Before you buy motor for an application, it's better that you know how it's wired and if the direction can be easily changed or not. You can easily change the direction of a three-phase induction motor which has three output wires (i.e. wired as star or delta in stator) by simply interchanging connections of two of the stator leads. For example if previously the connections phase were RST, interchanging the leads would change the phase to RTS or SRT and the direction would change.
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| Reversing direction of a three-wire, three-phase induction motor |
Unlike a three phase motor, reversing direction of a single phase motor can be a bit complicated. This is the problem that I recently had to face. I bought an old table saw and it came with a single phase motor and I had to reverse the direction of this motor. I would have used the motor in default configuration by simply using it from the other side, but it would have meant that the nut may get loose during operation which can be dangerous, so this is something that had to be done without fail. I followed the steps mentioned below to complete the task.
1. Identifying the motor type
Perhaps the first thing you should do is read the motor specifications (generally present on the motor itself). Along with specifications, instructions are likely to be present for reversing the motor direction. If the instructions are not present, you would need to find out the motor type and this would guide us how to change the directions since changing the direction is dependent on the type of induction motor. So you should find out the motor type among the following ones.
Capacitor start induction motor
Capacitor start, capacitor run motor
Shaded pole induction motor
Split phase induction motor
Permanent split capacitor motor
A capacitor start, capacitor run motor has two capacitors, while capacitor start induction motor and permanent split capacitor motor have just one capacitor while split phase induction motor and shaded pole induction motor have no capacitor.
Knowing this will help you identify the motor you are working on. There are other specific differences between motors and knowing these will help you identify the specific kind of motor you are working with.
2. Finding information specific to motor
Next logical step is to find more information specific to the motor, it may be whether the motor type allows for direction reversal, finding out the wiring diagram if it's not present on the motor etc. In my case, I could see straight away that there are two capacitors mounted on the motor casing, so I concluded that it's a capacitor start and capacitor run motor. My investigation then proceeded to find an appropriate wiring diagram that I could make sense of and related article that provide information related to reversing motor direction.
3. Rewiring
If your motor direction can be reversed, you should be able to find information related to this online. I would suggest, that you proceed with the rewiring only if you can absolutely confirm that the motor direction can be reversed. In my case, I found that a capacitor start, capacitor run motor can be reversed.
Furthermore, you can install a changeover switch to change direction as needed. In my case, I would be simply reversing the motor direction. However, I would not be able to following the connections as shown above since the motor I have is quite inexpensive and it does not have any provision for reversing direction. There are no metal links or a decent terminal box, so I will need to make do with what the motor comes with.
You cannot burn the motor so easily if you are mindful. In my case after analysing the windings, I got away by simply switching the two red terminals as shown in the picture. It was a fluke indeed since even after studying the wiring, it did looked like a mess and I was doubtful if it will work, but it worked. In case you are in a similar situation as I am, try to do this after analysing the windings and how the capacitors are connected, you can try switching the connections see if it works. A humming sound or in case if the motor shaft does not move upon switching the connections is an indication that connections do not work. In such a case, you should switch off the motor immediately.