Blue Sea 24V 500A ML-ACR Automatic Charging Relay

Heavy-Duty 24V Dual Battery Management for High-Output Systems

Managing large battery banks in commercial vehicles, marine vessels, and heavy-duty off-grid setups requires a switching solution that can handle extreme electrical loads without overheating or failing. This 24V DC 500A Automatic Charging Relay (ACR) uses advanced bi-stable magnetic latching technology to automatically combine battery banks during charging and isolate them when discharging or cranking the engine. Unlike conventional solenoids that rely on a continuous coil draw to stay engaged, this unit requires ultra-low current to maintain its state, eliminating heat build-up and preventing parasitic drain on your batteries.

Engineered for High-Amperage Reliability and Electronics Protection

Standard relays often struggle to support modern high-output alternators and large inverter banks, leading to voltage drop or welded contacts. Rated for 500A continuous current, this automatic charging relay effortlessly manages heavy charge currents across dual battery banks. Its dual-sensing capability monitors voltage on both the start and house battery banks, closing the circuit whenever a charging source is applied to either side.

To reduce the risk of voltage spikes or sags damaging critical onboard systems, the relay features configurable Start Isolation (SI) and Engine Isolation (EI). Start Isolation temporarily disconnects house loads from the engine circuit during cranking to protect sensitive navigation and communication electronics. Engine Isolation separates two engines while both are running, safeguarding engine control units and maximising alternator efficiency. In the event of a flat starter battery, the system also allows for the parallel connection of battery banks for emergency start assist.

Key Features and Technical Advantages

• Bi-Stable Magnetic Latching: Draws less than 40mA to monitor terminal voltage in the ON or OFF states, only drawing moderate current for a fraction of a second when changing state.
• Dual-Sensing Intelligence: Automatically detects charging voltages from alternators, solar charge controllers, or shore power chargers connected to either battery bank.
• High-Conductivity Connections: Equipped with 3/8"-16 (Approx. M10) tin-plated copper studs that suit heavy-duty lugs (up to 2 x 4/0 AWG or approx. 95mm2) to ensure maximum conductivity and corrosion resistance.
• Multi-Terminal Capacity: Generous 7/8" (22mm) stud length easily accommodates multiple heavy-gauge cable terminals required in complex power distribution setups.
• Live Load Switching: Constructed with robust silver alloy contacts designed to provide high reliability and longevity when switching live loads under heavy demand.
• Remote Status Monitoring: Integrated LED output wire allows for remote indication of when batteries are combined, isolated, in voltage lockout, or in Start/Engine isolation modes.
• Clean Installation: Includes tinned copper control circuit wires for corrosion resistance and integrated label recesses for clear circuit identification.

Important Configuration Note

Please note that this specific model (BS-7621B) does not feature a manual override control knob on the unit itself, nor is it supplied with the remote switch. For applications requiring manual override and emergency parallel control from the dash, the compatible ML-Series Remote Control Contura Switch (PN 2146) is available separately.

Upgrade Your 24V Power Distribution

Ensure your auxiliary and starting battery banks are charged efficiently and isolated safely. Integrate the 24V 500A ML-ACR into your marine, commercial, or industrial electrical system today for dependable, automated battery management.