THE FAILURE PATH
Plan for the instant the bank disappears.
If a battery management system opens its contactor while an alternator is producing current, the sudden loss of load can create a damaging voltage transient. A design needs an engineered way to manage that event. A DC-DC charger is useful for setting a charge-current ceiling and separating chemistries, but it is not a universal alternator load-dump protector.
- CHARGE LIMIT
- Wakespeed regulator strategy or a suitably rated Victron DC-DC charger
- BATTERY FEED
- Class-T fuse selected for fault current and coordination, with high interrupt capacity
- STANDARD
- Design and installation reviewed against applicable ABYC E-11 and E-13 requirements
Trace every charging path.
List each alternator and charger, then draw where current flows with the engine running, the BMS closed, and the BMS open. Decide what sustains the alternator field or absorbs its output during a disconnect. Confirm regulator support for the alternator and battery arrangement; do not assume a generic “lithium mode” covers it.
- Set a conservative charge-current ceiling based on alternator capability, pulley ratio, cooling, and duty cycle.
- Keep the start battery and alternator path stable when the house BMS disconnects.
- Place the Class-T fuse close to the lithium source and verify its interrupt rating against available fault current.
- Size conductors for the actual route, temperature, bundle, terminal, and voltage-drop target.
- Document service isolation, emergency combining, and charging behavior after a BMS fault.
ABYC standards are updated and their application depends on the vessel and installation. We use the current applicable edition during a project and verify product instructions instead of treating a single diagram as a certification.
ASK ABOUT A CHARGE-SYSTEM REVIEW