| Over-voltage at acceleration | When the frequency inverter runs at constant speed, DC voltage of the main circuit exceeds this set value. The detected over-voltage value is the same as above |
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ERR05 – Over-Voltage During Acceleration
What this means
ERR05 occurs when the VFD detects that the DC bus voltage has risen above a safe limit while the spindle is accelerating.
This may sound counterintuitive, since acceleration is usually associated with high current, not high voltage, but under certain conditions the motor can feed energy back into the VFD even during ramp-up. When the VFD cannot absorb or dissipate that energy fast enough, it trips ERR05 to protect itself.
Detected Over-Voltage Thresholds
The over-voltage thresholds are the same as ERR04:
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Level S1 (110 V systems): ~240 V
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Level S2 / T2 (220 V systems): ~400 V
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Level T4 (380–480 V systems): ~800 V
Most Common Causes (Real-World)
1. Input voltage is already high
If the incoming line voltage is near the upper limit of the VFD’s operating range, even a small regenerative event during acceleration can push the DC bus over the threshold.
This is more likely to happen:
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On lightly loaded circuits
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In locations with elevated utility voltage
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When the spindle accelerates rapidly
2. Acceleration and deceleration profiles fighting each other
This is surprisingly common.
Examples:
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Very short deceleration time combined with frequent start/stop cycles
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The controller issuing stop/start commands in quick succession
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Spindle being commanded to accelerate while still mechanically slowing down
In these cases, regenerative energy from deceleration can overlap with acceleration.
3. External forces acting on the spindle
Even during acceleration, the spindle can be mechanically driven by:
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Cutting forces
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Axis motion pushing the cutter
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Heavy material engagement
If the tool is being “pushed” by the material while the VFD is trying to accelerate, excess voltage can build on the DC bus.
4. Lack of braking capability
Without a brake resistor or braking unit, the VFD has limited ability to dissipate excess energy generated during transient events like rapid accel/decel.
This is more noticeable with:
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Higher spindle RPMs
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Larger spindles
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Aggressive motion profiles
What to Do First (Recommended Order)
Step 1: Verify incoming voltage
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Measure line voltage at the outlet while the spindle is running
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Confirm it is within normal range for your system
If input voltage is already high, ERR05 may occur even under moderate conditions.
Step 2: Increase deceleration time
Although ERR05 occurs during acceleration, deceleration time is often the real culprit.
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Increase the VFD deceleration time
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Avoid rapid stop/start cycles
⚠️ For Masso users:
Make sure spindle deceleration time in Masso matches the VFD’s deceleration setting.
Step 3: Soften acceleration
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Increase acceleration time slightly
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Avoid commanding the spindle to ramp up aggressively while under load
Step 4: Reduce cutting load at startup
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Avoid starting the spindle already engaged in material
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Use ramped entries instead of straight plunges
Step 5: Advanced solution – braking resistor
If ERR05 persists in high-speed or high-inertia setups:
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Installing a braking resistor allows excess energy to be safely dissipated
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Typically unnecessary for hobby or light-production use
Important Notes
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ERR05 is a protective fault, not a failure
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It does not indicate a bad spindle or VFD
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This error often appears in systems with aggressive accel/decel tuning rather than electrical faults
Summary
ERR05 means the VFD is seeing excessive DC bus voltage during acceleration, usually due to regenerative energy or timing conflicts between acceleration and deceleration.
In most cases:
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Increase deceleration time
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Avoid rapid stop/start cycles
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Soften acceleration profiles
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Verify incoming voltage
If ERR05 continues after these adjustments, contact support with details about your spindle voltage, accel/decel settings, RPM, and cutting strategy.
