Stabilization interactions in small permanent-magnet DC motors

In the small permanent-magnet direct current (dc) motor, the coupling between magnet and armature during start and stall has great influence on the motor´s size, cost, efficiency, and operating parameters. The interaction between armature and permanent magnet field arrangements is analyzed. Attention is focused on conditions which allow high-induction relatively low-coercive-force permanent magnets to be used to good advantage. The consequences of relatively high levels of armature flux and low levels of armature reaction are analyzed in terms of armature conductors, armature resistance, copper volume, and total motor volume. The analysis also contrasts the described approach with the widely used lower induction level ceramic magnets which are able to withstand very high levels of armature reaction.