Inductive versus Resistive Loads

What's a Load? We often get clients asking why they cannot power their 2000W AC air conditioning with a 2000W inverter. It seems simple enough--match the appliance and inverter wattage rating, and all should work, right? It's not that easy, since not all loads are equal. Here we'll discuss the two most common load types: inductive and resistive. 

Inductive loads use magnetic fields (i.e., wire wound coil), as in a windlass, air conditioning unit, or blender. The general rule is, if it moves, it is probably an inductive load, which pulls a large amount of current (inrush current) when it is first energized. But after a few cycles or seconds, the current settles down to a steady state. This steady state is typically the wattage rating you see on the product label. The peak wattage, which occurs with the inrush current, is normally found in the owner's manual. Resistive loads convert current into other forms of energy, such as heat. Hair dryers and heaters typically create resistive loads, characterized by not having large inrush currents. The wattage ratings of resistive loads can be taken at face value and are exactly as indicated on their labels. 

When sizing an inverter or when considering if you can use a certain appliance on an existing inverter, you need to assess what type of load you are dealing with. Remember that inductive loads can take up to six times their rated wattage. This explains why sizing watt for watt doesn't always work.