Stator assembly: single magnet, pick-up coils, and insulated powder core
Conventional magnetos are used primarily to generate high voltage for ignition systems in internal-combustion engines. They rely on magnets mounted directly to a flywheel to induce current in stator windings. But new magnetos from Magnequench Technology Center, Research Triangle Park, N.C., instead put the magnet on the stator and a bonded, insulated-iron powder on the flywheel. This allows greater rotational velocity and higher power output, according to company officials.
A flywheel-mounted magnet generates only one voltage pulse per revolution, says the company, and significant deadtime exists in the magneto's output signal unless additional magnets are placed on the flywheel. But a stationary magnet placed on the stator allows continuous generation of voltage pulses throughout a flywheel's revolution. The number of iron-powder poles placed on the flywheel equals pulses/rev. Fabricating multiple magnetic poles from steel laminations and fixing them to a flywheel can be expensive. The new, more cost-effective design uses nonconductive powdered iron integrated -- via a single pressing process -- into a nonmagnetic flywheel hub as multiple separate magnetic poles. This powder minimizes eddy-current generation, leaving the material's magnetic properties largely uncompromised which boosts power output. The powdered iron is also used on the new magneto's stator to further diminish eddy-current generation. The design has been tested to rotational speeds of 12,500 rpm without noticeable generation of eddy currents in the insulated-iron components. Negligible eddy-current losses mean magneto signal amplitude grows in direct proportion with rotational velocity. The results: the magneto produces more power at higher speeds.