What Our Research Says About Constant Force Spring Differences

Share Newsletter
Constant Force Spring Differences Blog Post - image of Helwig Carbon constant force springs

Many times, brush holders that use constant force springs are not constant force at all.  A proper constant force brush holder allows full spring force throughout the brush’s life.  Most brush holders are poorly designed and fail to be “constant force” for two main reasons:

  1. The spring diameter is too large
  2. Inferior backplate design
    • The spring starts too high in the brush box.
    • The spring does not sit properly on the top of the brush.

As a result of one or both, the brush will undergo accelerated electrical and mechanical wear as the spring recoils below its ability to apply its rate force.

For a spring to be a true constant force, the spring must be uncoiled one full diameter to be at the rated force, and when recoiled to less than one diameter, the force begins to drop off.

Typically, during sliding electrical contact applications, a carbon brush will experience both mechanical and electrical wear.  One major factor that affects wear rates is the spring force.  As spring force increases, the mechanical wear will typically increase, but the electrical wear will naturally increase while spring force decreases.

There is a stable range for spring forces to balance the mechanical and electrical wear that minimizes the brushes’ wear.

A few significant OEMs use brush holders with large diameter springs that do not offer constant force throughout the brushes’ life.  In fact, on some of the designs, the spring force drops off rapidly, causing increased brush wear and sometimes can even damage the commutator surface from intensified arcing.

On the contrary, Helwig Carbon has specifically engineered replacement spring assemblies that use a smaller diameter spring, resulting in an increased length of consistent force throughout the brushes’ life.

Helwig Carbon constant force spring differences to OEM

 

Helwig Carbon constant force spring differences to OEM

 

In addition, we have also redesigned the backplates to allow the springs to sit closer to the center of the brush, thus distributing the spring force evenly across the two brush wafers. Our precisely engineered springs create longer brush life and less likelihood of damage to the commutator surface with increased motor performance.

Lastly, one of our spring upgrade options is Brush Wear Indicators, which are the industry’s most convenient way to monitor brush wear. Using the red” danger strip,” our Brush Wear Indicators inform you the brush should be replaced. The other spring upgrade option is Helwig Quick Disconnects (HQDs), which lock together with a tight, positive locking action even under rough conditions, with no screws to remove, lose or replace!

Helwig Brush Wear Indicator

For more information regarding our pioneering research on spring pressure, please download our whitepaper: The Effect of Spring Pressure on Carbon Brush Wear Rate

Marvin Herche

Technical Service Manager
Special Products Division

Helwig Carbon Products, Inc. is the 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!