Electrical Ground

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Thread: Electrical Ground

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    Registered dsnellen's Avatar
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    Default Electrical Ground

    Quick question. On my ESS, MX4660, 2.2kw spindle setup, I have to use a separate clip-on wire ground connection to the spindle to zero the bit. This prevents, as far as I know, the auto-zero of bit changes. I am wondering if I can connect a "MX4660 system ground" to the spindle can I simply probe for the top of the +10 vdc contact and eliminate the clip-on connection? On my PC 690 system, which has a build-in ground, a separate ground wire is not used and it auto-probes at bit changes nicely. The system is well grounded in that any two metal parts have near zero or zero ohms resistance. No problems with electrical noise (thanks Al_the_Man). The question: Is there any danger to connecting the MH4660 ground with the earth ground? This would eleminate the clip on wire for and allow the system to auto-zero after bit change. Thoughts?
    Thanks
    Dave

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    Default Re: Electrical Ground

    My system is connected to ground by default and unavoidable and I have no problems, I just clip onto frame which is obviously earthed if I clip to endmill it will be the same result it is still earthed,



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    Default Re: Electrical Ground

    Maybe I wasn't clear in my question. "DC" ground as coming from MX4660 is not the same as "earth" ground coming from the AC side of things. With my spindle, I have to connect an alligator clip to the bit in order to complete the circuit when the bit touches the zero plate (which is +12 VDC). On the PC690 system, the alligator clip isn't necessary. I understand that since the PC690 is "earth" ground (3 prong plug) it is magically somehow also connected to the DC ground because the alligator clip isn't necessary. In fact, to attach it causes sparks!

    With the PC690, I have a table zero plate so I can zero the 1st bit to the top of the work piece, the machine goes to the table zero plate, probes that, and determines the offset. On bit changes, all I have to do is change the bit, the machine then motors over to the table zero plate, computes the height and starts cutting away.

    I want to impement the same system using the spindle. I am thinking that since the spindle requires an alligator clip for ground, why not simply permenently connect a DC ground to the spindle and forego using an alligator clip. This would allow me to remove a lot of manual operation with bit changes. Is there any issue with permently connecting the "DC" gound to the "AC" ground?



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    Default Re: Electrical Ground

    Quote Originally Posted by dsnellen View Post
    Maybe I wasn't clear in my question. "DC" ground as coming from MX4660 is not the same as "earth" ground coming from the AC side of things. With my spindle, I have to connect an alligator clip to the bit in order to complete the circuit when the bit touches the zero plate (which is +12 VDC). On the PC690 system, the alligator clip isn't necessary. I understand that since the PC690 is "earth" ground (3 prong plug) it is magically somehow also connected to the DC ground because the alligator clip isn't necessary. In fact, to attach it causes sparks!

    With the PC690, I have a table zero plate so I can zero the 1st bit to the top of the work piece, the machine goes to the table zero plate, probes that, and determines the offset. On bit changes, all I have to do is change the bit, the machine then motors over to the table zero plate, computes the height and starts cutting away.

    I want to impement the same system using the spindle. I am thinking that since the spindle requires an alligator clip for ground, why not simply permenently connect a DC ground to the spindle and forego using an alligator clip. This would allow me to remove a lot of manual operation with bit changes. Is there any issue with permently connecting the "DC" gound to the "AC" ground?
    I would worry if I'd see sparks when I connect something...

    Other than that, some PCs have common DC ground with earth, some don't. Typically, laptops don't have a common earth and DC ground, so you can't really clearly say what is right and what is wrong for your machine. I use isolated supply to my touch plate so I must connect the DC ground side to the bit and I think that is the best way to do it.



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    Default Re: Electrical Ground

    Can't say this is your case, but in many cases that I have seen with "gremlins", removing the connection between low voltage ground and chassis ground clears up the noise. Use a small relay to make the connection only during zero process and make sure there is opto isolation.

    Gary Campbell GCnC Control
    Servo Control & ATC Retrofits


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    Default Re: Electrical Ground

    If there is presently Galvanic isolation between the service GND and the P.S. Common then normally it can be earth grounded.
    One test is to measure between the P.S. common and earth, you might see some voltage there, now place a low value (~100ohm) resistor between the two and see if the voltage collapses, if so it should be safe to take it to earth GND.
    As a matter of course I try to earth connect all commons if possible back to the star point GND.
    Most suppliers of boards use isolation quoting noise separation reasons, but noise can be transmitted through a system inductively or capacitively with no physical connection.
    If you have a tower or desk P.C. it most likely is going to have the PS connected to earth.
    Al.

    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.


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    Default Re: Electrical Ground

    Al, have you encountered problems where joining commons to Earth ground introduces more noise than it removes? Do you also join shields to the common Earth ground point? I've grounded stepper motor drives only to have noise get introduced into the grounded cable shields. The elimination of noise, and different ground potentials, etc., seems often to require a good deal of art, and the big-names disagree in recommendations.



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    Default Re: Electrical Ground

    I have always preferred to connect all commons to earth ground where possible, and so far have not seen a problem, and also ensure the the machine has equi-potential bonding, IOW make sure that there is no possibility of ground loops.
    Al.

    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.


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    Default Re: Electrical Ground

    Everything pretty much works except for a weird limit switch issue. I use hall effect switches. On the Y axis, the sensor is mounted so it moves over the magnets. One magnet is used for Y Home and Y++, and another magnet for the Y--. For some reason, if the Y-- is set on, I get switch activation at random intervals. Usually it is so often I cannot do anything. Simply disabling Y-- makes the problem go away for the most part. Its a magnet about 48" from Home & Y++. The debounce is set to 5500. The Index Debouce is set to 10, but I don't know why.

    And I noticed today, the vacuum tripped the Y switch. This is new. Anyway, everything is grounded to everything else. From the spindle to the Z carrier to the rails to the aluminum bed to the control box to the MX4660, all grounded together. The reading is around 8-10 ohms or less allround. Shielded cables used throughout. I have some .01UF capacitors on-hand but not installed. The problem has to be electrical noise, but I am out of ideas where to look. Ant ideas? Thanks



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    Default Re: Electrical Ground

    What hall effect switches are you using?
    Al.

    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.


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    Default Re: Electrical Ground

    Quote Originally Posted by Al_The_Man View Post
    What hall effect switches are you using?
    Al.
    Hi Al,
    Using Digi-Key #55110-3H-02-A-ND



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    Default Re: Electrical Ground

    Quote Originally Posted by dsnellen View Post
    Everything pretty much works except for a weird limit switch issue. I use hall effect switches. On the Y axis, the sensor is mounted so it moves over the magnets. One magnet is used for Y Home and Y++, and another magnet for the Y--. For some reason, if the Y-- is set on, I get switch activation at random intervals. Usually it is so often I cannot do anything. Simply disabling Y-- makes the problem go away for the most part. Its a magnet about 48" from Home & Y++. The debounce is set to 5500. The Index Debouce is set to 10, but I don't know why.

    And I noticed today, the vacuum tripped the Y switch. This is new. Anyway, everything is grounded to everything else. From the spindle to the Z carrier to the rails to the aluminum bed to the control box to the MX4660, all grounded together. The reading is around 8-10 ohms or less allround. Shielded cables used throughout. I have some .01UF capacitors on-hand but not installed. The problem has to be electrical noise, but I am out of ideas where to look. Ant ideas? Thanks
    Sounds like you have some serious wiring problems to be have these problems

    Mactec54


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    Default Re: Electrical Ground

    Quote Originally Posted by dsnellen View Post
    ... everything is grounded to everything else...
    This can cause a lot of problems. If you don't know what you are grounding you may introduce a lot of new issues instead of solving them. Basically, there is no point in optical isolation if you ground them and connect to your frame and everything else.

    Of course, it can be your limit switches which are not meant to be used in machines, or just simply wiring issues. Don't add any capacitors on ANY limit switches. No, the problem is not necessarily electrical noise, can be bad wiring or even bad BoB or other components. Don't blame everything on electrical noise and don't assume you have done everything right just because "everything is grounded to everything else".



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    Default Re: Electrical Ground

    Are you using the recommended magnet H58?
    Do yoou see the LED indicator come on when it false triggers?
    The spec sheet also suggests a cap across the +v and common if transients are a problem, probably a .15uf would do it.
    Are you also grounding the shield?
    Al.

    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.


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    Default Re: Electrical Ground

    Thanks Al,
    No, I do not use the H58 magnets. Haven't seen the LED light up or observed an indication on Mach3. I put a .01uf as shown on the spec sheet. Have them on hand. If that doesn't work, I'll order the .15uf version. Which shield are you referring too?
    Dave



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    Default Re: Electrical Ground

    I thought maybe the lead out from the prox was shielded?
    Al.

    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.


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    Default Re: Electrical Ground

    No it's not shielded. The error message is "External EStop Requested". I thought adding the .01uf may have solved the problem but it didn't. Sometimes it runs for hours without problems and other times I can't get anything done. Almost like stray waves flying through the shop.



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    Default Re: Electrical Ground

    Ensure any metalic part of the machine is bonded to earth ground, this is called equi-potential bonding and prevents ground loops etc which can be the source of spurious noise.
    This includes any motor frames stepper/servo or spindle etc.
    Al.

    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.


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    Default Re: Electrical Ground

    The metal enclosure is earth grounded and everything else is connected to it. There is connectivity between all the components as measured by my fancy new digital volt/ohm meter. It reads 7-8 ohms. Inserting the .01 uf cap solved the problem of pressing "START" on the VFD would cause a fault. I have ordered a .15uf. What is so frustrating is the randomness. Sometimes I can run all day without any faults. Others time, can't do a damn thing.
    Dave



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    Default Re: Electrical Ground

    Al,
    Adding the .01uf to both the X & Y switches seems to have solved the problem. Running for days now without fault. Thanks for your help.
    Dave



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