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Pros and Cons of a Traditional Isolation Transformer

A marine isolation transformer is a versatile device that can be used to provide galvanic isolation from shore power systems, to enhance electrical safety and eliminate corrosion caused by stray currents. Some isolation transformers can also be used for raising the shore voltage to deal with voltage drop. Another common use is to adapt the vessel’s internal power system voltage to a higher or lower shore power supply. If isolation transformers are so useful why is every boat not equipped with one?

Charge Distribution

Quite often on boats there will be more than one battery bank that will be charged from a single source, as is very common with an alternator. There are several ways of distributing the power from the charging source to the various batteries allowing prioritization of current flow.

Battery Charging Rates

Slow and steady wins the race when it comes to battery charging. It is important to bring a flooded lead/acid battery to at least 14.4VDC to get the electrolyte circulating and avoid stratification. However, prolonged charging above 14.4VDC can lead to hydrolysis (cleaving of the water in the electrolyte into hydrogen and oxygen).

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.

VHF Antennas vs. VHF-AIS Antennas

I recently added a Transmitting AIS antenna to an existing (working) 8 foot Shakespeare VHF antenna with alarming results. It was giving me high VSWR alarms (3.5:1) despite it testing good (1.5:1) on the VHF.

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.

Engine Starter Circuit

A common calamity for which we often get requests for a service call is the engine failing to start or even “turn over”.

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