Many CNC accessories require 24V power, and it’s common to assume the VFD can supply it.
In reality, the VFD’s 24V output is signal-grade power, not a general-purpose power supply.
This article explains what that means, what you can safely power, and how to avoid ERR36 and related failures.
What the VFD’s 24V Output Is Designed For
The 24V output on the VFD is intended for:
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Logic signals
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Control inputs
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Status outputs
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Low-current signaling
It is not designed to power loads.
Think of it as a reference voltage, not a power rail.
What You Can Power Safely
The VFD’s 24V output is suitable for:
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Input signals to a CNC controller
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Relay coils designed for very low current
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Logic-level inputs on external devices
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Indicator LEDs with proper current limiting
These devices draw milliamps, not amps.
What You Should Never Power from the VFD
Do not power the following from the VFD’s 24V output:
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Solenoids
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Valves
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Pneumatic actuators
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Motors
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Pumps
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Fans
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Lights
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Any inductive or high-current device
Doing so can:
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Overload the internal 24V supply
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Trigger ERR36
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Damage the VFD’s control circuitry
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Cause intermittent faults that are difficult to diagnose
Why Solenoids Are a Common Problem
Solenoids are especially dangerous to power from the VFD because:
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They draw high inrush current
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They generate voltage spikes when switched
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They load the supply continuously while energized
Even small solenoids can exceed what the VFD’s 24V rail can safely provide.
What ERR36 Means
ERR36 – Power Fault
This error indicates:
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The external 24V supply is overloaded, or
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There is a short circuit on the 24V output, or
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The VFD detected an unsafe condition on its control power rail
This is a protective shutdown, not a defect.
The Correct Way to Power Accessories
For anything that consumes real power:
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Use a dedicated external power supply
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Match voltage and current to the device requirements
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Share ground reference only if needed
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Use the VFD or controller outputs only as control signals
This keeps signal and power isolated, which improves reliability.
How to Size an External Power Supply
When selecting a supply:
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Add up the current draw of all devices
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Include startup or inrush current
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Add at least 30% headroom
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Use a regulated supply
Undersized supplies cause voltage sag and unpredictable behavior.
Why Fusing Matters
Always fuse external power supplies appropriately.
Fuses:
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Protect wiring
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Prevent cascading failures
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Make faults obvious instead of destructive
A fuse blowing is far better than a damaged VFD.
Common Symptoms of 24V Power Issues
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ERR36 appearing randomly
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VFD resets when accessories activate
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Faults only when solenoids fire
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Works until multiple devices turn on
These almost always point to misuse of the 24V output.
Key Takeaway
The VFD’s 24V output is for signals, not power.
If a device does real work, it needs its own power supply.
Respecting this boundary prevents ERR36 and protects your VFD long-term.
