Single Phase Motor Direction 1

[micksouth]

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.

 

[waross]

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

 

[Skogsgurra]

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

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[jraef]

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

 

[Skogsgurra]

Had to find out about that citrus press...

So, I connected a Scopemeter and turned the mandrel by hand.

WOW! Lots of voltage there. Not for a weak heart.

See for yourself!

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[jraef]

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

 

[Skogsgurra]

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



Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[waross]

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

 

[Skogsgurra]

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

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[WoodrowJWeen]

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.

 

[Motorwinder]

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.