Minimum Power Inverter Wattage for Microwaves

Inductors

• Inductors are electrical devices that store energy by converting electrical power into a magnetic field. These devices resist changes in voltage and will attempt to maintain the voltage across the inductor until the stored magnetic field collapses. Inductors can be used in conjunction with magnets to create a motor to change electrical power into mechanical work. Inductors may also be used to increase or reduce AC voltage, such as in the case of a transformer, or to create a resonant circuit, such as in the case of a magnetron.

Cooking Power vs. Actual Power

• Microwaves are often advertised as having “600 watts of cooking power.” However, "cooking power" refers to the amount of power that is applied to the food being cooked inside the microwave chamber. The power required to operate the microwave is often much higher than the cooking power rating. For example, a microwave that may be advertised with a rating of 600 watts will often require 1100 watts of power or more to operate properly. To obtain the actual power draw for a microwave oven, check the back of the microwave where the electrical cord enters the microwave case. The power requirements will be stated in volts and amps (such as “120 volts AC, 9A”). You can obtain the power rating in watts by multiplying the voltage rating by the current rating as measured in amps.

Square-Wave vs. Sine-Wave Inverters

• It is important not only to consider how much power a power inverter can supply, but also the AC waveform that the power inverter puts out. Microwave ovens and other devices that have inductive loads may be operated using a true sine-wave inverter. While many inductive loads are capable of running when connected to a square wave power inverter, these loads will generate more heat and may be prone to failure more quickly.

Inductive Loads and Power

• An inductive load requires more power to start up than to continue operation. This is because a change in voltage will result in a change in the magnetic field through the inductor. Applying voltage across an inductive load such as an electric motor creates a phenomenon called a back EMF. A back EMF cancels part of the forward electromotive force of a motor. To overcome this, more power must be applied at startup than is required during normal operation. Therefore, a power inverter must have a surge rating that exceeds the power rating of the microwave oven and a continuous rating equal to or greater than the power rating.