The motor is the heart of your wind generator and with all the different kinds of motors available to you what type is best for your purposes? In this step we'll be covering the different types of motors and the pros and cons of using them.
Let's start out with a basic introduction to how motors generator power. If you were to take a motor apart you would find that there are magnets around the outside of the motor and there is a center part that has wire wound about a core.
Turbine Core
When the wound wire rotates inside the casing it cuts through the lines of magnetism that the magnets around the outside create. This causes electrons to jump about and produce electricity (essentially).
There are a couple different types of wind generator motors that you can use: alternators, induction, DC motors, and permanent magnet DC motors. Let's take a look at each of these different types of motors in a wind generator application.
Alternators
Very poor for a wind generator application. At first it seems like a great idea to use a car alternator for a wind generator because they're designed to produce electricity. Sadly, there are a couple of problems with alternators in a wind generator application. First, they are designed to generate electricity at much higher RPM's than a wind generator can produce. This means that you'll have to gear up the wind generator to get the alternator up to the RPM's that you need. That's if you can get it to turn first. You'll need fairly large blades and quite high wind speeds to get it to turn. Depending on the type of alternator that you use you may also need to power it up. You see, many alternators don't have permanent magnets in them, they use an electromagnetic field. The reason behind is power output. When your car idles higher you don't want the alternator to spike up to 100 volts and damage something, so they decrease the amount of electricity flowing into the electromagnet which decreases its output. Due to these factors we don't really recommend alternators as a generator for a wind generator.
Induction Motors
By themselves an AC induction motor isn't really going to work. The reason being that induction motors work on the same principle as an alternator. A current is applied to produce an electrical field inside the motor. The good news is that you can convert these motors by inserting some permanent magnets into them.
Converted motors are OK for a wind generator application, but suffer in a couple ways. The first being that a converted motor suffers from something called cogging. Cogging refers to when you turn the motor you'll find that during the revolution it will get harder to turn. This happens when the magnets line up with the coils and it's harder to move. This will affect the start up speed of the generator because the generator will have to have enough power to overcome the cogs in each revolution. The other downside is these motors have limitations in power output. There is a barrier where the motor will put out say 20 amps and simply won't put out anymore because of heat buildup in the motor.
These motors would work OK for your first generator, but they're not recommended for longtime use.
DC Motors
Probably the best motor to choose for a beginner. These motors produce DC output which is what's required by your batteries (or inverter if you're grid-tie). These motors are great for the first wind generator you build because they really need no modification at all... you can just slap them on and you're good to go.
That's not to say these motors are perfect. Since they produce DC current you'll need a fairly heavy gauge wire to carry the high current that they put out. Since they put out high current you're wind generator must also be located near your batteries or you risk losing power (low volts high current results in power loss, that's why power lines carry high voltage low current because it's more efficient to transmit power that way). These types of motors will also burn out because brushes or the commutator will wear out. These motors will produce at most 250 watts or so, but they're cheap and no modifications are necessary.
Permanent Magnet DC Motors
By far the best solution for a wind generator application. If you're budget will allow it we highly recommend using the DC-540 motor from windblue. Why are these motors better suited for a wind generator? First, they are designed to produce 12 volts at low rpms and they produce high volts, but low amps which is great if your wind generator is located some distance from your house. These types of motors produce 3 phase AC which is transmitted to your house where you'll turn it into DC current for your system using a rectifier.
These types of motors are also made to be low cogging. The DC-540 model that we recommend has zero cogging which means that it will start up in very low wind speeds. The other great thing is that the motor is rated for 10,000 RPM's so if it gets really windy you're not going to blow it up.
This type of motor is ideally suited for a low wind speed generator, or you're looking to upgrade the motor in your existing wind generator.
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