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In the last article, I discussed blade design for your wind turbine. Today I'm going to switch gears a little bit and talk about the alternator. This is the heart of the turbine and is what actually generates the power. A permanent magnet alternator will generate AC power at varying voltages and currents based on the speed that the turbine is turning.

Design of electric machinery is a very detailed topic, however there are some basic rules to follow when designing your own wind turbine alternator. First, the simplest design involves a stator (non-rotating part) which includes copper coils, sandwiched between two rotors carrying permanent magnets. As the rotors spin, the changing magnetic field induces a current in the copper coils. This is how power is generated by the wind turbine.

Generally, 3-phase AC is generated and rectified to DC in a home made wind turbine. This means that you need a minimum of 3 coils. Although in theory 2 permanent magnets on each rotor could generate power, the minimum recommended number of magnets is 4 per rotor. This keeps each coil within a magnetic field at all times and therefore generating power.

The coils are connected in either a Delta or Wye configuration. Generally the Wye configuration is preferred due to the fact that all three phases are connected to a common neutral or ground. In larger turbines, the number of coils can grow to 12 or 15 and the number of magnets per rotor can jump to as high as 16.

Once the magnets and coils have been tested, common practice is to set each rotor and stator in resin to ensure that the parts don't move relative to one another during high winds or vibration. This is another way to ensure that the efficiency of your generator does not degrade over time.

For more information on this and other DIY renewable energy topics, you can check out Earth4Energy or Home Energy Focus.

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