Inverter circuit diagram
The two final power of TR2-TR4 should be mounted on heatsink the right size, otherwise they will overheat. You can choose from MJ4033 – MJ3007 or more, provided that the NPN.
The maximum power output that can be used depending on the size of the core of the transformer T1, the VA is: with 50 VA can be taken in the secondary 230 V 0.2 A (current consumed by the end will be 4 A) with 90 VA can be taken on the secondary 230 V 0.4 a (current consumed by the end will be 7 A).
To power the circuit from the 12V battery, it will take over at least 1.8 millimeters in diameter, to avoid loss by Joule effect.