Motor run in reverse?

[midget]

So if you reverse the polarity on a motor, it runs in reverse, right? Well, what about if that motor runs off 220v? What happens if you reverse a hot and a neutral, but the other hot wire is where it is supsed to be?

Also, what about stuff you plug in? Like a vacum, or a garbage disposal...if the hot/neutral are revesed on the receptacle, do they run backwards, too?

 

[physis]

Re: Motor run in reverse?

To make a single phase motor go backwards you reverse the brushes. The leads are accessible on some motors.

 

[Ed MacLaren]

Re: Motor run in reverse?

So if you reverse the polarity on a motor, it runs in reverse, right?

No, reversing polarity will not reverse rotation of a single phase motor.

What happens if you reverse a hot and a neutral

You should never see a neutral wire connected to a motor.

To make a single phase motor go backwards you reverse the brushes

Obviously, this only applies to brush type motors.
The vast majority of single phase motors are induction motors.
For most of these, interchange the start winding leads. These will normally be red and black, or they will be numbered 5 and 8.

Three phase motors are reversed by interchanging any two of the supply conductors.

Ed

[ January 03, 2005, 07:46 AM: Message edited by: Ed MacLaren ]

 

[friebel]

Re: Motor run in reverse?

The following is how you would reverse a 120-volt or 240 volt split-phase motor.
Reverse the Start-Winding leads or the Run-Winding leads, but not both. This will reverse the direction of rotation for a split-phase motor.

To reverse the direction of a three-phase induction type motor, you can reverse the leads in the starter. T-1, T-2, T-3. For example: Reverse T-1 and T-2, or Reverse T-1 and T-3, or Reverse T-2 and T-3.

 

[Ed MacLaren]

Re: Motor run in reverse?

Reverse the Start-Winding leads or the Run-Winding leads, but not both

But, be careful if you try to reverse most dual-voltage motors by interchanging the run-winding leads.
There are two "sections" and both will have to be reversed in relation to the start-winding, to maintain correct run-winding polarity.

Ed

 

[rattus]

Re: Motor run in reverse?

The Universal Motor:

Someone mentioned brushes. Brushes and commutators are used on the "Universal" motor which is similar to a series wound DC motor but designed to run on AC or DC. This motor is used in small appliances, portable electric tools, etc. When you run your drill motor in reverse, you reverse the polarity of the field or the armature winding. This is not quite the same thing as reversing the polarity of the start windings on a split phase.

There is also a permanent magnet DC motor which has no field winding. You merely reverse the polarity of the supply to reverse rotation.

Oh, and synchronous motors use brushes and slip rings.

 

[Ed MacLaren]

Re: Motor run in reverse?

WARNING - This is a test.

The correct way to reverse the rotation of a synchronous motor is to interchange -

a. the leads of the rotor winding.
b. any two of the stator winding supply leads.
c. the leads of the field winding.
d. any two of the leads between the field winding and the field discharge switch.

Ed

 

[rattus]

Re: Motor run in reverse?

Give us a diagram so we can be crystal clear.

[ January 03, 2005, 01:50 PM: Message edited by: rattus ]

 

[steve66]

Re: Motor run in reverse?

Also, what about stuff you plug in? Like a vacum, or a garbage disposal...if the hot/neutral are revesed on the receptacle, do they run backwards, too?

No, they will run the correct direction. For a single phase motor (with only two leads), the motor can't see any difference between the two leads. Remember, it is alternating current. So one lead is positive on one half cycle, and the other is postitive the other half cycle. The motor doesn't have any idea which lead is the neutral.

On a single phase motor with a single winding, the magnetic field does not rotate, but it only gives a push then pull effect. The motor rotates in whatever direction it is given a push. This push is usually devoloped by a start winding.

Steve

 

[69boss302]

Re: Motor run in reverse?

Ed, the only way to reverse a synchronous motor is to exchange any two stator leads. Rotor or field pole leads should be reversed every 6 months to minimize pitting on the slip rings.

 

[midget]

Re: Motor run in reverse?

Why shouldn't you connect a neutral to a motor?

 

[jimwalker]

Re: Motor run in reverse?

it's done every day.Go check you frig or vac or 120 volt water pump

 

[benaround]

Re: Motor run in reverse?

And they will have 1 grounded & 1 ungrounded conductor

 

[charlie]

Re: Motor run in reverse?

A 1? motor without starting windings will start and run in the direction that it is starting to rotate. An example is the old electric razors with the thumb wheel. You would plug in the razor (no on/off switch) and use your thumb on a recessed wheel to give it a push. The razor would run in the direction of the push. This will work with any 1? motor that has not starting windings to start it.

 

[Ed MacLaren]

Re: Motor run in reverse?

Not many responses to my "test" question.
By my definition, neutral conductors only exist in multi-wire circuits.

Ed

[ January 03, 2005, 08:38 PM: Message edited by: Ed MacLaren ]

 

[rattus]

Re: Motor run in reverse?

Who remembers the old electric clock motors which had to be started manually? They would run backwards. Later clocks were self starting and some of these clock motors had a little pawl in them to force the motor to start in the proper direction.

 

[kiloamp7]

Re: Motor run in reverse?

Ed,- for whatever it is worth, I agree with your definition of the term "neutral".

As we all know, that term gets slurred around & used as slang, or used improperly all the time.

 

[physis]

Re: Motor run in reverse?

I remember those Rattus, they still make them.

There's a lot more motors than I'm familiar with or know the name of. Most of the motors I've dealt with had brushes. Some of the induction type I've used you'd have to remove and flip over the stator coils.

One of these days I'm going to get around to learning more about motors.

 

[crossman]

Re: Motor run in reverse?

repulsion start motor... reversing...

Only one I ever messed with was a Lab Volt demonstrator unit that had the brushes attached to a movable device... to reverse it, you rotated the brushes from one side of the neutral plane to the other.

So as far as reversing a real world repulsion start motor, must be something to do with the same principle?

On that demonstrator unit, if you were real careful and made minute adjustments at the neutral plane, you could get it to not start at all, it would just sit there and hum.

 

[crossman]

Re: Motor run in reverse?

Re: neutral connected to motor

Is there a hazard that I am not aware of concerning connecting a 120 volt 1 phase motor to a "hot conductor" and "neutral conductor" of a multi-wire branch circuit?

Or is this a semantics thing where the tap from the "neutral" to the motor is being called a "grounded conductor" instead of a neutral because that portion feeding only the motor is not carrying unbalanced current?