Re: [CAD_CAM_EDM_DRO] Motors

In a message dated 5/4/2003 8:37:35 PM Central Standard Time,
joevicar3@... writes:

> To have it reversible I think you need another set of windings. I don't
> know why, but they only run one way.

Simply because the type motor you think you mean has "stator windings" wound
either in series- or parallel-with the brushes, so that the armature winding
always has the SAME polarity as the stator, regardless of whether that's +,
-, or "±" (AC).

If you "swapped" the wiring to the stator, it would run the other direction
on any of the three. So, if you wired-in a DPDT switch for the stator
windings with respect to the brush-connections, you would have made it
reversible. HOWEVER, most reversible drills use PERMANENT MAGNET stators and
a little bridge-rectifier so that the MOTOR always "sees" DC, regardless of
which of the three power-polarities is applied.

The trigger on a VSR drill is NOT "just a variable resistor"! There IS a
variable resistor activated by the movement of the trigger, but this then
controls a SOLID STATE device, probably a power-transistor for a motor wired
for DC as I describe above. Else, a triac, if the AC goes all the way to the
motor, which then has STATOR WINDINGS instead of a PM stator. HTH and all
that! Jan Rowland







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