240 Volt AC System

In my last post about the electrical systems on Iron lady, I covered the 24 Volt DC system. This time around, I will cover the 240 Volt AC system, but as you will see shortly, it integrates in many important ways with the 24 Volt DC system.

First, the consumers. All the high amp draw devices on the boat are 240 Volt. The 4 air conditioners and their pumps, the speed oven, the induction cook top, the reverse osmosis watermaker, the washer and dryer, and two electric heating elements for domestic hot water (more about their multiple functions when we cover domestic hot water and heating the boat in a future post). Their are also 240 VOlt AC outlets in the galley and in the engine room – we use these to power 240 Volt appliances like our toaster, coffee grinder, bread maker and shop vac.

The primary source for 240 Volt AC power are three Victron inverters located in the basement. They operate in a number of different ways.

They can pass thru 240 Volt AC power when we are connected to shorepower, they can pass thru power from the 11.6 KW diesel genset when it is on, and they can produce 240 Volt AC power from the 24 Volt DC system.

The selector switch at the top left of the panel is used to select shorepower or the genset when they are available. When they are not, the switch is left in the center off position and the inverters can provide 240 V AC power from the alternators (if the main engine is running) and battery bank.

First, a few comments about the shorepower system. There are connection points in the forepeak and on the aft deck and we can use either depending on which is most convenient to the shorepower connection point dockside. All of the shorepower is routed thru an isolation transformer in the basement to protect the boat from stray currents. The transformer also provides a second function. When only 30 amp 120 Volt service is available in a US marina, the transformer steps it up to 240 Volts AC as that is all we bring aboard the boat.

When 240 volt shorepower (or 30 amp 120 V service stepped up to 240 volts) is present, the inverters match the incoming frequency and voltage and pass it thru to the 240 V AC buss that powers the consumers. An important point here – all of the 240 Volt AC consumers can run on either 50 cycle of 60 cycle power. This permits us to plug in to shorepower just about anywhere in world without worrying about whether it is 50 cycle (most of the world) or 60 cycle (primarily US). The inverters will happily match either and the consumers are just as happy either way. This is an enormous advantage as it eliminates the need to convert power depending on where you are in the world. All we have to have is the right plug to match the dockside connection and we already have a number of pigtail adapters made up for the common ones.

When the genset is on, it provides 11.6 KW of 240 Volt AC, 60 cycle power to the inverters pass thru to the 240 VAC buss.

Another important feature of the inverters when 240 VAC is present is that they can “support” or supplement available power. The inverters are controlled by the larger black panel on the top right of the electrical panel. In the picture, you can see the number 30 set on the display. We can tell the inverters how much incoming power is available for them to pass thru to the buss. In this case, it is 30 amps – pretty typical here in New Zealand. If the consumers are drawing more then this amount, the inverters supplement the shorepower with up to 7.5 KW (approximately 30 amps) of additional power by drawing it from the battery bank. This saves us from having to constantly monitor usage to stay within available limits when shorepower is limited. The inverters will also support the genset, but with 50 amps available when the genset is running, this would be pretty unusual. The meter to the left of the inverter panel displays current amperage that we are drawing at 240 VAC so we can keep an eye on consumption.

There is another switch on the inverter panel that allows us to turn the inverters on, off or charge only mode. Generally, when we are away from the boat, we set the inverters to “charge only” so they keep up the battery bank but do not invert if there is a loss of shorepower as this could run the batteries flat if shorepower is not restored.

Finally, there are a series of LED’s that tell us the status of the inverters including warnings.

When there are no external 240 VAC sources present, the inverters can draw 24 VDC power from the batteries and supply up to 30 amps of 240 VAC power. If the engine is running, the two big Electrodyne alternators can supply this much power so we can realistically power most of the 240 VAC consumers from the power generated by the alternators. If the engine is not running, the inverters produce 240 VAC from the 24 VDC battery bank.

Realistically, we limit power consumption when drawing strictly form the batteries to about 20 amps (or 200 amps at 24 VDC) so as not to overtax the batteries. Our primary use of 240 VAC power when running strictly off the batteries is cooking on the induction cooktop and in the speed oven.

Another note – the inverters do have a certain amount of overhead associated with having them on even when we are not using any 240 VAC consumers. This amounts to 8 or 9 amps at 24 VDC which adds up when the inverters are left idling for extended periods of time. Our normal procedure is to turn the inverters off when we are on battery power and do not need them.

Finally, if there is an issue with the inverters, we have the capability to bypass them entirely with a switch behind the salon electrical panel.

That about does it for the 240 VAC system. In future posts I will cover the 120 VAC and 12 VDC. systems.

Cheers