Alternator Theory

alternator schematic diagram10 ft alternator

The permanent magnet alternator is wired for 12, 24 or 48-volt battery charging depending on the size of wire and the number of turns per coil.

The alternator consists of a stator disc sandwiched between two magnet rotors.


  • Bearings - The blades and alternator are mounted on a hub, which rotates on a spindle with strong bearings. Besides having to withstand vibration and high rotation speed, there is a significant amount of thrust on the bearings from the wind, and it increases as the prop size increases. Vehicle wheel bearings are extremely useful because they are tapered and are designed to take the high axial thrust loads.
  • bearings
  • Air Gap  - This is the distance between two magnets in a dual magnet rotor design. The smaller the distance, the better is the alternator performance i.e. halving the air gap gives four times as much magnetic flux.
  • Number of Poles - A 'pole' is either the North or South Pole of a magnet. While building an alternator there is a need for a separate magnet for each pole. The faster that alternating north and south magnets poles pass the coils, the more voltage and current are produced. But the surface area is important as well. If the magnets used are very narrow (since many poles are being used), the field strength would be much weaker over a distance than a wider magnet. So there is a need to make a good compromise i.e. choose a number of poles that allows for reasonably sized coils and a good strong magnetic field through the air gap. The no of poles always has to be an even number. If it is to be a single-phase machine, the number of poles can be either same or twice as that of coils.
  • Coil Pattern- Series or Parallel / Star or Delta- When coils are connected in series, the voltage increases and so does resistance. When connected in parallel, voltage stays the same but amperage increases and resistance decreases.
  • Magnets - The larger and stronger the magnets, the more power can be produced in a smaller alternator. Neodymium-Iron-Boron ("rare earth", NdFeB) are by far the strongest permanent magnet (PM) known, and these are ideal for building PM alternators.
    neo magnet