Accurate Spring Force Adjustment for Optimal Brush and Holder Performance

The Importance of Proper Spring Force

Spring force has a critical impact on the life and performance of carbon brushes, as it directly influences both mechanical and electrical wear. In many cases, brush performance problems are caused by improper spring force rather than the carbon grade itself. Ignoring spring force can lead to inefficiency at best—or catastrophic equipment failure at worst. By measuring spring force, potential issues can be identified before they cause damage to brushes or motors.

Issues Caused by Improper Spring Force

• Accelerated brush wear

• Threading of brushes, and in severe cases, damage to the contact surface

• Fraying of wires, leading to reduced current capacity or complete wire breakage, which may cause unintended current paths and equipment failure

• High-intensity arcing that can create grooves in the brush track

• Increased metallic dusting, leading to flashover risks

• Commutator problems such as streaking, bar edge burning, and copper drag

Three Steps to Ensure Proper Spring Force

1. Measure Spring Force in lbs.

2. Calculate Spring Pressure

3. If any spring pressures are too light, replace all springs

1. Measuring Spring Force

• Constant Force Springs: Use a hanging balance scale such as the vocarbon DigiScale, which is widely adopted for accurate measurements.

• Helical Coil Springs: Use a precision force gauge to measure compression force.

How to Measure Constant Force Springs with the vocarbon DigiScale

• Power on the scale and ensure a zero reading.

• Attach the correct adapter to the DigiScale depending on spring type.

• Insert or hook the attachment under the spring, wear indicator handle, or torsion finger, depending on configuration.

• Pull the spring back to the approximate new brush position.

• Slowly allow the spring to recoil in the brush travel direction.

• Take the reading at approximately 1 outer diameter (OD) of the spring coil.

• Repeat for accuracy, and check all springs.

⚠️ Common mistake: Measuring force at maximum extension. Always measure at the position corresponding to a new brush in service.

For Helical Coil Springs

• Zero the force gauge.

• Attach the stylus or compression adapter.

• Compress the spring to the equivalent new brush position.

• Slowly release and record the force.

• Repeat for consistency.

2. Determining Proper Spring Pressure

Once force values are recorded, calculate the spring pressure to confirm whether it falls within the recommended range.

• Too little pressure = poor contact, arcing, rapid wear.

• Too much pressure = excessive friction, heat, and wear.

If brushes are beveled, adjust the calculated pressure downward according to the percentage loss chart.

3. Replace All Springs if Force Is Too Light

Even if only some springs measure too light, all springs in the system should be replaced to ensure uniformity and consistency—key factors in extending brush life and maintaining stable equipment performance.

vocarbon DigiScale

To simplify accurate measurement of constant force, torsion, and turbine-style springs, vocarbon DigiScale provides precise, reliable readings that help ensure brush holders operate at peak efficiency and prevent costly maintenance issues.