Wind Turbine Permanent Magnet DC Motors

Wind energy, being one of the most important renewable energy sources, and wind turbines, which are necessary for producing wind energy, are very important in today's environmentally aware world. Below we outline detailed information about generators, with many power options right up to 7 MW, as well as one of the most important components of wind turbines and motors that is used in place of generators in individually made wind turbines.

Permanent Magnet DC motors are the most important components that can be used in place of generators. The magnetic fields produced as a result of the spiral movement of the magnet within the component is that which produces electricity.

Why Use a Motor to Generate Electricity?

The most important reason is that it is cheaper than electric generators and it also contains many components we utilize in our daily lives. A motor is a device that converts electric energy into mechanical energy when electrified via its outputs; however, permanent Magnet DC motors can also have some adverse affects. The magnetic field created by the magnets causes a current to flow through a coil. You can see how electricity is produced in the below picture.

Permanent Magnet DC Motor Types for Generating Electricity

Permanent magnet DC motors are divided into two groups. The first is the permanent outer magnet and moving coil, while the second is the permanent coil and moving magnet.

Brushed DC Motor: These motors contain a permanent magnet and a moving coil within the magnet. The required electricity is produced by conveying the energy produced by the revolving brushes. Brushed DC motors are not the preferred method for producing electricity because the coil's, being in continuous motion, can have the following affects on the brushes:

a.) Degradation,
b.) Difficulty in producing electricity because of the brushes

You can see a brushed DC motor in the below;

Brushless DC Motor: These motors are the preferred choice of motors for producing electricity. Thanks to the moving magnet unit in the permanent coil, it easily produces electricity. Producing high efficiency and continuous electricity are the main features of brushless DC motors.

It is one of the most easily found motor types for those that want to build a wind generator at home. Wind energy is converted into rotation energy with the help of the blades installed on the edges of the motor and then converted into electricity with the help of the motor.

You can see images of the brushless DC motor below;

Working Principle of Brushless DC Motor

As mentioned above a magnet with two poles is rotated around a permanent coil to produce electricity.

Detailed information is given in the below picture;

Best Motor Types to Build Wind Energy Turbine

Some types of motors are more efficient than others. With the same wind speed one can produce 10W whereas the other produces 40W.

1.) Treadmill Motors: These motors are both robust and efficient. This is our top recommendation for motors for producing electric energy. You can find them easily online or in stores selling second hand products. They cost between $20 and $250. Because of its values in relation to output current and output voltage, it can easily be used as wind turbine generator.

2.) Stepper Motors: Although highly efficient, stepper motors have a lower output voltage and current than treadmill motors. It can be used in wind systems that have a lower power output.

3.) Standard Permanent Magnet Motor: These are for people who want produce electricity out of wind energy. They are cheaper than treadmill motors but some have higher HP levels. Sold for $20 - $1500, standard permanent magnet motors are our second choice for wind energy systems.

AC Motors to Generate Electricity

The most important component for producing electricity with motors is the magnet. There are no magnets in AC motors and the energy needed for the motor is provided by AC voltage.

How to Choose the Right DC Motor?

The details you need to pay attention to before you choose a DC motor for producing electricity are:

Power Selection: It is hard to rotate motors with high power capacity, therefore the wind turbine blades should be chosen in accordance to the motor power. If the area you set up the wind turbine does not have enough wind, it would be wise to use motors with 1 – 3 HP power. If the wind speed is regularly 15 Mph and over, you should use 10 HP motors.

Power Requirement: It would be better if you used a turbine that is in accordance with the need of energy of that area. The selection of motor is also important; it should be consistent with the size of the turbine. For example, if you need 2000 Whrs of power, you will need to install a 2500 Whrs system.

Blade Design: Along with the wind speed, the design of blades, which divert wind energy into rotation energy, is important. For example, the rotating speed of a 3-blade system and a 6-blade system differ from each other. Because of this, the motor you choose to use has to be in harmony with the blade design.

Motor Power: If you need 1500W energy and you use a motor that produces less than that, you could damage your motor. You should, therefore, use motors that are 30% stronger.

Wind Turbine Motor Basic Calculations

The motor you choose should be built according to variables such as wind speed, blade design, blade number, and rotor diameter. These variables in detail:

Wind Speed: Is the amount of wind passing through a specific area. It is defined by variables such as mph (mile per hour), kph (kilometer per hour), and m/s (meters/second). The wind turbines used today start to rotate with 5 mph wind speed and work efficiently between 25 and 60 mph.

Blade Design: Although wind speed is the most important factor for rotation, the blades are the main components for converting wind energy into mechanical rotation energy. For this reason the blade design is very important for efficiency.

Number of Blades: The number of blades influences the efficiency of the wind turbine. 2, 3, 5 blade wind turbines are frequently used. It is known that the more blades used, the more reliable and safe the wind turbine is. They work more silently and are more efficient. The cost is an adverse factor though.

Blade Efficiency: Is related to the blade design part we mentioned above. The more efficient the blades, the more energy produced.

Rotor Diameter: Meaning the turning diameter of the blades. More robust and big sized motors can be used in wind turbines with a high turning diameter.

TSR (tip speed ratio): If the wind turbines rotate too slowly they lose much of the wind passing over them, and if they rotate too fast it is as though they act as a wall, meaning degradation occur. For this reason, optimum tip speed ratio is very important for efficiency. Some TSR ratios are;

• 2 Blades: 9 – 10
• 3 Blades: 6 – 8
• 5 Blades: 4- 6

Basic Calculations: The average wind speed in your region as well as maximum wind speed must be taken into consideration before building a wind turbine. Suggested figures are:

Average Wind Speed = 25 Mph = 11 m/s
Max Wind Speed = 70 Mph = 31.4 m/s

If the region where you will build a wind turbine has a value of wind speed between the values above, you should arrange the variables like blade size and number. If you want to have 2500 W/hours, the blade length should be 1 – 1.5 meter (3 – 5 feet). The designs with 3 blades can provide 35% - 40% efficiency so we suggest 3 blade designs.

A motor which can generate 2500W power should have;

- 100A output current,
- 25V output voltage,

Or;

- 20A output current
- 125V output voltage.

For this motor to produce maximum power, it should rotate close to the maximum RPM it is intended for. For example, think that a 2500W motor’s RPM value is 1200. To acquire 2500w power in the outputs of the motor we need 1200 rpm (revolutions per minute). The lower the rpm speed, the less the output power.

Basic Power Formula;

Blade length, l = x meter
Wind speed, v = x m/sec
Air density, ρ = 1.25kg/m3
Efficient, Cp = average 0.3 – 0.4
Ptotal=0.5 (x) ρ (x) 3.14 (x) I2 (x) v3 (x) Cp

Examples

We have shown the calculations above but to make them a bit clearer there are some more examples below.

1.) Average wind speed: 35 Mph, Average Power Requirements 4500W, Blade Length =?

V = 35 Mph = 15.7 m/s
Air density, ρ = 1.25kg/m3
Efficient = 0.35
I2 = Ptotal/ (0,5*1,25*3,14*15,7*15,7*15,7*0,35)
I2= 4500/2658
I = 1.3 meter
The blade size should at least be 1.3 meters.

2.) Max RPM = 1200, Vout = 24V, Iout = 100A, Power Requirements = 1000W, Motor Speed =?

Total Motor Power = 24 * 100 = 2400 W
1200 RPM = 2400W
Each Watt = 2400/1200 = 2RPM
1000 = 2 * X
X= 500 RPM

Frequently Asked Questions

Q: What are the differences between the Permanent Magnet DC Motor and Alternator?
A: The Permanent Magnet DC Motor is used to convert electric energy into rotation energy and vice versa. The main purpose of alternators is to produce electricity and they have more production efficiency.

Q: Which is the best DC motor for electricity production?
A: Motors with a lower RPM value and high output voltage might be more efficient.

Q: What are the things that I should take into consideration when I purchase a motor?
A: The standard wind speed is 10–30 Mph, so the motor you will buy should have low RPM values. The blades connected to the motor can produce 400 – 600 RPM speed for a standard wind. For this reason a motor with a maximum 1000 RPM works inefficiently.

Q: How much voltage is required for a 12V battery?
A: To charge a standard 12V battery, 14-16V volts are needed. Make your calculations according to these values.

Q: Can you give details of a good motor?
A: Power = 1 HP, Max 300 RPM, 30 VDC, rpm/volt ratio = 10, 30A Current

Q: What brand and modal of motor would you suggest?
A: Ametek 080987K7 30VDC

Posted in: Wind Power