This depends on the structure of the electric heater, frequency converter can only change the frequency change of alternating current, so as to change the rotation speed of the motor to achieve the purpose of power output. The heater does not rotate, so the frequency conversion can not control the heating speed.

1. Half wave rectification, to change the effective value of alternating current, so that the electric heater can achieve the purpose of changing the heating power and heating speed; this method has the advantages of simple circuit structure and convenient operation.

2. Use small transformer to change the heating speed of electric heater. The advantage of this method is that it can be adjusted in many levels, but the disadvantage is that the circuit structure is complex and the production cost is high.