How efficient is a phase converter ?
A commonly asked question is what is the efficiency of a phase converter. Efficiency is a function of the useful power output so when expressed as a % it can be highly misleading if the useful load is very small. Instead it is more straightforward to discuss the parasitic power consumption of a phase converter. A typical 4-kW rotary has a fairly constant 500-W of parasitic losses (windage, bearing losses, iron losses, and copper losses). So at full power – supplying a 4-kW load, it is 89% efficient. Clearly as load falls off this efficiency figure worsens, e.g. to 80% for a 2-kW load, and 67% for a 1-kW load. This is one reason why it is better not to buy too large a phase converter as ideally one would like to keep parasitic losses to a minimum. In the UK the electricity companies charge for Watts consumed rather than current. This is important because the same 4-kW rotary phase converter that consumes 500-W when idling will actually draw about 8-Amps of current rather than the 2-Amps
