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Thread: static causing communication problems...again

  1. #11
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    Quote Originally Posted by Ken Sully View Post
    I agree with Jim.
    I you have two different grounds you will end up with dissimelar grounds and current can flow between them. Make suer your system is tied to the same ground. Not one from the house and one from your ground rod.
    Well this is all pretty overwhelming, particularly for someone who knows diddly about electricity.

    The only ground rod I am aware of in my shop is the one the electrician drove into the ground through the concrete. Isn't everything else grounded via the third prong of a plug right into the electrical system of the building?

    Isn't the ShopBot grounded simply by being plugged into its 220 outlet? I don't have any additional copper wires going from the machine to a ground. Never have.

    If I disconnect the copper ground wire that currently runs from the DC frame to the ground rod, how do I ground the DC? (It's an Oneida Gorilla Pro, and it came with a ground wire that runs from the top of the motor and clips to the metal mesh frame around the filter, which has always been attached). Run a copper wire from the metal ductwork to electrical conduit on the ceiling?

    The DC is literally a few feet from the ShopBot. Does that make the problem worse?

  2. #12
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    The problem with grounding and static is that static is extremely high voltage with very little amperage. It's very easy for electrons to leak all over the place and when they leak into the electronics of the controller, it gets messed up. The controller voltages are very low and that contributes to the problem. If you've ever worked on an old car with electrical problems, you have an idea of the importance of proper grounding.

    It may not be directly intuitive but having grounds in different places can actually cause problems. That's why you need to ground EVERYTHING to that rod the electrician installed. Otherwise, electrons can flow in unusual paths and end up in your Shopbot controller electronics. Electricity always seeks the easiest path to ground and if that's through your controller, then you get problems. Provide easy paths for those stray electrons. Ground everything carefully to that rod. Take the time to run individual lines to every moving part. You should be able to zap your machine anywhere with 40,000 volts and not have anything unusual happen. The only way to do that is to be positive about your grounding.

    I also agree with the others who have discussed ONE GROUNDING POINT.
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  3. #13
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    now I am confused. If he has his normal electrical ground for everything plugged in and a ground rod isn't that multiple grounds for him?

  4. #14
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    I wonder if the desire to help is causing people to solve problems that I am not having. The machine stuttering/loss of positioning problem happens ONLY when the DC is running -- and particularly with larger diameter bits making more chips. This leads to me to conclude that the DC is creating enough static to interfere with normal CNC operation. Which means that somehow I need to change/improve the grounding for the DC, right? Why would I need to ground, for example, the YZ car if it's the DC that's causing me problems? Admittedly I know little about this topic....just trying to be as analytical as possible.

  5. #15
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    Quote Originally Posted by bobmoore View Post
    now I am confused. If he has his normal electrical ground for everything plugged in and a ground rod isn't that multiple grounds for him?
    That was my point....If you have the control PC grounded through the 120V plug and the machine power grounded through the 240V plug (or fixed wiring) and additionally the machine frame itself through a ground rod that sounds like trouble.
    Box Joint, Dovetail, Guilloche and MazeMaker Software Here

  6. #16
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    The only ground rod I am aware of in my shop is the one the electrician drove into the ground through the concrete.
    Good. This is THE sole ground for your building. It should be connected directly to your breaker box, which in turn is the ground reaching to your outlets and any metal conduit running from the breaker box.
    (In other words, there is no ground coming to your building via the power lines) All things grounded eventually lead back to this single grounding point.


    Isn't everything else grounded via the third prong of a plug right into the electrical system of the building?
    The third prong of that outlet is grounded, but only because it's path eventually leads back to that grounding rod. Again, there is no ground fed to your building through the power lines.

    Isn't the ShopBot grounded simply by being plugged into its 220 outlet?
    Not entirely. The shopBot control box is grounded by doing so, but not it's metal frame.



    I don't have any additional copper wires going from the machine to a ground. Never have.
    I'd call this a bingo.
    It is imperative that a ground wire be run from the metal frame. Typically done near one of the feet, an un-insulated cable clamp is fastened to your machine, being careful to scrape away paint to establish a metal to metal contact. Better yet, drill a hole in the frame and use a self-tapping screw to attach. Clamp a relatively heavy gauge ground wire to it, and connect to ground. In my case, it is attached to metal conduit, which is attached to main breaker box housing, which as you may recall from above, goes to the main building ground, in your case, the grounding rod.

    If I disconnect the copper ground wire that currently runs from the DC frame to the ground rod, how do I ground the DC? (It's an Oneida Gorilla Pro, and it came with a ground wire that runs from the top of the motor and clips to the metal mesh frame around the filter, which has always been attached). Run a copper wire from the metal ductwork to electrical conduit on the ceiling?
    Not sure why a line goes straight to the rod - if it's plugged into a grounded outlet like any other machines in your shop, should be good.
    Either way,you don't want to disconnect it.

    HOWEVER: you must not let that DC hose ground make contact with any metal on the cnc framework (which by now should be grounded) or you'll make a ground loop, which would generate it's own set of problems.



    I sympathize, as I've been there with the comm's issue. Keep us posted, as we want to see you running smoothly.

    Jeff

  7. #17
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    Quote Originally Posted by jTr View Post
    Good. This is THE sole ground for your building. It should be connected directly to your breaker box, which in turn is the ground reaching to your outlets and any metal conduit running from the breaker box.
    (In other words, there is no ground coming to your building via the power lines) All things grounded eventually lead back to this single grounding point.
    Thanks, Jeff, for your support!

    Actually I suspect this driven rod is not the sole ground, as it was added after the fact. But I have no idea where the ground in the shop is. I rent the space....So maybe I should disconnect the copper wire from the DC to the new ground rod?

    The DC hose does not touch any metal on the machine. I was careful to figure that out last winter.

    Replaying everything tonight, I realize that the inner support wire for my DC flex hose (not the bare copper wire inside the hose) doesn't connect to the metal duct work at the top. So that's the first thing I will do tomorrow and then retest. Maybe that wire, although somewhat insulated in the plastic hose, was collecting static that had nowhere to go.

    If that doesn't solve things, I guess I need to take a fresh, comprehensive look at my grounding setup.

    I certainly wasn't prepared for this a year ago. I expected to deal with the learning curve, break bits, etc. But static interfering with operation? Wasn't on my radar, and frankly ShopBot isn't particularly helpful on this either....

  8. #18
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    Concerning the general nature of static and electrostatic discharges (ESD), this is a hugely complicated field. I am a degreed electrical engineer, (retired) and where I worked, we had two high-tech men who's job it was to test and harden complex microprocessor controlled products against the effects of ESD. These guys used Key Tech and Schafner ESD simulator guns to hit products under test with ESD events. They could spend a month to harden a system, AFTER they had become very experienced. While the work they did, and what they showed me, was above my pay grade, they made very clear that when dealing with ESD, just connecting a few wires and thinking you'd solve your ESD problems is as unlikely as winning the current $900 million lottery.

    The very nature of ESD events involves super fast rise-times, of just a few nano-seconds. When dealing with such huge bandwidth signals, the stray inductances of ordinary wires reduces them effectively to nothing more than open circuits (yielding them totally ineffective, even though an old DVM will show that at DC they are solidly to ground. Instead, effective low-inductance ground planes need to be established,,,, (very hard to do, even with multi-layer PCBS), with all possible discharge paths needing to be by-passed for the very highest rise-time discharges.

    Where I worked, our company could not tell our distributors/installers, "Oh, you are having ESD problems? Figure out how to ground our products properly...…. good luck..." No, to be able to sell our products, we had to sell products which our staff had hardened against ESD. And it was the work of these two brainy guys, working with the development engineers (of which I was but one), who had to harden our products so ESD would not affect them. (These staffers would go through many iterations of revised ground-planes, adding micro spark gaps, voltage clamps, small capacitors, and other such hardware to re-direct ESD discharges into non-damaging and non-disruptive paths. And their work also involved lots of software self-checking to make our products self-correct if fault modes were triggered. (Top level efforts as I recall, were to eliminate device destruction, and then eliminate/mitigate device operation disruption. Hugely time consuming to verify and validate all of the corrective measures...……..)

    From the little I remember, our ESD guys subscribed to ESD journals and went to conferences on the subject, and met with people from all manner of industries, that starting in the 1990s, were hit with the cursed interaction of ESD with the then new fangled microprocessor based systems just then coming to market. And our guys made clear that all manner of responsible companies had come to the realization that to remain viable, that they had to come to terms with ESD and be able to bring ESD hardened products to market. The lesson here, is that if an analogous set of market forces had come to bear on Shopbot, they would have had to hire to big brains like we had, and they would have had to harden the Shopbot product line against ESD.

    But perhaps the consumers of Shopbots are simply too disorganized, and willing to accept their ESD problems as being their own fault. Based upon what I saw in my work, the matter of ending the Shopbot ESD induced communication instabilities may well be corrected by ESD experts, hardening what Shopbot offers, instead of waiting for Shopbot to come out with some entirely new platform...… (But again, such an effort would not be a trivial undertaking...)

    (And that raises the corollary concern...…. What IF Shopbot comes out with a new platform, and then we find out that it too has not been ESD hardened? Just being new, and being free from USB doesn't mean the ESD susceptibility will magically disappear..... We had our ESD issues, without having any USB ports!)

    I didn't mean to ramble, and I am no expert in this. But I know enough to say ESD can't be fixed by just tossing a few ground wires here and there, and crossing your fingers...…….. Better luck with a rabbit's foot...… I would rather hope that Shopbot would hire a big-brained ESD expert to harden what they have...… Then that guy can work to make the new system be hardened against ESD..... Chuck
    Chuck Keysor (circa 1956)
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  9. #19
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    Brian,
    Do a continuity test using a multimeter on your bare copper ground wire inside the DC hose. You'll need a long insulated wire hooked to the spindle end of the ground wire to allow you to get your test leads on the other end. Test between the insulated 'helper' wire at the DC end and the DC chassis ground where your bare wire is terminated. It's really the only reliable way to test if your ground wire is doing its job & isn't broken. Then test your DC chassis ground (where the bare wire is terminated) and touch the ground lug in the electric panel or your driven ground rod. You should have continuity on both. Even a cheap HF meter will beep on continuity/a closed circuit path. This is the number 1 test method when troubleshooting anything electrical. Just because you don't know much about electricity now doesn't mean you're stuck that way - right?

    To reiterate - you want a bare copper wire (.023/030 Cu coated MIG wire is fine) that is tied to the DC chassis (which is tied to electrical sys gnd) on one end & running through the hose and only folded over the end of the hose @ the DC foot end. It needs to function as an antenna with nothing metal touching the tip or the rest of the bare wire until it gets to the DC termination point.

    -B
    High Definition 3D Laser Scanning Services - Advanced ShopBot CNC Training and Consultation - Vectric Custom Video Training IBILD.com

  10. #20
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    Quote Originally Posted by Chuck Keysor View Post
    I didn't mean to ramble, and I am no expert in this. But I know enough to say ESD can't be fixed by just tossing a few ground wires here and there, and crossing your fingers...…….. Better luck with a rabbit's foot...… I would rather hope that Shopbot would hire a big-brained ESD expert to harden what they have...… Then that guy can work to make the new system be hardened against ESD..... Chuck[/LEFT]
    Looks like I picked the wrong week to stop sniffing glue.

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