Re: Sewing machine motor - reversing direction

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "davep by way of Terry Fritz <twftesla-at-qwest-dot-net>" <davep-at-quik-dot-com>

 
> Unless your motor has a seperate series or shunt coil, and an armature
> coil,

	All the sewing machine motors i've seen do.  cf previous.

> reversing the connection to the brushes won't reverse the direction
> of the motor, since the power to the motor is AC.  The current is
> reversing direction constantly - it switches every ~8.33 mSec.

	In 60 Hz territory.  8)>>

> If the motor does have a second winding in it, then reversing the
> connection on one of the windings

	One can reverse either the field or the armature.  Not both,
	as accurately pointed out.

> will reverse the direction of the motor, since you are then
> reversing the relative magnetic fields, but that would most likely
> involve taking the motor apart.

	Or simply switching the wires.  (which may not be so simple.)

> I also doubt that a sewing machine motor is that complicated.

	All of them I've seen (greater than zero) use a series commutator
	motor.

> It probably just has permanent magnets on the outside.

	I've never seen on like that.  (hint: series motors
	are more powerful, per volume than permag, and permag tends
	to lose field under continual AC operation

> If you want to try reversing the wires, you won't harm the motor, but be
> careful, one of the wires from an outlet is 120 VAC with respect to ground,
> while the other is at ground potential. The motor case might be hooked to
> the neutral wire, in which case if you reverse them, the case of the motor
> could be 120 VAC from ground!

	THAT is a most valid caution.  That Said: most such are wired
	isolated from frame, as three wire plugs are NOT universal.

	best
	dwp