Problematic 600w Sine wave inverter

Bought an Ellies 600w 12V sine wave inverter a few years back....problem with it was that it would die after a few minutes with even just a 40 watt light bulb connected as load. The battery was not the problem but it was proved to be the inverter. What appears to happen is that there is a daughter-board inside on which some components get hot which in turn switch the unit off. If you blow cold air thru the unit with a hairdryer, the unit works perfectly, use hot air and it switches off. I now connected the internal fan to run continuously when on and there is no problem. Poor design and the last Ellies product I will waste money on.