Using Waste Motors to Create Wind Turbines

1. Introduction to Electric Motor

At present, electric bicycles all use DC rotary motors. According to the different ways of generating their magnetic fields, they can be divided into two types: excitation motors and permanent magnet motors. The magnetic field of a DC excitation motor is generated by coil windings. It has the characteristics of strong overload capacity and high output power. It is often used in high-power equipment such as electric tricycles. The magnetic field of a DC permanent magnet motor is generated by permanent magnets. Since no winding excitation is required, the electric energy consumed by the excitation winding is saved, which improves the conversion efficiency of the motor. Therefore, DC permanent magnet motors are widely used in electric bicycles and are also our first choice for modifying small wind turbines.

In order to keep the motor rotating in one direction, the current must change direction when the DC motor passes through the balance point. There are usually two methods:

One is to use a mechanical commutator (brush) to change the direction of the current when the armature coil passes through the equilibrium position, and the other is to switch the direction of the current when the armature coil passes through the equilibrium position through an electronic switch circuit. The former is usually called a DC brushed motor and the latter is called a DC brushless motor. In a DC brushed motor, the magnet is used as the stator, the coil winding is used as the rotor, and a commutator is installed on the rotor. The coil winding is connected to the commutator, and the commutator is connected to the external power supply through the brush. As the motor rotor rotates, the motor winding coil is alternately connected to the positive and negative poles of the power supply, thereby completing the commutation of the winding coil current and making the motor rotate continuously in one direction. In a DC brushless motor, the magnet is the rotor, the coil winding is used as the stator, and the stator coil is composed of three windings evenly distributed in space. When the current flowing into the coil is switched sequentially under the interaction of the position sensor and the electronic switch, a rotating magnetic field will be generated, thereby driving the rotor to rotate in one direction.

2. Modification and precautions of permanent magnet generator

According to Faraday's electromagnetic induction principle, a closed coil will generate an induced current when it cuts the magnetic lines of force in a magnetic field. The motors used in electric bicycles are all permanent magnet motors, which have a constant magnetic field, and the motor winding is a closed coil. At this time, as long as there is relative motion between the rotor and the stator of the motor, an induced current will be generated in the winding coil. Due to the difference in structure, the modification methods of brushed motors and brushless motors are slightly different, which are briefly described as follows:

1. Brushed DC motor

It can be used directly as a generator. At this time, the output is direct current. However, if the direction of the rotor rotation is different, the positive and negative polarities of the output voltage will be opposite. In order to keep the polarity of the generator output voltage constant, a bridge rectifier circuit can be added to the output end of the voltage. In this way, no matter what the polarity of the generator output is, the polarity of the output end can be guaranteed to be constant, as shown in the figure above. In order to make the generator output as much electrical energy as possible, the blades should face the wind direction. During production, a guide rudder can be added to the tail of the wind turbine (as shown in the figure below). If the wind turbine fails to face the wind direction, the two sides of the guide rudder are subjected to different forces, with the side facing the wind being subjected to greater force and the side facing the leeward being subjected to less force. At the same time, due to the larger windward surface of the guide rudder, the entire wind turbine will rotate under the action of wind until the plane of the guide rudder is parallel to the wind direction and the two sides of the rudder are subjected to equal force. Of course, at this time, the blades of the wind turbine are just facing the wind direction, and the windward surface of the blades is the largest, ensuring that the voltage output by the generator is the largest and the efficiency of outputting electrical energy is also the highest. Since the size of wind force is often not constant, and according to the different voltage levels of the selected DC brush motor, such as 24V, 36V, 48V, etc., the motor output voltage will be different. In actual application, the measured output voltage shall prevail. Because the modification uses the waste motor of the electric bicycle, some motors may have different degrees of damage. According to the author's modification experience, the DC brush motor winding coil rarely has problems, and most of them are damaged by the brushes and commutator. Because the brushes and commutator are in a friction state when working, after long-term work, the brushes will wear, and the commutator will be burned and contaminated. If the commutator is not seriously burned, the commutator can be polished with fine sandpaper and the brushes can be replaced to work normally. If the brushes and commutator are seriously worn and cannot be repaired, then simply remove the brushes, do not use the brushes, disconnect any point on the commutator, and lead out two wires as output lines, which can be used. However, the output current is no longer DC but AC at this time, and its frequency and voltage will change with the speed of the motor rotation, but after rectification and filtering, it can be converted into a relatively stable DC.

2. Modification of brushless DC motor

The modification of brushless DC motor is much simpler. You only need to find the three leads of the winding coil from the eight output wires. Usually, there are five thin wires among the eight output wires, of which one red and one black are the power input wires of the Hall position sensor; the other three are the signal output wires of the Hall position sensor, which control the electronic switch to provide power to the three winding coils in time, generate a rotating magnetic field, and drive the motor to rotate. These five wires have no effect in the modification, so you can wrap the joints and put them aside without paying attention. The other three thick wires are the winding coil output wires we need. The three-phase winding coil of the brushless DC motor adopts a star connection. When the rotor magnet rotates, the winding coil outputs three-phase AC power.

After three-phase rectification and filtering, it becomes a relatively stable direct current and can be used, as shown in the figure below. During the modification process, the author found that the falling off of the magnetic steel is also a common fault of the waste electric motor of the electric bicycle. Because the working environment of this kind of motor is bad, it is very easy to be affected by moisture and rust when used in rainy and humid environments. The generated rust expands between the magnetic steel and the bracket, props up the magnetic steel, and causes the magnetic steel to fall off or shift. This causes the stator and rotor of the motor to rub against each other (commonly known as sweeping and boring), so that the motor cannot work normally. At this time, you can open the motor end cover, find the magnetic steel that has fallen off or shifted, clean up the residual resin glue and rust, and use AB glue to re-stick the magnetic steel. When bonding, you should pay attention to correct the position of the magnetic steel in the original direction, and require it to be flat and consistent with other magnetic steel surfaces. After solidification, assemble the motor and it can be restored to use. When the rotor of the modified wind turbine is rotated by hand, the corresponding output voltage should be measured at the output end with a voltmeter. At this time, a permanent magnet generator has been successfully modified.

3. Voltage Regulator

Since the size of the wind is usually uncertain, the electricity generated by the wind turbine is often unstable and will change with the change of wind force. Such a power supply cannot be used in practice. For this reason, the author purchased a switching power supply from the market and made a simple modification. Since the switching power supply has a large input voltage range, high conversion efficiency, large output power and stable output voltage, it is an ideal choice for a wind turbine voltage regulator. Of course, readers can also design a voltage regulator to keep the output voltage of the wind turbine constant within the specified range.

4. Installation and debugging steps and examples

After the generator is modified, it is time to install the appropriate blades on the modified wind turbine. The author chose three blades from a large exhaust fan as the propellers. Since the motor and wheel hub are now connected together in electric bicycles, this greatly facilitates the modification. The three blades are spaced 120 degrees apart and fixed on the wheel hub (see the left picture below). A guide rudder is installed at the rear of the motor, and a rotating shaft is installed at the bottom of the motor, and a suitable metal pipe is put on so that it can rotate freely under the action of external force (see the right picture below).

Fix the modified wind turbine on the tower. The height should be appropriately higher, and the blades must not touch people and objects on the ground. At this point, the modification and installation of a wind turbine is completed and it can be tested for power generation.

A wind turbine generator modified with a 300W/36V DC permanent magnet brushless motor is selected. Under normal wind conditions (level 3-4, 4-7.5m/s), the generator can output an AC voltage of about 20V. After rectification and voltage stabilization by the voltage regulator, it can output a DC power of about 16V/1A to charge a 12V battery. Recently, the author has successfully modified several wind turbines for fishermen in nearby areas, and the results have been good.