ACSecondarySystems

ACAlternating current Secondary System

The boat'sSecond secondary electrical system is AC. The exact specification will be driven by the standards in the part of the world where you mainly operate and will source shore power and various appliances and tools. As much as possible minimize the use of AC, in part to reduce the size and cost of the inverter. Any large motors should be DCDirect current.

If you intend to operate globally you will need a voltage- and frequency-converting inverter. In North America electrical standards are 120-VACVolt alternating current 60 HzHertz, SI unit of frequency single phase or 240-VAC 60 Hz double phase. Elsewhere most countries use the European standard of 230-VAC 50 HZ single phase. The frequency difference means motors will run at different speeds.

For global operations the best choice is to default to the European standard of 230 VAC for the boat's internal AC system.

AAmpere (amp), SI unit of electrical current manual switch in the Pilothouse selects "boat power" (inverter) or "shore power" as the power source, with automatic detection of the voltage and frequency of the shore power. The shore side ground should not be connected to the boat's Common Grounding Point – an isolation transformer should keep the two sides apart. AC wiring should be stranded copper, not solid or tinned, to better resist breaking from vibration. All AC light bulbs adjacent to metal, especially in the engine room, are protected as shock hazards. All AC outlets are equipped with ground-fault-circuit-interruption (GFCIGround fault circuit interrupter) circuit breakers.

Inverter/Charger

A combination inverter/charger is attached to the house bank for generating AC from the batteries when offshore, and/or charging the batteries from shore power when in port. Points to consider in an inverter/charger are:

• Peak power output
• Peak charging current
• Continuous charging current
• Battery size AHAmpere-hours (A*H)
• Output voltage
• Output current regulation
• Safety factor of 30%percent
• Frequency conversion

Shore Power

Operating on shore power almost anywhere in the world requires voltage conversion and frequency conversion.

AC voltage conversion is readily done with a transformer having multiple taps that can step-up or step-down a range of voltages. For a specific input voltage, the corresponding tap is selected manually or automatically. The transformer then delivers the correct output voltage.

This fits well with best practices. Although there are several ways of bringing aboard AC, the best way is an ABYCAmerican Boat and Yacht Council-approved isolation transformer between the shore power inlet and the breaker panel. This avoids polarization issues and doesn’t require a reverse-polarity indicator. AC shore power is brought aboard through an electrically isolated marine-rated receptacle in the side of the Deckhouse. A multitap isolation transformer meets this specification.

The incoming AC is grounded (green wire) at the shore end but is not grounded to the hull. Frequency conversion may or may not be critical. Most modern electronic equipment is designed for 50-60 Hz, and should operate without difficulty (check the label).

The problem areas are timing devices that reference the AC, microwave ovens and AC motors, including those in domestic refrigerators. AC motors designed for 60 Hz will run more slowly on 50 Hz, and tend to overheat. To avoid this, you can:

• Use DC motors only
• Put AC motors on the inverter power only, not on direct shore power
• Install a voltage- and frequency-converting inverter/charger