ebm-papst Fans, Blowers and Technology

Armin Hauer, Advanced Technology Manager

An article in a recent issue of Sustainable Business examines the potential impact of the uncertain supply of rare earth magnets on manufacturing EC motors, noting that EC technology is reliant on rare earth elements. But this isn’t always the case…  

The manufacturers of electric motors struggle to predict the future costs of rare earth elements. As a result, user circles often regard permanently excited electric motors, which are particularly energy-efficient, as expensive. But highly efficient electric drives don’t necessarily depend on strong rare earth magnets. For example, "simple", cost-effective and – above all – readily available ferrite magnets suffice for energy-saving EC fan motors with an external rotor design. In some cases, these reach motor efficiencies of more than 90 percent.

How an EC motor works

A brushless DC drive (BLDC motor), a BLPM motor or an electronically commutated (EC) motor – exactly which motors are in the rare earth element discussion? These are all actually different names for permanently excited synchronous motors. These motors use electronic drives that are either AC line-powered or that use DC power supplies. The BLDC/BLPM motors usually operate with square-wave currents (block commutation). In contrast, EC motors can operate with both square-wave currents and with sinusoidal currents (sinusoidal commutation). The latter method achieves a significant noise and vibration reduction over the block commutation method. The design with sinusoidal currents corresponds to the classic synchronous motor.

Exploded view: The permanently excited synchronous motor, also called brushless direct current motor or EC motor.

An EC motor always requires a drive electronic that includes an inverter for the control of sequential and reversing current flows in all cores of the armature. This electronic commutation determines the strength and rotational speed of the resulting magnetic field that the armature generates. The permanent magnet rotor responds by revolving synchronously with the rotary field of the armature. In contrast, the speed of AC line-powered asynchronous motors depends on the frequency of the supply voltage and on the motor load. The torque-speed characteristic of an EC motor mimics a DC shunt motor, because both motor voltage and shaft speed, as well as motor current and shaft torque, correlate linearly. The angular rotor position is continuously determined by either sensor hardware in the motor, or the inverter senses the so-called counter-electromotive force and the motor currents for resolving the position mathematically. The idle motor speed depends on the applied voltage and the number of turns of the armature windings. Within the physical parameters of output power, torque and temperature exposure, nearly arbitrary motor speeds can be reached slip-free and synchronously with the rotating magnetic field. These speeds are completely independent of the AC line frequency.

Dynamic requirements determine magnet choice

As a result of their unique motor characteristics, external rotor EC fans seldom need strong rare earth elements. That type of magnetic quality is really only needed to minimize the moment of inertia for very dynamic servo motors.

Why our EC motors don’t need rare earth magnets

ebm-papst GreenTech EC motors for energy-efficient fans remain undisturbed by rare earth element scarcity, because the armature of a GreenTech EC motor is located inside and is surrounded by the rotor.

Cutaway: Centrifugal fan with external rotor motor.

Our energy-efficient fans remain undisturbed by rare earth element scarcity because the arrangement with external rotor motor achieves a higher torque than an internal rotor motor of the same size, magnet system and magnet thickness. An internal rotor motor has a restricted magnet volume, a reduced air gap surface and smaller radius. External rotor motors that use hard ferrite magnets cleverly applied to fans and blowers attain torque and efficiency levels that internal rotor motors can achieve only with rare earth magnets, due to limited volume and size.

A fan motor design with an external rotor has an additional advantage: The fan impeller mounts directly to the outer rotor, directly to the motor "housing". The result is a compact axial length and superior self-cooling of the external rotor motor.

To further discuss how our EC motors are different, contact us.

Dr Jürgen Schöne, R&D Director of Aerodynamics and Motor Technology at ebm-papst Mulfingen,Werner Müller, Manager of Motor Development at ebm-papst Mulfingen, Armin Hauer, Advanced Technology Manager at ebm-papst Inc.

Why brushless motor designs are gaining momentum for commercial truck and bus ventilation

By Bill McBaine

Not so many years ago, designers of commercial truck and bus ventilation systems had only a few choices for motors. These products offered economical solutions but were not without issues.

Then came a global fuel crisis, which forced truck fleet owners to re-think how they operate their vehicles. Because it was no longer fiscally practical to idle a large diesel engine during evening truck stops to power and ventilate the sleeper cab, HVAC manufacturers began to integrate their HVAC and power generation systems into auxiliary power units.

Mass transit authorities faced similar challenges: save fuel while providing adequate ventilation for passengers. They pushed for reducing buses’ down time and improving their life span, which required a new solution: a DC input motor device capable of drastically longer service life.

As a global manufacturer of air movers and drive systems, our challenge was to adapt to these new realities. The result? A brushless motor design that offers longer life, lower maintenance, better fuel efficiency and improved performance.

Let’s look at the old-versus-new options for powering ventilation systems in commercial vehicles.

Low voltage (12/24VDC) brush commutation motors, offered by many suppliers, were the standard for many years. Featuring a consumable carbon brush in contact with a commentator to provide power to various motor windings, they offered a simple, inexpensive approach. 

However, brush commutation motors have always been prone to wear-and-tear issues as they age.

The motor’s brush material is consumed over time through physical contact with the spinning commentator. This abrasive material becomes trapped within the motor, leading to bearing failure if it contaminates the grease. Typical brush life is 4,000 to 6,000 hours. “Long life” variations may exceed 10,000 hours but have unfortunately resulted in even greater amounts of abrasive brush material building up in the motor.

In addition, water penetration/condensation in brush commutation motors during extreme external temperature swings can result in moisture being drawn deep inside the unit (especially at the seams). Once trapped, this moisture cannot easily escape, leading to corrosion and shortened life span of the motor.

Another ventilation motor option, high voltage (230VAC) induction motors allow higher power levels at a lower amperage draw compared to 12/24VDC brush designs. On the down side, this approach requires a high-capacity AC power source, which adds a lot of additional expense to the system. These motors’ physical space requirements are also more suited to the mass transit industry/ bus market than for other types of commercial vehicles.

So what’s the third option? Automotive brushless commutation motors, which ebm-papst has refined over the past 10 years to offer truck and bus fleets better efficiency and performance.

The brushless generation of automotive motors introduces a Gortex membrane within the electronics components, allowing any condensation to be safely eliminated from the circuit board. Leading suppliers of HVAC systems within moving vehicles and equipment have embraced these designs, now used in quantities of hundreds of thousands of pieces in commercial and industrial vehicles.

Our third generation W3G300 fan, introduced to North America in 2011, and the new W3G385 fan, which joins ebm-papst’s brushless motor product family this year, build on the success of earlier models while offering new capabilities such as greater air performance, thinner and lighter construction, reduced power usage and lower noise levels.

As fuel prices continue to rise, we’ll keep listening to the needs of our mobile customers and their HVAC suppliers, developing and testing new improvements to our brushless motor systems.

If you’re a truck or bus fleet owner, manager or maintenance pro, we want to hear from you. What are your experiences with brushless motor systems? How can we continue advancing brushless motor designs?