Pool Motors & Their Functions
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Types of Pools and Pool Motors
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A different type of pool motor is used in each of the three different types of pool. A pool motor's purpose is to power a pump, which itself differs according to the type of pool. Every pump works to move water through a filtration system and may have a secondary purpose of passing water through a heating element to control the pool's temperature.
Above-ground swimming pools make use of the non-excited synchronous electric motor. Below-ground residential pools employ the single-phase induction motor. And commercial pools rely on the three-phase induction motor.
Motor for an Above-Ground Pool
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Above-ground pools set their filtration systems and heating elements below water level, outside the pool. For that reason, a relatively weak motor is sufficient, as it only has to aid gravity in moving water through the filters in a natural siphon action. The motor, a non-excited synchronous electric motor, is a hollow drum with a series of magnetized iron ridges ringing the interior, known as the stator. Inside the drum on a spindle is an iron cage similar to the running wheel used by hamsters or small rodents. This "squirrel cage" is called the rotor, and at no time does it touch the stator. Unlike most alternating-current-powered motors, the electricity passes through the stator rather than the rotor. The alternating current induces a constant switch in the stator's magnetic field, driving the rotor in sync, which causes the spindle to turn. The spindle is in turn attached to the driveshaft of the pool pump.
It should be noted that this motor requires an outward mechanical force to start working. At first, the positive and negative forces the stator exerts on the rotor are equal, so the rotor will not turn by itself. A lever or latch is often found on the exterior housing of this type of motor, and by pressing it the rotor will be nudged. This breaks the balance between magnetic forces and sets the rotor spinning.
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Single-Phase Induction Motor
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This form of motor is designed for all-purpose use. As an AC-type motor, the design is similar to that of the non-excited synchronous motor. The only real difference is that the electrical current is passed through the squirrel-cage rotor rather than the stator. This requires a greater amount of current to create a shifting magnetic imbalance to drive the rotor, but it creates both a higher torque and speed in the motor, thanks to the differences in the magnetic field. Such differences are attributed to a specific frequency in the magnetic field. This frequency is determined by the gauge of the wire making up the squirrel cage, which is important in considering how the three-phase induction motor operates.
Three-Phase Induction Motor
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The design of the three-phase induction motor allows for variable speeds. The squirrel-cage rotor is actually three squirrel cages, one nestled inside the next, each made of a different gauge of wire. This is important in situations in which a high torque is needed to get the driveshaft turning, such as with the industrial-sized centrifugal pumps commercial pools use. The innermost cage is the first in sequence to receive the electrical current, creating low speed and high-torque mechanical energy. A timed switch near the base of the spindle then switches the current to the next rotor, and then the next, until the motor has reached top speed.
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