How to rewind an Electric Motor

Hello, on this page i will present the basic steps in rewinding an electric motor. It is an undeniable truth that electric motors(induction motors) are the most widely used machines in all industries around the world for driving conveyors, pumping of liquids or petroleum products in conduits especially in oil companies. Despite the maximum protection put in place by protective relays such as thermal overload relays, magnetic relays, circuit breakers etc, the windings of this motors are still subjected to destruction due to improper installation or other faults such as single phasing, or maybe not using the right protective device for protecting the motor, or not using a starting method where and when necessary. In case of any of the above mention scenarios, the motor will be damage and unusable. So a very "smart" option will be to go for another one right? but how long have you used this one you just got for "$1000"? how much profit has it generated for you to just let go of it? I'm Sorry, this questions might not be answered if you just got your motor some few hours earlier. But fortunately for you REWINDING can answerer this questions so you will not feel frustrated. And the answer is you can "Rewind" this motor at a cause of just 10% of what you got your motor for, and that is only possible if you know how to. So just screw down the page to see how to.

Basic steps in rewinding an electric motor

Step1:External Study of the motor.

The very first thing to do on a faulty motor is to open the terminal box and make sure all the 6 terminals are free, then make a test for continuity on the terminals, the reading should be as follows under normal circumstances; U1 should read with U2, V1 with V2, and W1 with W2, if not then you can condemn the motor as faulty. Next, carefully study the motor externally for any mechanical defect on the yoke then put this down in your note book alongside with the information on the name plate of the motor and remember the most important one is the coupling method of the winding because you are going to need this after recoiling the motor, you can take a look at the image on your left to see how a motor should look while making external studies on it. Also try to rotate the shaft with your hand by applying some mechanical force on it, and remember under normal circumstances, the shaft should rotate freely with no stress and should produce no noise. With all this done, you can proceed to step2.

Step2:Internal Study of the motor.

At this point now, you carefully open the motor from both ends and again study the various part for any mechanical defect on them most especially the rotor and take down notes of any, then keep all this parts safely in a separate place. Now we are ready to begin work uh! good so now let's concentrate on the stator which is where all the magic takes place. We start by checking the insulations of the windings and if for any reason this insulation has been lost, then we can say the windings have been destroyed and the only remedy will be to replace(recoiling).Remember we are still studying the motor internally right? and we have some few steps to follow while doing this, so let's get on.

Step2-1:count the number of slots.

This is the total number of spaces where the 

coils will fit in, and make sure you write this

down in you note book. If you look carefully 

and try counting, you will notice that the one

you see in the picture on your left is having

36 slots

Step2-2:Checkout the span

The span is simply the number of slots between one coil counting from the slot where the coil begins up to where the coil ends and is read depending on the method of coiling. For instance a single coil with span of 8 is read 1:8, a double coil with a span of 8 on the first coil is read 1:8:10, a triple coil with a span of 8 on the first coil is read 1:8:10:12. If you take a very careful look at the image on your left, you will see that the motor is having a span of 1:10:12:14:16 Here is how it is interpreted, the first number is always  which represent the coil, the second number represent the span of the first coiling, the third number represent the span of the second coiling and so on. Also make sure you identify the method of coiling ie is it single-double, double-tripple, tripple-tripple etc and note this down in your note book.

Step2-3:Identify the start and the finish of each coil

At this point, we identify the start and finish of each coil. The start of a coil is the conductor that comes out of the coil representing the second digit in the span ratio while the finish is the conductor that comes out of the coil representing the
last digit in the span ratio. For instance let's consider the a coil with a span of 1:8:10:12 on the left, the start will be the conductor that comes out at the coil representing a digit of 8 in the span ratio while the finish will be the conductor that comes out of the coil representing a digit of 12 in the span
ratio.

Step2-4:Identify the type of connection

Now identify if the coils are connected in series or parallel, in other words check if the start or finish of a coil is going to the start or finish of another coil. If the start of a coil goes to the start of another coil or a finish of a coil goes to the finish
of another coil, we say the two coils are connected in parallel. But if the start of a coil goes to the finish of another coil or the finish of a coil goes to the start of another coil, then we say the coils are connected in series. So you have to carefully study and understand how the coils are connected. On the diagram at your left, the coils are actually connected in series,
but in rewinding we say the coils are connected in parallel since the starts are going to the starts and the finish going to finish.

Step2-5:Check the gab between the first-start and the second-start

You had identify the start and finish of each coil above, so now identify the number of slots between the start of one coil and the start of the next coil.

Step3:Drawing of the motor.

Here, I will explain with respect to the image of the motor drawn on the left. It's coiling is double-single, it has 36 slots and a span of 1:8:10 for the double coiling and a span of 1:8 for the single coiling. so you see now that we are going to make use of all the information gotten from Step3 above. In drawing a motor we follow the following steps.

1.)  Draw a circle of about 10cm diameter

2.)  Draw smaller circles which correspond to the number of slots you counted at step2 above because this circle are representing your slots, in our case we have 36 slots. This smaller circles should lie round the internal diameter of the of the bigger circle drawn earlier


3.)  Choose any slot as your starting point and make a loop that begins from this point, then count 8 slots starting from the first one then you loop through the eight slot, and from there count 9 slots in the backward direction and loop through, then finally count 10 slots in the forward direction and end the coil. then you have successfully made one double coil.


4.)  Go back to the point where you started the first coil and count 4 slots to the right then start the next coil from there and count 8 slots to the right and end the coil. Note, we are using 4 slots as the distance from one start to the other because that's the information we got while studying the motor.
So you have to understand for another motor, its going to be different. Take a closer look at the diagram on your left to really see how you drawing will look like. Also note that on the diagram, all the arrow heads pointing in are the starts while all those pointing out are the finishs

Step4:Removing old coils

So after you draw the motor, the very next step will be to remove the old coils from the motor. You do this by cutting the windings at the back end of the motor with a chisel, put the motor in an oven to be heated for some time so that the insulation gets weak, then use any metal rod to pull the coils out. when all the coils are out, you make sure all the slots are free ie all the insulation papers in the slots should removed, then try cleaning the slots very well, after you blow compressed air in to fully get rid of any unwanted particle. When you remove this coil, take one of them an count the number of conductors per slot, this will give you the number of turns, take one of the conductor and measure its diameter using a micro meter so that you will know the right one to use. Also use the same micro meter to measure the thickness of the insulation paper you removed from the slots so as to know the right one to use. After removing all the coils, the motor will look like the image on your left.

Step5:Inserting insulation papers

At this point you use a Card Chopper to cut the insulation papers following the measurements you obtained from the step above. Remember the number should equals the number of slots of the machine. Then also cut closers that will be used to cover the conductors in slots after inserting. This closers will be of the same length as the insulation paper but its width should be about 70% that of the insulation papers. Now fold the insulation papers at both ends and gently insert them in to the slots as shown in the image on your left until all the slots are occupied.

Step6:Making the coils

After inserting the insulation papers, its time to start making your coils, you first take a single wire and place it in to the coils how the coils are going to fit following the right span as seen in the picture by your side. Then use this coil to set the rewinding machine so that you can start making the coils as seen on the image by your side. Note, if the coil is a double one, you take your sample from the first span and place it on any strand on the rewinding machine, then the next strand will correspond to the second spand ie you rewind the first coil following the number of turns, the immediately proceed with the next coil without cutting the any conductor. After the first coil,

you test to see if its OK before proceeding with the next coils.

Step7:Inserting the coils

Now you start inserting the conductors in to the slots using what we call a conductor drive, and remember the conductor should go in with no stress, and you acheive this goal by making sure that your conductors are very straight and not crossing on each other when inserting them, if not the conductors will be stress up and it will make you feel as if the conductors are too many for that slot or the slot is too small for the conductor. I think at this time you should be able to determine your start and the finish coils, so when inserting the conductors, you should start with the start coil and end with the finish coil. Also note that you do this by following the diagram of the motor you drew in step4 above.Also, after inserting every coil, you use a closer to close it up so that they don't fall off. A closer is simply an insulation paper that is use for closing the coils inside the slots.

Step8:Separating the coils

At the back end of the motor (the side which has no terminals out), you use insulation papers to separate the coils from each other, then tie them up using a cord. This is done to ensure that the coils will be firm when the motor vibrates and should not have any contact with shaft. You can look at the image on your left.

Step9:Connecting the coils

Now, this is the most dedicate part which should employ no error. So go back to your diagram and carefully follow it very well to make the connections on the motor. ie you start from u1 and end with u2, and start again from v1 and end with

v2, then finally w1 ends up with w2 as on your diagram and test for continuity to see if u1 reads with u2, v1 reads with v2 and w1 reads with w2. Before making any connections, you have to clean off the insulation from the conductors using any sharp object then weld them up together using a 12V D.C with brasing and carbon rods or better still, sold them up using a soldering iron to create a proper link between them.

Then cover the joint using sleeves to ensure no contacts

amongst any of them and using a P.V cable, connect u1,

v1, w1, and u2, v2, w2 to the terminal box of the motor.

Then repeat step9 above to make sure that the coils are

firm.

Step10:Testing

At this point, couple up the motor for testing ie start from the terminal box and measure that u1, v1, w1 are one side of the terminal box while u1, v2, w2 are on the other side. Then check the nameplate of the motor on how the windings are connected. To do this, you take the voltage which correspond to your supply voltage and frequency, then use the corresponding coupling method to couple the windings. I don't think i should start

explaining how to connect in STAR or DELTA,

I think you know that already. So just do the

connections, couple up and supply the motor

and make a NO-LOAD test too see if it meet up

with specifications. Then dismount the motor

again and pore some vanish in to the coils and heat it up in the oven for about 45mins for proper insulation. Then couple up the motor and its ready for work.

Thanks for reading my post, and please leave a comment bellow.