Unstable speed is a common fault phenomenon in brushed DC water pump motors, and its root cause can be traced back to multiple levels, including the power supply, the motor itself, the load, the control system, and the environment. These factors affect armature current, magnetic field strength, mechanical resistance, or control signals, ultimately leading to speed fluctuations or abnormalities.
Power supply voltage fluctuations are the primary factor causing speed instability. Brushed DC water pump motors rely on a stable DC power supply. If the power supply voltage fluctuates periodically or randomly, the voltage in the armature and excitation circuits will change accordingly, directly causing the brushed DC water pump motor speed to fluctuate. For example, a sudden drop in mains voltage or a voltage sag caused by a sudden change in load can make the brushed DC water pump motor torque output unstable; improper parameter settings in the speed control system, such as an excessively large proportional coefficient in the PID controller, can also exacerbate the impact of voltage fluctuations on speed. In such cases, it is necessary to stabilize the voltage by adding a power filter, using a voltage regulator, or optimizing the speed control system parameters.
Defects in the brushed DC water pump motor itself are the intrinsic cause of speed instability. The contact quality between the brushes and the commutator directly affects the continuity of the armature current. Severe brush wear, insufficient spring pressure, or oxidation of the commutator surface can lead to increased contact resistance, intermittent armature current, and consequently, speed fluctuations. Furthermore, brushes deviating from the neutral line can disrupt the balance of electromagnetic torque, causing periodic oscillations in the brushed DC water pump motor. Short circuits or open circuits in the excitation winding can also cause changes in the main magnetic flux. For example, a short circuit reduces the main magnetic flux, leading to an increase in speed; an open circuit leaves only residual magnetism, potentially causing a sharp increase in speed to a dangerous level. Reversed winding polarity weakens the main magnetic flux, causing an abnormal increase in speed, while short circuits or open circuits in the armature winding directly disrupt the current balance, resulting in unstable speed.
Sudden load changes are an external cause of speed instability. During operation, the brushed DC water pump motor may face load changes such as variations in flow demand and fluctuations in pipeline resistance. If the sudden change in load exceeds the torque reserve capacity of the brushed DC water pump motor, the motor will be unable to adjust its speed in time to maintain stable operation. For example, a sudden closure of the pump outlet valve will cause a surge in system pressure, instantly increasing the load on the brushed DC water pump motor. If the motor torque is insufficient, the speed will drop significantly; conversely, opening the valve too quickly may cause a sudden decrease in load and a surge in speed. Furthermore, uneven load distribution, such as partial blockage of the pump impeller or bearing jamming, can also cause torque fluctuations, leading to unstable speed.
Control system malfunctions are the failure point for speed instability regulation. Aging of electronic components, resistance drift, or signal transmission interference in the speed control device or control circuit can cause abnormal control signals. For example, a damaged speed control resistor, PWM signal distortion, or sensor feedback errors can all cause instability in the brushed DC water pump motor's power supply voltage, thus leading to speed fluctuations. In a closed-loop control system, improper settings of the speed feedback loop parameters, such as excessively long integral time or overly strong derivative action, can lead to dynamic response overshoot or residual steady-state error, preventing the speed from stabilizing at the set value.
Environmental factors are potential sources of speed instability. High-temperature environments accelerate winding insulation aging, increase resistance, leading to increased current and excessive temperature rise, thus affecting the performance of the brushed DC water pump motor. High-humidity environments may cause winding short circuits due to moisture, disrupting magnetic field stability. Strong vibration environments can damage the precision of the brushed DC water pump motor's mechanical structure, such as rotor eccentricity and increased bearing clearance, exacerbating vibration and noise, indirectly affecting speed stability. Furthermore, dust or corrosive gases entering the brushed DC water pump motor can block heat dissipation channels or corrode metal components, leading to overheating or increased mechanical resistance, causing speed fluctuations.
