How to control the positive and negative rotation of DC series motors with contactors

To realize the positive and negative rotation control of the motor, any two phases in the power phase sequence can be reversed (we call it commutation), usually the V phase is unchanged, and the U phase and the W phase are relatively adjusted. In order to ensure that the phase sequence of the motor can be changed reliably when the two contactors operate, the upper connection of the contactors should be consistent when wiring, and the phase adjustment should be at the lower mouth of the contactors. Because the phase sequence of the two phases is opposite, it is necessary to ensure that the two KM coils cannot be energized at the same time, otherwise serious interphase short circuit fault will occur, and interlock must be adopted. For safety reasons, double interlocking forward and backward control circuits (as shown in the figure below) are often used, namely button interlocking (mechanical) and contactor interlocking (electrical). Using button interlock, even if the forward and reverse buttons are pressed at the same time, it is impossible for the two contactors of phase modulation to get electricity at the same time, which mechanically avoids phase-to-phase short circuit. In addition, because the contactors are interlocked, as long as one contactor is energized, its long closed contact will not be closed, so that under the application of electromechanical interlocking, the power supply system of the motor will not be short-circuited between phases, which effectively protects the motor and avoids the accident caused by burning the contactor due to short-circuiting between phases during phase modulation.