In this article, we’ll look at:
What are Brushed Universal Motors?
Brushed universal motors are based on a universal motor design, which uses a wound rotor and stator in series with one another. A commutator and carbon brushes serve as a high-speed mechanical switching system to serially distribute current to the rotor or armature coils and produce torque as they interact with the magnetic field produced by the stationary field coils.
In addition to the air-moving applications mentioned above, universal motors are commonly found in smaller, corded appliances, and have high speed and excellent starting capability. Their speed-torque characteristics make them ideal for driving fan loads. They speed up non-linearly as load decreases, and partly compensate for clogging filters in vacuum cleaners, delivering sustained performance. The workhorses of many applications, these motors are economical, having a high horsepower-per-pound ratio and are less costly than their brushless counterparts.
Design and Speed
When it comes to your application, you may have several goals to consider - vacuum or pressure, airflow, cost, life, and noise are just a few. Brushed motors are less expensive than their brushless counterparts. However, they do not provide the same features or life expectations. Brushes are consumable items.
While brushless motors do provide longer life, there is a cost for the magnets and electronics. Many brushless blowers also offer other technical features such as speed control, tach out signals, and programmability. Brushed motors are more basic but deliver a lot of performance relative to cost.
The output power of a motor is the product of torque and speed at a given point. Or:
P ~ T x N
By taking speeds up, torque requirements are reduced at the same power level. And torque is proportional to the copper and steel content of a motor. Fans are smaller and faster. So, smaller faster motors allow similar air performance (output power) in a smaller, lighter, and less expensive package.
When it comes to speed, brushed vacuum motors are fast. Historically, their standard speed was 15,000 to 25,000 RPM. This has been limited by component reliability. In recent years, however, material savvy design evolution has allowed the standard speed to increase to between 30,000 and 40,000 RPM in many models. Some designs routinely run 40,000 to 45,000 RPM, while others exceed 50,000 RPM.
Smaller and faster motors present challenges to rotating components. Therefore, manufacturers rose to the occasion.
Applications – Managing the Air Path
Vacuum blowers come in two basic styles, called thru-flow and bypass, referring to the relative paths of the working and cooling air. Each has advantages depending on the application.
In thru-flow motors, the dry, filtered working air travels through the fan system and is discharged directly over the motor windings as it exits. The working air provides the cooling air for the motor.
For thru-flow motors:
Thru-flow motors come in single- or two-stage configurations. Adding multiple fan stages allows pressure to build with each stage, delivering higher vacuum or pressure to the application. Single stage systems tend to provide better airflow at lower pressure/vacuum.
Your AMETEK DFS sales engineer can help you select the right motor for your needs.
Bypass Motors
The OEM designer must take care when designing a bypass motor into their system that:
Bypass motors come in peripheral and tangential discharge configurations and are available in single or multiple stages. Again, the purpose of the stages is to create more pressure or vacuum.
For bypass motors:
AMETEK DFS also offers bypass designs in various diameters from 4.2” to 9” in many vacuum and airflow ranges.
How to Determine the Ideal Design for Brushed Vacuum Motors
Since there are a variety of brushed vacuum motors available (currently over 1,400 unique AMETEK DFS models), there are questions you should ask to determine the ideal design for your application. Some of these questions include:
By taking the time to think about the answers to these questions and collaborating with one of our experienced sales engineers, you can determine the right vacuum blower for your needs.
Protecting Bearings Against Moisture
At AMETEK DFS, our Lamb® vacuum motors take the worry out of protecting bearings from moisture damage. Our engineers have developed several solutions to protect bearings in moist applications. We use a patented air seal technology where a small fan creates a localized pressure in a chamber near the bearing. The pressure pushes moisture-laden air away from the bearings to keep them free of contaminants.
In addition, we use a PTFE washer on the shaft and right below the bearings on the pressure side. It works to create a physical sliding seal and keep moisture away rather than using pressure to blow it away. Some motor designs incorporate both air seal technology and PTFE washers.
Our 6.6” and 8.4” bypasses have been designed with a physical separation between the bearing and the fan system, and they offer the ultimate bearing protection.
We prove our designs by using a specialized life test to ensure optimal moisture protection. The test exposes the bearings to detergent suds and proves the effectiveness of the bearing protection. We also choose precision ball bearings with specialized greases and seals for additional protection.
AMETEK DFS Patented Air Seal Detail