![]() You are on a 10 Amp EHU – How many Watt’s is that? How much current does a 1.2Kw kettle draw? (1.2Kw = 1200 Watts) Working anything out for mains appliances is the same. If we used the actual fully charged battery voltage we would get 13.5 x 10 = 135 Watts which if we used as the battery voltage dropped would overload the circuit – P / V = I or 135 / 12 = 11.25 Amps so greater than the 10 Amp fuse. Again we used the ‘nominal’ voltage for this calculation. The 12 volt accessory socket (cigarette lighter) has a fuse rated at 10 Amps – What wattage appliance can I plug in?Ī device with a maximum rating of 120 Watts can be used. When an Electrical Engineer designed the wiring for your caravan they will have used the ‘nominal’ voltage to choose the correct size cable and fuses for various circuits, with a little safety factor built-in of course. That’s what they have based their calculations on. What’s going on? Well manufacturers usually give a ‘nominal’ voltage rating, in this case 12 volts. We can see that the current drawn is less. If we are starting with a fully charged battery, the voltage might be 13.5 Volts, so working it out again for the corrected voltage we get: The reason is it’s highly unlikely that the voltage is exactly 12 volts. If we were to measure the current using our multimeter, we probably wouldn’t get a reading of 5.41 Amps. We know the voltage is 12 volts so using P / V = I we can now work out the current: ![]() The rated power for the television found from the manufacturers data is 65 Watts. Lets work out the current for a 12 volt television. (My old Physics teacher told us an easy way to remember them “The Vatican is Roman Catholic” and “The Pope lives in the Vatican and he’s Catholic” – I meaning Current)Īs we usually know two parts of the equation, it’s easy to work out the third. There are a few more and I’ve included a copy of the “Electric Wheel” at the end. You don’t need to know the theory behind the formulas, just remember these two triangles:-Įach triangle shows the three most used formulas that you will need. Resistance – measured in Ohms, Symbol Ω (Omega) If you have little or no electrical background it can get confusing, so hopefully this guide will make it clearer. A basic understanding of how to do this will help when fault-finding or deciding on the correct cable size when adding accessories. In some of the guides I have included calculations for working out current, resistance etc. A very basic introduction to some simple maths that allow you to work out power, current and resistance.
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