it kicks out a breaker.
 
What you need the switchery to do is:
 
(1) Remove all power to the motor until it has stopped.
(2) Change sense of start winding. ( Or run )
(3) Re-apply power.
 
Dave BC
I have a few modest talents. Knowing what I'm doing isn't one of them.