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Frequency inverter overloaded |
Motor and current exceed the rated load |
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ERR09 – Frequency Inverter Overloaded
What this means
ERR09 indicates that the VFD has detected a sustained overload condition.
In simple terms, the motor is being asked to deliver more torque or power than it is rated for, for longer than the VFD considers safe.
This is different from a momentary spike. ERR09 happens when the load remains too high long enough that the VFD determines continued operation could cause damage.
Why This Happens
The VFD continuously monitors motor current.
If current stays above the motor or VFD’s rated limit, the drive will shut down to protect both itself and the spindle.
This most often occurs during cutting, not at idle.
Most Common Causes We See
1. Cutting load exceeds spindle capability (most common)
Examples include:
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Large diameter tooling on smaller spindles
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Excessive depth of cut
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Feed rates too aggressive for the tool size
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Hard materials with conservative RPMs
A common example:
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A 1.5kW spindle being used with a 1/2” endmill at aggressive feeds
The spindle may run, but the VFD sees sustained overload and faults.
2. Locked or partially stalled spindle
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Chip packing
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Tool wedged in material
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Mechanical binding in the spindle or collet
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Tool collision
If the spindle cannot rotate freely under load, current spikes rapidly.
3. Acceleration or deceleration too aggressive
While more often associated with ERR02 or ERR03, aggressive ramps can still contribute to sustained overload if the spindle never reaches stable operating speed before cutting begins.
4. Incorrect spindle or VFD sizing
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Spindle is undersized for the application
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VFD rating too close to the spindle’s limit
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Heavy use in materials better suited for higher-power systems
What ERR09 Is Not
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Not a wiring issue
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Not a sensor problem
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Not EMI related
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Not typically a controller or software issue
This is a mechanical load vs available power issue.
What to Check First
Step 1: Reduce cutting load
Start with the simplest fix:
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Reduce depth of cut
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Reduce feed rate
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Increase spindle RPM (within tool limits)
Often, no parameter changes are required once load is reasonable.
Step 2: Inspect for binding
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Remove the tool and verify the spindle spins freely
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Check for chip buildup in the collet
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Ensure the collet and nut are clean and seated correctly
Step 3: Verify tool choice
Confirm the tool is appropriate for:
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Material
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Spindle power
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Machine rigidity
Smaller tools or reduced engagement often solve ERR09 immediately.
Step 4: Consider spindle sizing
If ERR09 occurs repeatedly during normal work:
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The spindle may be undersized for the application
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Upgrading spindle power may be the correct long-term solution
This is common when moving from router-based workflows to spindle-based expectations without adjusting strategy.
When a Larger Spindle or VFD Is Required
ERR09 is often the sign that:
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The machine is being pushed beyond hobby-level loads
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The workload has grown into light production or harder materials
In these cases, a higher-power spindle or system upgrade is the correct solution, not tuning around the limitation.
Summary
ERR09 means the spindle system is being overloaded beyond its rated capability.
Most commonly caused by:
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Aggressive cutting parameters
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Tooling that exceeds spindle power
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Mechanical binding or stall conditions
Start by reducing cutting load.
If the issue persists under reasonable conditions, the application may require a higher-power spindle system.
