Motors can be external or internal(Hermetic). If the motor and compressor are located inside a housing or dome, it is labeled as a hermetic electric motor. To be classified as hermetic, the encasement surrounding the internal operations of a system must be airtight not allowing the flow of air from inside to outside. Hermetic conditions may also be found in the area of semiconductor electronics, optical technology, thermostats, switches, and microelectromechanical devices.
Hermetic seals prevent the influx of dirt, grime, and fluids. They tend to be less noisy and produce less vibration than external motors. Electric motors that are hermetically sealed also tend to have a longer life. Therefore, manufacturers are more likely to see the unit with a generous warranty.
Because the hermetic electric motor housing is sealed, it is necessary the wiring connections be accurate and leakproof. The motor and compressor relationship must include an accurate alignment of the stator, rotor, and compressor for optimal performance. The motor must be adequately cooled and the wiring must be resistant to oil and chemicals found in refrigerants.
Hermetic electric motors are installed based on how they will start, whether under a balanced pressure condition, no-load, or under load. The elecrical characteristics of hermetic motors are the same as external ones in that they are both induction run.
Types of Hermetic Electric Motors
Hermetic Split-Phase Induction motors are used in small condensing systems. They contain two different windings. One winding is for starting and the other is for running. This motor is chosen for systems that require low start-up torque due to low start-up loads.
Split-Phase Induction motors are excellent with systems that contain an unloading device. There must also be an outside relay that is thermal, current or potential relay.
Capacitor Start, Induction Run(CSIR) motors are used often in refrigerating sytems. They have good starting torques due to the placement of a capacitor in series with the winding. Current, potential, and hot wire relays are used with this motor.
Capacitor Start, Capacitor Run(CSCR) uses two capacitors. They are both in the start winding but the start capacitor is controlled by the relay switch. The starting torque is high and when the unit reaches at least 60% of its capacity the relay opens leaving only the run capacitor engaged. Larger systems use this type of motor as they are efficient and powerful over an expanse of time.
Permanent Split Capacitor motors are often used in HVAC units. Current is directed to the start and running windings and no relay is used. The run capacitor is between the running and starting terminals and is in series with the start winding. Overheating may occur with these motors when voltage drops. This may also cause starting issues.
Hermetic Polyphase motors are most often three phase. They are very efficient and excellent prodcts for commercial applications. They may be wired for 220V or 440V. They are available in three phase at 1/2hp and larger and the building must be wired for three phase. Three phase motors use motor starters and no relays.