Excitation methods for DC motors

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Hello everyone, I’m an outsider when it comes to electricity. I’m facing a problem at work related to the excitation method of DC motors. The nameplate of this DC motor indicates that it is excited using a shunt excitation method, whereas we conduct tests in our factory workshop using a separately excited method. The problem we are facing now is that the excitation current has to be 20% higher than the value indicated on the nameplate in order to achieve the 220V DC voltage I need. Could this be related to the excitation method? Thank you all. Here is the definition I copied from Baidu. ==================== 1. Separately Excited DC Motor: A DC motor in which the excitation winding has no connection to the armature winding, and is powered by another DC power source, is called a separately excited DC motor. The wiring is shown in Figure 1.23(a). In the diagram, M denotes a motor; if it is a generator, it is denoted by G. A permanent magnet DC motor can also be regarded as a separately excited DC motor. 2. Shunt DC motor: The excitation winding of a shunt DC motor is connected in parallel with the armature winding, as shown in Figure 1.23(b). In the case of a shunt generator, it is the terminal voltage generated by the motor itself that supplies power to the excitation winding ； As a shunt motor, the excitation winding shares the same power supply as the armature, and in terms of performance it is similar to a separately excited DC motor.