Re: [A/S] Re: New Suburban furnace VS catalitic

["Dr. Gerald N. Johnson, electrical engineer" <geraldj@xxxxxxxx>]

It is but to reverse a motor you'd have to move the brushes more than 90
(and that depends on whether it has two or four poles) degrees. The
brush position is not a simple function of position. It has to be
refined to allow for the pole shifting that comes from the reaction of
the currents in the armature, then shifted a bit to minimize sparking.
Even swapping the wires to the brushes may not be a perfect solution if
the brushes are in the wrong place when the motor runs the opposite
direction. Because the armature reaction will be reversed also. Brush
position is also a function of how the armature winding is laid out with
respect to the commutator. A different winding arrangement can move the
required position of the brushes as much as half a pole space.