All hands-- The following was written by Maurice Nunas, a longtime Listee currently cruising in Malaysia aboard Akama, a Krogen 48 Whaleback. If you have any comments or questions, I'll be pleased to relay them to Maurice. --Listmeister Georgs Subject: Electrical Needs Aboard M/Y AKAMA (a bit technical) The electrical needs of a motor yacht, even one as small as AKAMA, are not much different from those of a house or an apartment. Indeed, when we are in a marina, hooked up to shore power, we are a floating apartment. Once away from the dock, however, we must make and store all of our own electricity. We have all the same household equipment and appliances. We consume about 8.6 kilowatt-hours (kWh) of electricity every 24-hour day, not counting big stuff (e.g., dishwasher, water heater, clothes washer/dryer, air conditioners and water maker). The electricity we use for the foregoing is stored in a 12-Volt house battery bank consisting of twelve golf cart batteries in series-parallel, which provides about 12 kWh of capacity (i.e., 1000 Ampere-hours at 12-Volts). To get the electricity out of the batteries for the household appliances, we have a black box called an inverter. The inverter takes the 12-volts DC and converts it to 240-Volts AC, at about 95% efficiency. The inverter can only supply up to about 2.8 kW, so we cannot use it to run the big stuff. Of course, what comes out must be put back in, or we will end up with dead batteries. With a stored supply of only 12 kWh and a daily demand of 8.6 kWh, one can readily see that we have enough electricity for about 33-hours. In practice its just about 24-hours worth, because totally discharging the house bank is hard on the batteries. We have two ways to recharge the batteries, the alternator and the generator set. The alternator is on the main engine; so it runs only when we are moving. It is similar to those on cars and trucks, except that ours is bigger and has a special regulator that enables it to produce more power. It can deliver up to 100-Amperes at 12-volts (1.2 kW) when the engine is run at full tilt (about 2800 RPM). Most of the time, however, we run the engine at about half speed; this produces about 65-Amperes (3/4 of a kilowatt), which is about the amount of energy needed to run a microwave oven or a small hair dryer. You will recall that our household needs average about 1/3 of a kW; also, when we are running, especially at night, we must run a lot of other equipment (e.g., GPS, Autopilot, RADAR, and navigation lights). At our cruising speed of six or seven knots and everything running, the alternator keeps up with the demand (except for the big stuff), with about 20-Amperes (250 Watts) left over for battery charging. We also have a large generator set that can produce up to 16.5 kW of electricity. Obviously, this is big enough to power everything aboard, including the big stuff, all at the same time, which is why we have one that big. When the generator set is running and powering everything direct, it also powers a 100-Ampere charger (actually, it is the inverter running backwards) that recharges the house bank. So, how does it all work? Well, at the dock, the shore power runs everything and the inverter/charger charges the batteries. All the circuit breakers are switched on, just like in a house. When we leave on a cruise the alternator keeps up with the demand; so everything remains on (except the big stuff). However, we often run our generator set while we are cruising, to run the air conditioners or the water maker. Once we arrive somewhere, we usually shut off the engine and the generator, leaving the house bank to run things via the inverter. Also, because the inverter runs totally silent we usually run off the batteries at night. To save energy when running on the inverter, we usually turn off the electric panel circuit breakers on circuits that are not being actively used, but which are still using electricity. For example, the TV, VCR and stereo use quite a bit of electricity when in standby mode; ditto for computer, printer and scanner. At night the only household circuit active is the one for the fridge and the freezer. However, we usually also run our anchor light, and our GPS, depth sounder and sometimes the RADAR in alarm mode. If we want to run the big stuff then we must start the generator set. This can be fairly frequent. For example, we often start it while making meals. This saves loading the batteries with the microwave oven, electric kettle and so on. Also, we consume about 500 US gallons of fresh water a week, which we usually must make with our water maker (desalinator). It makes about 20-gallons an hour, so it must be run about 3.5 hours each day to keep up with the demand. As we have a storage capacity of 500 gallons, we can schedule this whenever we wish. If we are doing things inside the boat on a hot day with no breeze, then we run the generator to poser the air conditioners. We take advantage of all this need to run the generator to give the battery bank some charging. However, this is usually not enough to keep the battery bank full. Sooner or later we need to run the generator set just to charge the batteries. On the average, it needs to be run about 6 to 8 hours a day or we will eventually end up with dead batteries. It can take twelve to fourteen hours of charging to bring a nearly depleted house bank back up to full charge. The rule of thumb is that for every ampere you take out of the battery you have to put back 1.2 amperes, due to inefficiencies of the charging process. Also, once the battery bank is nearly charged, it is no longer possible to push 100-Amperes of charge current into it without damaging the batteries. It is all quite complex and scientific, so we have a special meter that displays Volts, Amperes and Ampere-hours consumed. It also gives us a rough estimate of how many hours we can continue to run until the battery bank is depleted. It is a lot like the fuel computer on some of the up-market cars, except this one is for electricity. So, we are totally reliant upon our generator set. There are more hours on the generator set than there are on the main engine. As we write this, we are at anchor in Teluk (bay) Tekek on the west coast of Tioman Island (Malaysia). Weve been away from shore power for several weeks. The generator set is runninglife is good. Maurice & Louise-Ann Aboard Akama, a Krogen 48 Whaleback