How does an alternating current

Because you can't see, smell, or hear electricity (if everything is working properly), the technology can be harder to understand. However, over the past century we have relied more and more on electrical energy. All we have to do is cut off the power and we will realize how much our luxury, safety and comfort depend on electricity.

We also appreciate the luxury, safety and comfort that we take for granted at home and at work on board a yacht or in a mobile home. This also applies if we work at locations where a connection to a power station is not possible, such as on tugs, Rhine ferries or during road works.

For more than 25 years, Mastervolt has specialized in the reliable supply of electrical power in places without public power supply. So that you can better understand our subject, we would like to give a brief explanation of the most important terms.

Voltage and current deliver power

The main activity of Mastervolt is the conversion of energy. And the most important quantity that can be converted in the field of electricity is voltage. The electrical voltage is the potential difference between two points in an electrical circuit.

We distinguish between two types of voltage: alternating current (AC) and direct current (DC). Voltage is expressed in volts (V) and the alternating current frequency in Hertz (Hz). This is the rate at which the voltage changes.

  • Alternating current (Voltage) is the electrical current that comes out of the socket in the home and is used for most appliances. In Europe it is 230V 50Hz, in the USA it is 120V or 240V 60Hz.
  • Direct current is provided by a battery or solar panels. Batteries are particularly important because they offer a practical way of storing electrical energy. The battery voltages are typically 12 V or 24 V. Another option is 48 V, which is usually only used for electric sailing.

Although direct current is stored in the batteries, we actually need alternating current to supply our household appliances with electricity. Therefore, a conversion from direct current voltage to alternating current voltage is required.

Another term we use is Current (I), measured in Ampere (A). Electricity flows ’through the cables on board when electrical appliances are in operation. The amount of current that flows through the wiring can vary widely (depending on the connected load and the voltage used). This is why the correct cable diameter is so important - overheating of the electrical cables can have serious consequences.

A river with water flowing in it, a cable that carries electricity, or a cyclist riding against the wind ... you encounter resistance everywhere.

In the field of electricity this becomes Resistance (R) in Ohm (Ω) specified. Resistance is important because it creates losses that we need to consider. There is a loss of voltage in the cables. If this is not taken into account, there is not enough voltage at the end of the cable to supply power to the device we want to use.

The aforementioned variables all provide one Power (P) in the Watt (W) is expressed. Every electrical device refers to its output power in watts; Microwaves have 900 W, light bulbs 60 W, generators 4000 W and washing machines 2500 W.

To simplify terminology and descriptions, we always refer to kilowatts (kW), where 1000 W equals 1 kW. To relate consumption to a period of consumption, we use a unit of time in which electricity is generated or consumed, namely one hour. Together these are kilowatt hours (kWh).


The relationship between these units is expressed in formulas that represent the laws of electricity.

V. = the potential difference, expressed as voltage (V)
I. = Current strength in the unit amperes (A)
R. = Resistance in the unit ohm (Ω)
P. = Power in the unit watt (W)

Ohm's law is the most important formula.
V = I x R voltage [V] = current [I] x resistance [R]

Since we often use the term performance, the following formula is often used to determine performance:
P = V x I power [P] = voltage [V] x current [I]

The right wiring

Correct cabling is crucial for both safety and efficiency. Incorrect diameters can lead to overheated cables and cause a fire. This is not only true in theory: every year ships and mobile homes are lost to a fire caused by incorrect cabling.

The correct cross-section of wire is not only safer, it also ensures that your battery charger and inverter are performing at their best. If you use thinner cables than recommended between the battery charger and the inverter and battery set, this can lead to an excessive voltage loss in the cables and thus to an excessively low charging voltage at the battery terminals. This in turn means that the batteries are not being charged enough, which has a negative impact on their lifespan. If you use thinner cables for the inverter than is recommended, this will prevent you from using the maximum capacity of the batteries. In this case, the high (cable) losses cause the DC input voltage of the inverter to be (much) lower than the actual battery voltage, which is why the inverter switches off too quickly and does not use the full battery capacity. For this reason, cables that are thicker than necessary are often used.

Dimensions of the connection cables:

Since lower voltages imply higher currents, it is all the more important to use the correct size cable.

The current (A) is higher because the direct current with 12 V or 24 V is lower than alternating current with 230 V, while the (required) power remains the same. As a result, the current increases because P = V x I.

The following rule of thumb can be used:

  • For 12 or 24 V direct current systems, a current of 3 A per 1 mm2 cable diameter is used.
  • For 230/120 V AC systems, a current of 6 A per 1 mm2 cable diameter is used as a basis.

For example, if a battery or battery charger is expected to deliver 75A, you will need a cable that is at least 25mm2.

Generation of electrical energy

There are several ways to generate electricity:

  • With a fuel or diesel generator on board (usually AC, also available in DC).
  • By the alternator (s) on the main engine.
  • Mains (alternating current).
  • Solar panels (direct current).
  • Wind generator (AC or DC).


The energy generated can be used immediately or stored in the batteries with the help of a battery charger. A battery charger typically converts a low DC voltage of 12/24 volts to an AC voltage of 230/120 volts, 50 or 60 Hz.

You can also find DC-DC converters; these devices convert direct current voltage to another direct current value, for example 24 V of a battery to 12 V, to provide power to your navigation equipment.


The assembly of a complete electrical system requires detailed knowledge, experience, and information (this topic fills entire encyclopedias). The Mastervolt dealers who specialize in this are at your side.

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