Blue Sea 12/24VDC 65A m-Series Automatic Charging Relay

Automated Dual-Bank Battery Management for Marine and Mobile Applications

Managing multiple battery banks in a marine or off-grid electrical system requires reliable, automated control to prevent dead starting batteries and protect onboard electronics. The m-Series Automatic Charging Relay (M-ACR) is engineered to seamlessly manage charging current from alternators rated up to 65A, which are commonly found on most outboard motors and many compact inboard engines. Operating across both 12V DC and 24V DC systems, this voltage sensitive relay automatically combines batteries during charging and isolates them when discharging, eliminating the need for manual switch intervention.

Intelligent Dual-Sensing and Start Isolation Technology

Unlike standard single-sense isolators that only monitor the starting battery, the M-ACR features dual-sensing capability. It actively monitors voltage levels across both battery banks. Whether your charging source is the main engine alternator routed to the cranking battery, or a shore power charger and solar regulator connected directly to the house bank, the relay detects the rising voltage and closes to charge both banks simultaneously. Once the charging source is removed and voltage drops, it automatically opens to isolate the banks, ensuring your starting battery remains fully charged and isolated from house loads.

To safeguard modern marine electronics, the unit incorporates Start Isolation (SI) functionality. During engine cranking, heavy current draw can cause significant voltage sags and subsequent spikes that reset or damage sensitive navigation equipment, fish finders, and communication gear. When connected to the ignition switch, the Start Isolation feature temporarily isolates the house loads from the engine circuit during cranking, providing clean, uninterrupted power to your cabin and helm electronics.

Key Features and Technical Advantages

• Dual-Battery Sensing: Monitors voltage on both battery banks to facilitate bi-directional charging from alternators, solar, or shore power.
• Start Isolation Protection: Temporarily disconnects house circuits during engine cranking to shield sensitive electronics from damaging voltage fluctuations.
• Under-Voltage Lockout: Prevents the relay from combining if one battery is severely depleted or malfunctioning, reducing the risk of overloading the charging system or dumping charge into a dead cell.
• Flexible Mounting Options: Compact footprint supports surface, rear, or panel mounting configurations to fit tight marine engine bays and electrical lockers.
• Integrated Status LED: Provides immediate visual confirmation of relay combine Status, open state, or lockout conditions.
• Protective Insulating Cover: Features a pull-off, snap-on cover that shields terminals from accidental short circuits while allowing straightforward cable access.
• Robust Terminal Hardware: Equipped with 1/4"-20 (M6) stud terminals that accept heavy-duty cables up to 1/0 AWG (approx. 50mm2), alongside a 1/4" x 0.032" (approx. 6.3mm x 0.8mm) male quick-connect terminal for the ground connection.

Risk Reduction in Harsh Environments

Inferior charging relays often suffer from contact chatter, high parasitic draw, and thermal failure when subjected to continuous alternator output. The M-ACR mitigates these risks with engineered delay timers and a high-voltage lockout threshold that prevents overcharging. Its low operating current draw in the open state ensures minimal parasitic drain on your batteries during storage. To achieve the full 65A continuous and 115A intermittent ratings safely, installation with at least 6 AWG (approx. 13.5mm2) cable is recommended.

Upgrade Your Dual Battery System

Ensure dependable engine starts and protect your valuable onboard electronics on every trip. Add the m-Series Automatic Charging Relay to your marine or mobile power setup today for automated, worry-free battery management.