Blue Sea Systems Battery Isolators & Voltage Sensitive Relays

Blue Sea Systems Automatic Charging Relays & Battery Isolators

When it comes to protecting your onboard electrical system, few decisions matter more than how you manage multiple battery banks. Blue Sea Systems has earned a reputation as one of the most trusted names in marine and specialty vehicle electrical components, and their lineup of battery isolators and voltage sensitive relays reflects decades of engineering focus on reliability, safety, and intelligent automation.

What Are Battery Isolators and Voltage Sensitive Relays?

Battery isolators and Automatic Charging Relays (ACRs) — also called combiners or voltage sensitive relays — are all designed to keep a load from discharging the reserve battery system. That reserve system powers vital loads like engine starting, navigation, and communications. In practice, ACRs are automatic switches that close when the voltage on one battery rises to a level indicating the battery is connected to a charge source and is partially or fully charged, then share that charging current with the other battery until the voltage drops — preventing both banks from being drained when there isn't enough current to charge both simultaneously.

Blue Sea Systems' ACR Product Lines

Blue Sea Systems offers purpose-built ACR solutions scaled to different vessel and vehicle needs. The flagship SI-ACR (Start Isolation Automatic Charging Relay) is one of their most recognized products. The SI-ACR automatically combines batteries during charging and isolates them when discharging and when starting engines. A key feature of this design is its Start Isolation function: Start Isolation protects sensitive electronics by temporarily isolating house loads from the engine circuit during engine cranking, shielding the house circuit from voltage sags and spikes. The SI-ACR provides 120 continuous amps at 12/24V DC, 210A for 2 minutes, and 280A for a 5-second surge. It is ignition-protected for use aboard gasoline-powered boats and features a remote LED output that indicates relay state away from the ACR itself.

For smaller outboard and inboard applications, the compact m-Series Mini ACR (M-ACR) is an excellent fit. The M-ACR is designed to manage charging current from alternators up to 65 amps found on most outboards and many inboard engines. Its compact design allows for three mounting styles: surface, rear, or panel mount, making it highly versatile for tight installations.

For high-current applications, Blue Sea Systems offers the ML-Series ACR. The ML-Series Automatic Charging Relay is engineered specifically for high current applications. This 500-amp magnetic latching (bi-stable) relay automatically combines batteries during charging and isolates them when discharging and when starting the engine.

Why Choose Blue Sea Systems?

Blue Sea Systems develops and manufactures dependable AC and DC electrical products for marine and specialized vehicle applications — designed in the USA and engineered to excel in challenging environments. Industry involvement ensures their products meet ABYC, NMMA, and Coast Guard standards, giving installers and end-users confidence in every installation. The SI-ACR is waterproof rated at IP67 for temporary immersion for 30 minutes, a testament to the durability built into every product. The ACR simplifies system design because chargers and regulators that work with a single battery bank will still work with a multiple battery bank — reducing complexity without sacrificing performance.

Whether you're outfitting a fishing boat, a cruising sailboat, an RV, or a specialty vehicle, Blue Sea Systems' battery isolators and voltage sensitive relays deliver intelligent, automatic battery management you can depend on when it matters most.