Benefits of Helwig’s Multi-Flex or Tri-Flex Brush Design Over Solid Brushes

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multi-triflex and multiflex brushes

Choosing the right carbon brush for any motor or generator involve many factors including the operating conditions such as environment, motor loading, and grounding. 

In all cases, the carbon brushes are the fuse of the DC motor or generator circuit.  

Carbon brushes are designed to fail to save the motor. Which means carbon brushes must cover a certain amount of commutator (comm) bars to maintain full motor nameplate operation. 

In addition, the brush must move freely inside the brush box. The spring assembly must be set to the operating conditions to balance the mechanical and electrical wear. And seating brushes ensure the brush maintains good contact. Thus, extending brush and comm life. It also reduces costly downtime.

How does this work?

Dynamic Points of Contact

A single wafer or solid brush is typically used on low-voltage DC machines up to 230 VDC. The solid brush surface generally has a few large current contact points across the brush face. 

With voltages from 230 VDC to as high as 750 VDC, or with high electrical stress such as vibration, shock, copper drag, high bars, high mica, etc., then multi-wafer brushes increase the number of contact points with the commutator. This happens because of the number of brush-faces available for contact. It also raises the resistivity.

Resistivity measures the restriction by the brush to current flow like a hose containing the flow of water. Resistivity varies with temperature. Carbon brush resistance goes down as the temperature rises. The cooler the brush, the more current it can carry without harming it. An exception is when the brush is exposed to extreme cold.

Brush with sparks

Brush with sparks

Brush without sparks








What are the benefits of Helwig Carbon’s Multi-Flex or Tri-Flex brushes over solid brushes?

red top graphic

Figure 3, L to R: Single Wafer Brush, Multi-Flex Brush, Tri-Flex Brush. P equals pressure from spring assembly.

The benefits of Helwig Carbon’s Multi-Flex and Tri-Flex designs are twofold: a multi-wafer brush can ride over uneven comm surfaces better than a solid brush. The resistance of the individually wired wafers into one terminal reduces circulating currents in the brush.

Splitting the DC motor brush into multiple wafers creates more contact points between the brush surface and the comm. Then Newton’s Second Law comes into play, by cutting the brush into smaller wafers, the spring requires less force but is evenly spread on the wafers to maintain better contact points on rough or uneven surfaces. 

The most common use for split brushes? High voltage motors with high electrical stress. Also reversing motors because the brushes adapt quickly to the running surface. It is commonly used with elevators, slip rings, and in heavy industry such as papermills, and railroad.

Advantages of Helwig Carbon’s Patented Red Top Pad red top technology

Vibration or shock can be caused by out-of-round commutators, flat spots, high bars, light electrical loads, or sudden mechanical loading to name a few. 

The Red Top Pad excels when a lot of vibration occurs. It keeps the carbon brush in closer contact with the comm. It also reduces or eliminates brushes chipping and breaking.

The pad is made up of two layers of material. The bottom layer is a resilient, high temperature rubber. The rubber dampens the brush movement. This allows free movement between the brush sections. The top layer is hard fiber or insulator. The hard fiber top protects the rubber from being damage by the spring. It also spreads the spring force evenly to all brush sections. Another benefit, it protects the spring from the current and extends its life.

Are Multi-Flex or Tri-Flex Brushes Right for Your Project?

Helwig Carbon Products, Inc. will help you find the right brushes for your unique project. For more information or to request a quote, contact us.


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