Shipboard Emergency Battery Low-Voltage Disconnect (LVD) and Alarm System

Emergency battery banks on ships typically 12 V or 24 V batteries to power critical systems such as GMDSS equipment, emergency lighting, navigation instruments, and engine-starting circuits. A common hazard is deep discharge caused by unattended auxiliary loads. This can permanently degrade battery capacity or prevent the high cranking current needed for engine restart a potentially catastrophic failure at sea. This paper presents the design, implementation, and simulation of a PIC16F84A microcontroller-based Low-Voltage Disconnect (LVD) system for shipboard emergency battery banks, featuring a two-stage alarm and automatic load-shedding function. The microcontroller runs at 4 MHz and was simulated using Proteus Design Suite. An LM358 op-amp, configured as a voltage comparator with a resistive divider reference, continuously monitors battery terminal voltage and signals the microcontroller via input pin RA0 when a threshold is crossed. Protection operates in two stages. At 11.5 V, a buzzer and warning LED pulse at 1 Hz via output pin RB1 to alert the crew. If voltage drops further to 10.8 V, the firmware disconnects non-essential loads such as pumps and fans by de-energizing a relay via output pin, preserving residual energy. Loads are only reconnected once voltage recovers to 12.6 V, indicating active alternator charging, preventing repetitive cycling and ensuring stable operation. The system was validated through simulated discharge cycles in Proteus simulation, achieving good accuracy in threshold detection, alarm activation, and relay switching. Results confirm the system as a reliable, low-cost embedded solution for shipboard emergency power protection in demanding marine environments.