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  1. #21
    Join Date
    Apr 2006
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    362

    Hmm

    When wiring up a two phase stepper, I would run individual cables to each phase. Each cable should be a twisted pair with a braid screen. The braids should be earthed at the driver end, and not connected at the motor end. It is a "belt and braces" approach, and there will be some who will say it really isn't needed.

    Cable is cheap, problems are not.


    I like that answer very much. It makes sense to me. It separates the phases and provides for two good ways (twisting and shielding) of eliminating a problem. I like it. Now I just need to decide about gauge and whether the tiny wires coming from my motors will cancel out any advantage of going with heavy wire.

  2. #22
    Join Date
    Apr 2006
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    362

    Upgrade?

    Thiner wire has more resistance so the thinner you go the more voltage loss to the motor.
    A thicker wire will also allow you to upgrade your motors at a later date without worrying.


    What hurts about that is that my motors are brand new 640oz. I suspect that skinny wires coming from the motors is standard. So I don't know that there IS an upgrade.

  3. #23
    Join Date
    May 2005
    Posts
    405
    Quote Originally Posted by IQChallenged
    Thiner wire has more resistance so the thinner you go the more voltage loss to the motor.
    A thicker wire will also allow you to upgrade your motors at a later date without worrying.


    What hurts about that is that my motors are brand new 640oz. I suspect that skinny wires coming from the motors is standard. So I don't know that there IS an upgrade.
    Those are big steppers, so you do need a heavy cable.

  4. #24
    Join Date
    Jan 2005
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    746
    Years ago when I worked with audio equipment, I used an 18 guage twisted/shielded pair for line level wires. It was made by Alpha Wire, I can't remember the stock number for it though.
    If it's not nailed down, it's mine.
    If I can pry it loose, it's not nailed down.

  5. #25
    Join Date
    Apr 2006
    Posts
    362

    Alpha

    Getting ready to leave for work. A quick look at Alpha's online catalog looks promising. Will study it tonight when I get home. Thanks

  6. #26
    Join Date
    Dec 2005
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    1408
    Quote Originally Posted by IQChallenged
    [COLOR=DarkGreen] Now I just need to decide about gauge and whether the tiny wires coming from my motors will cancel out any advantage of going with heavy wire.
    Dear (modest) IQChallenged,

    The skinny wires (probably about 6 inches, or 150mm long) that come out of your motor are designed to take a sufficient current to make the motor perform as per specification.


    You will almost certainly need to extend these skinny wires in order to get power back to your drivers boards, and the extension cable that you will need may be a few metres (yards).

    IMHO the factors you should consider are...

    1) voltage drop down the extension cable(s)

    The skinny wires supplied with your motor will take the spec. current, but if you extend the cable with the same CSA (cross sectional area) cable for a few metres, the voltage drop from your driver boards may be considerable.

    This may degrade the performance of your motor because it will not be supplied with the voltage that you anticipate.

    The voltage drop follows the V=IR rule.

    V= voltage drop
    I= current
    R= conductor resistance

    Look at the specs of any cable you might consider and they will give a figure for a maximum current. This is actually limited by the maximum temperature rise that the conductor insulation can take under ambient conditions. If you exceed the rated current, the insulation may melt.

    The cable spec.s also give a figure for resistance (ohms) per unit length.

    Calculate how long your extension cable is going to be, and double that length, to work out the total resistance in the formula above.

    From that, you can work out what the voltage is that your motor will actually "see" as opposed to what the drive is "sending out".

    2) Shielding, grounding, screening etc.

    This is probably the BLACKEST of all arts!

    I do not even pretend to be an expert, and I have absolutely no doubt that there will be better people than me to shine lights on the matter.

    Get out your searchlights dudes.

    The cables that supply power to your motors will not, by themselves, interfere with each other and do not, in a perfect world, need any form of screening. Unfortunately...

    a) they may run close to low level logic signals that control limit switches

    b) they may ditto to the control signals from your PC that run the driver board.

    c) if you have (say) 4 amps running each phase of a bipolar chopper drive, with a 20 kHz chop rate, the motor supply cable will radiate a significant amount of interference that could cause havoc with your logic signals, hence the importance of screening them. Screen the logic ones as well!!!!.

    d) if you run one screened twisted pair per phase (on a two phase motor), the screen of each cable is only having to handle half the EMI. (Actually, is that true????)

    d) if you are unlucky, the grounding arrangements may actually provide a logic level ground loop via the motor screens.


    Best wishes

    Martin

  7. #27
    Join Date
    Nov 2005
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    938
    Martin,

    I have not seen it put so eloquently before. Great job at explaining it. Most people strive for brevity and end up using to few words. You used the perfect number or words for us amatures to understand.

    Steven

  8. #28
    Join Date
    Apr 2006
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    362
    The skinny wires (probably about 6 inches, or 150mm long) that come out of your motor are designed to take a sufficient current to make the motor perform as per specification.

    Yes. I recently came to realize that the manufacturer knows more than I do about what's needed. It just seemed so wrong to have such a small wire. I realize now that the use of such a small wire does not have anything to do with the gauge needed to extend it. But the issue needed to be put to bed, and we have.

    Calculate how long your extension cable is going to be, and double that length, to work out the total resistance in the formula above.

    What is the purpose of doubling the answer?

    a) they may run close to low level logic signals that control limit switches
    b) they may ditto to the control signals from your PC that run the driver board.


    I think you're saying that the limit switch cable may read the stepper signals intended for the motors and then respond to those signals causing unintended consequences? Yes? No?

    c) if you have (say) 4 amps running each phase of a bipolar chopper drive, with a 20 kHz chop rate, the motor supply cable will radiate a significant amount of interference that could cause havoc with your logic signals, hence the importance of screening them. Screen the logic ones as well!!!!.

    This statement needs a response all to itself.

    d) if you are unlucky, the grounding arrangements may actually provide a logic level ground loop via the motor screens.

    It is my understanding (from previous posts) that leaving the far end of the screen open will prevent this. Yes? No?

  9. #29
    Join Date
    Apr 2006
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    362

    In search of... understanding

    c) if you have (say) 4 amps running each phase of a bipolar chopper drive, with a 20 kHz chop rate, the motor supply cable will radiate a significant amount of interference that could cause havoc with your logic signals, hence the importance of screening them. Screen the logic ones as well!!!!.

    hence the importance of screening them

    Screen the logic ones as well!!!!

    Will you please discuss the distinction between "them" and "logic ones".

  10. #30
    Join Date
    Dec 2005
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    1408
    Quote Originally Posted by sdantonio
    Martin,

    I have not seen it put so eloquently before.
    Steven
    Dear sdantonio,

    Thank-you for those kind words.

    I'm just waiting for the "searchlight dudes" to shine a light in the darker corners. My knowledge is incomplete, and they will help everybody hereabouts.

    Best wishes

    Martin

  11. #31
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    Dec 2005
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    1408
    Quote Originally Posted by IQChallenged
    c) !

    Will you please discuss the distinction between "them" and "logic ones".

    Dear IQ(not) Challenged,

    Sorry, the truck broke down, and everything went t#ts up.

    Will reply shortly,

    Best wishes,

    Martin

  12. #32
    Join Date
    Dec 2005
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    1408
    Quote Originally Posted by IQChallenged
    [COLOR=DarkGreen]
    Calculate how long your extension cable is going to be, and double that length, to work out the total resistance in the formula above.

    What is the purpose of doubling the answer?

    To complete the electrical circuit, current must run from the power supply, to the motor, and back to the power supply, that means that the total length of travel is twice the length of the extension cable (if it has two current conductors)

    a) they may run close to low level logic signals that control limit switches
    b) they may ditto to the control signals from your PC that run the driver board.


    I think you're saying that the limit switch cable may read the stepper signals intended for the motors and then respond to those signals causing unintended consequences? Yes? No?

    Absolutely YES!!

    There are likely to be high current AC signals from the driver to the motor. These will radiate interference. The purpose of screening these cables is to stop the interference from being picked up by low level control circuits which typically work at less than 16 mA.

    No screening is perfect, so some of the interference will escape from the motor cables. It is therefore a very good idea also to protect your logic signals with screened cable. Not to do so is, frankly, reckless.


    c) if you have (say) 4 amps running each phase of a bipolar chopper drive, with a 20 kHz chop rate, the motor supply cable will radiate a significant amount of interference that could cause havoc with your logic signals, hence the importance of screening them. Screen the logic ones as well!!!!.

    This statement needs a response all to itself.

    I think that has been covered.

    d) if you are unlucky, the grounding arrangements may actually provide a logic level ground loop via the motor screens.

    It is my understanding (from previous posts) that leaving the far end of the screen open will prevent this. Yes? No?

    It is a big subject, and it would take a book to cover all the angles.

    I'm really sorry but I just can't do it here.

    The very best book on all these matters is The Art of Electronics by Horowitz and Hill Somewhere in those pages you will find the answer to almost everything. They are better men than me.


    Best wishes,

    Martin

  13. #33
    Join Date
    Dec 2005
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    3319
    Re: shield grounding = YOU DO NOT TIE BOTH ENDS OF THE SHIELDING TO GROUND, only tie one end.

    For starters, I tend to tie the shielding to ground at the signal initiation point as this is generally going to be closer to system ground.

    There are more goofy problems that are related to RF emissions than necessary and most are due to bogus or non-existant shielding.

    However, sometimes you have to "work" with shielding as those inducted electrons can be crafty devils and go places where they shouldn't. Sometimes simply NOT running wires parallel to each other will do the trick. Twisted pairs helpds too and so on.

    As Martin's book reference in the prior post suggests, electronics is not only a science but it is can also definitely becomes an art and at some points in time, black science.....

  14. #34
    Join Date
    Oct 2005
    Posts
    1237
    Just wanted to say thanks for someone willing to ask questions and those willing to answer them. Made good sense to me, and it will help make a selection of cables for my project easier.

    Sort of like, "What is the best fit for a bearing." A .002 PF on the shaft, and a .003 on the race.... (chair)

    But no one answered the question on if we can twist an 18ga. lamp cord and then wrap it in tinfoil as sheilding for field wires. (wedge)

  15. #35
    Join Date
    Dec 2005
    Posts
    3319
    AAARGH. A 0.002" press is NOT the best fit for a bearing nor is 0.003 on the race!!!!

    Reason: if you have a bearing with only 8-10 microns clearance, that much press will result in NEGATIVE clearance which doesn't do anybody or anything any good.

    If you really want to know how to determine/establish press fits, check out these websites:

    http://www.bardenbearings.com/literatr.htm

    http://www.timken.com/products/bearings/catalogs/

    http://www.jp.nsk.com/app01/en/catal...gi?ec=bearings

    I HIGHLY recommend getting the NSK E1102 catalog for starters

    Unless this bearing clearance reference was a joke, it is a good excellent example why "quickie" off the cuff, sage wisdom answers are NOT the best purveyors of knowledge.

    Re: lamp cord and tin foil. Life is too short to take that much time to make something that you can so readily buy.

    Besides, the foil on shielded cable is continuous which facilitates the transfer of errant electrons - simply making contact isn't sufficient when you're talking the transmission of induced currents. IN a pinch fix, maybe but not something I'd do for a long term "solution"

    Besides, shielded cable has tested and proven shielding capabilities. Goodness knows how well and if foil wraped lamp cord will work and how long it would do so...

  16. #36
    Join Date
    Dec 2005
    Posts
    1408
    Quote Originally Posted by NC Cams
    Re: lamp cord and tin foil. Life is too short to take that much time to make something that you can so readily buy.

    Dear NC Cams,

    I absolutely agree.

    I looked into making heavy duty twisted pairs using professionally made metal braid eg Raybraid 101. The braid costs a fortune and doesn't make economic sense. If you need to have high current screened cables, I would try and get hold of something like flexible control cable used for robotics. In the UK it is called Type CY and has an overall braid. There is bound to be the same type in the States, but it will probably have another name. I'm not sure if the conductors are twisted though. The current rating can be as high as 20 amps depending on the CSA. Three core 6 amp version costs about $1.75 per yard in Europe.

    Best wishes

    Martin

  17. #37
    Join Date
    Dec 2005
    Posts
    1408
    Quote Originally Posted by IQChallenged
    c) if you have (say) 4 amps running each phase of a bipolar chopper drive, with a 20 kHz chop rate, the motor supply cable will radiate a significant amount of interference that could cause havoc with your logic signals, hence the importance of screening them. Screen the logic ones as well!!!!.

    hence the importance of screening them

    Screen the logic ones as well!!!!

    Will you please discuss the distinction between "them" and "logic ones".
    Dear IQChallenged,

    Sorry, I didn't explain it very well.

    "them" are the motor cables carrying high current which, in chopper drives, may have a 20 kHz frequency. You should try and stop these cables radiating EMI by screening them.

    "logic ones" are the low level signals from your PC to the drivers (usually sourced from the printer port).

    Your limit and home switches may or may not carry "logic" level signals eg TTL, cmos or whatever, but they will almost certainly be low voltage and low current. Such signals are prone to the EMI radiated from the motor cables. It will do no harm to screen these as well, and may well be essential depending on the particular application.

    Hope this clears things up.

    Best wishes

    Martin

  18. #38
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    Apr 2006
    Posts
    362
    Hope this clears things up.

    Yes. It does. Thanks

  19. #39
    Join Date
    Jan 2005
    Posts
    746
    Over the weekend I was rooting thru the garage for something and came across some of that Alpha wire. The stock number on it was 2422, 18 guage twisted pair with a foil shield and a wire.
    If it's not nailed down, it's mine.
    If I can pry it loose, it's not nailed down.

  20. #40
    Join Date
    Apr 2004
    Posts
    44
    Hi, Regarding Flexible Cable, just how many strands are required in a 14 AWG conductor to be considered for "Continuous Flex" ?
    Also I am seeing AC specifications stating: "Shielding suitable for drives subject to non-linear power distortions" how does this relate to the shielding requirements of a DC drive like the Rutex R2020.
    Thanks

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