Finally working – VFD noise issues

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  • November 25, 2014 at 11:42 pm #7021
    mort
    Member

    I’ve been having a lot of trouble with my Chinese made 6040 CNC machine, which turned out to be mostly due to the VFD for the 800 watt spindle. I’m posting here in case others are using a similar configuration and having similar problems.

    I’m using a v7 TinyG as the controller for it, currently running 438.02 firmware.

    To begin with I was using CoolTerm to send the g-code files to the TinyG, and fairly frequently the machine would depart from the g-code and head off in some random direction, typically for about 100mm or so before returning a few lines ahead of where it left off. This almost always ruined the workpiece and ran the risk of hard crashing one of the axises.

    I switched to tgFX which resolved that particular issue. Every second piece I’d cut or so the machine would freeze and not resume. I’d also get much smaller departures from the g-code. This all got much worse when I moved the cnc to a dedicated workbench, which also moved the VFD closer, and it got to the point where I was having to restart jobs 4 or 5 times to get them cut.

    To cut a long and very frustrating story short I identified the culprit after I tried a longer usb cable and got continuous disconnects of the tinyg from the computer as soon as I started the VFD.

    The fix is to install a EMI filter in the mains power line very close to the VFD, and to add ferrite bead on the VFD output (near the VFD and near the spindle) and a ferrite bead on each of the connections to the stepper motors (as close to the TinyG as possible). I already had an EMI filter on the tinyG and stepper motor power supply, but I’d recommend doing that if you haven’t got that.

    Once I did this I was able to run 8 separate pieces in the time it was taking me to do 1 previously. No crashes, no weird departures, no new holes in my spoil board or hold down clamps. That was the first time for me to do that many pieces at once.

    One issue I have noticed is that if you run a number of jobs one after the other with out resetting the TinyG it will slow down a lot. This normally manifests very noticeably on the third job, but that might be a factor of the g-code I was using for the test. I’ll post the g-code file shortly.

    November 25, 2014 at 11:57 pm #7022
    mort
    Member

    To reproduce the slow down bug I used the g-code in the file here.

    To reproduce it just run it multiple times in a row without resetting the TinyG. On my v7 (438.02 firmware) everything slows down a lot on the 3rd run through, and is very noticeable.

    for the curious I was making a set of hopping kangaroos for my nephew, based on this instructable . The 0,0,0 location for the g-code is bottom left and top. I think the material was 12mm thick. Cutter is a 3.15mm end mill.

    November 26, 2014 at 6:06 am #7023
    cmcgrath5035
    Moderator

    Interesting find.
    If you get a chance, identifying the source of your ferrite beads and perhaps a photo of you implementation might be helpful to others.

    Here is a suggested way to may such info available:

    December 3, 2014 at 10:04 pm #7081
    Zootalaws
    Member

    I would love to see how you installed your ferrite beads, Mort.

    Also, you said “The fix is to install a EMI filter in the mains power line very close to the VFD”

    Can you expand on that? What is an EMI filter and how would I install one?

    December 4, 2014 at 7:03 am #7091
    cmcgrath5035
    Moderator

    Here is just an example of an industrial noise filter

    They are numerous on ebay, relatively inexpensive; removed from decommissioned machines I assume.
    Tolkin is one of many suppliers, Google around a bit and you’ll find a catalog.pdf. You have to buy for the right voltage, current and single/3 phase.

    I bought and installed one of these last year for my AC Blower, an electronically controlled torque motor. I am suspicious that my TIG Welder, with hi frequency arc-starter, took out the electronic controls.
    TIG draws 50A, those were hard to find, but motor sized filters were plentiful.

    December 4, 2014 at 7:57 am #7096
    Zootalaws
    Member

    The Bay’s no good for me – they usually won’t ship to these parts, but thanks. It’s enough for me to find something.

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