NW Explorations
DREAM CATCHER OPERATING MANUAL
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Here are some estimates of AC power consumption for typical appliances:
Water Heater
15 amps
Inverter
up to 22 amps
Hair Dryer
12 amps
TV
1.5 amps
Coffee maker
10 amps
Microwave
12 amps
Toaster
12 amps
Air Conditioning
up to 40 amps
4G: Electrical Systems, DC
4G1: DC Concepts
Each year it seems more folks are confused by the operation of electrical systems on yachts than by any other subject!
Don’t feel discouraged if something isn’t clear: you’ve got company in your confusion. So let’s try to cover some theory
here first.
Most of the equipment on any boat is run by 12-volt DC electricity from the boat’s batteries. This is true because DC
should always be available: we have batteries aboard even when there is no shore power! If the batteries aren’t run
down, everything should work, just like in the family car.
Since the batteries are used so much, we have to replenish, or charge them. The most important way we do this is by
alternators on the ship’s engine. In most cases one engine will provide enough electricity in most every case to run
everything, and still have some energy left over to add back to the battery, that is, to charge it.
Ah, but what if the engine isn’t running? Then, the batteries are slowly depleted until they have “run down” and there
is no more electricity stored in them . . . a big problem, because then we not only can’t run all the neat stuff on the boat,
we can’t start an engine to get more electricity.
So a good skipper and crew has “electrical power management” in mind whenever they turn an electrical gadget on or
off!
It is with this concern that we can cite a reality: If we need more electricity than the batteries alone must provide, and
if the propulsion engines aren’t running, we will need to get our electrical power from an alternative source! That’s the
most important reason why we plug the boat in to shore power or use a generator: To keep from running down the
batteries. For by using battery chargers getting their power from shore power or the generator, we can keep the batteries
charged, or, at least, from getting too low.
In modern, luxury cruising boats, however, there is another important factor: Some of the “goodies” we like to have on
board such as hair dryers and microwave ovens require ordinary household electricity. This is 110-120 volts AC. It is
different from DC. So if we want to use these things when we’re not at a dock, we must have another way to get 110-
120 volts AC, and for this we use a generator or an inverter, the latter an amazing high tech gadget that takes 12 volts DC
from the ship’s batteries and makes it into 110 volts AC!
So here’s what we’ve got:
• A lot of stuff running on 12 volts DC with that electricity from the batteries;
• To keep the batteries from running down, we have alternators run by the engine, and battery chargers that get
their power from shore power or the generator;
• For the stuff that runs on 110-120 volts AC, we have shore power, the generator, or, for making 110-120 volts AC
out of DC from the batteries, the inverter.