Inverters - Sizing, Installation and ABYC Standards


An inverter is a power electronic device that converts direct current (DC) to alternating current (AC); the converted AC can be at any required voltage and “frequency” with the use of appropriate transformers, switching, and control circuits. 

Inverters are usually used to supply AC power from DC sources such as solar panels or batteries. It will be useful for emergency electric source


DC power, from a hybrid battery for example, is fed to the primary winding in a transformer within the inverter housing. Through an electronic switch (generally a set of semiconductor transistors), the direction of the flow of current is continuously and regular broken (the electrical charge travels into the primary winding, then abruptly reverses and flows back out). 


 Output Signal

According to output voltage form they could be rectangle, trapezoid or sine shaped. The most expensive, yet at the same time the best quality inverters, output voltage in sine wave.  

There are three basic types of dc-ac converters depending on their output waveform: square wave, modified sine-wave, and pure sine wave. 
(see the diagram below) 

Get here the Marine Electricity Handbook where you can find all the information on this and many other topics.


A true sine-wave inverter produces output with the lowest total harmonic distortion (normally below 3%). 

It is the most expensive type of AC source, which is used when there is a need for clean sinusoidal output for some sensitive devices such as medical equipment, laser printers, stereos, etc.

For Zero interference and hum, pure sine-wave inverters are available at significantly higher cost.


Input Power Vs Output Power
Early inverters for the consumer market were used mainly for mobile applications like boats and recreation vehicles, and most were designed for 12-volt DC battery ignition systems.
Due to an upper capacity limit of approximately 200 amps for the internal power components and heavy welding cables that were being used for connecting typical mobile 12-volt systems, 2,400 watts was about the largest capacity inverter that could be made for these applications (12V x 200A = 2,400 W). 


Learn more in the following video

Sizing an Inverter Battery Bank

Watts = Volts x Amps.

Battery capacity is expressed by the amount of Amps per hour that a battery can deliver to support the load applied.

For a 12-Volt inverter system, each 100 Watts of the inverter load requires approximately 10 DC Amps from the battery

For a 24-Volt inverter system, each 200 Watts of the inverter load requires approximately 10 DC Amps from the battery.

The first step is to estimate the total Watts  of load, and how long the load needs to operate.

The first step is to estimate the total Watts  of load, and how long the load needs to operate .

This can be determined by looking at the input electrical nameplate for each appliance or piece of equipment and adding up the total requirement.

For example, a full-sized refrigerator (750-Watt compressor), running 1/3 of the time would be estimated at 250 Watts-per-hour.

After the load and running time is established, the battery bank size can be calculated.

The first calculation is to divide the load (in Watts) by 10 for a 12-Volt system or by 20 for a 24-Volt system resulting in the number of Amps required from the battery bank..

The batteries will need to deliver 24 Amps to run the refrigerator (240 Watts/10 Volts = 24Amps/Hr).


If you want to ask questions about this matter directly to Mr. Lopez, or want to receive remote troubleshooting for your boat, schedule a video call with Mr. Lopez.

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