Hello Kirstie
Graham is correct, but I think it might be helpful to add a little more meat to the bones.
In essence an inverter could be called a constant "Power" converter. In other words power out equals power in. So whatever power is needed at the output (which is determined by the appliance being used), must be available at the input. Inverters are manufactured with different maximum power ratings, and you must not attach an appliance which uses more power than the inverter rating, however it does also mean that if you have an appliance that is rated below the capacity of the inverter, the inverter will only draw enough current from the supply to meet the demand of the appliance.
In electrical terms Power is measured in Watts (W), and is simply derived from multiplying the Voltage (V) by the consumed current (A). In the case of an inverter, the value of Watts must be the same for both input and the output of the device.
This leads to a simple equation:
Output Power = Input Power, or Vout x Aout = W = Vin x Ain
If we consider your domestic kettle, look on the data plate you will see that it will be given a power rating in Watts or kiloWatts (1000W = 1kW). Most jug kettles are rated at about 2.2kW at 230Vac. We can calculate the current draw (2200W/230V = 9.6A)
Substitute into our inverter equation, and also consider the input side
230Vac x 9.6A = 2200W = 12Vdc x 183A
You can see that it would require a very large 12V current to produce the 2.2kW power needed to run the kettle.
Caravan batteries have a limited maximum current output, and most would not be able to provide the current for your inverter and kettle. I would only consider a maximum of 300W for short periods.
Large inverters are available, they are need heavy wiring, and are expensive. They are used on boats where weight is not and issue. You can buy a lot of gas for the same money.
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