SV0307 APC Alarm: Battery Low 1 fault in Fanuc drive

SV0307 APC Alarm: Battery Low 1 fault in Fanuc drive

Description

SV0307 is the single most important "Pre-Alarm" in the Fanuc ecosystem. It indicates that the backup battery voltage for the Absolute Pulse Coder (APC) has dropped below the warning threshold (typically around 4.5V for a 6V system). Unlike SV0306 (which means the data is already lost), SV0307 is a grace period. The position data is still safe, but the battery is nearing end-of-life. Ignoring this alarm will inevitably lead to SV0300/SV0306 and the loss of the machine's Home Position.

Cause

• Natural Discharge: Batteries (Alkaline or Lithium) have a lifespan of 1-3 years depending on how often the machine is powered off. The encoder draws power from the battery only when the main power is cut.
• Bad Connection: Corrosion on the battery box terminals in the electrical cabinet (for Alpha-i) or on the drive faceplate (older Alpha).
• High Drain: A defect in the feedback cable insulation causing a slight current leak to ground, draining the battery faster than normal.

Solution

CRITICAL: Do not power off the machine to change batteries.

1. Keep Power ON: Engage the E-Stop, but leave the Main Control Power ON. This ensures the encoder is powered by the drive, so removing the battery won't lose the position data.
2. Locate Battery: It is either a yellow case on the front of the amplifier (CX5X) or a separate black box via a cable.
3. Replace and Cycle: Remove old batteries, install new ones. You must usually power cycle the machine (Turn off, wait 10s, Turn on) to clear the SV0307 message from the screen.