Marine DC Power Systems
Salt, dampness and vibration make a boat the harshest home an electrical system will ever have. A reliable marine setup keeps the engine-start battery isolated from the house loads, charges the house bank from the alternator, solar and shore power, and protects the people and the hull with the right isolation and circuit protection. We supply inverters, deep-cycle batteries, DC-DC chargers, isolators and monitoring for launches, yachts and commercial vessels, and the NOMAD NPS inverter range is designed for mobile, marine and fixed installs.
Two things protect the boat and everyone on it. Battery isolation keeps the house loads from ever flattening the battery you need to start the engine, and a voltage-sensing relay or a battery isolator does that automatically with the VSR being the better choice, as it doesn't rely on a human operator remembering to operate it. Galvanic isolation protects against the stray-current corrosion that shore power can drive through the hull. Boat electrical installations in New Zealand are covered by AS/NZS 3004.2:2014, and for shock protection it requires Type A RCDs with a residual operating current of 30mA or less.
Charging is where a boat differs from a van. A large alternator plus a big shore charger can push a bank hard, so the maximum output of all chargers that will operate at a single time must be within your battery bank's maximum charge rate limitation. And the cable runs to big momentary loads like a windlass have to be heavy and short, a 12V windlass can pull ~85A running and ~140A surge. We spec these components to be compatible with each other, which is what gives you the reliability for many years.
Tell us the vessel, the loads you run overnight at anchor and how you charge, and we'll design the bank, charging and protection as one system. More answers in our Marine FAQ.
Common questions
How do I stop my house loads flattening my engine-start battery?
Keep them on separate batteries with isolation between them. The engine-start battery is reserved for cranking, while a deep-cycle house bank runs your lights, fridge and electronics and is charged through a DC-DC charger. A voltage-sensing relay or a battery isolator makes the split automatic, so an evening at anchor never leaves you unable to start the engine, with the VSR being the better choice, as it does not rely on a human operator remembering to turn it off and on.
Which rules apply to the wiring on my boat?
AS/NZS 3004.2:2014, Electrical installations, Part 2: Boat installations, for recreational boats up to 50 m. For ships of 24 metres or less, Maritime NZ rules require the electrical system to comply with the applicable parts of it as well. In practice that means the shore-supply connection done properly, shock protection, and earth-leakage protection on the AC side. If you're not sure which parts touch your boat, ask us.
Do I need an RCD on my boat?
Yes on the AC side, especially where shore power comes aboard. AS/NZS 3004.2 requires RCDs installed for personal protection to be Type A with a residual operating current of 30mA or less. That's the device that stops a fault in a shore lead or an appliance becoming a shock through a wet deck.
AGM or lithium for a boat?
AGM is sealed, tolerant of the marine environment and doesn't mind being tucked in a locker, which is why it's the dependable choice for most boats. Lithium saves weight and gives more usable capacity, but it's dearer, hates being charged cold and needs a charger and BMS matched to it. For a boat that isn't weight-critical, lead-carbon usually wins on total cost, safety and compatibility.
What size inverter do I need for a boat?
Size it from what you actually run at once, fridge, lights, electronics and any 230V appliance, using the largest simultaneous load plus surge headroom from the sum of all those loads together. Keep it on the isolated house bank, never the start battery, and size the cable for the current on the 12V or 24V side, which is far higher than the 230V figure suggests, for example 1000W at 12V is ~83A.