Applicable Systems
EFC
FEX
FEI
HNC
Symptoms
Speed limit exceeded. The drive has detected that the actual motor speed has exceeded the configured maximum speed limit. The motor is decelerated to a stop.
Possible Causes
- Speed feedback device (encoder) giving erroneous readings
- Speed limit parameter set too low for the application
- Load driving the motor (overhauling load)
- Speed controller gain too high causing oscillation
Troubleshooting Steps
- Step 1: Check encoder mounting and coupling for looseness or damage
Encoder firmly mounted; coupling intact and aligned - Step 2: Verify the maximum speed parameter (P-0-0404) matches the application requirement
Parameter value matches motor nameplate rated speed - Step 3: Inspect for overhauling loads that could drive the motor beyond set speed
No mechanical conditions causing regeneration or overhauling - Step 4: Reduce speed controller gain if oscillation is observed during operation
Smooth speed response without overshoot or oscillation
How to Reset
1) Investigate encoder feedback. 2) Check speed limit parameter. 3) Address mechanical causes. 4) Adjust controller gains if needed. 5) Reset fault after root cause is resolved.
Frequently Asked Questions
- Q: Why does F8079 trigger during deceleration?
During deceleration of high-inertia loads, the motor acts as a generator. If the regenerative energy is not absorbed by the brake resistor, the motor may briefly exceed the speed limit, triggering F8079.
- Q: How do I increase the speed limit?
Adjust parameter P-0-0404 in IndraWorks AS. Ensure the new value is within the motor's rated speed to prevent mechanical damage.
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Source: Rexroth IndraDrive HCS/HMS Fault Code List, Bosch Rexroth AG
Category: PLC & VFD
Published: 2026-10-28
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