With the controller you can increase the voltage from 0 V to 1500 V in 32 steps. At that time the amperage of the motors are increasing (while the resistance is constant). After that with 'electric field weakening-handle' (in 4 more steps) you can reduce the electrical resistance (the amperige is repeatedly increasing). The operation of these locomotive engines can be explained in the simplest way with Ohm's law: I = U / R (I : amperage; U : voltage; R : resistance)