powerflex 700 overvoltage fault troubleshooting

Staring at Fault 5 on your PowerFlex 700? This Overvoltage guide explains why the DC bus spikes, how to check braking resistors, and the parameters to adjust.

If you are standing in front of an Allen-Bradley PowerFlex 700 and the HIM module is flashing Fault 5 (Overvoltage), your drive is protecting itself from a surge of electrical energy.

In simple terms, the "DC Bus"—the drive's internal reservoir of power—has become over-pressurized. For a standard 480V drive, this usually means the voltage has spiked above 810V DC. To prevent the capacitors from failing, the drive trips. Let’s look at how to find the source of that extra energy.

Common Causes of Overvoltage in PowerFlex 700

When a PowerFlex 700 trips on Fault 5, it’s usually due to one of these three scenarios:

• Regeneration (Deceleration): This is the #1 cause. When you try to stop a heavy load (like a fan or a centrifuge) too fast, the motor turns into a generator and sends electricity back into the drive.
• High Line Voltage: The incoming AC power from the factory is consistently too high or has a temporary surge.
• Failed Braking Hardware: The internal braking transistor or the external braking resistor has failed, leaving the energy with nowhere to go.
• Surge from Other Equipment: Large motors or capacitors starting nearby on the same power grid.

Step-by-Step Troubleshooting for Fault 5

1. Check the DC Bus Voltage (Parameter 012)

Before you start changing wires, look at what the drive is actually seeing.

• On the HIM (keypad), navigate to Parameter 012 [DC Bus Volts].
• In standby, it should be about 1.41 times your incoming AC voltage (e.g., ~650V to 680V for a 480V line).
• Watch this parameter while the motor is decelerating. If it climbs rapidly to 800V+, your Decel Time is too short.

2. Lengthen the Deceleration Time (Parameter 142)

If the fault only happens when the motor is stopping:

• Go to Parameter 142 [Decel Time 1].
• Increase the time (e.g., from 10 seconds to 20 or 30 seconds). A slower stop allows the energy to dissipate naturally without overwhelming the DC bus.

3. Inspect the Braking Resistor

Does your application require a fast stop? If so, you likely have a large cage-like resistor mounted on top of or near the cabinet.

• Check the resistor for signs of heat (discoloration).
• Measure the resistance with a multimeter (Power OFF and Discharged!). Ensure it matches the Ohms value required by the drive manual.
• If the resistor is open-circuit (reads infinite Ohms), it’s dead. The drive has nowhere to dump the regen energy, causing Fault 5.

4. Use the "Bus Regulator" Feature

The PowerFlex 700 has a "smart" feature that can automatically slow down the deceleration to prevent an overvoltage trip.

• Check Parameter 161 [Bus Reg Mode A].
• Ensure this is set to "Both" or "Adjust Freq". This allows the drive to automatically extend the ramp-up/down if the DC bus gets too high.

The "Input Surge" Fix

If the fault happens randomly while the motor is just "cruising" at a steady speed, the problem is likely your incoming power quality.
Installing an Isolation Transformer or an AC Line Reactor on the input side of the drive can help "choke" those voltage spikes before they hit the drive's internal bus.

How to Reset the Overvoltage Fault

1. Clear any mechanical jams and ensure the braking resistor is cool.
2. Press the Stop/Reset button on the HIM keypad.
3. If the fault happens the moment you apply power (before you even hit start), you may have an internal hardware failure in the drive's voltage sensing circuit.

Summary

The PowerFlex 700 Fault 5 is a common "Regen" issue. If you are stopping a heavy load, you either need a slower Decel Time (P142) or a Braking Resistor to handle the heat. Check your DC Bus (P012) first—it’s the fastest way to see if the problem is coming from the motor or the power grid.