Inverters take the direct current (DC) power supplied by a storage battery bank usually at 12 – 48 V and electronically convert it to alternating current (AC) power of 120 – 240 V.
An inverter used for backup power in a grid-connected home will use grid power to keep the batteries charged, and when grid power fails, it will switch to drawing power from the batteries and supplying it to the building’s electrical system. In a stand-alone renewable power system, whether residential, industrial, marine or RV, the inverter allows AC electrical appliances to be run from the storage battery bank.
Inverters, besides coming in a wide variety of power capacities, are distinguished primarily by the shape of the alternating current wave they produce. The least expensive type of modern inverter produces modified sine wave power. The waveform looks like a stair-step, where the power rises straight from zero to upper peak voltage, straight back to zero, and straight to lower peak voltage, resting at each point for a moment. Sensitive equipment like battery chargers, tools with variable speed motors, laser printers and certain heating controllers may run erratically or not at all with modified sine wave power. The power supplied by utility companies and engine generators is a true sine wave form. This is the most reliable waveform. True sine wave power passes from the upper and lower peak voltages in a smooth curved wave, rather than the stair-step of the modified sine wave. True sine wave inverters will produce AC power as good as or
better than utility power, ensuring that even the most sensitive equipment will run properly.
Inverters have two different capacity ratings. One is the inverter's continuous output rating. This is the maximum wattage the inverter can output on a long-term basis.The second rating is the inverter's surge capacity rating. This is the maximum wattage the inverter can output on a momentary basis such as when starting motors in pumps or refrigerators.