Permanent magnet alternators and generators Buying guide 2019 to understanding what to buy.
Hi Anthony Jones from Hurricane wind power here and today I wanted to take a few moments and write up a short buying guide for permanent magnet alternators and generators. While we have done a lot of youtube videos on this subject which we will embed at the end of this discussion we recognize that as portion of our audience would rather read an article and do not like video. Therefore I wanted to take a few moments here to clear up some confusion and direct our customers to the best model for their application. We will not be getting into alternator math and deep technical stuff but find it necessary to write a basic guide on how things work for the 1st time customer who has never has experience with a permanent magnet alternator.
The first thing we would like to talk about is the voltage ratings on the turbines. Most of the pma's and or pmg's depending on which terminology you prefer are rated at a voltage which is realistic to reach a cut in point at an RPM form 150-225 RPM depending on the alternator. Unlike an basic car alternator which is uses a field coils which is energized by electricity and is turned on and off in a charging system to regulate the voltage a permanent magnet operated alternator does not have the ability to turn on and off. This has it's advantages and disadvantages depending on the application. While the permanent magnet alternator has the ability to produce energy from a dead state i.e. no energy to energize a field coil so long as there is a source to provide input into the shaft it will produce power. On the downside of that it cannot be turned off which means that it need a controller such as a diversion load to send the power to another source once the battery or source no longer needs power. This is typically how it is done in wind turbine applications because many of these machines with enough surface area to generate any real amount of power rely on the turbine to remain under a load to keep the turbine from being damaged by excessive rotation speed. The downside of this is that the alternator remains under a load constantly so long as wind or water in a hydro application flows. When we get into the longevity of the life of a winding the constant use can produce more heat than in a field wound application wjere the alternator goes through a charging cycle then turns itself off after the battery is full. In applications where the pma is not being used in a wind application a voltage sensing device can be used and once the full charge state of the battery has been reached a normally closed relay can be set to open. This is a solution we employee in applications where the load is not needed to keep the RPM from exceeding excessive conditions to damage wind turbine and or alternators.
As we began discussing in the previous paragraph it is important to note that the voltage is not regulated within the alternator. All of our alternators and for that matter most on the market period are 3 phase wild AC output with all three legs being hot. This is rectified externally in Hurricane units to keep the heat build up in a rectifier from decreasing alternator efficiency. The load on the charging side of the generator is what holds the voltage down. It is important to understand that just because you have a 48 volt application you do not necessarily want to buy a 48 volt alternator for example. All of the alternators have different power output characteristics which are determined mainly by the windings of the particular unit. Therefore in the example where a consumer buys a permanent magnet alternator for an application where it is driven by a motor or other high rpm drive system using a 48 volt alternator is a disadvantage. In this instance using possible a 12 or 24 volt winding which is capable of driving 48 volts at the higher RPM also uses a thicker winding which allows more current to flow. In this example using the formula VOLTS time AMP's = Watts it is easy to understand the power potential increase from changing a winding capable or outputting 40 amps versus 10 in a 48 volt application. In this example 48 x 10 would procude about 480 watts where as the latter would allow the production of closer to 2000. More importantly in this example with the use of a higher horsepower input application the thicker winding provides more current thicker wire to carry the current and less heat build up.
So what about cogging? Is it important?
We are the original low or no cogging alternator and we did this my properly machining our alternators with the proper air gap and mgnetic saturation characterized by a signature old school pole claws which provide a superior waveform and efficiency producing less heat and startup easier. It is important to note however that regardless of how easy an alternator is to start up when it reaches the cut in point and or is put under a load it becomes harder to turn. This is where having enough torque in your project to drive the alternator to generate power comes into play. This is a simple concept yet most failed DIY projects overlook this elementary concept. I am going to post the link to some of our videos but here it is in a nutshell
1 determine the cutin RPM of your project.....how fast with the RPM of the shaft we going when we expect the unit to start producing power.
2. Determine the normal operating range or VOC of the application when possible being careful to take saftey into consideration as unregulated alternators can product high amounts of voltage.
3. Determine how much torque your wind turbine water wheel and or other application can produce.
4. When you have thought about these issue and have done your best and cannot determine the right alternator for your project do not just buy and hope! We talk to people all of the time who feel ashamed to reach out for help. That is what we are here for and at the end of the day there was a time when we were also beginners. Some of this stuff is a little but complicated and we love to talk to people and provide the best customer service to make our brand the preferred brand on do it yourself worldwide.
Hurricane is the home of the Cat IV V, White Lightning and Air Boss line of permanent magnet alternators. While we refer to these as their proper names because the produce alternating current we as a matter of semantics do not care if your want to call the permanent magnet generators or permanent magnet motors. We still understand what you are talking about