PMA Alternator

The Permanent Magnet Alternator, or PMA, is the workhorse that allows alternate energy projects to succeed. These devices are similar to an automotive alternator but they deliver more output current. As the name implies, they contain permanent magnets. Automotive alternators contain electromagnets. The difference is that the automotive alternators will only be magnetized when a supply voltage is applied to them. This requires the use of several amps of electrical energy before the alternator can produce any of its own power.

Because the vehicle has a gasoline or diesel engine that can rotate the alternator at very high speed, the alternator is capable of delivering more output amperage than what is supplied to it. With an alternate energy project, this is often not the case. If a wind turbine is turning very slowly in light winds, there may only be a few amps produced by the alternator. If the wind turbine was connected to an automotive alternator, these few amps would not exceed the amps used to power the electromagnets. Thus the wind turbine would only be useful in much stronger winds. With permanent magnets in a PMA, the wind turbine is able to produce usable power in very light winds.

PMA alternators are similar in price to automotive alternators, in small quantities such as are required for normal alternate energy projects. They often are housed in the same alternator case. This makes a PMA as easy to install as an automotive alternator. A PMA is heavier than an automotive alternator. For this reason, they have not been used in modern automotive applications. For an alternate energy project, however, an increase in weight for the alternator is usually not a worrisome design concern.

Like an automotive alternator, the PMA produces alternating current internally. This energy is usually converted, or rectified, to direct current that can be stored in a battery. A series of diodes is used to rectify the alternating current. Depending on the alternator, the rectifier may be installed inside the alternator or installed as a separate component some distance away from the alternator. The principle is the same and the project designer can evaluate which option works best for the installation. Typically, there is an advantage to separating the rectifier if the power is produced a long distance away from the point where the energy is used. There can be a voltage drop if the power is transmitted over a long cable. This can be lessened with larger cable. Alternating current is less affected so some projects transmit this energy over smaller wires and convert it to direct current at the point of use.