Delta MS300 Fault ovd (Overvoltage During Deceleration)

Getting the "ovd" (Overvoltage During Deceleration) fault on your Delta MS300 VFD? Learn how to fix your ramp-down times, check your braking resistor, and stabilize your drive.

 

If your Delta MS300 drive trips and displays the ovd fault, the DC bus voltage inside the drive has exceeded its safe limit while the motor was decelerating.

This is a classic "energy management" problem. When you command a motor to slow down, the kinetic energy of the rotating mass (the fan, pump, or conveyor) is converted back into electrical energy by the motor, which then acts like a generator. That energy is sent back into the drive. If the drive cannot dissipate that energy quickly enough, the DC bus voltage spikes, triggering the ovd fault.

Why Does ovd Occur?

• Ramp-Down Time Too Short (Pr.01-13): You are trying to stop the load faster than the drive can handle the returning energy.
• High Inertia Load: Large fans or heavy flywheels hold a lot of kinetic energy. Stopping them quickly releases a massive "surge" of power.
• Overhauling Load: Gravity is pulling the load faster than you want to stop, such as on a crane, hoist, or downhill conveyor.
• Braking Resistor Issues: The braking resistor is missing, disconnected, or damaged, meaning there is nowhere for the excess energy to go.

Step-by-Step Troubleshooting Guide

1. Extend the Deceleration Time

The simplest fix is to give the energy more time to dissipate.

• Locate Pr.01-13 (Deceleration Time 1).
• Increase the time value (e.g., if it is set to 5s, try 10s or 15s).
• If the drive stops without faulting after increasing the time, your original setting was simply too aggressive for the load.

2. Check the Braking Resistor

If you need the machine to stop quickly, you cannot just increase the deceleration time. You need a way to burn off that extra energy.

• Verify if a braking resistor is installed and wired correctly to the (+) and (BR) terminals.
• Measure the resistance of your braking resistor with a multimeter (with power OFF) to ensure it hasn't burned out (compare to the manufacturer's recommended Ohmic value).
• If the resistor is physically hot or the wiring is broken, the drive has no way to dissipate the energy.

3. Enable Overvoltage Stall Prevention

The MS300 has a built-in feature to prevent overvoltage trips by automatically extending the deceleration time when it detects the DC bus voltage rising too high.

• Check Pr.06-03 (Overvoltage Stall Prevention). Ensure this feature is enabled if your application permits a slightly longer stop time when the voltage spikes.

4. Check Input Voltage Stability

If your input power is already at the very top end of the drive's tolerance (e.g., a 480V drive running at 500V), the drive has very little "room" before it hits the overvoltage threshold.

• Use a multimeter to measure your incoming AC line voltage (R, S, T terminals). If it is consistently high, you may need a buck-boost transformer.

How to Reset the ovd Fault

1. Wait for the DC bus voltage to drop (the drive screen will typically return to normal).
2. Press the [RESET] key on the keypad.
3. If the drive trips immediately upon the next stop command, do not keep resetting it—this can damage the drive's internal components. Extend your deceleration time or check your braking resistor first.

Maintenance Tip

If you are running a high-inertia load, your braking resistor is working hard every time you stop. Check the resistor for signs of heat discoloration or a "burnt" smell. A resistor that is failing will often work for a while before the resistance changes enough to cause the drive to trip on overvoltage.