Motorcycle Starters and Geopolitics

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Kevin Cameron has been writing about motorcycles for nearly 50 years, first for <em>Cycle magazine</em> and, since 1992, for <em>Cycle World</em>. (Robert Martin/)

“That tiny thing is the starter?”

This is a typical reaction from people who see a late-model motorcycle starter for the first time. Starters have become remarkably small and light in the past 10 years thanks to the availability of so-called “rare-earth magnets.” Because their magnetic flux is much higher than that of traditional alnico or other magnetic materials, the torque necessary for starting an internal combustion engine can now be designed into a much smaller, lighter package.

If you read the technical (or economic!—Ed.) press at all, you know that rare-earth elements (REEs) are at present mainly sourced from China, but that there are workable ore deposits within the US as well. A moment’s further thought reveals that greatly increased REE production is essential to a future of wind turbines, electric cars, and indeed any technology that depends upon powerful magnetic fields (MRI medical imagers, rail guns, earbuds, microwave sources).

How a Magnet Is Made

When I had my TD1-B’s magneto rotor remagnetized in 1967, I saw the technician orient the rotor inside maybe three turns of thick copper conductor, then hit a button on a power supply, which in turn charged a large bank of capacitors. Once they were charged to the desired voltage, he tapped another button and the rotor and the coil around it jumped. The extremely high current from the capacitors’ discharge across the coil created a pulsed magnetic field powerful enough to reorient tiny magnetic domains within that Hitachi magneto rotor.

This was a slightly more sophisticated version of the “old way” of magnetizing an iron bar: aligning it with the earth’s magnetic field and then whacking it with a hammer. The disturbance of hammering, combined with the earth’s weak magnetic field, was enough to jar a small population of magnetic domains in the iron to align with the field. The result was a net magnetization of the bar.

As we know from grade-school science experiments, a magnetic field is created at right angles to an electrical conductor along which a current is flowing. Wind a wire coil around a compass, send direct current through that coil (typically from a battery), and see the compass needle deflect to align with the coil’s magnetic field.

Rare-earth magnets have allowed starter motors to be small enough to use on single-cylinder motocross bikes without a substantial weight penalty. (KTM/)

The same happens within ferromagnetic materials such as iron, nickel, and cobalt. The whirling of electrons in atoms is also charge in motion (each electron has a single negative charge), so it produces a magnetic field. Electrons “like” to exist in pairs oriented such that their magnetic fields cancel. But find a material in which one or more of each atom’s electrons are not paired and you have the makings of a magnet.

Magnetic Alloys

Before the availability of extremely strong rare-earth magnets, less magnetically powerful materials such as Alnico, an alloy of iron, aluminum, nickel, and cobalt, served in permanent-magnet electric motors, hi-fi speakers, and so on. That material was cast into its final form, then later heated above its “Curie point” (a temperature above which thermal activity in the material randomizes any magnetic alignments), and then placed in a strong magnetic field to cool. The external magnetic field acted to align magnetic domains in the Alnico, and cooling to below the Curie point (or Tc) “froze” them in that alignment. The result was a magnet much more powerful than the previous technology of magnetized iron.

During the late 1960s and ‘70s the US Air Force conducted research aimed at creating even more powerful magnetic materials which would have major military applications. It was known that certain rare-earth elements had electron arrangements resulting in more than one unpaired electron, suggesting that this could be a path to the desired result. But the Curie temperatures of such materials were so low that they would have to be refrigerated to retain their extraordinary magnetism. This led to alloying experiments whose goal was to create a material with a usefully higher Tc which enabled such magnets to be used not only at room temperature, but at the considerably higher temperatures present in electromagnetic machines such as motors and generators.

Eventually an intermetallic compound of the REE neodymium, plus iron and boron, was found to have the desired properties. Unfortunately, the processing required is neither simple nor inexpensive. The material is also vulnerable to corrosion, requiring that it be plated or encapsulated in a protective substance. At present a whole range of such materials is available over a range of Tc. These materials are now essential in the production of compact permanent-magnet electric motors for electric vehicles, and of generators light enough to be placed at the tops of wind turbine towers hundreds of feet tall. And much else besides.

Rare-Earth Magnets and China

Politicians fret over China’s dominant position in rare-earth ores and their specialized processing. Investors have shied away from the substantial outlays required to bootstrap a Western alternative; what if the Chinese cut the price and we lose everything? Why not a government-backed program? These days that sounds too much like the old Soviet “planned economy” to be safe politics. Environmentalists compile lists of problems expected to accompany greatly expanded mining and processing of rare-earth elements.

For the moment, turn the key, hit the button, and enjoy the compact starter on your late-model bike or auto as it spins the engine to life.

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