Popular Woodworking 2000-11 № 118, страница 7

ifeUCTlOlN MOTOR

Induction motors are found in heavy-duty stationary machines, such as this JET table saw.

are made from a carbon-graphite material and are usually held in place against the commutator by small springs. When you turn on a universal motor, current travels in what's called a "series circuit." One side of the electrical line goes through the field, then through the brushes, into the commutator, then the armature, and back to the other side of the line. Each of the bars in the commutator changes polarity as it contacts a brush, and this changes the polarity in the magnets in the armature. The magnetic forces in the armature react with the electromagnets in the field coils and the motor develops torque.

Universal motors make a lot of noise because they spin at a dizzying speed — sometimes seven times faster than an induction motor — and their fans suck a lot of air through the motor, which makes noise. Universal motors are less reliable for three reasons. The motor generates more heat, which can cause the components to break down. Second, the carbon brushes wear out. If they can be replaced then it's a quick fix. If they can't, you've

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Holds the rotor in place inside the stator.

ROTOR

Spins freely inside the stator.Its magnets are attracted and repulsed by the magnets in the stator

CAPACITOR Gives the rotor the boost it needs at startup.