| Over-Current at deceleration | When the frequency inverter decelerates, output current exceeds over-current |
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ERR03 – Over-Current During Deceleration
What this means
ERR03 occurs when the VFD detects excessive current while the spindle is slowing down. This happens during deceleration, not while accelerating or cutting.
When the spindle decelerates, the motor effectively becomes a generator. If the energy being fed back into the VFD cannot be safely dissipated, current rises and the VFD trips ERR03 to protect itself.
Most Common Causes (Real-World)
1. Deceleration time is too aggressive
This is the most common cause of ERR03.
If the spindle is commanded to slow down too quickly, the regenerative energy generated during braking has nowhere to go fast enough, causing a current spike.
This is especially noticeable with:
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Larger or heavier spindles
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Higher RPM operation
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Frequent start/stop cycles
2. Controller and VFD deceleration times do not match
On controllers like Masso, the controller expects the spindle to slow down within a defined time window.
If:
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The VFD deceleration time is short, but
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The controller is commanding rapid stop events
the mismatch can cause over-current conditions during braking.
3. Sudden load changes during stop
Examples:
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Emergency stops
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Abrupt feed hold or program stop
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Spindle stopping while still engaged in material
These can force rapid deceleration and trip ERR03.
4. Electrical supply limitations
Although less common, low or unstable input voltage can:
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Reduce the VFD’s ability to absorb regenerative energy
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Contribute to current spikes during deceleration
5. Lack of braking capability
Without a brake resistor or braking unit, the VFD has limited ability to dissipate energy during fast deceleration.
This becomes more noticeable with:
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Higher spindle RPMs
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Larger spindles
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Frequent tool changes or stops
What to Do First (Recommended Order)
Step 1: Increase deceleration time
This resolves the majority of ERR03 cases.
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Increase the VFD deceleration time
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Avoid commanding the spindle to stop abruptly
⚠️ For Masso users:
Make sure the spindle deceleration time in Masso matches the VFD’s deceleration time.
Step 2: Avoid abrupt stops
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Use controlled stop commands instead of emergency stops when possible
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Avoid stopping the spindle while fully engaged in material
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Allow the spindle to coast down naturally when appropriate
Step 3: Check wiring and grounding
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Inspect motor cable connections
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Confirm proper grounding
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Check for pinched or damaged motor cables
Step 4: Consider a braking resistor (advanced)
If ERR03 persists in high-speed or high-inertia setups:
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Adding a braking resistor allows excess energy to be safely dissipated
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This is typically only needed for aggressive deceleration profiles or industrial-duty use
Most hobby and light-production setups do not require a brake resistor.
Important Notes
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ERR03 is a protective fault, not a failure
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It does not indicate a damaged spindle or VFD
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Repeated ERR03 events mean the spindle is being stopped too aggressively
Summary
ERR03 means the spindle is being slowed down too quickly.
In almost all cases:
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Increase deceleration time
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Match controller and VFD deceleration settings
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Avoid abrupt stop commands
If ERR03 continues after increasing deceleration time, contact support with details about your spindle RPM, deceleration settings, and how the spindle is being stopped.
