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How Do I Troubleshoot a PowerFlex Drive That Will Not Start?

This article provides a basic troubleshooting process for a PowerFlex drive that will not start. It covers drive status, faults, start commands, speed references, permissives, safety circuits, and external control signals to help determine whether the issue is with the drive or the control system.

 Start With the Drive Status

Before changing parameters or wiring, determine the current status of the drive.

Check the HIM or drive software and determine:

  • Is the drive powered up?
  • Is the drive Ready?
  • Is the drive Faulted?
  • Is the drive indicating a Stop or Inhibit condition?
  • Does the drive show that it is receiving a Run or Start command?

If the drive is faulted, record the fault code and description before clearing the fault.

Check for Faults

If there is an active fault, troubleshoot the fault before investigating the start command.

Also review the fault history, especially if the problem is intermittent.

Record:

  • Fault code
  • Fault description
  • When the fault occurs
  • Whether it occurs during starting, running, or stopping
  • Any recent changes to the machine or drive

Do not repeatedly clear a fault without determining what is causing it.

Determine Where the Start Command Comes From

Identify how the drive is supposed to receive its Start or Run command.

Common sources include:

  • HIM/keypad
  • Digital inputs
  • EtherNet/IP
  • DeviceNet
  • PLC or other network controller

Verify that the drive is configured to accept commands from the intended source.

A drive can be operating correctly but fail to start because it is waiting for a command from a different source.

Determine Where the Speed Reference Comes From

The Start Command and Speed Reference are separate functions.

A drive may receive a valid Start command but still have a speed reference of 0 Hz.

Common speed-reference sources include:

  • HIM/keypad
  • Analog input
  • Preset speed
  • EtherNet/IP
  • DeviceNet
  • PLC/network reference

Verify that the drive is receiving the expected speed command.

Check Digital Inputs

If the drive is controlled from the terminal block, verify the status of the digital inputs.

Check that the drive is actually seeing the required inputs change state when the machine commands it to run.

Depending on the application, these inputs may include:

  • Start
  • Stop
  • Run Forward
  • Run Reverse
  • Enable
  • Jog
  • Speed selection
  • Other machine permissives

Checking the drive's digital input status is often more useful than measuring the signal at the terminal alone. It confirms that the drive itself recognizes the input.

Check Stop and Enable Conditions

A valid Start command does not necessarily mean the drive is permitted to run.

Check for any Stop, Enable, or Inhibit conditions that may prevent operation.

The drive may be receiving a Start command while another input or control source is simultaneously commanding it to stop.

When troubleshooting, determine both:

Is the drive being told to run?

and

Is anything telling the drive that it cannot run?

Check the Safety Circuit

If the drive is equipped with Safe Torque Off (STO) or another safety option, verify that the safety circuit is satisfied.

An open safety circuit can prevent the drive from producing torque even when the normal Start command is present.

If the safety circuit is not satisfied, troubleshoot the machine safety circuit rather than changing drive programming to work around it.

Never bypass or defeat a safety circuit for troubleshooting.

Check Network Control

If the drive is controlled by a PLC or industrial network, verify that communication is healthy.

Check:

  • Is the drive communicating with the controller?
  • Is the PLC actually sending a Run command?
  • Is the commanded speed greater than zero?
  • Are there network faults?
  • Are the drive's command and reference sources configured correctly?
  • Is machine logic preventing the Run command?

A drive that will not start under PLC control does not necessarily have a drive problem.

The issue may be in the PLC logic, communications, machine permissives, or another part of the control system.

Try Local Control When Appropriate

When it is safe and appropriate for the application, operating the drive locally can help isolate the problem.

For example, if the drive:

Runs correctly from the HIM but will not run from the machine controls

the drive and motor are likely capable of operating, and troubleshooting should shift toward the external command source, I/O, communications, or PLC logic.

If the drive will not run locally either, continue investigating drive status, programming, safety conditions, motor configuration, and faults.

Always make sure the machine can be operated safely before attempting local operation.

Did Something Change?

If the equipment previously operated correctly, determine what changed before the problem began.

Examples include:

  • Drive replacement
  • Motor replacement
  • Parameter changes
  • PLC programming changes
  • Network changes
  • Maintenance work
  • Control wiring changes
  • Installation of an option module
  • Machine safety changes
  • Power outage or electrical event

This can significantly narrow down the cause of the problem.

Basic Troubleshooting Flow

A useful troubleshooting sequence is:

1. Is the drive powered and communicating?
↓
2. Is the drive Ready or Faulted?
↓
3. Are all Stop, Enable, and Safety conditions satisfied?
↓
4. Is the drive receiving the Start/Run command?
↓
5. Is the drive receiving a valid speed reference?
↓
6. Does the drive run under local control when safe to test?
↓
7. If local operation works, troubleshoot the external control system.

Following this sequence helps avoid changing drive parameters before determining what is actually preventing operation.

Key Takeaway

When a PowerFlex drive will not start, first determine whether the drive cannot run or simply has not been given everything it needs to run.

Check the problem in this order:

Drive Status → Faults/Inhibits → Safety/Enable → Start Command → Speed Reference → External Controls

Avoid changing parameters until the source of the problem has been identified. Random parameter changes can make troubleshooting more difficult and introduce additional problems.