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Slowing down grinder with variable speed/dimmer controller

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  • Slowing down grinder with variable speed/dimmer controller

    So I have a DF64 and have toyed with the idea of using one of those Ebay plug and play variable speed controllers to adjust the grinding speed.
    I had tried it in the past with a xeoleo which worked well.
    Looking further into it there is a post from 2014 saying this is a bad idea due to increased strain and heating of the motor and a specialised speed controller for AC is required.
    Wondering if there are any new solutions for altering grinding speeding that have come out since then or is this still a bad idea? Cheers

  • #2
    I have seen this done on youtube before. I think it might have been CY from Cafe Martella in Singapore

    https://www.youtube.com/watch?v=SpQ7YIJDzeQ

    Biggest problem you will have is burning out the motor if it stalls at lower speeds.
    Small adjustments in speed are probably okay, but then whats the point for only minor adjustments.

    Snobs with the Lagom etc could probably chime in and say that speed differences are very minor in final flavour in the cup - but I have zero experience here.

    CY does do some Q&A on the whole mod:

    "Yes the rpm mod don't really improve the result on espresso grind and the will have a greater impact on filtered coffee grind when rpm is lowered."

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    • #3
      Dimal ....any thoughts, comments on the electrical / engineering / elektrickery of it?

      Obv entered my mind more than a few times in recent years.
      Particularly when reading the excellent thread by Stavros during his grinder build
      in recent years.

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      • Dimal
        Dimal commented
        Editing a comment
        With Single Phase Squirrel Cage AC motors, a practical option for reasonable cost is not really available. DC motors though, offer much more in the way of practical solutions to provide high torque, variable speed.

    • #4
      Would a Pulse Width Modulator (PWM) controller work? Essentially same tech as dimming LED lights. Instead of reducing voltage/current, it turns the LEDs/motor on and off very quickly to give the illusion you are controlling the brightness/speed. see google to the rescue here

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      • #5
        Originally posted by Superman View Post
        Would a Pulse Width Modulator (PWM) controller work? Essentially same tech as dimming LED lights. Instead of reducing voltage/current, it turns the LEDs/motor on and off very quickly to give the illusion you are controlling the brightness/speed. see google to the rescue here
        I assume it would have an AC motor, not a DC motor. So a PWM would not work.

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        • #6
          I'll see what CY had to say. Thanks!

          Comment


          • #7
            Originally posted by WhatEverBeansNecessary View Post
            I have seen this done on youtube before. I think it might have been CY from Cafe Martella in Singapore

            https://www.youtube.com/watch?v=SpQ7YIJDzeQ

            Biggest problem you will have is burning out the motor if it stalls at lower speeds.
            Small adjustments in speed are probably okay, but then whats the point for only minor adjustments.

            Snobs with the Lagom etc could probably chime in and say that speed differences are very minor in final flavour in the cup - but I have zero experience here.

            CY does do some Q&A on the whole mod:

            "Yes the rpm mod don't really improve the result on espresso grind and the will have a greater impact on filtered coffee grind when rpm is lowered."
            Well its reasurimg I'm not missing out on much!

            Comment


            • #8
              Originally posted by Superman View Post
              Would a Pulse Width Modulator (PWM) controller work? Essentially same tech as dimming LED lights. Instead of reducing voltage/current, it turns the LEDs/motor on and off very quickly to give the illusion you are controlling the brightness/speed. see google to the rescue here
              PWM reduces the average voltage available by turning the supply on and off quickly: with a low pass filter (a simple cap will suffice) the output voltage will be equal to the supply voltage times the mark to space ratio.

              Since the speed of an AC motor is not primarily a function of supply voltage this will not work.

              The stator field in an AC motor spins at the line frequency. The rotor tries to catch the stator field and usually fails* so most motors will run a bit slower than the field speed by a factor called "slip"

              To control speed you can change the frequency or increase slip.

              It is very difficult to get a frequency changing supply (AKA a VSD) to work with a single phase motor so you won't see this in a coffee grinder.

              Anything that increases slip also reduces the torque available from the motor. This works well for low torque applications like fans but not so well for things like a coffee grinder.

              If you want variable speed drive it is much, much easier to use a DC motor. PWM works a treat for these.





              * Permanent magnet synchronous motors and the increasingly rare hysteresis synchronous motors are the exceptions. For reasons that you don't care about (but I do, so ask if you dare) you won't see either of these in a coffee grinder.

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