Q12. What are “continuous” and “surge” power capacity ratings for DC-AC inverters?
A12: How much load can an inverter handle? Its power output is rated in Watts..There are two levels of power rating ---a continuous rating and a surge rating. Continuous means the amount of power the inverter can handle for an indefinite period of hours. When an inverter is rated at a certain number of Watts, that number generally refers to its continuous rating. The “surge power” indicates the power to handle instantaneous overload of a few seconds to provide the higher power required to start certain type of devices and appliances.
Q13. What types of electrical loads require “surge power”?
A13: Resistive types of loads (like incandescent lamps, toaster, coffee maker, electric range, iron etc) do not require extra power to start. Their starting power is the same as their running power. Some loads like induction motors and high inertia motor driven devices will initially require a very large starting or “surge” power to start from rest. Once they have started moving and have attained their rated speed, their power requirement reduces to their normal running power. The surge may last up to 5 seconds. TVs and microwave ovens also require surge power for starting. The manufacturers’ specification of the appliances and devices indicates only the running power required. The surge power required has to be guessed at best. See below under “Sizing of inverter for loads that require starting surge”
Q14. How do “surge power” electrical loads affect DC-AC inverter operation?
A14: If an inverter cannot efficiently feed the surge power, it may simply shut down instead of starting the device. If the inverter’s surge capacity is marginal, its output voltage will dip during the surge. This can cause a dimming of the lights in the house, and will sometimes crash a computer. Any weakness in the battery and cabling to the inverter will further limit its ability to start a motor. A battery bank that is undersized, in poor condition, or has corroded connections, can be a weak link in the power chain. The inverter cables and the battery interconnect cables must be sized properly. The spike of DC current through these cables is many hundreds of amps at the instant of motor starting.
Q15. How should I size my DC-AC inverter to operate a microwave?
A15: The power rating of the microwave generally refers to the cooking power. The electrical power consumed by the microwave will be approximately 2 times the cooking power. The “surge power” of the inverter should be 2 times the electrical power (i.e., 4 times the cooking power). Please note that the surge power of the microwave is not as long as the motor load and hence, the surge power of the inverter can be considered to determine adequacy of meeting the starting surge power.