Fractional Horsepower Brush Design

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Fractional Horsepower Brush Design | Fractional HP Brushes | Helwig Blog

Fractional HP (FHP) motors are multi-purpose motors used for a wide range of applications. As space is limited and performance is key, brush-type DC FHP motors offer a significant advantage over brushless motors and AC motors for cost.

In the carbon brush world, there is a lot of emphasis put on carbon grades. Carbon brush grades and the knowledge on how to apply them appropriately certainly ranks very high on our list. As every grade has unique properties and characteristics that allow each material to perform differently under different operating conditions. The capacity of the grade is often misunderstood and misused, what works in one application may not work in another. 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.

It is important that the brush and the brush holder geometry allows for optimum performance to give the carbon grade the best chance for success. It is also important to remember that you may already 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. This is especially true when it comes to coil spring brush designs like those pictured below:

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

Externally accessed coil spring brush designs are typically found in fractional HP motors. This type of fractional horsepower motors are 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. These brushes utilize a helical spring to maintain electrical contact. We know that helical springs, or compression springs, do not have a linear performance curve, this means as the brush wears the spring force will decline. In a world where electrical contact is key, the reduction in spring force can lead to rapid brush wear and subpar motor performance. It is imperative that the brush, holder, and helical spring are designed to be compatible with each other.

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hand-held polisher used in Fractional Horsepower Brush Design blog

Hand-held Polisher

Many variables are present when it comes to these types of brush designs. What may seem like a small change could potentially cause significant problems. Changing the number of turns on a coil spring, adding or reducing brush length, or changing to a different type of terminal all can have a negative impact on performance. Therefore, at Helwig, we like to know the dimensions of the brush holder. Many times, customers share the existing brush specifications or send in their brush to be reverse-engineered. While gathering brush specifications, it is extremely important to gather holder specifications to help our Engineering group from inheriting a design flaw when reverse-engineering the customer’s sample.

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

Brush Holder in a Fractional HP Bodine Electric Motor

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.

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!

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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