ATV320 OBF fault during deceleration, what to check?
I'm getting an OBF (DC bus overvoltage) fault on my Schneider ATV320 drive. It only trips when the machine decelerates or stops. What should I check first?
An OBF fault on a Schneider Altivar ATV320 drive indicates a DC bus overvoltage. This typically occurs during deceleration, with an overhauling load, or if the supply voltage is too high. Since the fault only appears during stops or speed reductions, the most likely causes are related to braking or deceleration settings.
Likely causes and checks
1Deceleration time is too short
- Points to it
- The drive is tripping because the deceleration is too sudden for the inertia of the load, causing regenerative voltage to build up on the DC bus.
- Check
- Increase the [Deceleration] DEC time parameter in the drive settings and observe if the trips stop.
2Braking resistor is missing or undersized
- Points to it
- For fast stops of heavy loads or loads that drive the motor, a braking resistor is often necessary to dissipate excess regenerative energy. If one is not installed or is incorrectly sized, the DC bus voltage can rise too high.
- Check
- Determine if a braking resistor is required for your application based on Schneider's data and install one if necessary.
3[Dec.Ramp Adapt] BRA function is off
- Points to it
- The BRA function helps manage deceleration ramps, but it is often set to 'No' when a braking resistor is not fitted or if brake logic is assigned. If compatible with your application, activating it can help prevent overvoltage.
- Check
- Check if the [Dec.Ramp Adapt] BRA function is active. If not, activate it, ensuring it is compatible with your application (e.g., not used with positioning on a ramp or a braking resistor).
4Supply voltage is too high
- Points to it
- While less likely if the fault only occurs during deceleration, a high supply voltage can contribute to the DC bus overvoltage. If the supply voltage is consistently high, it can push the DC bus voltage over the limit during regenerative events.
- Check
- Measure the supply voltage at the drive input terminals and compare it against the drive's rated input voltage.
Next check: First, try increasing the [Deceleration] DEC time parameter. If the fault persists, investigate the need for a braking resistor or check the status of the [Dec.Ramp Adapt] BRA function.
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