| Over-voltage at constant speed |
When the frequency inverter runs at constant speed, DC voltage of the main circuit exceeds this set value. Detected DC over-voltage value: Level S1 : 240V Level S2/T2 : 400V Level T4 : 800V |
|
ERR04 – Over-Voltage at Constant Speed
What this means
ERR04 occurs when the VFD detects that the DC bus voltage has risen above a safe limit while the spindle is running at a steady speed.
This is not a startup or braking error. It happens while the spindle is already at RPM and cutting or free-running.
In simple terms, the VFD is seeing too much voltage on its internal DC bus, so it shuts down to protect itself.
Detected Over-Voltage Thresholds
The exact voltage depends on the VFD class:
-
Level S1 (110 V systems): ~240 V
-
Level S2 / T2 (220 V systems): ~400 V
-
Level T4 (380–480 V systems): ~800 V
Most Common Causes (Real-World)
1. Input voltage is too high
This is the most straightforward cause.
Examples:
-
A 110 V VFD fed from a circuit that regularly exceeds spec
-
A 220 V circuit that runs hot when lightly loaded
-
Incorrect wiring to a higher-voltage supply
While uncommon, some locations do see elevated line voltage, especially when loads are light.
2. Regenerative energy during cutting
Even at constant speed, a spindle can regenerate energy back into the VFD if:
-
The tool is being mechanically driven by the material
-
The spindle is being “pushed” rather than pulling the cut
-
The axis motion or cutting forces momentarily drive the spindle faster than commanded
This regenerated energy raises the DC bus voltage and can trigger ERR04.
3. External force driving the spindle
This is rare but important to understand.
Examples:
-
Material forces forcing the spindle to overspeed
-
Mechanical drag from belts, gearboxes, or external systems
-
Improper toolpaths that cause the cutter to be driven by motion rather than motor torque
4. Electrical noise or unstable supply
Voltage spikes or transient conditions can briefly push the DC bus over its limit, especially if:
-
Wiring is marginal
-
Grounding is poor
-
The electrical environment is noisy
What to Do First (Recommended Order)
Step 1: Verify incoming voltage
If you have a multimeter:
-
Measure line voltage at the outlet with the spindle running
-
Confirm it is within normal range for your VFD type
If the input voltage is consistently high, the VFD is doing its job by protecting itself.
Step 2: Review cutting strategy
-
Avoid toolpaths that “drive” the cutter
-
Reduce feed rate or depth of cut slightly
-
Avoid conditions where the material is effectively forcing the spindle to spin
This is especially relevant in harder materials.
Step 3: Check mechanical drag
-
Ensure the spindle spins freely by hand (when powered off)
-
Check for anything that could mechanically force rotation
Step 4: Inspect grounding and wiring
-
Verify proper grounding of the VFD and spindle
-
Check for loose or questionable power connections
Important Notes
-
ERR04 is a protective fault, not a failure
-
It does not indicate a bad spindle or VFD
-
Over-voltage can occur even on a “correct” circuit if cutting forces are feeding energy back into the drive
Summary
ERR04 means the VFD is seeing excessive DC bus voltage while running at speed.
In most cases:
-
Confirm input voltage is within spec
-
Adjust cutting strategy to reduce regenerative effects
-
Ensure wiring and grounding are solid
If ERR04 persists after these checks, please contact support with details about your spindle voltage, RPM, material, and cutting parameters.
