Working principle: The solar or mains power comes from the UPS. The AC is converted to DC and this DC is constantly charging the battery. The output of the battery is fed to the Sine wave inverter and which converts DC to AC and this feeds the equipment. Since power out is always drawn from the battery, there is no time lag when the mains switches off or power is lost; it just stops the battery from being charged and the UPS continues to supply power till the battery runs out Solar charging priority over city power mains charging. Solar power chargers battery as a primary power source, if solar power is not available then the inverter will automatically be switched to charge the battery from city power electricity as a secondary source 2 in 1: INVERTER + UPS -LCD displays include voltage input, output frequency, output voltage, load, battery capacity, normal, unusual, and overload. -Low frequency and high quality, Automatic protection function -Can use AC power supply to charge battery (UPS function) -Advanced performance by CPU control -Auto voltage regulation (AVR), wide input & output voltage 145V~275V accurate output, AVR function -Generator compatibility and external battery connection are achievable -Adapts to all kinds of bad electric environments -It can automatically start up with the mains supply -Advanced automatic constant charging circuit, prolongs battery life -It has battery under-voltage, overload, over-discharge, and short-circuit protections Features: Type: line Interactive DC to AC inverter Compatible battery: 4 x 12v Lead-acid, Gel, or deep cycle batteries (Lead acid is recommended) KVA ratings: 5000VA Peak power: 7000W/7KW Rated power: 4KW DC voltage: 48VDC Inverter structure: Power frequency structure Inverter output: 220VAC/50Hz Output waveform: Pure sine wave Display: LCD Range of applications: mobile phone charging, laptops, lamps and lanterns, camera, TV, shaver, CD, fan, video games, security, professional tools, and instruments of all electrical power.