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issue: October 2006 APPLIANCE Magazine - Part 2: Motors & Air-Moving Devices

Motors and Air-Moving Devices
Continuously Variable


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by Erin Biesen, Associate Editor

Appliance manufacturers are turning to variable speed motor technology to help increase energy efficiency, reduce noise and cut cost in product design.

The DECV 50/5 is a compact, digital, velocity controller designed for controlling brushless motors up to 250 W equipped with hall sensors. The controller is suited for high-speed applications where 4-quadrant control is required. There is also a ready output as well as speed and current monitor outputs.

While variable speed motors are not the new kids on the block, they may be the most popular. For years, the appliance industry has been gravitating to these motors, including electronically commutated motors (ECM) and particularly brushless DC (BLDC) motors. Variable speed motors help improve efficiency and reduce noise. Now motor suppliers are seeing a big push from appliance manufacturers to integrate BLDC motors into product design as a way of staying competitive.
One characteristic that makes many of these motors more energy efficient than induction motors, according to Tim Neal, industry leader for Commercial Refrigeration at GE ECM by Regal-Beloit, is that many ECM motors use permanent magnets, which eliminate the motor’s need to use electricity to induce a current across the gap to the rotor.
At one time these BLDC motors were mostly found in high-tech applications but in recent years have trickled down to the appliance industry. “Military and aerospace would use them all the time and didn’t care that they cost more,” notes Lincoln Dreher design engineering manager from Hansen Corporation (Princeton, Indiana, U.S.). “It took some doing to get the quantities up, to drive the prices down, so it would become affordable for the more price-sensitive industries.”
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.”

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Applied Motors

Larger appliances like washing machines are also making a major move into permanent magnet BLDC motors. Not only does this improve 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
the Lexington, Massachusetts, U.S. based-STMicroelectronics. “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 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.”
A variable speed motor can have varying benefits in different applications. “In heating appliances, it allows you to keep a consistent temperature inside the house,” notes Bob Garrison, applications engineering manager for Fasco. “Instead of firing up to be warm and then cooling off and then firing back up, now the motor can just run continuously.”
Les Lyons, senior application engineer, explains another advantage to an HVAC application: when the homeowner is shutting off vents in particular rooms in the house, variable speed motors help overcome the difference in the duct system pressure.
Fasco has developed a draft inducer for a 90 plus furnace industry. “The 90+ inducer housing design increased our static pressure by 15 percent at the blower operating point, improved our sound level by 4 dBA and improved the blower static efficiency by 5 percent to 10 percent while we were able to keep the same mounting footprint,” says Garrison.

Fasco offers this in either classification of motor, variable speed BLDC or induction.

Cost Control

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 Dreher of Hansen.
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.

The Smart Drive motor is a direct drive, three-phase permanent magnet motor that has withstood the test of time.

Knocking Noise

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, therefore creating 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 company the ability to test the motor, and even run the entire appliance, in the sound lab in actual operating conditions. Olson tells APPLIANCE that the company does this so, “We can isolate what is causing the objectionable frequency and come up with a solution by changing the motor or component in the blower, or even suggesting a change in the design of the appliance itself. Sometimes you can just move a bracket or change the aerodynamic shape of a part and it will minimize noise.”
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.”

Fisher and Paykel opened a plant to produce washing machines, clothes dryers and Smart Drivemotors in Clyde, Ohio, U.S.

A Motor Ahead of its Time

APPLIANCE magazine first reported on the Smart Drive motor in the August 1992 Motors and Air-Moving Devices Part II. Over the years, the motor has proved it could withstand the test of time and even cross the Pacific Ocean to broaden its market. While there have been some modifications over the years, the general concept of the motor has remained the same.
Fifteen years ago, Auckland, New Zealand-based Fisher and Paykel Appliances Ltd. set out to design a range of products to suit various markets, one of them being the U.S. The company brought its products to the U.S. in the 1990s and grew the business until the U.S. became its biggest regional market. It made sense to move manufacturing to the country where it sells most of its products. In February 2006 the company opened its Clyde, Ohio, U.S. plant, which manufacturers washing machines, clothes dryers and Smart Drive motors.
“We designed a range of sizes, models of washers and equipment that would be able to make that complete range. The production machinery side of the company also developed the machinery in a modular form so that it could be shipped practically,” says Nairn Henderson, engineering manager of the Clyde factory. “The strategy has been for a long time to be able to build plants in New Zealand and move them to the markets where demand is strong, and our market growth in the U.S. has justified us doing that. We moved the washer plant from Australia and the motor and dryer plants from New Zealand to support the demand and reduce the shipping costs.”
When the company began to design this washing machine platform, it wanted to completely understand the wash process. It quickly learned that due to various types of load sizes and wash requirements there was no one way to wash clothes. “It lead us in the direction of wanting to have a computer-controlled motor, and we went looking for a production version,” says Henderson. But in the early 1990s, electronically controlled washer drives were not common. “We eventually came to the conclusion that there is actually no one around that was going down that path, so we said ‘Ok, no one is doing it, we will do it ourselves’.”
The Smart Drive motor is a direct drive, three-phase permanent magnet motor, with the stator integrated on to the outer bowl of the washing tub. The rotor is directly coupled to both the agitator and the spin bowl. The spin bowl is de-coupled from the drive system by a method the company developed, which involves floating the bowl in the wash water for the agitation phase of the wash.
“The wash action is controlled electronically using sensors that are mounted in the stator itself, and they are always monitoring the position of the rotor or the magnetic field of the rotor,” explains Keith Ferguson, product design engineer for electric motors in New Zealand. “Through the electronics the sensors control the speed and direction of the rotor for agitation.”
These basic functions are unchanged from the original Smart Drive motor. Two changes that have been made were in the materials.
One of the more unique features of the Smart Drive motor is that it has an all-plastic construction. “When I designed it to be constructed in plastic, everyone said ‘Are you crazy? That will never work’,” Ferguson says. “And that is always an incentive to make sure you achieve your goal, and we did achieve it.”
In 1994 the company made a cost savings change when it switched from a polyethylene terephthalate (PET) material to a polybutylene terephthalate material for the molding that coats the steel stator.
Then the company changed the rotor from the PET material to a glass filled polypropylene. “That was a cost savings, but it was also done in conjunction with a change of design from neodynium magnets to ferrite magnets,” notes Ferguson. “ The ferrite magnets gave us a substantial strength increase in the rotor so we were able to go to a much less expensive material.”
The cross section of magnetic wire has gone down in size twice over the years. First it went from 1 mm to 0.71 mm, and then eventually from 0.71 mm to 0.53 mm. Electronic devices improved and began to switch at higher voltages, which allowed the company to use a lower current because it had more turns per pole with the smaller wire, and reducing the switching current even more resulting in the opportunity to use even less expensive electronic devices.
Finally, the company changed the number of magnetic poles on the rotor in relation to the wound poles on the stator, which changed the ratio from 42:56 to 36:48 poles to reduce the cogging torque. Fisher and Paykel uses a similar motor in its dish drawers and says it could be used in clothes dryer applications as well.
In 15 years the Smart Drive motor has experienced several changes and modifications, and the technology is still ahead of its time. “In our machine you can load the clothes in, add some detergent, push the go button, and the machine will determine the rest for you,” says Henderson. “It will sort out the water level, it will sort out what cycle best suits those garments and wash them and spin them out appropriately.”

 

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