Asynchronous single-phase motor

Written by: roboguru

Picture of Asynchronous single-phase motor

Sorry, I'm French and my english is not very good.

This instructable shows a demonstration of a single-phase asynchronous motor (induction motor).
I made some pieces with a metal lathe, but you can customize the implementation using a simple drill and recycled materials (metal, plastic, wood, cardboard).

Step 1: materials and tools

Picture of materials and tools

Some Duplo bricks (like Lego but slightly larger)
2 or 3 x relays (I use only the 12V coils)
1 x capacitor 4.7µF
1 x used bicycle dynamo (I need only the magnet)
1 x transformer 110 or 230V / 12V
Some pieces of metal (aluminum tube, brass rod)
A few pieces of plastic
A few pieces of epoxy copper plates for printed circuit boards (PCB)

Tools :
Drill (preferably drill press)
Possibly a little lathe
Saw, file, soldering iron, glue

Step 2: AC generator

Picture of AC generator

A rotating magnet in front of a coil produces an induced current. This is the principle of the bicycle bike and alternators.

I mounted the magnet on an axis. It runs horizontally in front of a relay coil.
A LED is connected to the coil.
Turning the magnet, a current flows through the LED. The LED lights.


Step 3: rotating magnetic field

Picture of rotating magnetic field

A rotating magnet induced an electric current in the cylinder. This current produces a magnetic field that opposes the magnetic field of the magnet. /

I made a rotor from an aluminum tube 30mm diameter. I glued a plastic disk on one side of the cylinder. In the middle of the disc, a piece of brass used as a pivot. It rests on a steel needle (a sharp nail). The rotor can rotate almost without friction.

The magnet is placed in front of the rotor, with a gap of about 1mm.
Note that the rotor is non-magnetic metal (aluminium). It's the induced current which bring rotation.


Step 4: AC power

Picture of AC power

In a transformer, the alternative current through the primary coil produces an alternating magnetic field.
This produces an alternative induced current in the secondary coil.

Step 5: induction motor

Picture of induction motor

In the experiment of the rotating field (step 4), we will replace the magnet by 2 coils.

An alternating current flowing through a coil produces an alternating magnetic ( field poles North - South - North - South etc ...
Depending on the country , the mains frequency is 50 Hz or 60 Hz There will therefore be 50 or 60 times per second a North Pole.

The coil L1 is directly fed 12V AC transformer.
The coil L2 is fed through a 4.7 uF capacitor.
The capacitor causes a delay of the current.
If L1 has a North Pole, L2 present a North Pole a few milliseconds later.
Everything happens as if the North Pole had turned.
This rotating magnetic field produces the same effect as the rotating magnet. The rotor rotates.

Construction :

The coil support is made with pieces of copper plate for circuit board. This is easy to cut and weld.
The coils are placed near to the rotor (gap 1mm or less ) .
The rotor rotates on a steel tip. And friction is reduced. We have low power.


The coils must be arranged as close as possible to each other.

Step 6: Why my motor has low power compared to a real engine?

Picture of Why my motor has low power compared to a real engine?

Because my coils produce a weak magnetic field.
Because I only have two coils (in the real engine they are arranged around the rotor).
Because the gap between rotor and inductor in a real engine is reduced.