ROTARY CONVERTERSHistorically, these type of power sources were developed first for arc welding applications and even now these types are popular. These rotary converters are of two types: namely motor driven and engine driven. The engine driven type also comes in two models. Diesel engine driven generators (with auxiliary power output for grinder, etc) are very useful in heavy duty structural applications and for pipeline work. Petrol Engine driven generators which are light and portable are useful for light duty and repair works at site. The efficiency of rotary converter is rather low (60 % for motor driven & Engine driven) and the maintenance is also costly due to wear and tear of rotating machinery.