Broken PWM motor controller?

Discussion in 'General Electronics Chat' started by Rawjcl, Oct 6, 2015.

  1. Rawjcl

    Thread Starter New Member

    Oct 1, 2015
    [I went crazy writing the question, so I'm putting the TL; DR version before the original post:
    - I bought a cheap Chinese PWM DC motor control. No name. No instructions. Label on chip was sanded off.
    - after I hooked it up, the voltage, current and torque changed when I turned the knob.
    - am I using it wrong, or did I break it?
    -if broken, can I fix it without knowing the chip's part number?
    Thanks in advance.


    I don't know if this thing is broken, or if I'm just using it wrong. There wasn't a manual included, so I'm afraid I did something stupid hooking it up. Any help is appreciated.

    I bought a no-name Chinese PWM motor speed control on eBay that has a range of 6v-90v DC.

    I bought it for a 90v motor that I have been running with a 30v power supply. I need it to run at 2-10% of its normal speed, but have enough torque to turn a conveyor belt.

    This 90v motor worked in my application but when I lowered the voltage to decrease the RPM to the range I needed it wouldn't run.

    The power supply has 4 wires and puts out 3v, 30v and some voltage I can't remember.

    The 30v wires are blue and brown and I got the polarity mixed up for a fraction of a second. I assume this was enough to damage the IC, but I'm not entirely sure.

    When I turn the knob CCW voltage and current (and as a result, the motor's torque) are reduced. Not what I was going for, but is it possible this is normal behavior for this chip?

    There are 3 wires going from the potentiometer to the circuit board... maybe disconnecting will make PWM work?

    I saw something in the listing about removing the potentiometer and connecting it to an automated controller, so that's why I ask.

    What if i just need to change the IC? They sanded off the label so I can't tell if it's a 555, op amp or microcontroller.It's a DIP with 8 pins, but that hasn't helped my search for a part number much.

    Is there a way to tell which chip it is by looking at what's connected to the pins and possibly the part numbers of the transistors? I've noticed that some op amps have the same pinouts. Is it possible to substitute a different op amp or maybe program a ATTINY to work in its place?

    Sorry for all my ignorance. Deeply sorry.

    Thanks in advance.
  2. MaxHeadRoom


    Jul 18, 2013
    IME, These are very cheap (simple) circuits based on a 555 ic and a couple of Mosfets for simple PWM control.
    You reduce the PWM and hence the Average current = torque, if you need constant torque through the RPM range then you need a feedback/PID controller.
    If you remove the pot, you can supply it with a 0-10v analogue control, but still no torque control without feedback.