You should think of the current and voltage as being inversely proportional in cases where the power is the constant. That would include changing winding configurations in motors or transformers and switching power supplies. Think of a 24 volt control transformer that can have the primary windings in parallel for 120 VAC or in series for 240 VAC. Whether it might draw 1 amp in the first case or .5 amp in the second case, each winding still has 120 volts across it and .5 amp flowing through it. But yet the second case will likely be more efficient as a system because of less I squared R loss in getting to the point of use.
In the case of motor starting currents you're waiting for the motor to spin up and for the counter EMF to reduce winding currents. Here you shouldn't think of the voltage at the motor where you are observing it but at some point upstream before all the I^2 R loss that is the cause of the lower measurements.
Now if you have a purely resistive load, the current will vary directly with the voltage. Just don't think of nichrome heating elements as fitting into that classification since the resistance increases with temperature.
Happy New Year!
Joe
Last edited by JoeTestingEngr; 01/01/08 12:01 PM.
