how to reverse direction of electric motor?

[bob sesti]

Does anyone know how to reverse direction of electric motor? I have a 1/2 hp motor that I would like use for buffing,but it goes the wrong way.

 

[Bill Turpin]

Depends upon the motor

three phase: reverse any two leads. Single phase: there should be a diagram on motor or inside terminal cover. Direct current (VDC): swap the leads. If on single there is no diagram: probably not reversible except by a motor rewind shop.

 

[Fred Belknap]

What Bill said.
Maybe you can turn the motor around physically.

 

[Bill Boehme]

Some general purpose replacement motors will have the necessary terminals already available in the motor's terminal box. Otherwise, it might take a bit more work. If the motor is a capacitor-start induction motor that has a centrifugal switch to disengage the start winding once the motor is nearly up to speed, then it can be done without too much trouble provided that you are fairly knowledgeable when it comes to electrical stuff. Otherwise I suggest taking it to a motor shop and let them do it. If the motor is a split phase motor without a start capacitor, the wires that you need to access are likely to be buried within the field windings. In that case, don't bother because the motor's windings might be damaged in the process of making the mod.

Here is what you need to do to reverse the direction of a capacitor-start induction motor, but first it helps to understand what is going on:

• First, this type of motor has two separate windings. One is the run winding and the other is the start winding which is connected in series with the capacitor. There is also a centrifugal switch in series with the start winding and capacitor. When the motor is stopped or turning slowly the contacts of the switch are closed so that power can flow through the start winding. The centrifugal switch has weights and springs so that when the motor reaches a certain speed, the centrifugal force on the weights will overcome the spring force and the contacts will open.
• So why do we need the start winding if this is all that it does? The answer is that without the start winding, the motor has no idea which way to turn when power is applied so it just sits there and hums and gets warm -- very warm. In order to tell the motor which way to go, it needs a torque acting on the part that rotates (the armature or rotor) telling it which way to go. It does this by creating a torque that appears to be racing around the motor in the desired direction. The capacitor helps to do this by shifting the timing of the voltage and current in the start winding so that it is different than the voltage and current in the run winding. When these two torques acting on the rotor are combined it looks like a torque that is racing around the motor.
• OK, so now we apply power to the motor and it knows which way to turn. Once the motor is going and nearly up to full speed, the start winding is no longer needed because it has fulfilled its purpose. At this point, the centrifugal switch contacts open up and power no longer flows through the start circuit. Until the next time that the motor is started, the start winding is just along for the ride, but is not doing anything.

Now that we know what the start winding does, the procedure for getting the motor to run in the opposite direction should make a bit more sense. Here is basically what is needed:

• The start winding tells the motor which way to turn by combining its torque with the torque created by the run winding to create a rotating torque. If we want the motor to run in the other direction then the direction of the rotating torque needs to be reversed.
• We can change the direction of the rotating torque by reversing the power applied to the start winding. It is important to point out that we can't reverse both the run and start power inputs or else we have not accomplished anything.
• So how do we do this, you ask? This is where you will need to do some tracing of the wiring to the start winding so it would help greatly to have a multimeter. The object is to find both ends of the start winding circuit and separate them from the run winding wires so that they can be swapped. This is easy in some cases, but not always. The easiest scenario would be if the capacitor is on one side of the start winding and the centrifugal (or inertial) switch is on the other side.

• I have a couple diagrams to show the wiring on my Delta 1440 lathe motor which I modified to run in either direction. The first diagram shows the wiring before the modification.

• Next, is the modified wiring. I show a double-pole double-throw switch (DPDT) which allows me to change the direction of rotation, but if you want to make the change in direction permanent, then the switch is not needed.

• The following image shows the motor of my Delta lathe opened up and various components identified.

• The following image points out the wires that need to be identified so that they can be swapped to reverse the motor direction.

As a final note, it is worth pointing out that this type of motor can't be reversed on the fly -- or what is known as "hot plugging". While hot plugging a three phase motor works (for a while) until the windings overheat and possibly burns itself out, nothing happens with a single phase motor if the switch shown in the second figure is flipped to change the motor's direction. The reason is that no power flows through the start winding until the next time that the motor is started from a stop.

 

[Greg Keddy]

Turn it around or, depend on the size of what you're buffing, you can just use the portion of the wheel below the centerline, which is spinning away from you

 

[bob sesti]

Thanks Bill you have been very helpfull.I hope I can pull it off. I'll give it a try and we'll see what happens.
There are quite a few wire in the terminal box.

 

[bob sesti]

Greg and Fred If I turn it around the beall buffs will spin off the mandrel?

 

[Greg Keddy]

Greg and Fred If I turn it around the beall buffs will spin off the mandrel?

Perhaps, some loctite, lock washer, or lock nut would reduce this likelihood. If you use the bottom half of the wheel then you'll not have any problem

 

[Bill Boehme]

Greg and Fred If I turn it around the beall buffs will spin off the mandrel?

I presume that what you are saying is that the motor is currently rotating clockwise when viewed from the shaft end. Even if there was not a problem with the hardware unscrewing itself, simply turning the motor around -- or walking around to the other side of the motor means that you would need to buff on the lower side since you would want the rotation to be away from you.

However, this brings up an important point about reversing the motor rotation direction. After the motor rotation has been reversed to CCW, you will also need to turn the motor around if you wish to use the upper side of the buff. Sometimes it is more advantageous to buff on the lower side such as when doing the interior of a bowl because it enables you to better see what you are doing. This is a reason for having access to both sides of the buffer or to be able to easily turn it around.

Instead of rewiring the motor, have you considered using lock nuts or jam nuts to keep thing tightened?

 

[ray hampton]

I not trying to hijack this thread but if the motor pulley is a step pulley and 2 belts 1 belt running to the right and 1 belt running to the left to pillar blocks,will the buffing wheels on the pillar blocks rotate the same way or not ?

 

[bob sesti]

Bill, thats it,you did it, the wiring diagram helped alot. I took a shot and switched the blue and the black and bingo it's going the other way. Thanks again Bill

 

[Bill Boehme]

Bill, thats it,you did it, the wiring diagram helped alot. I took a shot and switched the blue and the black and bingo it's going the other way. Thanks again Bill

Wonderful. I am glad that thing worked out, but you are a brave guy to take a chance (unless you did follow the wires to see where they went before doing the smoke test).

I not trying to hijack this thread but if the motor pulley is a step pulley and 2 belts 1 belt running to the right and 1 belt running to the left to pillar blocks,will the buffing wheels on the pillar blocks rotate the same way or not ?

Ray, it would not matter whether you used jack shafts on pillow blocks because the direction of rotation will still be the same unless you twist a belt in a figure-8. However, twisting a belt is not a good idea although I remember when I was a kid, my Dad used a round leather belt twisted in a figure-8 to run reel type lawnmowers backwards to sharpen the blades -- carborundum valve grinding compound was smeared on the rotating reel blades as well as the fixed blade.

 

[ray hampton]

twisting a belt that turn at low RPM is very different compare to a high speed belt twist,could you use a idler pulley to keep tension on the belt ?

 

[Bill Boehme]

twisting a belt that turn at low RPM is very different compare to a high speed belt twist,could you use a idler pulley to keep tension on the belt ?

A standard v-belt would wear out very rapidly under such abuse even at low RPM, but the issue being discussed is about a motor running at either 1800 or 3600 RPM (minus sync slip) which is not at all slow.

Now, a round belt could be used, but one should consider the cost and complexity of Rube Goldberging a mechanical solution (not that there is anything intrinsically wrong with it) as opposed to simply making some electrical changes within the motor.

 

[Michael DeWald]

Yes, about the only idea I could think of for a mechanical solution is a round belt. Vacuum cleaners use this all the time. Since buffing is really not that much of a high torque situation, it might be possible to scavenge some pulleys and try to locate a nice long vacuum cleaner belt. A little wire tracing and a simple switch is much more practical solution. By the way, what part of the wheel you buff with will not make any difference whether the buff comes loose. If the rotation direction is wrong, it's wrong. I'm not sure I'm understanding what those comments were about.

 

[ray hampton]

Yes, about the only idea I could think of for a mechanical solution is a round belt. Vacuum cleaners use this all the time. Since buffing is really not that much of a high torque situation, it might be possible to scavenge some pulleys and try to locate a nice long vacuum cleaner belt. A little wire tracing and a simple switch is much more practical solution. By the way, what part of the wheel you buff with will not make any difference whether the buff comes loose. If the rotation direction is wrong, it's wrong. I'm not sure I'm understanding what those comments were about.

I were thinking of a flat belt which will perform better when twist, the older machines [before printed circuits ] would use a twist belt to turn the chuck CCW OR LEFT-HAND ,I mention this to show the hard way to do a reverse

 

[Bill Boehme]

CCW is the normal forward direction for a lathe chuck. It is also the normal direction for a buffing wheel if it is mounted on a RH threaded mandrel.

Most of the vacuum cleaner belts that I have seen are a bit on the small side although they do not really need to be large for a buffer. The kind of round belt that I was thinking about is used in industrial machinery and runs in standard v-belt pulleys. They have even been used as automotive fan belts in the distant past.

Ray, are you talking about the really really old industrial lathes that were powered off line shafts during the 1800's?

 

[Syd Sellers]

Changing rotational direction

The simplest method is to mechanically reverse the rotor with respect to the stator. Nothing else needs to be done.

 

[ray hampton]

CCW is the normal forward direction for a lathe chuck. It is also the normal direction for a buffing wheel if it is mounted on a RH threaded mandrel.

Most of the vacuum cleaner belts that I have seen are a bit on the small side although they do not really need to be large for a buffer. The kind of round belt that I was thinking about is used in industrial machinery and runs in standard v-belt pulleys. They have even been used as automotive fan belts in the distant past.

Ray, are you talking about the really really old industrial lathes that were powered off line shafts during the 1800's?

No, I am talking about a more modern metal lathe [screw machine] that use a flat belt which could be made longer by adding extra length of belt which would allow you to twist the belt into a figure 8 and charge the rotation of the chuck [motor were built in ] but the idea of the belt possible came from the line shafts