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17 August, 2017

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Solar EV race spawns axial-flux brushless motor
Published:  15 June, 2009

An Australian company has developed an axial-flux brushless DC motor which, it claims, offers higher efficiencies and lower running costs and noise levels than induction motors in applications such as pumps.

Although axial-flux motors are already used widely in applications such as computer disc drives, Fasco Australia – owned by the US motor-maker, Regal Beloit – claims that its imPower motor is the first volume-produced version for applications such as pumps, fans and mixers.

The pancake-style motor has its origins in a machine developed by Charles Darwin University for a trans-Australian race for solar-powered vehicles that took place in 1993. Following the race, a company called In Motion Technologies (IMT) was set up to commercialise the technology. One IMT development was a version of the motor to power bicycles.

In 2006, IMT was bought by Fasco, which has continued to develop the technology and has put it into production as the imPower motor.

Unlike radial-flux induction motors, where a cylindrical rotor rotates inside the stator, the axial-flux motors use disc-shaped rotors and stators located next to each other to create an axial air gap. The motors, which incorporate powerful rare-earth (NdFeB) magnets and electronic speed controls, are said to deliver a higher performance than radial-flux machines, in a smaller package, using less active materials.

The motors (shown in a cutaway version above) are designed to operate at one of three speeds selected by the user using pushbuttons, or via digital inputs. This allows them to drive pumps at slow speeds most of the time to save energy, but to run at full speed when required. In swimming pool pump applications – one of Fasco’s key target markets – full-speed operation is used for vacuuming and backwash operations that need high flow rates.

A particular attraction of using the motors to power pool pumps in Australia, is that some local authorities ban the use of conventional pump motors at night because of the noise they make. According to Fasco, the imPower motors are about 10dB quieter than standard motors and are “almost silent” during filtering operations.

The motors’ high efficiency – claimed to be around 80% over the entire speed range – also results in lower running costs. For a typical swimming pool, the savings would be around A$215 (US $175) a year. This gives a payback period of about two years for the motors, which cost about three times more than comparable induction machines.

At present, Fasco is marketing a 1hp (745W) version of the motor that operates in the speed range 500–2,850 rpm and delivers 2.5Nm of torque. The 4.5kg motor is 211mm long, including its control electronics – about 50mm shorter than an equivalent induction motor, according to Fasco.

The company plans to start selling a 2hp (1.5kW) version this year, and has built prototypes up to 50kW. It is also working on a smaller design (with a diameter of about 75mm and a power rating of around 120W) that it plans to launch in 2010 for applications such as small fan drives.

Other potential applications for the technology include electric bicycles, golf carts and spa pools. The motor’s original developers also demonstrated its use in ceiling fans, air conditioning and tidal turbine generator applications.

Fasco is building the TEFC (totally-enclosed, fan-cooled) motors in a factory in Thailand, using stators stamped out of strip steel.

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