Your guide to Inverters

Choose your inverter according to the type and power rating of the appliance your want to connect and remember that the starting current of your appliances must be much higher than their nominal consumptions.

Important Calculations:

1. Convert Amps to Watts as follows:

If AC Voltage is 120: Amps x 120 + Watts AND Watts ÷ 120 = Amps

Normally an appliances Watts rating x 2 = start-up load, but be warned: Induction Motors such as air conditioners, refrigerators, freezers and pumps may have a start-up surge of 3-7 times their continuous rating.


2. Calculate how long you can run the inverter on your battery as follows:

Watts + 10% ÷ 12 = Amps AND Amps hours ÷ amps = run-time in hours

E.g. Power drawn through a 150W inverter at full capacity is: (150W + 10%) ÷ 12Volts = 13.75 Amps.

*Waeco inverters require 10% to power themselves



Therefore a 105Ah battery could run that appliance via the inverter for (105 ÷ 13.75 =) 7.6 hours

Always Remember:

  • If you are in doubt about any appliance, please ask the manufacturer whether it is compatible with a modified sine wave inverter.
  • Read your inverter manual carefully
  • When connecting the inverter to the battery, use the thickest wire available, with the shortest practical length.
  • For two or more appliances, switch them on one at a time, starting with the appliance with the highest watt rating.