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issue: October 2008 APPLIANCE Magazine
Motors & Air-Moving Devices
Motor Selection when Designing Appliances |
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by Roger E. Hollis, SMMA board of directors and vice president of sales, ElectroCraft Inc.
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Engineers involved in the design and manufacture of a wide variety of products in the appliance industry are increasingly faced with new state and federal regulations governing the energy efficiency of the products they are designing.
As many of these products require motors for a wide variety of applications, the engineer is faced with the problem of determining the most energy-efficient motor while at the same time designing a cost-efficient product to meet market pricing.
In order to provide the most energy-efficient and cost-efficient motor, it is helpful to have a good understanding of the various types of motors available in the marketplace, along with their relative costs.
Table I provides a comparison of the more common motors used in the appliance industry.
| Motor Type |
Efficiency |
Relative Cost |
Comments |
| AC C-frame shaded pole |
25–30% |
1 |
Limited torque range |
| AC 3.3-in. shaded pole |
30–35% |
3 |
Good torque range for the price |
| AC PSC |
35–70% |
5 |
Best efficiency for the price |
| EC (Electronically Controlled) |
80+% |
8–9 |
Requires electronics to control the motor |
| Table I. A comparison of the more common motors used in the appliance industry. |
An EC motor in the table refers to any motor that is electronically commutated but in most instances is actually a brushless dc (BLDC) motor. In some motors, the electronics are integral to the motor itself and can be attached directly to ac. In other cases, the motor electronics are packaged with an existing circuit board in the appliance and the motor is a lower-cost 12-V-dc brushless motor with a small circuit board attached to house the Hall devices (for commutation).
An ac, three-phase motor can produce efficiency in the 70–90% range but has not been included in Table I. That is because most appliances are run on single-phase ac.
The challenge facing the appliance engineer is to select the best option that provides the lowest-cost device while meeting the energy standards mandated by government regulation. In addition to the motors shown in the table, there are many other motor types (stepper motors, dc servomotors, variable reluctance motors, etc.).
The Motor & Motion Association (SMMA; www.smma.org) provides a variety of motor-related courses, including “Motor Fundamentals for Appliance Engineers,” through the SMMA Motor & Motion College.
