issue: January 2003 APPLIANCE Magazine  Print this page

Motor Technology
Variable Speed Drive for Appliance Motors

A new a.c. drive from Rockwell Automation (Mequon, WI, U.S.) is said to provide cost-effective, powerful speed control for appliance motors.

According to Rockwell Automation, drives such as the Allen-Bradley PowerFlex 4 can benefit commercial washing machines by providing variable speed throughout washing, rinsing, and high-speed spinning cycles. In laundromats, where customers tend to overfill the washing drums, the drive maintains consistent motor speed to help eliminate tripping due to overload conditions. This can save wear and tear on the motor and, ultimately, improve end-user satisfaction.

Available in power ratings from 0.2-3.7 kW (0.25-5 hp) and in voltage classes of 115, 230, and 480 V, the Allen-Bradley PowerFlex 4ª has reportedly been designed to meet OEM demands for flexibility, space savings, and ease of use for speed control of many appliance applications.

"The Allen-Bradley PowerFlex 4 variable speed a.c. drive benefits numerous appliance applications, especially appliances with fans or compressors, such as residential and commercial HVAC equipment," Stan Ho, Allen-Bradley drives product line manager, tells APPLIANCE. "Drives provide soft starting - as opposed to the typical motor starting procedure of applying full power with a simple off/on switch. The soft starting decreases energy consumption and stress on the motor," he adds.

Mr. Ho says drives such as the PowerFlex 4 can also offer flexibility. "Drives also add flexibility for higher appliance performance. For example, designers of commercial floor-care appliances can apply variable speed drives to provide both low-speed for scrubbing and high-speed for waxing," he explains. "Many drives can provide good torque at high speeds, but the real challenge is providing good torque at low speeds. In the case of a floor buffer, poor low-speed torque might result in improperly applied wax. The PowerFlex 4 and its sensorless vector performance help appliances maintain even, consistent operation at low speeds for improved performance."

The drive's three different voltage options also makes it compatible with commercial and residential voltage ratings. "Most drives on the market feature only 230- and 480-V models, requiring designers to provide a transformer or a secondary power source in machines to step the 120 V up to 230 V. That takes up space and adds weight," Mr. Ho explains. "Rockwell Automation engineers designed the PowerFlex 4 with a 120-V input and - within the drive - steps it up to three-phase, 230-V output. This saves the cost, weight, and space of a transformer."

The drive's preset speeds can be especially beneficial to appliance OEMs with varied product lines, says Mr. Ho. "Designers can take advantage of this feature if they're making appliances with multiple models," he explains. "[For example], an economy model that might feature a push button with low and high speed, and a deluxe model that might have two low speeds and two high speeds."

Available in 152 (H) x 80 (W) x 136 mm (D) (5.90 x 3.15 x 5.35 in), the PowerFlex 4 features Zero Stackingª, which allows the drive to be mounted side by side, saving panel space. It also has a relay-driven output with a normally open and normally closed contact, which means engineers can use the output to send a signal that illuminates the fault indicator on applications such as a washing machine or buffer, according to Mr. Ho. "In a sense, the output gives end users a window into the motor status," he says.

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