Blue Sea 500A HD-Series Heavy Duty 4 Position (OFF/1/2/1+2) Battery Selector Switch w/ AFD

Confident control of dual battery banks for marine and RV power

Managing multiple battery banks on a boat, 4WD or caravan often means balancing two priorities: keeping critical loads powered and protecting your charging system. The Blue Sea HD-Series 4-position battery selector switch with AFD is built for high-current installations where dependable changeover and battery isolation matter. It gives you clear, manual control to run from Battery 1, Battery 2, both combined, or OFF—helping you reduce the risk of accidental battery drain and simplify troubleshooting on-board electrical systems.

For Australian conditions and demanding marine environments, this selector switch is designed to suit heavy-duty cable runs and high-load circuits. The HD construction, robust terminals and practical mounting options make it a strong fit for new installs and upgrades where reliability and serviceability are priorities.

Why AFD matters when switching under charge

When an engine is running, abruptly disconnecting the alternator can contribute to voltage spikes that may stress sensitive electronics. This model includes AFD (Alternator Field Disconnect), supporting safer switching practices for systems that require alternator field management. Combined with a make-before-break contact design, it allows you to transition between battery banks without the momentary loss of power that can reset devices such as radios, navigation equipment and onboard control modules.

Built for marine safety and installation flexibility

On petrol-powered vessels, component safety ratings matter. This switch is ignition protected, making it suitable for installation in engine spaces where ignition protection is required. The enclosure is also designed for practical installs, offering surface or rear panel mounting to suit dashboards, switch panels and electrical lockers. With clearance and terminal design intended for large battery cables, it supports tidy, professional cable routing in tight compartments.

Ideal applications

This heavy duty battery isolator/selector is commonly used in:

• Boats with house and start battery banks
• 4WD touring setups with dual batteries and accessory loads
• Caravans and camper trailers needing selectable battery sources
• Workboats and commercial vehicles where downtime and power interruptions are costly

Key features

• 4-position selector for OFF / Battery 1 / Battery 2 / Combined operation
• AFD support to assist alternator field disconnect requirements
• Make-before-break switching to help minimise power interruption during changeover
• Ignition protected design for use on petrol-powered boats where applicable
• Flexible mounting options for cleaner installs and easier servicing
• Heavy duty terminals designed to suit large battery cable connections

Practical benefits for owners and installers

Compared with lighter-duty battery switches, the HD-Series format is aimed at high-current systems where heat, vibration and frequent use can expose weak points. By giving you a clear operating mode and robust changeover, it can help reduce nuisance shutdowns, simplify battery management, and support safer isolation during maintenance. It’s a straightforward upgrade for anyone looking to improve confidence in their marine electrical system, dual battery setup, or auxiliary power distribution.

If you’re building or refreshing a system, pair this switch with correctly sized cables, appropriate circuit protection and a wiring layout that matches your alternator/charging method for best results.