Installing boat power inverters have many advantages. Many sailing yachts, motor boats, canal boats and barges, including my own have a DC/AC inverter on board. I also have an AC generator as well as the shore power. When you are anchored in some quiet cove or tied up on some peaceful canal, away from the shore power, the peace and tranquillity are disrupted when running a generator.
Boat power inverters allow use of the video and television, the microwave and other appliances. Inverter technology has advanced considerably in the last few years. They range from small portable inverter units of just 150W up to the large fixed systems of 5kw with some units that can be paralleled with an automatic synchronisation module. The combination charger and boat power inverters are also very common.
One big area of change is that transformers have been reduced in size and weight as the conversion is now done at very high frequencies. The reliability of most systems is also greatly increased over earlier units that unfairly gave boat power inverters a bad reputation.
Output wave-forms are an important consideration when looking at proposed inverter application
The Trapezoidal Waveform The majority of boat power inverters have a trapezoidal waveform. This is suitable for operating most equipment, but microwaves and some inductive loads such as motors do not operate at full output, dropping efficiency by some 20% or more in some cases. Fluorescent lights may also be less efficient at starting and often require a capacitor to be installed across the input, which will improve starting characteristics. Interference is also possible with these wave-forms.
The Modified Sine Wave-form
Some boat power inverters have what are called a modified or quasi sine wave output, which closely resembles the pure sine wave you have at home. It is not exactly the same and offers slightly reduced performance. Interference is also possible on these wave-forms.
Appliances and equipment such as microwaves and VCR units with clocks often run either slower or faster. Battery chargers for cordless portable drills are also susceptible to early failure. If a charger gets excessively warm or hot turn it off as some incompatibility may exist. A device called a ferro-resonant line conditioner can be used to improve performance.
The Sine Waveform
Sine wave output inverter units are the ideal and offer quality better than shore mains power but are more expensive. If you are using sensitive equipment then a sine wave should be used. They are available in most ratings up to 1800W in 12-volt systems, with outputs at 230V RMS +/- 5%. Frequency stability is typically +/- 0.05%. Quality units have a low harmonic distortion, typically less than 3%, and low EMI (Electromagnetic Interference) levels.
Typical boat power inverters are capable of drawing very large DC current loads from the battery. It is essential that battery capacity is capable of supporting these loads without affecting the existing electrical system and connected loads, particularly electronics equipment. A simple method of calculation is to divide the power in watts by 10 for 12 volt systems or 20 in 24 volts systems. It should be noted that some manufacturers offer inverters for 12, 24 and 48 volts inputs depending on system voltage.
The minimum battery capacity required for an inverter is 20% of the inverter capacity, i.e. 2000 watts 400 Ah capacity. Most boats and barges will require a relatively large house battery bank if they intend to use the power-inverter frequently. On my former Dutch barge I had a 24 volt battery bank, which is more efficient than 12 volts systems.