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Vibration Motors Burning Out Using PCA9685BS

Question asked by ling ling on Sep 25, 2017

Good day,all

I have 16 dc vibration motors bought from Ali, rated at 0.1A, Vdc 3-9v. In fact they consumed 0.15-0.18A from 9V. Armature resistance varied from 20 to 30 ohms.

I connected all 16 motors to PCA9685 16-channel pwm controller that runs at 1.6 kHz. I have 8 identical pcb boards as shown below, each pcb is connected to its pair of motors. The power source V1 is supplying all boards and is capable of 11A / 9V. The diode and capacitor is near the motor. Each motor is connected by two copper multi-strand non-shielded wires, 1.6 mm sq diameter, 16 ft. length.

During testing I had been having blown fuses and motors with degraded armature resistance (almost short circuited). Not all of them, not in one time. I haven't observed any spikes on power source terminals. Some motors heated more than the others. I've got two motors at 60°C but quickly disarmed them. Others were not more than 10°C above ambient temperature. As a safety measure I programmed soft pwm transition, lowered maximum duty cycle, lowered the power source voltage to 8V. So far looks like it helped.

schematic

The actual questions are:

  1. What else can I do? I have a low budget so I cannot implement current sensing. Do you think linear voltage regulators could help to protect the motors?

  2. From your experience, can you say that the motors were doomed to burn in my setup or not?

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