Brush Holders & Spring Assemblies: Research
Industry-Leading Brush Holder & Spring Assembly Research & Guidance
Since 1928, Helwig Carbon has been driving the brush holder industry forward. Many of our innovations have become industry standards because they improve performance and increase brush life.
Learn about our groundbreaking research and utilize our resources to ensure proper holder installation, maintenance, and spring force to eliminate many common brush system problems such as brush sparking and commutator problems like streaking, threading, grooving, bar edge burning, and copper drag.
Technical Papers
Brush Holders and the Performance of Carbon Brushes
Brush Holder Coatings for Resistance to Acid Fume Exposure
Effects of Spring Force on Carbon Brush Function
Brushes, Sparking, and Machine Maintenance
Carbon Brush Pocket Guide (Includes Holder Information)
Product Literature
Brush Holders
Spring Assemblies
Helwig DigiScale
Teflon™ Coated Holders
GE Single Pocket Holder Upgrades
Additional Education, Installation, and Troubleshooting FAQ
Proper spring force and holder replacement, care, and use are critical to maximizing the service life of carbon brush systems. Our detailed FAQs provide guidance and solutions for common issues, including:
- Problems caused by weak spring pressure
- Problems caused by how holders are used and maintained
These FAQs offer practical, technician-focused recommendations designed to improve uptime and reduce maintenance costs.
Ensuring Proper Spring Force
Why is Spring Force Important?
Spring force can have a dramatic effect on the life and performance of carbon brushes because it has a strong influence on mechanical and electrical wear. Many brush performance issues are resolved by the spring rather than the carbon grade, and the consequences of ignoring spring force can be inefficient at best and catastrophic at worst. Measuring spring force allows you to detect issues before any damage is done to the brushes or motor.
What are the Signs of Spring Force Problems?
Issues with Spring Force Can Cause:
- Rapid brush wear.
- Threading of brushes and, in extreme conditions, even the contact surface.
- Fraying of wires resulting in loss of current carrying capacity. If not addressed, the wire can break, causing current to follow unintended paths leading to other issues or failure.
- High-intensity arcing that could cause grooves in the brush track.
- Increased dusting with metallic dust from the contact surface that is more conductive and can cause flashover.
- Other commutator issues including streaking, bar edge burning, and copper drag.
What are the three steps to ensure proper spring force
- Measure Spring Force in lbs.
- Calculate Spring Pressure.
- If any spring pressures are too light, replace all springs.
Measuring Spring Force in lbs.
The first step is to get the right kind of scale depending on the type of spring you are measuring.
- For constant force springs, hanging balance scales, like the Helwig DigiScale , are most popular.
- For helical coil springs, use a force gauge.
To Measure Constant Force Springs with the Helwig DigiScale
Before starting, it is important to know the approximate position of the coil for new and used brush.
- Turn ON the scale and ensure zero reading.
- Connect appropriate attachment to bottom loop of DigiScale, based on type of spring.
- Insert roller attachment inside constant force spring or under the red handle of Helwig wear indicator if applicable, slide strap around torsion spring finger, or hook turbine-style attachment under lip of Helwig wear indicator.
- Pull spring back to approximate new brush location (Figure A).
- SLOWLY let the spring recoil in the direction of brush travel.
- Observe spring force and take reading at approximately 1 outer diameter (OD) of the spring coil (Figure B).
- Repeat and record.
- Be sure to check ALL springs.
A common mistake is pulling the spring to its maximum extension and measuring the force. Instead, pull the spring to the position it would be in with a new brush in the holder. Then, let the spring move downward in the direction of brush travel. Stop when only one coil’s outer diameter (OD) of the spring is left extended, and then measure the force. Measuring the force when the spring is fully extended or when it is under one coil’s OD can lead to significantly different results.
The finger style spring in the old ratchet style holder should be adjusted to position in use as values will change.
To Measure Helical Coil Spring:
These springs are not constant force, and their force constantly varies based on compression length throughout the life of the brush.
Instructions:
- Turn ON the force gauge and ensure zero reading.
- Connect appropriate attachment or stylus.
- Push or compress spring to approx. new brush position.
- SLOWLY release to free length.
- Repeat and record.
Calculate Spring Pressure
Now that you have your spring force measurement (see “Measuring Spring Force in lbs.”), it is time to do a calculation to find whether the spring pressure is appropriate (too low is especially damaging but too high is also a problem).
Step 1: Complete the following equation
Step 2 (only necessary if your brush has bevels on the top and/or bottom, i.e. if your brush is cut at an angle other than 90 degrees on top and/or bottom):
If your brush has bevels, you need to reduce the spring pressure found in Step 1 by the percentage listed in the “loss in downward force” column in the following graphic. If you have both top and bottom bevels, add the two percentages in the “loss in downward force” column together and reduce by the combined total percentage.
If Any Spring Pressures Are Too Light, Replace All Springs.
Customers can always contact us to verify PSI calculations and provide comments and recommendations based on their application.
Best Practices for Replacing Springs
If springs are to be replaced, replace all springs at the same time to avoid selective action as old springs could be weak compared to new springs. Selective Action is unequal distribution of electrical current among brushes, which can result in uneven brush wear, sparking, damage, and/or reduced efficiency).
Dos and Don’ts of Brush Holder Replacement, Care, and Use
Do - Check Spacing
The brush holders should be spaced no more than 0.125” (3.175 mm) from the commutator surface to ensure that the brushes are properly supported on the commutator.
Helwig can provide Helwig Commutator Install Pad spacers to assist in brush holder installation. Brush holder spacing around the commutator should be checked to ensure that there are an equal number of bars between each brush.
Do - Check Pockets
The pockets in the holders should be checked to make sure that brushes move freely. Holders that have been overheated may become distorted and cause the brushes to jam in the holders.
Do - Replace Conventional Springs with Constant Force Springs
Conventional spring finger-type holders should be replaced with constant force spring holders to ensure that the pressure applied is more uniform through the usable length of the brushes. Using constant force holders will dramatically improve brush life and help eliminate selective action (Selective Action is unequal distribution of electrical current among brushes, which can result in uneven brush wear, sparking, damage, and/or reduced efficiency).
Don’t Modify Brushes to Fit a Different Holder
Don’t Mix Holder Types
Don’t mix different holder types. Most likely the spring force at the brush face will be different causing selective action and misleading results.
Don’t Hammer Brushes Out of Box
Don’t hammer the brushes out of the box. The holder squareness could be compromised for the next set of brushes. If you absolutely must hammer out metal brushes that are stuck in holder, check for squareness of holders after removing the brushes.