396 . ELECTRICAL ENGINEERING 



fore to spread out the two halves of the current wave so that they 

 overlap and produce in the load circuit a direct current with only 

 a slight pulsation. 



252. Currents and Voltages. The voltage is controlled by a 

 regulating reactance connected in the alternating-current supply 

 circuit and in the ordinary rectifiers the direct voltage ranges from 

 20 per cent to 52 per cent of the alternating voltage while the alter- 

 nating current ranges from 40 per cent to 66 per cent of the direct 

 current. 



Rectifiers are designed for direct currents of 10, 20, 30 or 40 

 amperes and can be built to operate on any required voltage and 

 any frequency. 



253. Losses and Efficiency. Since the counter e.m.f. of the 

 rectifier is approximately constant independent of the load, the 

 power -losses vary directly as the current instead of as the square 

 of the current. Neglecting the losses in the reactance coils and 

 regulator the efficiency of the rectifier is constant at all loads and 

 is higher the higher the voltage. Values up to 80 per cent are 

 reached with rectifiers supplied from a 220-volt alternating-current 

 circuit and delivering 1 10 volts direct current. 



The power factor of the rectifier is high and under ordinary con- 

 ditions may be assumed as about 90 per cent. 



