To generate electricity, a magnetic field needs to pass a coil of wire. In a permanent magnet generator, the magnets are on rotors which spin as close as possible to densely packed coils of copper wire which are embedded in the stator. Both are mounted on a bracket, which in turn is mounted on a pole or tower, and a wire runs from the stator down to the ground. The blades catch the wind, and are mounted on a hub. The hub is attached to the rotors, so that when the blades turn the magnets spin past the coils in the stator.
The componemts available from the products pages are described below, together with what is needed to assemble or construct a complete system.
Note that stainless steel bolts, nuts and washers are recommended. Standard mild steel will work as well, and be considerably cheaper, although it will rust if exposed to the weather. Stainless steel will not rust.To receive an occasional email about available parts, enter your name here.
|Assembled kits||Kits||This is an assembled kit, as in the image on the right below. A reinforced marine ply hub for attaching the blades is also included.|
|Bracket assembly||Bracket||Fits on top of pole or tower and holds stator mounting bolts and rotor shaft in place|
|Shaft||12mm stainless steel shaft which fits into centre hole of bracket, and centre holes of the two rotor bearings|
|Swivel mount||This allows the generator to rotate freely as the wind changes direction.|
|Rotor assembly||Rotor plates||2 plates of 5mm mild steel on which magnets are mounted|
|Magnets||24 powerful magnets (rare earth), 12 for each rotor, to fit in circle with outside diameter < 250mm|
|Bearings||One bearing for each rotor, to fit on shaft|
|Rotor drive bolt & nut set||12mm stainless steel bolts which pass through both rotor plates and the hub|
|20 stainless steel nuts 12mm - 5 for each drive bolt|
|8 lock washers (star, NOT split ring), and 16 to 32 flat washers (used for spacing)|
|Stator assembly||Stator||9 coils of copper wire connected as three phases|
|Stator bolts, nuts & washers||4 x 10mm stainless steel bolts (or threaded rod cut to size)|
|12 x 10mm stainless steel nuts|
|12 x 10mm star stainless steel lock washers, 16 x 10mm flat washers|
|Electrics||Rectifiers||2 x rectifiers required to convert the variable AC from the stator coils into DC suitable for charging a battery|
|Wire||A few short lengths of wire (>1.5mm) to connect coils to the rectifier inputs, and rectifier outputs to main wire connectors|
|A long wire to connect to the the main wire connectors at the top of the pole/tower, run down inside the tower/pole, and reach the switch box and battery housing|
|Connectors||5 x Crimp on spade connectors (alternatively wire can be soldered directly to rectifiers)|
|2 x pair of crimp on connectors for connecting rectifier output to main wire (runs down inside of pole/tower)|
|Note that crimp on connectors should be soldered as well as crimped!|
|Hub||Hub||Marine ply hub with 12mm holes for drive bolts. The blades are mounted on the hub either with wood screws or 6mm bolts and nuts.|
|Bolts/screws||For attaching the blades securely to the hub. At least four per blade recommended. If bolts, then nuts, flat, and lock washers are also needed. Nyloc nuts can be used in place of normal nuts and lock washers.|
The above is the complete generator unit. To actually charge a battery, you will need to add the following:
These convert wind into rotational energy. The most important factor determining how much power the generator will make in a given location is the diamter of the blades. The bigger the area swept by the blades, the more power... but also the more force on the root of the blades. So bigger blades need to be much stronger.
Ideally the blades need to be twisted so that the tips are flatter. The angle of the tip determines the tip speed ratio (TSR), which is the ratio between the wind speed and the sped the tip sweeps through the air. If the blades are too close together, the turbulence or 'wake' from each blade interferes with the next, so the practical ideal is usually 3 blades.
The simplest blades are made by cutting a section out of a plastic drainage or sewerage pipe. Carving blades from wood is also a popular option. Metal is usually not used because of the dangers of metal fatigue.
|Vane||A vane keeps the blades facing into the wind. It can be made from a pipe which will slide over the 12mm rod at the back of the bracket, bent so that it extends backwards parallel to the ground. A flat piece of wood or plastic is then attached to it.|
|Mounting||The generator needs to be mounted on a pole or tower, so the first step is to mount the 38mm tube at the bottom of the bracket is such a way that it can be rotated by the vane as the wind changes direction (the 1.5mm wall bracket can be mounted using the swivel mount). Then the generator needs to be lifted up safely. Finally the pole or tower may need stays to prevent it swaying in the wind - stainless steel cable is best for this since it doesn't stretch.|
A normal car battery does not last long in this kind of application - perhaps 6 months or so. The deep cycle marine, or golf cart batteries are ideal. I use 'high' cycle batteries, which are designed for trucks, and are cheaper than deep cycle, but last longer than normal (or starting) batteries.
A good rule to follow if you want to your battieries to last a long time time is NEVER allow them to discharge below 12.2V.
IT IS ESSENTIAL TO INCLUDE A FUSE AS CLOSE TO THE BATTERY AS POSSIBLE.
There are two things that can be protected electronically - the generator, and the battery. The battery needs to be protected from overcharging, and being drained too low. The generator needs to be protected from over-speed, which happens when the battery is full and there is therefore less resitance in the generator.
A dump load controller protects the generator from overspeed, and the battery from overcharging by diverting excess power to light bulbs or a heater.
A low voltage disconnect circuit protects the batteries from being drained too low by disconnecting it when the voltage drops below a preset level.
|Wiring and appliances|
Most systems include some sort of appliance(s), such as lights or a water pump. These need to be installed, and wired to the batteries. Note that for 12V systems, a lot of current is required for powerful appliances, 1 ampere per 12 watts, so appropriately thick wire is needed. An advantage of 24V systems is that half the current, and therefore 1/4 of the thickness of wire is needed. A DC-DC convertor can be used to convert 24V to 12V for those appliances which need 12V.
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