Inovance Drive Err12 Input Phase Loss

Is your Inovance VFD showing Error Code Err12? This guide explains how to troubleshoot Input Phase Loss, check external circuitry, and identify internal hardware failures.

 

If you are using an Inovance Variable Frequency Drive (VFD), such as the popular MD500 or MD200 series, seeing Err12 on the keypad is a signal that your power supply is unstable. This specific code stands for Input Phase Loss.

When Err12 occurs, the drive has detected that one of the three incoming AC power phases (R, S, or T) is missing or significantly weak. If the drive were to continue running under a heavy load with a missing phase, the internal rectifier bridge would overheat and likely explode. To prevent this, the drive trips for safety. Here is how to diagnose and fix it.

Common Causes of Err12

Err12 can be caused by problems outside the drive (your facility's power) or internal component failures. The troubleshooting process should always start from the outside and move inward.

Step-by-Step Troubleshooting Guide

1. Check the External Power Supply (Abnormal Input)

The most frequent culprit is a physical break in the power line before it even reaches the drive.

• Measure Voltage: Use a multimeter set to AC Voltage. Measure between the input terminals: R-S, S-T, and R-T. All three readings should be balanced (e.g., 400V or 480V depending on your grid).
• Check Upstream Fuses: A single blown fuse in your main disconnect will cause an input phase loss.
• Inspect the Contactor: If you use an input contactor to feed the drive, ensure the contacts are not pitted or burnt. A "dirty" contact can drop a phase under load.
• Check Terminals: Ensure the screws on terminals R, S, and T are tightened to the correct torque. Loose wires create high resistance and voltage drops.

2. Inspect the Drive Board

If your multimeter shows perfect, balanced voltage at the drive terminals, but Err12 remains, the drive’s internal sensing circuit may be failing.

• The Drive Board (or power board) contains the circuitry that monitors the DC bus ripple. When a phase is missing, the DC bus "bounces" (high ripple), which triggers the error.
• Check for loose internal ribbon cables between the power module and the control board. Vibration can sometimes loosen these connections.

3. Lightning Protection Board Failure

Inovance drives are equipped with a lightning protection/surge board. This board is often the first point of contact for the incoming power.

• If your facility recently experienced a lightning strike, a power surge, or a high-voltage spike, the components on this board (MOV or capacitors) may have sacrificed themselves to protect the rest of the drive.
• Remedy: If this board is burnt or damaged, it will misreport the phase status. This is a hardware issue that requires the board to be repaired or replaced by a professional.

4. Control Board Malfunction

The "brain" of the drive processes the signals from the sensing boards. If the control board's Analog-to-Digital (A/D) converter is faulty, it may see a "ghost" phase loss where none exists.

• The "Last Resort": If you have verified the input power is perfect and the internal connections are tight, try restoring the drive to factory defaults. Occasionally, a software glitch in the memory can cause false trips.
• Hardware Failure: If a factory reset does not clear the Err12 after a power cycle, the control board or sensing circuit is permanently damaged.

Summary Checklist for Err12

Checkpoint	Action Required
Line Voltage	Measure R-S-T terminals; ensure phases are balanced.
Fuses/Breakers	Check for any tripped or blown upstream protection.
Internal Cables	Verify ribbon cables between boards are secure.
Hardware Repair	If power is good but Err12 stays, replace the surge or control board.

How to Reset the Fault

1. Resolve the external power issue (replace fuse or tighten wire).
2. Press the [STOP/RESET] key on the Inovance keypad.
3. If the fault triggers immediately upon a "Run" command, double-check your DC bus voltage using a multimeter on the (+, -) terminals. A very low DC bus indicates a failed rectifier.