Fractional Horsepower Motors & Carbon Brushes

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Fractional Horsepower Brush Design | Fractional HP Brushes | Helwig Blog

Fractional Horsepower (FHP) motors are multi-purpose motors used for a wide range of applications including anything from small household appliances to large aircrafts. With these applications, space is often limited but optimal performance is crucial. Brush-type DC fractional horsepower (FHP) motors offer a significant advantage over brushless motors and AC motors for cost and reliability.

In this blog, we will explore the different aspects of carbon brush design that contribute to optimal functioning of fractional horsepower motors.

Choosing the Right Brush Grade for FHP Motors

In the carbon brush world, there is a lot of emphasis put on carbon grades. The capacity of the grade is often misunderstood and misused, what works in one application may not work in another. Helwig Carbon’s engineers have a deep understanding of brush grades and how to apply them appropriately in different applications. Every brush grade has unique properties and characteristics that allow the material to perform differently under different operating conditions. 

Many factors affect brush life such as load, spring force, vibrations, humidity, etc. Operating conditions must be known by collecting the required data and only then can the experts who understand the composition of the grade, provide the best recommendation for your application. There are only a limited number of experts left in the industry that can provide this skill set, but it is crucial to optimize the function of FHP motors. Contact Helwig Carbon’s team of experts today to learn more about choosing the best brush grade for your application.

Optimizing Brush Designs in FHP Motors

It is important the brush and brush holder geometry allows for optimum performance to give the carbon grade the best chance for success in fractional horsepower motors. You may have the correct grade for your application, but if your brush and holder design does not allow for good electrical contact, your grade is going to underperform.

Example: Coil Spring Brush Design

Externally accessed coil spring brush designs are often found in fractional HP motors like those pictured below: This type of FHP motor with a coil spring brush design is commonly found in residential blenders, power tools, vacuums, and other general-purpose applications. This brush type can also be found in commercial, defense, and aerospace applications.

Fractional HP Brush - Grade H27 with helical spring, used in Fractional Horsepower Brush Design | Fractional HP Brushes | Helwig Blog

Fractional HP Brush – Grade H27 with helical spring

The Challenge

Coil spring brush designs rely on a helical spring to maintain constant contact with the motor’s commutator. However, as the brush wears, the spring’s force naturally weakens. This can lead to insufficient contact, sparking, and accelerated wear, compromising motor performance and shortening brush life.

The Solution

Many variables are present when it comes to coil spring brush designs in FHP motors. What may seem like a small change could potentially cause significant problems. To avoid inadvertently carrying over design flaws during reverse engineering, Helwig Carbon partners closely with clients to gather existing brush and brush holder specifications. This comprehensive approach allows us to understand your specific application needs and tailor the brush design for maximum benefit. This might involve adjustments to:

  1. Number of turns on the coil spring: Affecting spring force and contact pressure.
  2. Brush length: Balancing contact area with friction and heat generation.
  3. Terminal type: Optimizing current transfer and connection reliability.

The Result

Equipped with application information and holder specifications, Helwig can provide a coil spring brush design that will keep the pressure (PSI) at the brush face, within the recommended range, throughout the life of the brush. This will ensure that the brush makes proper electrical contact with the rotating surface. Helwig has provided many different solutions to a vast array of customers by simply redesigning the geometry of the carbon brush and coil spring.

Extend the Brush Life in Your FHP Motor with Helwig Carbon’s Expert Solutions

If you are having issues with your current brush and want to see how we can improve brush life and motor performance, contact us at (800)-962-4851 or [email protected] and let us help you!


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hand-held polisher used in Fractional Horsepower Brush Design blog

Hand-held Polisher


Brush Holder in a Fractional HP Bodine Electric Motor, used in Fractional Horsepower Brush Design

Brush Holder in a Fractional HP Bodine Electric Motor

Admir Karabegovic
Application Analyst
[email protected]

Helwig Carbon Products, Inc. has been a premier, family-owned, American manufacturer, of carbon brushes, brush holders, spring assemblies, bearing protection kits, metal graphite brushes, and mechanical carbons since 1928. We have forged innovations that have since become industry standards and requirements. We pride ourselves on manufacturing all of our products to the highest standard and performance because we know your application depends on it!


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