One more advantage claimed for brushless d-c drives is high starting torque, "A brushless d-c drive at a given horsepower will outperform a brush-type d-c of the same horsepower in terms of starting torque," says Lee.
Also, brushless d-c motors are not subject to thermal problems at very low speeds, which Lee singles out as a drawback of a-c drives.
High accuracy is said to be inherent feature of brushless d-c drives.
Lee claims that the high power factor of brushless d-c drives - 0.
Lee says that improvements in magnet technology have made brushless d-c drives more widely available.
Although he says there is no practical limit to brushless d-c motor size, Lee concedes that limitations of power-switching devices presently restrict affordable controllers to 300 hp.
A number of extruder manufacturers have reported good success with brushless d-c drives in a variety of applications.
feels that brushless d-c drives have potential in downstream equipment, such as vertical cooling stacks of cast film lines.
Although Smith says brushless d-c drives are a bit more expensive than their brush-type d-c counterparts, he adds that the difference is offset somewhat by the reduction in mechanical equipment such as gearboxes.
NRM-Steelastic, Columbiana, Ohio, initially experienced signalling problems with tach response when it first installed brushless d-c drives on a sheet line in its lab, according to process engineer Timothy Womer.
Womer feels that brushless d-c drives work well, but adds that the motors should be sized for adequate torque requirements.