Now that you understand the concept of a voltage pushing a current through a resistance, we can now introduce the concept of electrical power.

Put simply this is mathematically just voltage multiplied by current to represent the amount of overall electrical power.


  1. Understand the unit of Electrical Power and how this knowledge can be put to use within a small craft DC electrical system.


During this section you will:

  1. Calculate the Watts from a given voltage and current.
  2. Calculate of Current from a given Wattage and Voltage.
  3. Calculate of Voltage from a given Wattage and current.


Electrical power represents the overall value of electrical energy based on both the Voltage and Current, so the overall energy measured in Watts (W) and is simply:

Volts X Amps = Watts

And this can be transposed as

Watts / Voltage = Amps

Watts / Amps = Voltage

Devices that consume electricity, known as 'loads' are often rated by their power in Watts, such as lamps for example, this refers to how much overall electrical energy the device consumes and offers some indication of how much work the device will do.

However, devices that provide a source of electricity, such as batteries, cables and fuses are rated by the current in Amps. For this reason we need to be able to work out the Current based on Wattage รท Voltage = Current.

The video lesson below covers this in great detail.



  • 1200W load on a 12V supply will consume 100 Amps (1200 / 12 = 100 Amps)
  • 1200W load on a 24V supply will consume 50 Amps (1200 / 24 = 50 Amps)
  • 1200W load on a 48V supply will consume 25 Amps(1200 / 48 = 25 Amps)
  • 1 X 50Ah 12V Battery contains 600Wh of energy (50 X 12)
  • A 10A load on a 12V system is 120W (10 X 12)

Complete and Continue