AC And DC Motors Reviews

Electricity is a strange source of power. You can't see it, but you can certainly see its effects in the form of lights and sparks. It is a versatile power source in that it can be used in the form of a motor to drive machinery, as a source of easily controllable heat and light, and for powering electrical devices. It can also be used to generate magnetic effects. It is the versatility and convenience of electricity which makes it such a good source of power in a boat.

Electrical systems use metal wires to transport energy from where it is generated to where it is stored and used. The wire has to be insulated in order that the electrical current follows only the chosen path, because any current leaking from the wire or a connection can lead to trouble. Much of the secret of a sound electrical system is ensuring that the current flows only where you want it to go; in some respects it can be likened to a water supply which is contained within pipes. However, while you can see and hear if the water is flowing, electricity is generally silent, making leaks and other problems hard to locate.

One of the major difficulties on a boat is that in addition to being carried by metal, electricity can also be conducted by water. Anyone who has owned a boat knows how damp it can be both inside and out and the marine environment is a tough one in which to make electric systems operate satisfactorily. Electricity tends to follow the easiest path which could well be the route provided by water if it comes into contact with the system. An additional difficulty is that salt water is also very corrosive, so it is important to remember that, in the marine environment, electricity and water should not mix. If they do, the water will win, causing a breakdown of the electrical system. Water will not only provide an alternative path for the electric current, but also begin the process of corrosion which, if left without attention, can have serious consequences.

Electricity comes in two forms, direct current (DC) and alternating current (AC). AC is the form we enjoy at home as it is easier to transmit over long distances and offers greater flexibility in the higher voltages needed in the domestic environment. AC motors and generators are also more compact and reliable than DC. With AC current, the power flows in alternate directions many times a second, hence AC power might be described as 240 volts, 50 cycles per second (the number of cycles being the number of times the current changes direction every second).

In boats, AC power suffers from the major disadvantage that it cannot be stored in a battery but has to be supplied on a continuous basis by a generator. On a boat you don't necessarily want a generator running all the time. Moreover, a generator still needs power to start its engine. This means that a battery is needed to store electricity that is available for use when required. The battery will store and produce DC power only, so a boat's electrical system has to be based on this current.

DC power travels in only one direction along a wire which, in terms of the system itself, makes very little difference. It is the ability to store current in a battery which is such a vital element. Not only does this ability enable you to use electrical appliances when the charging system is not operating, it also fulfils the vital engine starting role, which in turn allows the generator to start, so producing current to recharge the battery and supply the onboard systems.

Boat Refrigerators and Freezers

Like most electric motors, the refrigerator motor will use a high current when starting up, after which the current will drop back to the continuous use level. Refrigerators and freezers may be rated with the current they will use when the motor is running or they may have the average consumption per hour listed. When you arrive at your boat the refrigerator will have to run continuously for an hour or more before it gets down to its normal operating temperature after which it will run intermittently. Typical small boat fridges will consume around 4 to 5 amps per hour, although during the time the motor is running the consumption could be as high as 12 amps, so the circuits must be rated higher than this to cope with the higher starting power needed.

Boat refrigerators are one of the few motor units on board which run on a more or less continuous basis. This means that when the engine is stopped it will be one of the main users of current and the most likely cause of a flat battery if care is not taken. Some refrigerators include a device in the control circuitry to warn if the battery voltage is dropping. In some cases this will automatically switch off the refrigerator if this occurs, in order to prevent the battery from becoming deeply discharged.

It is possible to buy dual voltage refrigerators so that they can operate on battery power at sea and mains power in harbour. Another option is a refrigerator which can operate from either bottled gas or battery power.

Boat Heaters

Marine heaters tend to be gas or diesel powered because the electrical loads would be too high unless shore supply or generator power were available. The main requirement with the diesel type of heater is for a power supply for the fan and ignition circuit; here the electrical load is low, probably around 2 amps on a 12 volt system at the higher rated units, and perhaps 0.5 amps on smaller units. Some heaters can incorporate water heating, using diesel or gas. The hot water system is usually controlled and powered by the cold water pressure pump.