Solar Mini Inverter

The mains power comes to the Inverter. This is directly sent to the output but the AC is also converted to DC and this DC is constantly charging the battery. A sensor and relay mechanism checks whether the mains is ON or OFF. When the main switches OFF, the relay actuator triggers to switch from mains to inverter. Rest is same like the UPS. Because of this sensor and relay, there is a gap between triggering. UPS involves more costly circuits and is therefore more expensive to make and sell. Apart from these there is another difference. The AC supply has a pure sine wave whereas in an offline UPS the output is a near sine wave, not a pure sine wave where as for an inverter its step wave. This is the reason that we hear a hum when we attach a inductive load to a UPS or a inverter but we do not hear anything when its on AC supply.