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Time for a new capacitor - Compak K3?

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  • Time for a new capacitor - Compak K3?

    Does this sound like a capacitor on the way out?

    A few times recently, my 10 y.o. Compak K3 has just buzzed/hummed when turning on the grind switch (no grinding). On 2 separate days I switched it on and off a couple of times and it then started grinding.

    Today I had to remove the hopper, tip out the remaining beans in the grind chamber and manually turn the bottom burr back and forward to clear the remaining whole and partly ground beans. Nothing foreign or odd inside that I could see and it wasn't jammed. Same grind setting and beans which were used over the last few days without issue. Switched on and it began grinding no problem.

    It's happened 3 or 4 times so far. Never missed a beat before this.

    Haven't looked inside yet but it appears the K3 uses a 6.3 µf 450v 50/60hz capacitor similar to / like the one below. (Compak Part# K.409)

    Click image for larger version

Name:	Compak K3 Capacitor Ducati energia.jpg
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    DUCATI Energia Series 4.16.10.10 (or equiv. ?)

    If it needs replacing, what brands do I look for to avoid the "duds"?
    Last edited by CafeLotta; 13 September 2019, 08:05 PM. Reason: replaced image (No company watermark)

  • #2
    Have you tried contacting any of our Site Sponsors who sell Compak grinders?
    Coffee Parts have equivalent items in stock...
    https://www.coffeeparts.com.au/parts...tor-6-3mf-450v
    Failing that, they would be easily obtained from any of the major electronics suppliers as e14, RS or even Wiltronics for example.

    Mal.

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    • #3
      Have had a quick look earlier at E14 & RS but can't find the DUCATI Energia Series 6.3 µf 450v (4.16.10.10). Can find a 6 µf in the same series but don't know enough about them as to whether this would suit? I read the replacement should be exactly the same rating as the original?

      Not sure which of the other brands are worth looking at or which to avoid.

      Am aware I need to check and discharge the old one before removal.
      Last edited by CafeLotta; 13 September 2019, 11:48 PM.

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      • #4
        The run capacitor is there to supply a second phase that runs "across" the main supply (90 degrees out of phase). If you draw the two phase waves you'll see that this angle "fills in" the valley in the waveform*.

        The phase shift is given by SQRT (LC) where C is the capacitance and L is the inductance of the motor winding. From this, if the 6.3 uF gives exactly 90 degrees (not necessarily the case) 6 uF will give 88 degrees.

        I used to design tiny electronic motor drives with variable phase angle, a 2 degree phase shift was detectable but not problematic.

        *The motor responds to the square of the current because energy in the winding is I^2L. If the two phases are equal in magnitude, the torques sum to a constant because sin^2(x) + sin^2 (x + 90) = 1. The 2 degree phase shift makes the torque function sin^2(x) + sin^2 (x + 88) which varies from 0.97 to 1.03, so there is a 6% variation of torque at 100 Hz, which creates noise.
        Last edited by Lyrebird; 14 September 2019, 10:11 AM.

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        • #5
          Thank you for the detailed reply Lyrebird. Exactly the info I was after.

          Are there any brands of capacitors to avoid?

          Might just go with the 6.3 µf capacitor Mal referenced from Site sponsor Coffee Parts. They appear to be a Chinese brand called "Last One"?

          Thinking about the grinder's recent behavior, I also wondered if the installation of new burrs a few weeks ago might have contributed. I did notice I was getting more fines than previously. I'll need to take the top burr off this weekend and see if these fines are collecting anywhere and loading things up a bit, making life harder for an older grinder.
          Last edited by CafeLotta; 14 September 2019, 04:39 PM. Reason: Added Coffee Parts reference. Added "Last One" brand name.

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          • #6
            For the most part, "brand" is inconsequential...
            You don't need to find a Pirelli capacitor, the one I linked to is perfectly fine.

            Mal.

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            • #7
              I agree with Mal re brand, at least for metallised polypropylene capacitors (which is what these are). Electrolytics are a whole different ball game.

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              • #8
                I need a capacitor myself...

                I'm slow to start in the morning and just whine...

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                • #9
                  As do we all.

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                  • #10
                    After a dismantle and full clean today I checked the original capacitor specs. Turns out it's an "Inco Sintex" 6µf with the date (07/09) matching near enough the grinder build date. I'd imagine there's been a couple of changes in the newer model like motor and matching 6.3 µf capacitor.

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                    • #11
                      As Mal said, capacitor brand is immaterial. The three things that matter are the same microfarads, at least the same voltage....and phyical size so it slots into the space.

                      Capacitors are cheap. Buy and try.

                      Be very careful handling it though. Even though it has been removed from power it can be loaded with dangerous elecrical power. So with a plastic handled screwdriver short the contacts before touching them with your hands.

                      There are reliable unreliable ways to test with a multi-meter... but just get a new one and see if that fixes the problem.

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                      • #12
                        Need to be game though, to short out a (possibly) charged capacitor with a screwdriver....
                        Not without eye protection at least.

                        Mal.

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                        • #13
                          Originally posted by robusto View Post
                          As Mal said, capacitor brand is immaterial. The three things that matter are the same microfarads, at least the same voltage....and phyical size so it slots into the space.

                          Capacitors are cheap. Buy and try.

                          Be very careful handling it though. Even though it has been removed from power it can be loaded with dangerous elecrical power. So with a plastic handled screwdriver short the contacts before touching them with your hands.

                          There are reliable unreliable ways to test with a multi-meter... but just get a new one and see if that fixes the problem.
                          The type of load the cap is designed for is relevant too. Buying one made from the same material should ensure you're all good.

                          In this type of installation (with a motor) the likelihood the cap is still charged is nil as long as both leads are still connected. In old CRT screens yes they'll hold a potentially deadly charge for 6 months or so, but this one will have been discharged within a couple of seconds of the grinder being turned off. And don't go shorting capacitors if you don't know what you're doing, they can get very nasty and explode and/or produce a nice arc-flash.

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                          • #14
                            Thanks for all the info guys.

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                            • #15
                              Get a Rubicon cap if you can.

                              Also there is a difference between domestic caps and automotive. It might be just the temperature rating, but they are more hardy

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