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January 10, 2008
While variable speed motor technology is not new by any means, it seems to be the technology of choice for appliance manufacturers around the world. For years, the appliance industry has been gravitating to these motors, including electronically commutated motors (ECM) and particularly brushless DC (BLDC) motors. It is widely known that variable-speed motors help improve efficiency and reduce noise—two features that drives many appliance OEMs to use the motors as a competitive advantage.
According to Tim Neal, industry leader for Commercial Refrigeration at GE ECM by Regal-Beloit, one characteristic that makes many of these motors more energy efficient than induction motors is that ECM motors often use permanent magnets, which eliminate the motor’s need to use electricity to induce a current across the gap to the rotor.
There are a variety of other reasons that appliance manufacturers are turning to variable speed motors now that the cost has decreased. “Some of them want to achieve more performance in a smaller package. Some want to achieve higher efficiency. Some of them want to achieve comfort benefits to the end user,” says Mike Smith, advanced engineering manager for Fasco Motors Group, in St. Clair, Missouri, U.S. “Even people who just a few years ago didn’t see any need for it, now are beginning to ask for it.”
Appliance OEMs want the benefits these motors offer, but the industry is always watching cost. Mike Rogen, vice president of electronic sales and marketing for Maxon Precision Motors, tells APPLIANCE, “In general, OEMs want high efficiency, smaller size, light weight, low electrical noise, and long life—those features are always on the wish list. But if it costs too much to get those features, then you don’t have a successful product, so cost is always an issue.”
OEMs are placing a high priority on the need to differentiate their products in the market. “There’s a lot that can be achieved in portable products, for example, with an optimized motor,” Smith says. “Producers want higher efficiency, especially if they are working off batteries, but they also want to be able to make units more compact and lighter weight. We are seeing customers that want to design their own special characteristics into their motors and often times variable speed motors allow them to do that.”
Motors in Action
Larger appliances like washing machines are also making a major move into permanent magnet BLDC motors. According to Geneva, Switzerland-based STMicroelectronics, this improves the energy efficiency of the appliance, but it can also improve the mechanics by eliminating the transmission. “A standard washer made 10 years ago had a motor that was coupled with a big belt to a transmission, and the transmission made the agitator move back and forth,” notes Tom Hopkins, director of application engineering for STMicroelectronics in Lexington, Massachusetts, U.S. “Today the trend is to direct drive, which eliminates the transmission, and the motor drives the agitator and the tub directly.”
Washing machines are moving away from mechanical agitation and braking and companies are beginning to use electronics to agitate and brake the motor. Patrick Heath, strategic marketing manager, Digital Signal Controller Division for Microchip Technology Inc. tells APPLIANCE, “A very fast CPU with DSP capability, and a fast and accurate ADC, is needed for these software and agitation method changes.”
Energy use is an even higher priority for users of commercial appliances than for homeowners, as motor maker Regal-Beloit found when it performed a foodservice equipment user survey.
“Many business owners have come to realize that reconfiguring their 5-year to 10-year-old refrigeration equipment with ECM motors can produce sizable energy savings,” Neal says. “Many are even retrofitting new equipment, depending on electric rates and payback.” Using ECM motors would vary with installation cost for each market; however, Neal says the payback period could be as little as 6 months, which is short compared to the average 15-year lifespan of these commercial appliances.
There is still room to improve the efficiency of washing machines and to make that motor smaller. The same opportunity applies to dishwasher engineering. Aengus Murray, director of I-motion product management at global control supplier International Rectifier notes, “We’re seeing appliances with pretty low power usage, in the 100-W power range. Dishwashers, for example, use very small motors.” He says the size ratio of the induction motor to the permanent magnet motor can be 2:1 in a dishwasher.
I-motion was released about 5 years ago as a platform that integrates digital controllers, analog interface and power silicon for variable-speed sensorless motor control in permanent magnet synchronous motors. Over the years, IR made additions to the platform and now is focusing on cost reduction, including integrating all current sensing electronics into the control IC. Murray says, “The I-motion controller gives the design engineer three systems in one. They are getting an analog interface to the inverter, they’re getting the control engine that’s driving the motor and they’re getting a microcontroller that can control the appliance.”
Murray is seeing the HVAC industry moving to BLDC motors as well. Acquiring motor speed control capabilities can result in better energy efficiencies. In air-conditioning, the increased U.S. SEER requirements that went into effect in January 2006 are leading HVAC manufacturers to look at the efficiency of their product when it is operating in a low power range in addition to operating in a maximum power range.
Air-conditioners, refrigerators and washing machines are all making the move to variable-speed motor control. Heath of Microchip says this is happening: “Even though this change requires more electronics and better microcontroller control, which may increase cost.” He also notes that the change will generally raise efficiency into the high 90-percent range and new software with sinusoidal output helps decrease motor noise.
In comparison to the BLDC motor’s 90-percent efficiency, shaded-pole motors run in a range of about 40-percent efficiency. Despite lower efficiency, shaded-pole motors have been widely used due to their low component cost.
“I’ve been working actively with most of my customers that were using shaded-pole motors in applications from range hoods to ovens that are now saying, ‘OK, we need to achieve so many watts in a particular application and we’ve got to get these efficiencies in so many different areas,’” says Vince Daddese, sales manager for Davidon Industries, Inc., located in Warwick, Rhode Island, U.S. “They are obviously looking at the motor, because that is one of the biggest draws of power in any appliance and so they migrate to a permanent split capacitor motor or brushless DC motor where possible.”
Keeping Costs Low
As steel and copper prices continue to go up, motor manufacturers are looking at new options for bringing their costs back down. “BLDC motors use about 60 percent of the copper of an AC induction motor,” says Steve Caldwell, director of the home appliance solutions group for Microchip Technology Inc. (Chandler, Arizona, U.S.). “They tend to be smaller as well, so there is going to be a smaller steel component in the motors.”
Companies are also looking at alternative materials. “With the high costs of copper right now, we’re looking at possibly going to aluminum wire,” says Mark Olson, global market manager for ventilation and refrigeration at the Tipp City, Ohio, U.S.-based A.O. Smith.
But making the switch is not always an easy replacement. Hansen Corporation is using computer analysis to help solve its material cost issue. “Everywhere we are using copper, we are looking through computer analysis to see if we can reduce the amount we use, or we’re looking to see if we can use aluminum as an alternative,” says Lincoln Dreher, design engineering manager, Hansen Corp. (Princeton, Indiana, U.S.).
Those companies that don’t see replacing these basic materials as a viable option are exploring other cost-cutting measures. “There are no alternatives for the basic raw materials, such as steel and copper, but we are continuously looking for new assembly technology and also for other new materials,” says Giovanni Bigatti, research and development for Vemer Siber Group (Verona, Italy). “Ceramic, autolubricant materials for bearings, new lubrication systems, new thermoplastic materials for increasing thermal class are only some examples of our material sourcing optimization.”
While BLDC motors have many benefits, one downside is the cost of the magnets. Rare earth magnets or neodymium iron magnets are the most expensive type typically used, but they enable a motor to deliver a large amount of torque from a small package. The other commonly used rare earth magnet is the samarium cobalt magnet, for applications exposed to high temperatures. “Less expensive magnets are ferrites or alnico, and if size is not critical, we can use a less expensive magnet to get the same performance, but the size of the motor would just be a bit bigger,” says Rogen of Maxon.
BLDC and ECM motors help meet noise reduction goals in appliances. A shaded-pole motor basically runs at one speed, and ECM motors can fluctuate. In commercial refrigeration this is important because they may have large rooftop condensers. During the day when the stores are open, the fans need to be running at full speed, but at night the fans can go at a lower speed, which creates less noise. “A shopping center in the middle of a residential neighborhood can have anywhere from 12 to 30 of these condensers sitting on the roof top, and it gets quite noisy,” says Daddese of Davidon. “We have actually had programs where customers have come to us to meet the noise criteria and they have done it successfully with ECM motors.”
A.O. Smith is putting its resources into testing motors and ensuring the sound levels. The company installed a large semi-anechoic test chamber and spent the time and money needed to develop computer modeling expertise. This gives the motor supplier the ability to test the motor, and even run the entire appliance, in the sound lab in actual operating conditions.
Vemer Siber also sees the importance in testing noise levels. “The noise level must be tested by the OEM because the motor sliding noise is amplified by the resonance box created by the appliance,” says Bigatti. While ECM motors diminish these issues, Vemer Siber also looks for solutions in changes to sleeve bearings, ball bearings, plastic, or metal brackets.
Consumers are going to continue to demand appliances that will keep their homes silent and energy efficient. Appliance manufacturers know their products must keep changing to meet these needs. They will continue to turn to motor suppliers to find solutions in the form of variable-speed motors.
“It’s easy to see why the appliance industry is interested in ECM technology. The motor performance speaks for itself: excellent energy efficiency, greater design flexibility, a wide range of speeds, field-proven performance, and programmable features that just can’t be achieved with conventional motors,” says Neal of GE ECM by Regal-Beloit. “In the end, it’s about customer needs—which is why we’re going to keep on hearing about ECM technology for the foreseeable future.”
By Erin Biesen