INDUCTION MOTORS

• 1.Induction motors power stationary machinery that must run for hours on ends.

• 2.Induction motors are rugged, quiet, large, heavy, turn more slowly and can be stalled under heavy use. They are great for the long haul.

• 3.It is called induction motor because of the way they convert electricity into a spinning rotor.

• 4.Power flows into the stator and magnetizes it. The stator is a mass of copper windings that surround the rotor in the center, which is what spins the saw’s blade through a series of belts and pulleys. Inside the stator are two or four poles that become magnetically charged because of the electricity running through the wires. When the electricity changes direction or cycles (frequency), each pole changes its magnetic strength, from a positive to a negative value or vice versa. The induced poles in the rotor are then attracted and repulsed by these ever-changing electromagnets in the surrounding stator.

• 5.A starting winding/copper winding is needed with a capacitor to give a shot of power to start the motor running. The capacitor helps with the starting torque.

• 6.When the motor reaches 85 percent of its speed, the capacitor and the starting winding drop out of the circuit and the motor runs on its main winding.

• 7.The rotor spins because it is induced by the electromagnets in the stator.

• 8.Induction motors are large and heavy because the induction process takes a lot of iron and copper.

• 9.Induction motors are reliable because they are simple, their parts are built for long life and they run at slow speeds, thus they do not generate as much motor damaging heat.

• 10.A well-built induction motor should not heat up more than 40 degrees centigrade over room temperature.

• 11.Induction motors are slow because the rotations per minute (rpms) are governed by how many poles are inside the stator and the number of times per second that your electricity cycles – (50 or 60 HZ).

UNIVERSAL MOTORS

• 1.Universal motors power mostly hand-held machineries.

• 2.Universal motors have a shorter life span, they are smaller, they make more noise, they operate at very high speeds, they offer the most horsepower per pound of any alternating current motor, and they are very difficult to stall.

• 3.Universal motors provide large amounts of power in quick bursts with constant torque and at variable speeds.

• 4.It is called “universal” from the fact that many of them can operate on both alternating current and direct current.

• 5.Universal motors have an armature that spins in the center. Instead of a stator, universal motors have a field, usually consisting of 2 coils surrounding the armature.

• 6.On one end of the armature is a part called the commutator. This part is round like the armature, but it is usually smaller in diameter and is made of small bars of copper. It is through these bars that the armature winding is energized.

• 7.Universal motors also have brushes, made from carbon-graphite material and are usually held in place against the commutator by small springs.

• 8.When the universal motor is on, current travels in 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 electromagnets in the field coils and the motor develops torque.

• 9.Universal motors make a lot of noise because they spin at a dizzying speed – sometimes 7 times faster than an induction motor – and their fans suck a lot of air through the motor, which makes noise.

• 10.Universal motors are less reliable for 3 reasons:

• a.The motor generates more heat, which can cause the components to break down.

• b.The carbon brushes wear out in time, and if they cannot be replaced, then it is trouble.

• c.The big fan that cools the motor brings in a lot of junk such as sawdust and foreign objects. This will damage the windings and insulation.

FAST FACTS ABOUT MOTOR

• 1.746 watts = 1 horsepower

• 2.Actual horsepower = (amperage of a tool X Voltage)/746 Watts = Actual Hp

• 3.When looking for a good motor, look for a motor with the highest efficiency, highest amps and best horsepower for a particular job.

• 4.The smaller the bars, the better the motor. Smaller bars mean there are more coils in the armature winding, and that makes a smoother-running motor.

• 5.220-240 volts: this heavy duty circuit uses 2 hot lines from the main panel that act as returns for one another. These are good for several reasons.

• a.The machines on these circuits use only half the amperage as they would on 120-volt circuits, so it is less likely to trip a breaker or blow a fuse on a well-wired 240 circuit. 240 circuits are much less prone to voltage drops than 120 circuits.

Operating a motor at low voltage causes the torque to drop and the motor to heat up, shortening the life of the motor.

One-phase power means that there is one electric pulse changing direction 60/50 times a second. Three-phase power has three of those pulses changing direction at slightly different times. The fluctuations are times so that when one phase is at its lowest power, another is at its highest. The result is a very steady stream of energy. Three-phase power is typically used in factories, not homes. A special motor is needed to run three-phase power, but three-phase motors are less expensive, extremely reliable, and more efficient than single-phase motors.