AC condensate pump is designed for the automatic collection and removal of condensate for air conditioning, refrigeration and dehumidification equipment.
A shaded pole motor is a traditionally used motor for AC condensate pumps in the HVAC industry. Let’s spend a few minutes exploring the reason to use a PM synchronous motor.
What is the PMSM?
The full name of PMSM is permanent magnet synchronous motor. It is a synchronous electric motor whose inductor consists of permanent magnets. Let me see the inside structure of PMSM and how it works
It contains a stator, rotor, and windings, the stator windings connect to the AC power as an induction motor, the rotor turns at the same rate in synchronization. The stator magnetic field rotates in synchronous based on the line frequency.
What is the shaded pole motor?
The shaded-pole motor is a kind of AC single phase induction motor. The shaded pole motor consists of a stator and a squirrel cage rotor. The stator has a protrude pole on its inner periphery, the poles are laminated to reduce eddy current losses.
Each pole is slotted on the side like the pole is divided into larger and smaller parts. A copper ring is placed on the smaller parts, that’s why the poles are named as shade poles.
We could see the construction of shade pole motor in the diagram below:
What is the difference between them?
- Efficiency: shaded pole motor is a low torque motor, it can only run in one direction and does not use capacitors. PMS motor’s full load efficiency is higher than shaded pole motor as an AC induction motor
- RPM: The speed of the synchronous motor is synchronized with the electromagnetic speed, while the speed of the shaded pole motor is lower than that of the electromagnetic speed.
The speed of the synchronous motor will not change as long as it does not lose step regardless of the loading. The speed of the shaded pole motor always changes with the change of the load.
The RPM of the motor rotor. i.e the synchronous speed N, Is
N=120f/P=60f/P
Where f is the frequency of the AC supply in Hz, P is the number of poles (per phase), and P is pair number of poles per phase and PMSs ability to maintain full torque at lower speeds
- Torque: Pole shade induction motors, there are no rotor bars and consequently no torque-producing current flow in the rotor. The torque of a synchronous motor is produced by the phase difference between the rotating magnetic field and the rotor.
- Precision: PMS motor is classified self-excited as a synchronous motor, Its magnetic pole is energized by the motor itself. it provides accurate performance even if low fractional horsepower. so it is useful where precise timing is desired
- Cost: shaded pole motor as a kind of induction motor has no brushes, commutator, or similar moving parts, it is cheaper than a PMS motor. for example, high-horsepower synchronous ac motors, while more expensive than three-phase induction motors.
PM Synchronous motor could be the better choice for AC condensate pump
We choose supply power 120V and 220V 60Hz of PM synchronous motor used for AC condensate pump, we test performance from these important aspects: flow rate, toque, max discharge head, RPM, and Amp.
| Power supply | 120V/60Hz | 220V/60Hz |
| Max flow per min | 230cc | 230cc |
| Flow at 6M per min | 220cc | 220cc |
| Max discharge head | 8.5M | 8.5M |
| RPM | 10R | 10R |
| Amp at 6m | 0.043 | 0.09 |
We request Max discharge head 8.5Meters at a speed of 10R. The pull in torque must be more than 8kgf.cm that is developed only when synchronization of the motor is maintained.
Obviously once up to speed, the PMS motor will maintain synchronism with the AC power source and develop torque.
AC condensate pumps require high-efficiency performance and smaller sizes which makes installation and maintenance much easier, no doubt the PMS motor could be the better choice and PMSMs’ability to maintain full torque at low speeds.
The trend of shifting
Many design engineers and manufacturers are starting to install more PMS motors solutions for fan and pump applications considering their higher efficiencies and smaller size.
In spite of this, PMS motors tend to be more expensive than pole shade AC induction motors. However, China refrigeration organization integrated HVAC downstream and upstream manufacturing resources to carry out raw material centralized purchasing and help save purchasing cost and have a built-in standard feature to control PMS motor without extra cost
