ACSecondarySystems

ACAlternating current Secondary System

The boat'sSecond secondary electrical system is AC. In Europe it will be designed for 230-VACVolt alternating current single phase. In North America it will be either 120-VAC single phase or 240-VAC double phase. 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. In the boat, the green AC ground wire is connected to the Common Grounding Point – the white ground wire is left floating. 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.

Alternator

Each engine (if there is more than one) will have a high-capacity dual-output alternator and multistage regulator, with separate charging circuits for the starter and house batteries. A backup manual switch and regulator are provided. The regulator must be suited to the type of battery: Flooded cells require an equalization charge after the main charge; whereas gel and AGMAbsorption glass mat cells usually do not. Typical vendors are: Ample Power, Balmar, Hehr Power Systems, JackRabbit Marine and Sea Air Land Technologies, Inc.

If the boat will be unattended for periods at least one engine must autostart on a schedule to keep the batteries charged.

Trickle Charge System

In case the main charging system fails while the boat is unattended, a DCDirect current trickle-charge system can be provided. Trickle charging is also a good idea because there are usually parasitic loads on a battery system that will slowly discharge it. Deep discharge batteries do not want to be trickle charged at a high rate: 3%percent is recommended. Thus a boat with a house bank of 1000 AHAmpere-hours (A*H) requires a trickle charge of 30 AH.

Wind turbines and solar panels are ideal for a trickle-charge system; although they are not suited as a main power source. Unfortunately, as a main power source, each of them has a significant performance drawback in the context of a small- to medium-size boat. They simply need too much real estate.

Inverter/Charger

A combination inverter/charger is attached to the house bank for generating AC 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 AH
• Output voltage
• Output current regulation
• Safety factor of 30%

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 HzHertz, SI unit of frequency, 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 shore power
• Install a voltage- and frequency-converting inverter/charger