Newmar 1-3-120A Isolator 1AIT 3BATT 120AMP

Why Your RV or Boat Needs a Reliable Battery Isolator

Imagine heading out on a long road trip or anchoring in a quiet cove, only to worry about your house batteries draining your starter battery overnight. That's where a heavy-duty battery isolator like this one steps in, ensuring each battery stays charged and isolated exactly when you need it. Designed for demanding environments, it smartly manages power from a single alternator to up to three batteries, prioritizing the engine start battery while feeding auxiliary banks only after it's fully topped up.

This isolator excels in real-world scenarios where power reliability is non-negotiable—think extended off-grid camping, commercial fishing trips, or overland adventures. Its robust build handles the vibrations, moisture, and heat of mobile setups without flinching, keeping your electrical system humming smoothly.

How the 1-to-3 Battery Isolation Works

At its core, this isolator uses high-quality diodes to create one-way power flow. When the alternator kicks in, it first charges the primary (starting) battery. Once that reaches a sufficient voltage threshold—typically around 13.2-13.5V—the isolator bridges the circuit, allowing charge to flow to your secondary batteries (like house or accessory banks). When the engine stops, the diodes block any backflow, preventing your charged auxiliaries from powering the starter or vice versa.

This automatic, need-based charging prevents overcharging and extends battery life, especially with mixed battery types like AGM, flooded lead-acid, or lithium setups in 12-48V negative ground systems. No more manual switches or constant monitoring—just set it and forget it.

Standout Features for Tough Conditions

• Heavy-Duty Build: Rust-proof anodized aluminum heat sink dissipates heat efficiently, paired with stainless steel hardware that laughs off corrosion from salt air or road spray.
• Versatile Voltage Handling: Seamlessly supports systems from 12V up to 48V, ideal for everything from standard RVs to high-voltage commercial rigs.
• Terminal Protection: Snap-on covers shield connections from shorts, dirt, and accidental contact—crucial in tight engine bays.
• Optimal Cooling: Mount it vertically for best airflow; expect just a 5°C rise at full load, keeping diodes cool under continuous duty.

Performance That Delivers in the Field

Engineered for reliability, this isolator maintains low voltage drop—0.7V at half load, 0.9V at full—minimizing power loss during charging. It thrives from -40°C freezing mornings to +80°C engine bay scorchers, with a continuous duty cycle up to 50°C (derating linearly to 70% at 80°C). Pair it with 120A alternators for balanced charging without strain.

Installation Tips for Seamless Setup

Mount in a well-ventilated spot near your alternator output, using the included hardware. Connect the alternator post to the common terminal, starting battery to output 1, and auxiliaries to outputs 2 and 3. Use appropriately sized cables (at least 2/0 AWG for 120A) fused close to the batteries. Always disconnect batteries before wiring to avoid sparks. Pro tip: Add a temperature sensor if your setup runs hot for even smarter monitoring.

A quick multimeter check post-install—confirm no continuity between outputs with engine off, and charging voltage across all with engine running—verifies it's good to go.

Perfect for RV, Marine, and Off-Grid Power Systems

RVers love it for separating chassis and coach batteries during boondocking. Boaters rely on it to keep thruster and electronics banks isolated from the house bank. Truckers and solar enthusiasts use it in custom dual-alternator or hybrid setups, ensuring endless runtime without cross-discharge headaches. Its conservative diode ratings mean it outlasts cheaper alternatives in vibration-heavy applications.

Maintenance and Troubleshooting Advice

Keep it simple: Inspect terminals yearly for corrosion, tighten connections, and ensure vents stay clear. If charging seems sluggish, check diodes for heat buildup or verify alternator output. Overheating? Confirm vertical mounting and adequate airflow. This unit's serviceable design means diode replacement is straightforward if needed after years of abuse.