IntelliTec Battery Isolation Relay

IntelliTec Battery Isolation Relays: Built for Dual-Battery Systems

In a coach or boat with separate starting and house batteries, the isolation relay decides how and when power flows between them. IntelliTec has spent more than 40 years building electrical controls and monitoring systems for recreational vehicles, and its isolator relays reflect that background. They are designed to keep a chassis battery ready to start the engine while still letting the auxiliary bank charge whenever the alternator is working.

Isolator Relays: 100A and 200A Big Boy

IntelliTec's core isolator relays are used to separate two battery systems. According to the manufacturer, the design lets the relay operate with almost no voltage across its contacts, which avoids the voltage drop associated with diode-style isolators. Two current ratings are offered:

• 100A Isolator Relay (77-90000 series): Handles up to 100 amps continuous duty and is intended for most common gasoline engines, with both 12V and 24V versions.
• 200A "Big Boy" Isolator Relay (77-90006 series): Carries 200 amps continuous with short-term surge capability of 1200 amps for 30 seconds, making it suited to heavier-duty applications and the large starter currents of big diesel engines. It is also used as a replacement part in many motorhomes and marine electrical systems.

Both relays are ignition protected, so they can be mounted conveniently near the battery. They can be switched manually from a dash-mounted switch or paired with IntelliTec's isolator controls for fully automatic operation. Rated operating temperatures run from -40 to 85 degrees C, which suits engine-compartment and under-coach installations.

Relay Delay and Bi-Directional Technology

What sets IntelliTec apart in this category is the control logic built around the relay. The Isolator Relay Delay/E waits until the alternator voltage rises above roughly 13.3 volts for about 12 seconds before closing the relay and connecting the auxiliary battery. That lets the engine charge the main battery first and warm up before a deeply discharged house battery loads the alternator, and it also allows use of self-exciting alternators. When the ignition is switched off, the relay opens immediately.

The Bi-Directional Isolator Relay Delay (B.I.R.D.) goes a step further. Rather than charging the house battery only from the engine's alternator, it charges both batteries when either one is receiving a charge, such as from shore power, solar or a generator-fed converter. If neither battery is charging, the two remain fully isolated. The controller also senses heavy loads on either battery to help prevent the wrong battery from being inadvertently drawn down. IntelliTec offers B.I.R.D. versions for both gas and diesel platforms, and an integrated RV-C version that monitors two battery sources and links them automatically when charging is available and needed.

What to Consider When Choosing

• Current rating: Match the relay to the alternator output and starter demands. The 200A Big Boy suits larger diesel coaches.
• System voltage: Many models are available in 12V and 24V.
• Charging source: If you charge from shore power or solar as well as the alternator, a bi-directional design is worth considering.
• Hardware: Some part numbers ship with mounting hardware and others do not, so check the listing details.

For a broader look at the manufacturer, visit the IntelliTec brand page. To compare relays from other manufacturers, see the full Battery Isolation Relay category.