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Help on reversing direction of motor if possible

Shaybuilder

Cast Iron
Joined
Sep 24, 2006
Location
Nevada
I have a flexible tapping arm machine that I installed a electric motor on to use as a drilling machine for some parts I make. It works great except the motor turns the wrong direction and I have to use 3/32" dia. left hand drill bits which don't last very long and I find it hard to see them good enough to re-sharpen them. I tried to find carbide drills but no luck. The motor is a 15th HP Dayton 115 volt AC-DC motor and looks like a sewing machine motor. I think the label says universal motor but that part is pretty much missing. Also wondering if I run it on DC if it would reverse by switching the wires, just don't know how many volts it would take if that would work. I would like to run it at about half the max RPM. Currently I am using a foot rheostat for speed control.

Any help would be appreciated,
Ken
 
If the motor has brushes, then switching the wires to the brushes should reverse the direction. I have done this with AC, brushed motors and it works well.

If it works when you reverse them, you can extend them outside the motor to a Double Pole, Double Through switch and make it switchable.
 
That is only true for permanent magnet, DC motors. He said it is an AC/DC motor which will have both field and armature coils and if you reverse the wires to the motor you reverse both of those coils which will result in rotation in the same direction.



If it’s DC, simply reversing the polarity will reverse the motor. I think reversing the leads will also change direction of an AC motor
 
I am pretty sure that the key word here is universal. It has been my experience that if a motor is universal then it has brushes and yes you can reverse the motor by reversing the polarity of the supply (DC of course). I also think that what Spruewell meant is that on an ac motor you can change the direction not by reversing the leads but changing a few jumpers inside the motor housing (usually spade lugs with directions for reversing on the inside of the cover plate). It all depends on the type of motor. Some you can reverse, some you can change from 110 to 220 etc. If this is in fact a sewing machine type motor then it probably has brushes and is in fact "universal" and can be reversed. You would just need to solder in a full wave bridge rectifier in the supply and reverse the now dc supply to run it the way you want. Another nice feature of a universal motor is that you can put a cheap light dimmer in the line and adjust the speed with no harm to the motor.
 
EPA is correct. As a general rule, any brush type motor is reversed by switching the brush connections. With a permanent magnet field motor, reversing the incoming leads amounts to that since it only connects to the brushes. A simple shunt wound motor can be reversed by switching the field, which is useful since you are switching a lower current, but that is an exception. Larger motors than the one in question frequently are compound wound, having both shunt and series fields. Because you have to maintain the relationship of the series fields to the shunt ones, reversing the brush leads is the only option.

When you take the motor apart, remember to remove the brushes first. If the brushes are left in place, sometimes they will pop out and snag the bearing that comes out with the shaft and break off.

Bill
 
I am pretty sure that the key word here is universal. It has been my experience that if a motor is universal then it has brushes and yes you can reverse the motor by reversing the polarity of the supply (DC of course). I also think that what Spruewell meant is that on an ac motor you can change the direction not by reversing the leads but changing a few jumpers inside the motor housing (usually spade lugs with directions for reversing on the inside of the cover plate). It all depends on the type of motor. Some you can reverse, some you can change from 110 to 220 etc. If this is in fact a sewing machine type motor then it probably has brushes and is in fact "universal" and can be reversed. You would just need to solder in a full wave bridge rectifier in the supply and reverse the now dc supply to run it the way you want. Another nice feature of a universal motor is that you can put a cheap light dimmer in the line and adjust the speed with no harm to the motor.

Not so. To reverse a universal motor, you have to get inside it and switch leads on either the fields or brushes. A rectifier in the circuit will not help.

Bill
 
One more thing to note:

On a universal motor run on AC power, the direction can be changed by switching the connections inside the motor, but that doesn't guarantee that the speed and power will be the same thereafter. I took home a small motor that was otherwise going to go to scrap, slow rotation, anemic power. Switched the jumpers, and boom, worked perfectly again going the other direction.
 
One more thing to note:

On a universal motor run on AC power, the direction can be changed by switching the connections inside the motor, but that doesn't guarantee that the speed and power will be the same thereafter. I took home a small motor that was otherwise going to go to scrap, slow rotation, anemic power. Switched the jumpers, and boom, worked perfectly again going the other direction.

If it was compound wound, you can get the series and shunt fields opposing each other and have that effect. A typical capacitor start induction motor (no brushes) can also act that way if you get the jumpers wrong.

Bill
 
While it is true that most brush type motors can be reversed by reversing the wires to the brushes, all brushes are not created equal. Most brush type motors, especially the older ones, will have the brushes set exactly 90 degrees to the field. These motors will run equally well in forward or reverse. BUT, some brush style motors will have them offset from that position for one reason or another. If the brushes are offset from 90 degrees, then the motor is optimized for running in it's forward direction and, while it will run in reverse, it will not be optimal.



One more thing to note:

On a universal motor run on AC power, the direction can be changed by switching the connections inside the motor, but that doesn't guarantee that the speed and power will be the same thereafter. I took home a small motor that was otherwise going to go to scrap, slow rotation, anemic power. Switched the jumpers, and boom, worked perfectly again going the other direction.
 
While it is true that most brush type motors can be reversed by reversing the wires to the brushes, all brushes are not created equal. Most brush type motors, especially the older ones, will have the brushes set exactly 90 degrees to the field. These motors will run equally well in forward or reverse. BUT, some brush style motors will have them offset from that position for one reason or another. If the brushes are offset from 90 degrees, then the motor is optimized for running in it's forward direction and, while it will run in reverse, it will not be optimal.

True, and there have been thousands of words written about adjusting the brushes on Monarch 10EE motors. Before there were simpler speed controls, motors were made with adjustable brushes with a handle to move them.

Bill
 
Thanks for the information. I reversed the wires to the brushes as mentioned and the motor now turns in the correct direction.

Ken
 








 
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