Notes from Windward: #68


Assemblying the Axial-Flux Alternator

Oana tells of Machining Rotors
and Linking to the Steam Engine

  October 20:

Oana writes:

     Sustainability begins on a small scale. Parts are made, tested, and later hooked up to work together. This is a replica of an ecosystem: each living thing has a special niche to fill, a special talent, but life would not go on without the collaboration of each organism. Building a sustainable community requires that each plant, person, and machine make the most of its niche with a mind to better the system as a whole. Every brick in a house is important.

     Each year, we build another room onto our energy house, metaphorically. Piece by piece, we're constructing the components needed to increase our energy security in terms of fuel and electricity.

The steam engine
with the compressed air control and guage

     As for electricity, there are many ways to take advantage of the copious amounts of sunshine Klickitat County receives (for FREE!). One way is to use a "solar boiler," to turn water into steam. Then we can use the steam to drive a steam engine that converts the heat of the water into the rotational motion that will drive the shaft of an axial-flux alternator. An AFA generates electrical energy using high power rare-earth magnets and coils of wire, but no parts (such as brushes) that will wear away over time and need replacing. Once the alternator is built, it can produce electricity for a lifetime with minimal attention. We can also use this type of low-RPM alternator to glean energy from wind or from snowmelt runnning in our creek in the early spring.

     Our 1 horsepower steam engine [1 hp is the equivalent of 700 watts] is designed to rotate at a modest 500 rpm. An automobile alternator rotates at ten times that speed, at 5000 rpm or more, which means that the parts for automotive alternators must be a hundred times more precise in order to counteract the stresses resulting from the higher speed of rotation. That's one reason why we're working to understand the AFA's low-speed, human scale design.

     So far, Walt and I have put together the skeleton of the axial-flux alternator. The alternator has 2 rotors, which rotate around a fixed stator. The magnets are epoxied to the steel plates and are spun by the steam engine. Regular steel instead of aluminum or stainless steel is used because it enables the magnets to create a stronger magnetic field.

checking out the steel plates what will spin the magnets

     The stator is designed to have 9 coils of wire wired up as three sets of three, so the AFA will initially be generating three phase alternating electricity. Each phase will be fed through its own bridge rectifier to convert the three phase alternating current into direct current with a smooth wave-form.

     Each rotor plate will have 12 permanent, high-strength NdFeB magnets--24 in all. As the magnets rotate, they pass close by the coils of wire. The rotors have been machined carefully and mounted on the shaft which connects the alternator to the steam engine.

     It may not look like a lot of work, but this was the first time in my life I have used a drill press or a hand drill to machine holes into metal, making sure the screws fit perfectly.

     There is great value in knowing how to use many different tools. If it cannot be done a certain way, it is easy to give up and say it cannot be done at all. Having options does not give you that excuse until you've tried all your tools, thought about it, and tried some more. There has been a cultural push towards specialization, towards being really good at one thing. "So... what do you DO?" is a question I hear a lot when I talk to people about sustainability. I am not a physicist, nor a gardener, philosopher, or cook. I'm not especially good at any one thing, but I can do lots of different things which, put together, get the job done well.

  October 27:

Walt writes:

     Now that we've made sure that the magnet plates mount correctly on the shaft that will be driven by the steam engine, the next step is to glue the high-power permanent magnets to the steel plates. Otherpower, the company we bought the plates and magnets from, also offers a nifty alignment tool made out of high-strength aluminum. I'm pleased that we spent the extra to get the gluing template because working with this level of magnetism is quite surprising, and not all of the surprises are the nice kind. It's easy to misjudge their ability to grab any loose steel that comes within a foot of them--they're like something out of a Road Runner cartoon come to life. In testament to that, Opalyn has a nickel-sized black and blue spot on her thumbnail from where she got "bit" by two of the magnets. In short, it's important to remember that they're not like anything you're used to handling.

     When operating, these magnets will be spinning at 500 revolutions per minute, so we're taking care to insure that the magnets remain securely attached to their steel plate rotors. One way we're doing that is by using slow cure epoxy to hold the magnets in place since the cyanoacrylate type glues become brittle after about a month. That type of glue is great for holding things in place short-term, but we're looking for a more permanent bond.

     In addition to the epoxy, the magnets will be embeded in castable resin, and backed up with a stainless steel band to add a third layer of security.


     The first step was to use some sand paper to scuff the surface of the steel to give the epoxy a better grip. Then the aluminum template was bolted into place, two-part epoxy was mixed and spread on the steel plate, and the first of the magnets slid into place.

     In order for the rotator to work, each successive magnet has to be rotated 180° from the previous one, so before the second magnet could be placed, the polarity--relative to the first magnet--had to be determined. Oana did that by holding the next magnet firmly in the center of her fist and bring it near the first magnet to see whether the second magnet was attracted or replused.


     It was likely that when mounting the magnets some epoxy would be squished out from between the magnet and the steel plate, and we wanted to make sure that the extra glue didn't glue the template to the steel plate. So, once the first four magnets were in place at the 12, 3, 6 and 9 o'clock positions, the template was removed and cleaned, and the rotor was left near the woodstove to cure.


Notes From Windward - Index - Vol. 68