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Watts & Amps Some basic science behind using electricity when camping

Graham Leslie

Using electricity safely while camping requires some basic knowledge to avoid electrocuting yourself or burning your caravan/camper down. This article explains some of the science behind this.

Electricity at its most basic is the flow of electrons along a wire. Electric power is a combination of two things: how many electrons are going along the wire — Amps; and how much force is pushing the electrons along — Volts. It is a bit like using a water blaster, where the power comes from how much water comes out and what pressure it comes out at. 

Electric power it is measured in Watts. For example, a LED light bulb might use about 8 Watts, a laptop 30 to 70 Watts and an electric kettle uses 2,000 Watts. The power consumption is normally written somewhere on the appliance.

The power or Watts is calculated by multiplying Volts by Amps. So if you run a 240 Watt appliance on mains power of 240 Volts, you will only need 1 Amp of electricity. But when you run the same appliance on a 12 Volt system you will need 20 Amps of electricity.

240 Watts = 240 Volts x 1 Amps or240 Watts = 12 Volts x 20 Amps

In simple terms, when you have lots of Volts (240 Volts at home) you don’t need many Amps and when you don’t have many Volts (12 Volts camping) you will need heaps of Amps. 

So, when camping with a 12 Volt system you use heaps of Amps to get the same amount of power as you would at home. 

The more Amps you use, the quicker you use up the electricity stored in your battery. Look at the Watts on your device and if you are using a 12 Volt battery divide it by 12; this is the Amps the device uses each hour it is on. For a 150 Watt appliance: 150 Watts divided by 12 Volts: 150÷12= 12.5 Amps

Remember Amps are the number of electrons flowing down the wire. Using the water blaster analogy, Amps are similar to the amount of water flowing. If you need more water to go down a hose then you will need a thicker hose. So, if you need more Amps to flow down a wire you will then need a thicker wire. 

Typical cross section of wires 

240 Volt home wire needs more insulation. Lots of insulation to avoid electrocution from high Volts. Not much copper wire because not many Amps. (Using a water hose analogy; not much water but under lots of pressure.)

12 Volt camper wire needs more copper wire.Not so much insulation because Volts are low. Lots of copper wire to carry lots of Amps and avoid power loss and fire risk. (Using a water hose analogy; lots of water but not much pressure.)

Big enough wire

If the wire in your camper is not big enough then you can lose power as it goes down the wire. At the battery you may have 12.5 Volts, but at other end of the wire where the appliance is you may only have 11.5 Volts. The power drop increases with large loads. 

The power drop along the wire means there is less power available to run your appliance and it may not run properly. The power lost along the wire turns into heat and sometimes this generates enough heat to melt the insulation off the wires and start a fire. See arrows in the photo. 

To reduce these issues and the fire risk, in 12 Volt RV wiring, you need really fat cables going the shortest possible distances because you are using heaps more Amps than you would with 240 Volt mains power. For instance:

A 2,000 Watt kettle draws 8 Amps at home, but in your camper, with an inverter, it would draw 167 Amps (2000 ÷ 12).

For that many Amps your cables need to be huge. What might seem like not much power at home could be very different when you are off the grid. 

240 Volt mains power and 12 Volt battery systems are both dangerous but in different ways.

Why is 240 Volt mains power dangerous? 

Compared with 12 Volts from your battery, 240 Volts mains power is a bit like a high-pressure hose and the electricity really wants to get out and escape through whatever is close or touching it, including us (which would electrocute us). So electrical equipment with higher voltages (240 Volts) has more insulation around it to keep the electricity in the wire.

Why are 12 Volts battery systems dangerous?

12 Volts does not have as much force to push electricity to escape. It is more like very, very low water pressure. So there is less chance of electricity being forced to flow through us and give us an electric shock. However, to get enough power and make up for the lack of pressure (Volts) we increase Amps or current flow. If the wires are not big enough to carry that much current, they can heat up and become a fire risk. 

Tips for installing a 12 Volt to 240 Volt inverter

  1. Set the inverter up as close as possible (short fat cables) to the battery and if need be run an extension cord from the inverter to the appliance.

  2. If you are buying an inverter with a big power capacity (anything over 150 Watts) get it professionally installed.

campers need really fat cables going the shortest possible distances

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