Transformer efficiency/primary current (help!!) Real transformers are not 100% efficient. That is, the efficiency, in percent, is represented by e = (100%) Ps/Pp. A step-down transformer has an efficiency of 92.5% is used to obtain 23.0 V from the 125 V household voltage. The current in the secondary circuit is 27.0 A. What is the current in the primary circuit? I have tried basically everything but I cannot seem to figure it out. Help???