36Key information May 2009 edition / subject to change max on DC motor and max on EC motorKey information The motor as an energy converterThe electrical motor converts electrical power Pel (current I and voltage U) into mechanical power Pm e c h (speed n and torque M). The losses that arise are divided into frictional losses, attributable to Pmech and in Joule power losses PJ of the winding (resistance R). Iron losses do not occur in the coreless maxon DC motors. In maxon EC motors, they are treated formally like an additional friction torque. The power balance can therefore be formulated as:The detailed result is as followsElectromechanical motor constantsThe geometric arrangement of the magnetic circuit and winding defi nes in detail how the motor converts the electrical input power (current, voltage) into mechanical output power (speed, torque). Two important characte-ristic values of this energy conversion are the speed constant kn and the torque constant kM. The speed constant combines the speed n with the voltage induced in the winding Uind (=EMF). Uind is proportional to the speed; the following applies:Similarly, the torque constant links the mechanical torque M with the electrical current I.The main point of this proportionality is that torque and current areequivalent for the maxon motor.The current axis in the motor diagrams is therefore shown as parallelto the torque axis as well.See also: Technology – short and to the point, explanation of the motor Motor diagramsA diagram can be drawn for every maxon DC and EC motor, from which key motor data can be taken. Although tolerances and temperature infl uences are not taken into consideration, the values are suffi cient for a fi rst...
