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Interface touch problems

Discussion in 'Interfaces' started by Sondergaard, Dec 26, 2021.

  1. robin lawrie

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    When I say chassis, I mean the case all my electrics are in, rather than the machine itself..
     
  2. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    Just an example. Not saying it is that - but EMI/Grounding is less science and more intuition. Radiated interference, can induce voltages in ground cables, that can create loops where you don't intend for them to be -it happens - and if you observe Earthing to be related to the issues, a little experimentation may be needed
     
  3. robin lawrie

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    Ok so I tried with all components running from bench psu.. No glitches.. I also tried isolating my psu from ground (no earth!). Still glitchy.

    So I'm guessing that leaves a bad psu. V annoying.

    I did find a meanwell 24v 350w on amazon, discounted to 44 euros.. However before ordering, I wanted to check.. Is it going to be sufficient? My machine will have 4 steppers (2 on y) and I got beefy 4.2 amp ones. I know the black box can't arrive at that power level, but I don't want issues on a hard cut with movement on all 3 axes.. Having said that I've no idea how likely it is to actually max out all steppers simultaneously? This is my first cnc machine.

    The psu I have is supposedly a 20amp one, so like... 480w?

    The 350w meanwell is exactly the same size.. Unfortunately the 500w meanwell is too big to fit in the space I have
     
  4. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    4.2amp peak motors, but at what voltage.
    Gonna use our motors for the math because I know the specs by heart but the concept should translate:

    Our regular NEMA23s are 2.8A peak, at 3.0V coil voltage. We feed 24V into the driver but it "chops" it up into a pseudo sine wave to send to the motor. The driver limits the current to a set point - lets say 2.5A (you don't run any motor at MAX - it won't last). So to deliver 2.5A into the coil (specific resistance of R=V/I where I=2.5, V=3 = approx 1.2ohm) means its limiting the voltage to around 3v too. 3V * 2.5A = 7.5w per coil.
    Two coils (bipolar motor) means 2x7.5w = 15w per motor. x 4 motors = 60w. Now even if we factor in doubling the wattage to account for acceleration peaks, driver losses, wire resistance, etc etc and even a 150w PSU would run the motors fine.

    Most power is drawn when the machine is stationary (both coils powered to lock motor in place) - in use it drops the average down a little lower than that too.
     
  5. robin lawrie

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    Ok I was doing a simple 24v x 4.2a x 4 motors..

    I see mine are specced at 3.78v and 4.2a, with a resistance of 0.9 ohms.

    So ill get the meanwell then :)

    Hard to believe these motors only draw circa 30w and will move a chunky cnc machine!
     
  6. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    Leadscrews for the win :)
     
  7. robin lawrie

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    Ballscrews actually...
     
  8. robin lawrie

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    ok new psu ordered, fingers crossed
     
    Peter Van Der Walt likes this.
  9. robin lawrie

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    Just a quick note to say: new psu arrived and installed.. Fortunately the screw holes matched so it was an easy swap.

    Interface is now working as advertised :)


    But big :( to OpenBuilds Italia for selling me a crap psu.

    This is the one they sold me:

    Alimentatore stabilizzato 24V 20A – OpenBuildsItalia

    The label says "each italy" as the brand.

    Seems to be this:
    https://amzn.eu/d/ad4ZynD

    But sold with a fat markup to almost the price of the meanwell.

    The purchase was made almost a year ago so not sure wether it's worth asking for a refund.
     
    Peter Van Der Walt likes this.
  10. robin lawrie

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    ive written to openbuilds Italy .. at least to let them know im not happy.

    its impressive, they literally sold me the absolute cheapest 500w 24v psu available on amazon italy (actually cheaper than any of the 350w ones too) but at almost double the price.
     
  11. Pke84

    Pke84 New
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    Hello,
    I'm having similar touch-issues with my interface on a blackbox x32. (all up-to-date regarding FW)
    As long as the Spindle motor is off, there are no problems what so ever while jogging in continuous mode.
    However, the jogging movement gets interrupted, as soon as I start the spindle,.
    Everything works fine again, when I touch the interface button while also touching the PS-casing or the Mill.
    Jogging via pc & usb works always without problems.

    So I guess that I need to ground the interface somehow, right?
    But how do I do that? The X32 is only connected to V-/V+ of the PS and the Interface only has this one cable without ground.

    My setup uses a Vevor sewing-servo motor and I use a PS from Meanwell similar/same to the one sold by Openbuilds.
     
  12. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    David the swarfer likes this.

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