How to Choose an Electric Motor: Brushless DC Motors

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Video Transcript

This is Janette and I’m Joe with Groschopp and we have reached our final motor type, the Brushless DC motor, in the seventh video of our “How to Choose an Electric Motor” series.

Brushless DC motors, or BLDC, are suitable for a range of applications. Their maintenance-free design and high power density make them a good solution for applications that require variable speed or no maintenance.

Although considered part of the DC motor family, the construction of a BLDC motor is more closely related to AC motors. However, the rotor is constructed of rare earth permanent magnets to produce the field. They’re electronically commutated by a control. They can receive feedback from sensors that determine the rotational location of the rotor or by measuring voltage in the coils as the motor is operating to determine rotor location.

BLDC motors have speed-torque characteristics similar to brushed DC motors, however, they require hall-effect sensors and a motor control to commutate. The use of a control makes them suitable for variable speed applications.

A BLDC motor takes the advantages from AC, DC and Universal motor types and combines them into one unit.  It has the long life, low maintenance, quiet operation, and variable speed ability of an AC motor; the high starting torque and linear speed-torque curve of a DC motor; and like both AC & DC motors, it works well with gearboxes. Brushless DC motors have a high power density, second only to the Universal motor, and they have the best efficiency rating of 65 to 80 percent.  

Despite these advantages, there is one major weakness: cost. The cost of the rare earth magnets and controls drive the initial motor costs higher than a DC motor. But, when you weigh the initial cost over the life of the motor and its strengths, Brushless DC motors can be worth the investment for some applications.

The speed-torque curve for a BLDC motor is very similar to that of a DC motor. This curve represents the motor performance with full voltage applied, but without the control impacting the performance. Since a control is always used with this motor, there is a lot of flexibility with brushless DC motor operating ranges.

Take a look at the gold shaded area on the curve. The motor can be operated anywhere within this area.

The key to rating a BLDC motor is torque. This particular design is rated at 6.9 inch-pounds of torque and like all brushless DC motors, the maximum torque rating is independent of speed. The only limitation is that when the speed is lower than 300 rpm, cogging may occur with the motor. The cogging can be lessened by using a more sophisticated control and feedback system.

Well, that rounds out our look at our four motor types.  Let’s summarize with a comparison, and discuss how to apply this information to your application design process.

As you look at the curves for the different motor types individually, it’s difficult to get an accurate comparison. That’s why we’ve created this graph to compare the speed-torque curves of all four motor types. We are using the same scale to clearly illustrate the differences between the motors.

For instance, you can see the dramatically higher no-load speed of a universal motor, the purple curve, and the significantly higher starting torques of DC and brushless DC motors.

I’d like to point out that all of these motors are roughly the same physical size despite their significantly different performance curves. You can download this graph from the link below.

We’ve also put together this chart to quickly compare motor types and provide a “starting point” when you have an application in mind.  Once again, this chart compares motors of roughly the same physical size.

Stay tuned for the next video where we will discuss customizing a motor. Remember to check the links below for the speed, torque and efficiency graph as well as the motor comparison chart. For more information about Groschopp or our Brushless DC Motor products, check out our website at www.groschopp.com

Additional Videos

How to use the Motor Search Tool

Narrow your search by selecting motor type, gearbox, voltage, and phase options for your desired motor.

Select a dominant variable: choose one of the three parameters to narrow your search. The selected variable determines which slider bar you will be able to manually move.

Use the slider corresponding to your dominant variable to further narrow your motor selection. The other sliders will automatically move to show available ranges based on the range of your selected variable.

Results will upload as your search criteria changes. If you have any questions regarding your results or how to use the search tool, you can chat with us using the green tab on the left-hand side of your screen.

Note: Groschopp Universal motors are custom built to fit your application so no additional options are available to narrow the search. Selecting the Universal motor type will prompt a message taking you to the Universal product page.

Not sure what you need?

One of our team members would be happy to help. Contact us at 800-829-4135 or by email at sales@groschopp.com. You can also chat with us using the green tab on the left side of your screen.

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Universal Motors

Groschopp Universal motors are custom built to fit your application so no additional options are available to narrow the search. Standard frame sizes and motor features can be found on the Universal page.

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