Blue Sea 12V 500A ML-ACR Automatic Charging Relay

Heavy-Duty 500A Dual Battery Management for High-Output Systems

Managing large, multi-bank 12V DC electrical systems requires switching hardware capable of handling extreme electrical loads without generating excess heat or draining your power reserves. The Blue Sea Systems 500A Automatic Charging Relay (ACR) is engineered to automatically combine battery banks during charging and isolate them when discharging or cranking the engine. Built with a massive 500A continuous rating, this magnetic latching relay seamlessly supports high-output alternators and large inverter/charger setups found in commercial marine vessels, heavy-duty off-grid RVs, and specialised service vehicles.

Ultra-Low Power Draw with Magnetic Latching Technology

Standard solenoids and conventional relays require a constant electrical draw to keep their contacts closed, which can gradually deplete your batteries and generate unwanted thermal build-up. This unit utilises advanced bi-stable magnetic latching technology, meaning it only draws a moderate current for a fraction of a second while changing states. Whether in the open or closed position, the relay draws less than 40mA solely to monitor terminal voltage. This efficiency prevents parasitic battery drain and significantly reduces heat generation during prolonged charging cycles.

Intelligent Dual Sensing and System Protection

Designed for versatile integration, the relay features dual-sensing capability, allowing it to detect a charging source on either battery bank. Whether your system is receiving power from the main engine alternator on the starter battery or a solar charge controller and shore power charger connected to the house bank, the relay will automatically close to charge both banks simultaneously. Once charging ceases and voltage drops, it isolates the banks to ensure your starting battery is never discharged by auxiliary house loads.

To protect expensive onboard electronics, the unit can be configured for both Start Isolation (SI) and Engine Isolation (EI):

• Start Isolation (SI): Temporarily isolates sensitive house loads from the engine circuit during engine cranking, preventing voltage sags and spikes from resetting or damaging navigation equipment,fridges, or inverters.
• Engine Isolation (EI): Isolates two engines while both are running to safeguard engine electronics and maximise alternator output across the system.
• Emergency Parallel Function: Allows you to manually combine battery banks from the helm or dashboard for emergency engine starting if your primary starter battery fails (requires remote switch).

Marine-Grade Construction for Harsh Environments

Every component of this charging relay is built to withstand corrosive marine and high-vibration automotive environments. It features 3/8"-16 (Approx. M10) tin-plated copper studs that provide maximum conductivity and corrosion resistance. With a generous stud length, the terminals easily accept multiple heavy-duty cable lugs up to 4/0 AWG (Approx. 95mm2) x 2 to meet full current ratings. Internally, silver alloy contacts deliver exceptional reliability for switching live loads up to 100,000 cycles, while pre-wired 20 AWG (Approx. 0.5mm2) tinned control wires simplify installation.

Key Features

• 500A continuous current rating supports high-output alternators and heavy-duty 12V DC systems
• Bi-stable magnetic latching design requires minimal current (<40mA) to maintain its state
• Dual voltage sensing monitors and distributes charge from either battery bank
• 3/8"-16 (Approx. M10) tin-plated copper studs accommodate heavy-duty 4/0 AWG (Approx. 95mm2) cabling
• Configurable Start Isolation and Engine Isolation protect sensitive marine and RV electronics
• Dedicated LED output wires allow for remote status indication of combined, isolated, or lockout states
• Integrated label recesses for clean, professional circuit identification

Important Exclusion Note

Please note that this model (BS-7620B) does not feature a manual override knob on the relay body itself, and the ML-Series Remote Control Contura Switch (PN 2146) is not included. The remote switch is available as a separate item if you require manual remote control or emergency parallel switching from your dashboard.

Upgrade Your Dual Battery System

Protect your starting power and streamline your auxiliary charging setup. Add the 500A Automatic Charging Relay to your system today for reliable, automated battery management in demanding marine and off-grid applications.