Generator Choices

A DC permanent magnet ( PM ) motor when turned will produce electricity. How much depends on the rating of the motor. A motor rated at 12V 2500RPM ( typical rating for a car cooling fan motor ) will produce about 10Volts when turned at 2500 RPM. The motor must be turned over its rated RPM to actually produce 12V. A PVC 3 Blade wind turbine will not easily spin over 1000 RPM. Expect it to spin at about 200-500 rpm in moderate to stronger winds. To get the motor to spin faster you need to gear it up. This makes construction rather more complex. Ideally a DC motor rated at 30V or higher and an RPM rating of about 325 RPM should be used. This means the blades can be directly mounted on the motor making it easy to construct. A very popular motor used in this kind of application is the Ametek 30VDC motor. These motors were used in old tape drives for backing up computers. They can still be found on ebay and are sometimes still new. But they are becoming less available and their prices are rising. Currently you will pay about $35 – $50 for such a motor.

Car alternators are easy to get and can produce a lot of electrical power. However, most car alternators must be turned at about 2500 RPM before they produce usable current. This means that the wind turbine system must be geared up. To a ratio of 3 to 1, 4 to 1 or 5 to 1. Depending on your average wind-speed and the blade size and type. Even though using car alternators are not very popular to use for wind generators for the reason that they must be geared up, it might be a good choice. Many car alternators can produce up to 3kW of power. Car Alternators are cheap. If you construct this kind of turbine system you will get the most cost effective electricity generator of them all, even though not the easiest to construct. You must keep in consideration that a cheap car alternator does not have any permanent magnets and the rotor coil must be exited before it will produce power. You may have to change a fan belt after some years of use, but it still remains the best choice if you need a lot of power at low cost. Alternators were made to spin very fast and they will last long in an application like this. A DC motor may not last as long. Mounting blades directly onto a motor or alternator puts horizontal stress on it which it was not designed to handle. A direct mounted DC motor will not last very long. The permanent magnets of DC motors in an application like this also tend to come loose. Some people put extra epoxy on the magnets before using the motor.