Service Questions with Dakota: Understanding Variable Frequency Drives (VFDs)

Variable Frequency Drives (VFDs) are becoming an essential component in modern rock crushing operations, offering improved control, efficiency, and protection for your equipment. By precisely regulating motor speed and torque, VFDs help reduce mechanical stress, optimize energy usage, and adapt crusher performance to varying feed conditions. But beyond their operational benefits, understanding how your VFD functions, and the early signs of potential issues, is key to implementing effective preventative maintenance. A well-monitored VFD can extend the lifespan of your crusher, minimize costly downtime, and ensure consistent production output.

Where are VFDs Usually Found on Rock Crushers

VFDs are used on rock crushers and are usually found controlling the feeder speed to offer adjustability to target a nominal material feeding into the crusher. They can also be found on closed circuit plants controlling the return conveyor. Offering a speed adjustment on a return conveyor via potentiometer (speed pot) allowing you to speed up or slow down the conveyor to ensure proper loading and conveying of the product. VFD controllers are usually found in the main control panel.

VFD Faults and Alarms

A VDF fault is an error detected by the drive that indicates something is preventing it from operating correctly. When a VFD fault occurs, it will have a fault code associated with it to lead you to potential errors. Faults can occur from both mechanical issues and electrical issues but may not always occur together.

During a VFD fault, it may open the circuit and de-energize the motor it relates to. Once you read the fault code, the associated fault with the code can be found in the manufacturer’s operating manual. The VFD operating manuals will offer possible causes of the fault, helping you to find the issue and resolve it quickly.

VFDs can also present alarms, which are different from faults. Depending on the way the VFD is configured, an alarm may have a code associated with it but may not enter a shutdown condition.

An image of the VFD controller where the code will display.

Common VFD Faults

One of the most common VFD faults seen is output overcurrent. This fault is often found associated with either the acceleration time being programmed too short or the feeder could be rubbing the hopper. If a feeder is rubbing against the hopper, it can cause an excessive amp to draw on the feeder motor and in turn enter a fault condition to protect the motor.

An example of a poorly maintained VFD and control panel.

Maintaining Your VFD

When it comes to the maintenance of any VFD, you will first need to lockout/tagout the main control panel and wait at least 5 minutes for the stored electrical energy to dissipate before performing any maintenance task.

Some general maintenance items would include:

• Inspecting the cooling fans to ensure there is no dirt buildup
  • Dirt buildup can damage the cooling system, leading to catastrophic VFD failure.
  • When it comes to the cooling system, there are fan change intervals, and you will need to refer to the specific VFD manufacturers’ guidelines found in their manual.
  • Dirt buildup can be reduced by keeping your control doors shut other than when performing maintenance.
• VFD’s can be damaged by vibration
  • It’s best to remove the main control panel from the plant before you start crushing.

Always refer to your operator’s manual for your equipment’s specific maintenance needs and requirements.

Knowing Who’s Got Your Back

When you understand the role your VFD plays and incorporate it into your preventative maintenance program, you’re not just protecting a single component, you’re safeguarding your entire crushing operation. Regular inspections, performance monitoring, and proper troubleshooting can keep your VFD running at peak efficiency, which in turn helps your crusher perform reliably day after day.

If you have VFD issues that you cannot resolve with your operator’s manual, you can always reach out to Eagle Crusher’s Service Team or their network of authorized dealers.