Flow Ctrl Tech Engineering

PLC Memory Loss After Power Outages: Diagnosing Dead Batteries & Capacitor Depletion

What to do when an older PLC (Allen-Bradley SLC 500, Siemens S7-300, Mitsubishi FX) loses its program after a weekend power outage: battery replacement protocols and EEPROM backups.

  • Older PLCs store program logic in volatile SRAM maintained by a 3.0V or 3.6V lithium thionyl chloride battery.
  • If power is cut when the battery is dead, the memory loses electrical charge, wiping the entire program.
  • Always replace PLC batteries while the control cabinet remains POWERED ON to prevent memory dump.

Flow Ctrl Tech Engineering: Turnkey industrial automation, PLC programming, SCADA development, HMI, fieldbuses, and IIoT architectures. Contact our engineering center at [email protected] or phone +91 91110 91005.