Not able to PWM for berd air pump



  • @dc42 I was travelling and could not reply you faster. Here is the configuration for fan

    M106 P0 S255 I0 F25000 H-1

    I tried both S1.0 and S255 but nothing happened with PWM fans. As I mentioned, the pump works fine with always on fan ports.

    What is the difference between S factor mentioned in M106 and slider used in Duet web control? Do they perform the same function.

    While I am typing this my config.g got deleted automatically and I see config.g.bak. Any idea how to recover my config.g file



  • Took the SD card out, renamed the config.g.bak to config.g, the duet is back online but still I have this problem with the pump

    Cheers,
    Vasan


  • administrators

    @sm3d said in Not able to PWM for berd air pump:

    @dc42 I was travelling and could not reply you faster. Here is the configuration for fan

    M106 P0 S255 I0 F25000 H-1

    I tried both S1.0 and S255 but nothing happened with PWM fans. As I mentioned, the pump works fine with always on fan ports.

    What is the difference between S factor mentioned in M106 and slider used in Duet web control? Do they perform the same function.

    While I am typing this my config.g got deleted automatically and I see config.g.bak. Any idea how to recover my config.g file

    Does it work if you short out the thermistor? I don't recommend running it like that for long, but I recall that someone else found that the thermistor stopped the motor from starting - indicating that a physically smaller thermistor is needed.



  • @dc42 I connected the positive from the pump directly without the resistor. I also tried by touching both the legs of transistor together effectively shorting them(hope I am correct) still no luck.


  • administrators

    @sm3d said in Not able to PWM for berd air pump:

    @dc42 I connected the positive from the pump directly without the resistor. I also tried by touching both the legs of transistor together effectively shorting them(hope I am correct) still no luck.

    That's odd, because with the FET shorted its Fan connector is in parallel with the always-on connectors, and you said that the pump works on those (even with the thermistor).



  • Yes I agree with you that its odd. I don't know what to do. Thanks @dc42 for your suggestions so far.

    Cheers,
    Vasan


  • administrators

    You could use a multimeter to check for low resistance between the VFAN pins of the always-on and controlled fan connectors. Also to check for low resistance between the mosfet source pin and the ground pin of the always-on fan connector.

    Then connect the pump/thermistor combo to a controlled fan output, set that fan to full PWM and not thermostatic control, switch your multimeter to Volts and measure between the VIN ground terminal and each of:

    • FAN- output on the controlled fan connector
    • VFAN output on the controlled fan connector
    • Mosfet source pin

    Take great care when measuring these voltages! Many users have shorted the fan output pins together when trying to take similar measurements, resulting in a blown mosfet. So plan how you are going to do it with no risk of shorting anything, and do a dummy run with power off first.



  • Hi David @dc42 ,
    Thanks for your help and suggestions! My knowledge in electrical engineering is very limited so pardon my silly questions. I use duet v1.01, may I know where is the MOSFET source pin? I am trying to write the procedure in steps based on my understanding.

    Step 1:

    Check the resistance between V_FAN pin of FAN_0 and V_FAN pin of Always on Fan

    Step 2:

    Check the resistance between MOSFET source pin and ground pin of Always on Fan - Where is the MOSFET source pin in Duet wiring diagram

    For Step 1 and 2 what are the typical resistance values?

    Step3:

    Connect the pump with thermistor to one of the PWM control fan pins then measure the voltage between:

    (i) Negative pin of the PWM fan connector and VIN Ground terminal (-ve pin of the power input)

    (ii) Positive pin of the PWM fan connector and VIN Ground terminal (-ve pin of the power input)

    (iii) Mosfet source pin and VIN Ground terminal (-ve pin of the power input)

    In the duet wiring diagram, if you can indicate where is the MOSFET source pin, it will be helpful.

    If it involves a high probability of blowing up a MOSFET, I rather prefer not to do it because I do not have the skills to solder them back.

    Thanks again for your help!

    Cheers,
    Vasan



  • Same issue there, thermistor doesn't close the circuit.

    I've removed it for the moment, hope not for too long 🙂

    @dc42 mentionned in a another post that it may be due to the motor not drawing enough current to heat up the thermistor (Posting this to merge backlog discussion in this dedicated topic)



  • @dc42 @Hergonoway The problem is solved. I reduced the frequency F parameter to 10 to see what happens and voila, PWM worked. Then I raised it to 100, still worked. I am yet to check higher frequencies (will do in the evening).

    Previously, I used F25000, F500 and F100 but it did not work. Now out of the blue it works. I haven't changed anything in my setup.

    Cheers,
    Vasan


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