×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Single Phase Motor Direction

Single Phase Motor Direction

Single Phase Motor Direction

(OP)
Hi All,
This may at first sound like a really basic question.
Does anyone know how manufacturers ensure a single phase motor runs in a specific direction i.e. for a angle grinder/bench drill etc.
And if there is a way of knowing this during motor construction, is it possible to reverse the direction or is it more cost effective to buy a new piece of kit.
I am guessing a lot of equipment is two direction anyway so it makes no odds but just wondered if there is a simple answer.
As you can tell, motors are not my strong point.
Thanks very much.

RE: Single Phase Motor Direction

Yes. The direction that the starting winding is wound in relation to the run windings determines the direction of rotation. Rotation is reversed by reversing the connections of the starting winding.
The rotation of a shaded pole motor is determined by the position of the shading coils relative to the main windings. The rotation of a shaded pole motor is generally fixed however some models may be reversed by interchanging the end bells so that the shaft is on the other side of the stator. There have been reversing shaded pole motors constructed with two rotors on one shaft passing through two stators. One stator runs the motor cw and the other stator runs the motor ccw.
It is not random.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Single Phase Motor Direction

A complete answer from Bill there.

To that, one might add that angle grinders usually have universal motors with a commutator and are, in a way, DC motors that have been trained to also 'eat' AC. Their direction of rotation is determined by internal connections and can usually be changed if the machine is opened.

There are also small appliances like citrus presses that actually can (and do) start in random direction. They have no shaded poles and no auxiliary winding. Also, they usually/sometimes have a permanent magnet fine-toothed rotor.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Single Phase Motor Direction

Be forewarned however that some motors are sealed and cannot be changed because the mfr does not provide access to the connections. OEM tool motors are notorious for this, because either the machine might be damaged if run in reverse, or they want to charge you extra for the "reversing option upgrade" knowing that 99% of consumers don't realize it's just switching a couple of wires.

 

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
  
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies  

RE: Single Phase Motor Direction

I hope you didn't disassemble the juicer to do that Gunnar... If you did, does Karin know yet? If not, you can blame the dog.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
  
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies  

RE: Single Phase Motor Direction

Actually, I made her hold the plug. That was one impressive jump!

 

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Single Phase Motor Direction

Your a brave man, Gunnar.
Is the motor in question a slow speed motor, to the point that you could manually turn it faster than normal operating speed?
Is this a type of synchronous motor with a multi-pole permanent magnet rotor. The direction of rotation depending on the position in which the rotor poles stopped in relation to the stator and the polarity of the first half cycle of current?

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Single Phase Motor Direction

Yes. I probably turned it three or four times normal working speed.
I told my wife that it *could* be nasty. I had tried it myself and knew what it felt like.

I don't know why it decides to start in one direction or the other. It 'wiggles' for a split second before it starts and then, the direction is purely random.  

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Single Phase Motor Direction

The turntable in many microwaves also starts in a random direction.  Anyone want to hazard a guess as to what type motor these are?  And no, I'm not going to take my microwave apart just to find out.

RE: Single Phase Motor Direction

One lead of the start windings tap in the run windings internally. A motor shop can lift the connection and bring out the second lead for the start windings. Not a job for a novice.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources