Articles: DC Electrical Components

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Negative Battery Switching Troubles

We recently had to trouble shoot a problem on a boat that had negative battery switching instead of positive. In North America, everything is switched (and fused) on the positive side of the battery. In Europe, some boats have both positive and negative battery switching (i.e. Beneteau) however, we have never seen a negative only battery switching before.

Voltage Drop in Primary Distribution

Most marine electrical systems will have a DC (direct current) system as part of their electrical design, and for most boats it may form the largest and most intrinsic part of the electrical system. With lower voltage electrical systems, those below 50V, it is of paramount importance that particular attention is paid to distribution of the power and maintaining voltage drop to a minimum.

ELCI Breaker with an Inverter/Charger

Equipment Leakage Circuit Interrupter (ELCI) breakers are fairly new in the North American marine industry. Older boats are not equipped with them however they are now in the ABYC standards for new boats and refits. They are similar to a GFI outlet (like in your bathroom) but they protect the whole boat and trip at a higher level, 30mA instead of 5mA.

Thermal vs. Magnetic Circuit Breakers

Thermal circuit breakers respond to over-current situations, as their name implies, by the circuit generating an inordinate amount of heat causing the bimetal contacts inside the breaker to disengage due to unequal expansion. A magnetic circuit breaker responds to over-current situations by a loading coil inside the breaker lifting the contacts apart when the current flow through the coil is sufficient to overcome the spring force holding the contacts together.

Battery Bank Sizing

There are a lot of factors that go into determining the appropriate sized battery bank for a boat, and no hard and fast criteria. However, there are some general guidelines that can help in setting up a bank of batteries that will provide enough power for the DC systems on board without sinking the boat or your finances.

Electromagnetic Fields on Your Boat

Electromagnetic forces (EMF) are one of the four fundamental forces in nature, and although they exist naturally, they can also be created. Any wire carrying any amount of electrical current will generate a magnetic field,

Tachometer Signals

Tachometers all look pretty much the same, but there is some variation between the methods that tachometers get their signal information. The function of a tachometer is to display the RPM (revolutions per minute) of the engine. Typical RPMs will be in the 10s of hundreds, so the method for counting the revolutions must be quick and accurate.

Plugging Into Shore Power

It is easy to become complacent when it comes to plugging an electrical cord into a socket. This convenient arrangement for making an electrical connection has become such a casual part of our lives. It is commonplace to just plug-in if it fits and sometimes, with a little encouragement, it can be made to fit.

Battery Capacity vs. Discharge Rate

There are fundamental electrical principles, many based on Ohms law, that are constantly presenting themselves in various situations. The fact that Watts is equivalent to Volt x Current is always at the forefront of most design considerations. When it comes to battery capacity the amount of current being pulled from the bank has an important consequence to the overall capacity.

Engine Switches and Senders

Most boat operators are familiar with their gauge set and are aware that there is a device on the engine providing a signal to the gauge that allows it to provide useful information. However, many boaters are unfamiliar with the nature of those engine mounted devices.

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