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  1. #81
    The AXBB-E is not a bad option...also easy to connect your inductive proximity switches directly to the inputs.

  2. #82
    Quote Originally Posted by ericks View Post
    The AXBB-E is not a bad option...also easy to connect your inductive proximity switches directly to the inputs.
    If/when I ever decide to build another machine from scratch and move away from the dirt-cheap LinuxCNC/Chinese BoB controller, that looks like a good alternative.
    An optimist says the glass is half full, a pessimist says the glass is half empty, an engineer says you're using the wrong sized glass.

  3. #83
    Quote Originally Posted by Kitwn View Post
    Embarrassing but I must own up: I realised during my tests that for all these years I've left the 36V supply for my stepper motors floating. Neither rail was grounded so the whole supply was bouncing up and down by 8 Volts at several KHz. It's a miracle the machine worked at all! Any way that's now fixed and some of the bits from RS have arrived, though not the screened cable for re-wiring the sensors yet.
    -
    Attachment 27796
    I am just rewiring my control panel and realised that my 48V to the drivers was also floating.

  4. #84
    Muzzer's Avatar
    Lives in Lytham St. Annes, United Kingdom. Last Activity: 6 Hours Ago Has been a member for 4-5 years. Has a total post count of 369. Received thanks 47 times, giving thanks to others 7 times.
    I found that those clip-on ferrite clamp filters are pretty good at dealing with some of the noise spikes you get in installations like these. With switched mode power supplies, VFDs and stepper / servo drivers all doing their little thing, there are lots of noise sources thrashing away. Just a few of those spikes getting in to the step / direction etc lines can cause lost or gained steps or gradual creep of the table.

    You can get them from ebay, CPC etc for peanuts and they are very simple to fit, without needing to disconnect anything. The actual specs probably aren't massively important as long as they actually fit over your cables(!). Worth having a few handy or even just a good idea to fit some by default.

    I got some of these randomly chosen Chinesium Mystery Brand filters that work out about a quid a pop for the 9mm version. Other brands are available.....
    https://www.ebay.co.uk/itm/402221769539

  5. #85
    Neale's Avatar
    Lives in Plymouth, United Kingdom. Last Activity: 13 Hours Ago Has been a member for 9-10 years. Has a total post count of 1,660. Received thanks 292 times, giving thanks to others 10 times.
    I'm pretty sure my 68V DC driver supply is also floating, and has been for the last 3 years or so. Why not? So, it bounces around a bit, but considering that you are generating 4A+ spikes of current up the power leads generating lots of potential EMI, what does a potential difference between the wires and some arbitrary ground point mean?

    One good point about leaving it floating is that if there is an accidental short to earth of a motor lead at some time, you are less likely to make a driver go pop.

    I have my "naive" hat on here but isn't there an argument that says that leaving it floating is less likely rather than more to inject random noise into the environment?

  6. #86
    Muzzer's Avatar
    Lives in Lytham St. Annes, United Kingdom. Last Activity: 6 Hours Ago Has been a member for 4-5 years. Has a total post count of 369. Received thanks 47 times, giving thanks to others 7 times.
    Yes, a lot of the big industrial gear does that. They use a ground fault detection circuit to look for a fault to ground and flag up a warning if one is seen, rather than bombing out immediately. That allows the system to continue running until it can be brought safely to a halt. This can be handy if you happen to be operating eg an elevator lift or a paper / steel mill at the time.

    You can always connect the floating node to ground via a Y cap to stop it flying about so much. This gives the noise a path back to ground without the danger of a DC path popping your drives or controller.

  7. #87
    Muzzer, Neale,

    My original issue with this was in regard to noise getting into the BoB supply which appeared to have been a major part of my problems. It seemed obvious at the time, but I take the points you both make. As long as the BoB supply and the motor supply are completely separated and the cable screens effectively grounded it should not be an issue. I have my machine working now and am keen to start using it to make things but I thing the next time I decide on a significant upgrade it will have to include a complete rebuild of a new controller in a better enclosure with a far more comprehensive approach to noise screening.

    The clamp-on ferrites look like an excelent idea and I'll order a bagful.

    Rob,
    As you'll see from the above replies, you shouldn't be changing that anytime soon. My reasoning lacked the rigourous engineering logic it should have had.
    Last edited by Kitwn; 29-04-2020 at 01:20 AM.
    An optimist says the glass is half full, a pessimist says the glass is half empty, an engineer says you're using the wrong sized glass.

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