Electric Boat 20-24S 96V 400A Contactor BMS JNFN ANT 24ZMB Marine Pack

An electric boat places demands on a battery system that a road vehicle never does: long periods at a modest cruising current, followed by short, violent demands from a bow thruster or a docking manoeuvre. The JNFN ANT 24ZMB was engineered around that duty profile, with a 96 V platform, 20 to 24 series cells, 400 A continuous and 800 A for five seconds, and a contactor-based switching stage rather than a MOSFET bank — because a 400 A marine bus is not a place for semiconductor losses to accumulate in a sealed locker.

The board carries a pre-charge path that limits inrush every time the contactors close, isolation resistance monitoring that flags a degrading insulation path before it becomes a fault, and a master-slave link so two packs can share the propulsion load without one dumping current into the other. In a hull, the difference between a good installation and a marginal one is usually the alarm path: the 24ZMB drives a helm annunciator and a contactor trip input, so an over-temperature event is visible at the console rather than buried in a phone application.

• 400 A Contactor Stage with Pre-Charge: Two heavy-duty contactors replace the MOSFET bank, and a resistor-limited pre-charge sequence brings the inverter capacitor bank up before the main contactor closes. Connector and contactor life extends dramatically compared with a hard-closing design.
• 800 A Five-Second Surge Capacity: Thruster and docking loads are short and brutal. The current path, busbar cross-section and thermal model are dimensioned for that surge without derating the continuous rating.
• Isolation Resistance Monitoring: The board measures the insulation path between the high-voltage bus and the hull ground reference, raising a warning at a configurable threshold. On a saltwater installation this is the single most useful early indicator of a chafed cable or a damp junction box.
• Dual Pack Master-Slave: Two packs can be tied over a dedicated link with current sharing weighted by state of charge and internal resistance, so a bank can be expanded later without replacing the first pack.
• IP65 Sealed Enclosure with Salt-Mist Coating: Gasketed lid, coated control section and tinned copper terminals address the condensation and chloride exposure that a bilge compartment delivers year round.
• Helm Alarm and Emergency Stop Input: Two dry contacts and a dedicated input for the emergency stop circuit let the management board participate in the vessel safety chain instead of running as a separate system.
• Event Log with Fault Snapshot: The last two hundred events store a snapshot of cell voltages, temperature and current at the moment of the fault, which shortens diagnosis after an unexpected shutdown at sea.

Electric day boats, inland cruisers and small workboats running 96 V propulsion are the primary fit, particularly retrofits where a diesel engine has been replaced and the existing locker must hold the pack. The contactor architecture also suits trolling motor banks and research vessels that need a clean high-current disconnect.

Because the board can be operated as a master with a second pack as slave, it fits builders who start with a single pack and add capacity after the first season, and it fits yards that standardise on one board across several hull sizes.

The unit ships with the board, contactor harness, pre-charge resistor assembly, four NTC probes, a CAN service lead and a wiring diagram. Each board is load tested with a simulated thruster profile before packing, and the contactor timing is verified against the pre-charge sequence.

Ordering: prototypes from one unit, volume programmes from twenty. Harness length, contactor coil voltage and alarm logic can be specified against the vessel drawing. A 24-month limited warranty applies to the management board.