# Rewinding 3 Phase Motor

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Hello everyone, i am Niko and, in this instructables i will show you, how to rewind and renew old three phase electric motor.

If you are searching for rewinding of one phase motor you can find it here.

In this insctructables, i am going to make step forward. In next steps I will show you how to analyse motors winding, disassemble motor, remove bearings, calculate new winding, rewind motor, reassemble it with new bearings and test motor. Rewinding is very long process. It took about two days to rewind it, replace all old parts and reassemble it.

If you have any questions you can easily message me.

## Step 1: Analyse Motor

I got this motor at my university.

Three phase asynchronous motor is most common used motor in the world. It has very good efficiency and low manufacture and maintain costs. Two main parts of motor are rotor and stator. Rotor is usually made as squirrel-cage, and it is inserted in stators hole. Stator is made out of iron core and winding.

Stator is used to generate magnetic field. 3 phases generates rotation magnetic field so we don't need capacitor on three phase motor. Rotation magnetic field "cut" squirrel-cage, where it induces voltage. Because cage is short-circuited, voltage generates flow of electric current. Current in magnetic field generates force.

Because magnetic field must rotate faster than rotor to induce voltage in rotor. That's why motor speed is a little bit less then magnetic field speed ((3000 rpm [Magnetic field] -- 2810 rpm [Electric motor])). That's why we call them Three phase ASYNCHRONOUS electric motor.

## Step 2: Analyse Motor

Motors Inscription board

On the motors inscription board we can find most useful information about motor:

• Motors nominal voltage (for star (Y) and triangle (D) motor connection) [V]
• Motors nominal current (for star (Y) and triangle (D) motor connection) [A]
• Power of the electric motor [W]
• Power factor cosFi
• Rotation speed [rpm]
• Nominal frequency [Hz]

## Step 3: Analyse Winding

Open the cover of conduit box.

Before measuring remove all connections in conduction box. Measure resistance for each winding, resistance between two different winding and resistance between winding and motors frame.

Resistances of three winding should be same (+/- 5%). Resistance between two winding and winding - frame should be more than 1,5 Mohm.

You can detect burned motors winding by unique smell (smells like burned lacquer).

## Step 4: Disassembling Motor

Take few picture of motor. Mark spots between first cover and stator and second cower and stator (we will need this marked points at motors assemble).

Remove covers from motor. Usually they are attached on stator by long screws. If you cant separate cover and stator you can use rubber hammer. Gently hit cover and try to rotate it. If that wont works, heat it.

## Step 5: Disassembling Motor

Remove rotor from stator. You can gently hit rotors axis with rubber hammer.

## Step 6: Disassembling Motor

Remove ventilator from rotors axis. I had metal ventilator so i heated it up. I separated it very easily from axis.

Remove clamp, and safety ring if you have one. Then remove second cover.

## Step 7: Removal of Bearings

Use puller to remove bearings on both sides. You must be careful because you can easily damage the axis of rotor.

## Step 8: Removal of Old Winding

First you need to cut old winding from stator. For this job use hammer and chisels. Try not to damage stators lamellas.

Do same on both sides of stator.

## Step 9: Removal of Old Winding

Remove connections and conduit box from stator. In next step you will need to heat up old coils, and conduit box must be empty.

## Step 10: Removal of Old Winding

Heat up winding with flame torch to burn out the rest of lacquer.

If you burned old lacquer you should be able to push remain winding out of stators gaps.

## Step 11: Sandblasting

Sandblasting is process where sand hits surface of workpiece with very high speed and slightly damage it.

You can easily remove old colour form motor with sandblasting. While sandblasting you need to be careful, that you don't damage surface too much, especially edges of cowers.

## Step 12: Paint Motor

The colour must withstand at least 100 degrees Celsius. Make sure you don't paint inscription board.

## Step 13: Identification of Old Winding

You can find all information about type of old winding in "winding head". Winding head is part of winding where all connections are made.

By the winding head (Type of winding), number of wires in each gap and thickness of the wire you can rewind new motors winding without doing calculations in next step.

## Step 14: Calculation of Parameters for New Winding

New winding of motor depends of stators package (dimensions of iron core). For better presentation i made 3D model of my stators package.

You need to measure following things:

• Length of stators package: lp= 87mm;
• External diameter of statros package: Dv= 128mm;
• Inner diameter of stators package: D= 75.5mm;
• Number of stators gaps: Z= 24;

## Step 15: Calculation of Parameters for New Winding

Now measure dimensions of stators slot.

• Width of stators slot: b1= 6.621mm; b2= 8,5mm;
• Height of stators slot: hu= 13.267mm;
• Opening of stators slot: b0= 2mm;
• Height of slots "neck": a1= 0.641mm;
• Tooth width: bz= 3.981mm;

## Step 16: Calculation of Parameters for New Winding

If you have other shape of slot you look at upper picture.

I copied this picture from book [Neven Srb; Elektromotori].

## Step 17: Calculate Number of Pole Pairs

Number of pole pairs depends on nominal frequencies and rotation speed of magnetic field. You can get rotation speed of magnetic field by rounding motors speed (2810) to closest value (3000, 1500, 1000, 750...).

## Step 18: Calculate Number of Pole Pairs

I calculated that my motor has 2 pole pairs and it generates magnetic field as you can see on upper picture.

## Step 19: Calculate Pole Stepp

Pole step is distance on inner circle of stator, and it marks size of each pole.

## Step 20: Calculate Pole Surface

Pole surface is marked red on picture two. One pole surface is exactly half surface of stator, that is because i have 2 pole motor.

## Step 21: Calculate Pole Surface

Because iron core of stator is not made out of pure iron we need to calculate real package length. You get iron filling factor from upper table. It depends on type of isolation.

## Step 23: Calculation of the Height of the Yoke of the Stator

Stators yoke is part of stators package which extends from stators tooth to end of package.

## Step 27: Choosing the Type of Winding

I chose type of winding based on my motors specifications. In winding books there is a lot of different types of winding diagrams. Each one is drown for different amount of pole pairs.

I took winding on the picture from winding book. My new winding was three phase single layer concentric winding.

## Step 30: Winding Factor

There is a table in upper picture. You cant pick up winding factor from table if you have one layer winding.

## Step 31: Induction in the Air Gap

Select appropriate value of induction in air gap from table. It depends on number of pole pairs. If motor is older chose column I, else chose value from column II.

## Step 37: Determine the Filling Factor

To get right filing factor you need to have surface of your slot. Then you easily write down filling factor from upper graph. Filling factor must be between upper and bottom recommended line.

## Step 39: Calculation of Thickness of Wire

According to the result you pick a wire which is in +/-2% range of result. I picked 0,8mm wire.

## Step 40: Winding Diagram

I remade winding diagram from book, so it fits into my stator. I draw new winding diagram which i had used at winding motor.

Second picture is showing the magnetic field generated by stators winding. O and X are showing direction of electric current. Current which is flows inside picture has clockwise direction of magnetic field. If would had 4 pole motor we would have 4 areas instead of 2 areas of magnetic field.

## Step 41: Isolating Stators Slots

Measure length of slot, and add about 16mm (depends of how you will twist paper). Cut it and twist it as I have done on gifs. Put isolate paper on table, and place ruler on it, so you get about 4mm gap in witch you will insert isolate paper and then twist it. Use screwdriver to bend it and insert it in gap. It should fit perfectly so you cant pull it out.

## Step 42: Measure Length of Coils

Make model of coil. Place model in right slots, leaving some free space. You must not leave too much space, because winding would be too bit, and you must not make it too small, because you will not be able access to all slots.

## Step 43: Winding Coils

Place model in special tool. Free 3d model of winding tools are available on "Rewinding one phase motor" instructables. Make sure you wind correct number of turns. After you wind coil you need to tie it up with piece of wire. Then you can take it of winding tool.

## Step 44: Inserting Coils in Stators Slots

Careful place coils in stators slots. This can take a long time to do. Be gently so you don't damage wires lacquer. Rotate coils so their end wires will come out on the side, where is the hole from stator to electrical clips. You can use wooden stick to put winding in slots.

Mark ends of coils!

## Step 45: Connecting Coils

Wire coils together according to winding diagram. Solder and isolate them. End of each coil wire to conduit box and extra isolate them.

## Step 46: Bind the Coils

Bind the coils with the stator lacing thread. Sew stator lancing thread around coils, as you can see on pictures. Tight winding well.

## Step 47: Varnishing the Motor

1. Heat up cooking oven to 100 °C. Put motor in it.

2. When motor heats up, spills lacquer on motors coils as you see on pictures

3. Turn motor around and do the same

4. You can reuse old lacquer.

5. Put motor in hot oven, and cook it for about 4 hours

6. Take motor out and clean edge (so cover will fit perfectly).

DON'T DO IT INSIDE BUILDING OR KITCHEN!

## Step 48: Reassemble Motor

Attach new bearings. Lubricate axis of rotor. You find type of bearing on side of bearing. If you cant find it, you can measure it and find number in catalogue on internet.

## Step 49: Reassemble Motor

Attach cover on stator. Watch marks to put it into right place.

## Step 50: Reassemble Motor

Put rotor in stator, and close it with second cover. Screw motor together.

## Step 51: Reassemble Motor

Connect end of coils to clips, according to picture from analyse motor.

## Step 52: Reassemble Motor

Put ventilator and last cover on motor. If you have iron ventilator heat it.

## Step 53: Measurement

I took refurbished motor to university to make measurements. We mounted motor on special test device, and connected it with measurement equipment. We tested next things:

• Resistance of winding
• Free running test of an electric motor
• Test of the loaded electric motor
• Optimal voltage test
• Short circuit test
• Torque characteristic

*PF = Power factor

## Step 54: Conclusion

It took me about a week to rewind this motor. Most time i spent on calculation of new winding. I had a lot of problems with calculation but i solved them and i got same parameters of winding as were on old one.

I had a lot of problems with winding new winding too. First i made coils too small, and i couldn't insert last coils in slots. I couldn't access to them because other winding were too small. Then i decide to make bigger one but i found problem again. This time winding was too big and i couldn't close the cover of motor.

Third time i successful rewind motor. Because gap between stator and cover was very small, i decided to do a little bit bigger first coils, and a little bit smaller last coils. You can se that on measurment of resistance where, winding resistances aren't identical. But in next measurement we can see that resistances do not dramatically affect on electric motors performance.

I made all tests with two different voltages. Motor was made for voltage 380V, but now we have 400V in EU.

In upper table there is data from manufacturer in first line. In second line is measurement at 380V and third line at 400V. If we compare all data we can see that motor isn't bad at all. All parameters are very close together.

I took all electrical equations and orientation tables from book: Neven Srb ELEKTROMOTORI

I hope you enjoined my presentation of rewinding a three phase motor. If you have any questions please ask, and i will try to answer ass soon as possible. Thank you for your attention.

Best regards Niko

Runner Up in the
Make it Move Contest

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## 56 Discussions

Hi.
You calculated Bz as induction in theet of stator and Bj as induction in stator yoke, but you never use these values while u r calculation of number of turns in coil or calculation of cross section of wire.
So there is no relation between Bz, Bj with wire turns in slot and wire cross section?
Can you please explain it to me?

If i have 2 wire at hand and i want to change wire gauge size ,which formula can you give me to use

There are some calculations but you should test wire by wire

how can i decide connections of wires in electric motors ?

this is very good Niko thanks for the information. but how can I find or buy that Neven Srb ELEKTROMOTORI book in English?

6 replies

I'm also looking for book in english, looks like this ELEKTROMOTORI book is very helpful when you just want rewind a motor and not understand how it works.

Hello Niko, thanks for sharing this information. Please which similar books can you recommend

can you advise me a book about electric machinery i need that formulas

Hi Niko, thanks for this amazing walkthrough. I have few questions.
1. What is a - number of parallel branches and why you used 1 (step 25)?
2. Does it matter for rewinding if motor is connected in star or delta?
3. Can I assemble motor without spilling lacuer just to test if it works before final assembly?
4. It is possible to rewind motor for higher speed (1450 to 2900 )?

hello nick, thanks very much for this very amazing article, i have some questions for you....

is that possible for making common 3 phase asynchrounous induction motor for electric vehicle ?

but the rated speed of the motor need more than 3000 rpm, so my question is,

is it possible for rewinding common 3 phase asynchrounous induction motor became 6000 rpm or more ?

and have you ever heard about motor AC-50 kit in market for electric vehicle ? (i attached the photo for you).

actually from i read at the google, the motor AC-50 is custom wound AC induction motor, but it's produce very big power and torque...where the dimension of the motor AC-50 is 8 inch, and the weight is about 122 lb (55Kg), but it had about 70 horse power and the torque 110 ft-lbs, if we compare with common 3 phase asynchrounous induction motor maybe the dimension same with 10 horse power common 3 phase asynchrounous induction motor.

why motor AC-50 have very big horse power but the dimension very small ? where the motor methode is using induction motor (same with motor that you have) ?

and please let me know if it possible for making common 3 phase asynchrounous induction motor became like AC-50

regards,

thanks

2 replies

Max speed is 3000 rpm in EU (50 Hz), if you want more you need frequency converter.
I don't know the answer on your second question sorry :) You should research a little bit. I checked second motor and saw that it has 650A input current. If you multiply its voltage (50V) and it current (650A) we get around 32kW, my motor had around 1,5kW, so there is a difference.
Best regards Niko

Hi Niko. Please how can one determine the power a particular iron core size can handle.
I once followed a toroidal transformer calculation which stated that "the area of core is equal to the square root of power(A=√W)". But I am sure the formula in the case of motors is different. Waiting

Hello niko ..
Its such a good information about electric motor rewinding
Butt i wanna more help about motor from you so plz

Hi Niko. I'm Laszlo from Hungary. If I ask you nice, could you send me this full documentation in pdf? I need it because I can not download it and this topic would be of interest to me. My email address is: sintcrom@gmail.com Originally I am an electrician, but I am particularly interested in the rewind and repair of three-phase asynchronous motors.