Thread: Cnc wiring!

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  1. #1
    Hi guys,
    Need some help, the size of wire required for cnc is confusing me!
    I am going to be running nema 23's 425oz drawing 3amps. However, I am undecided as to whether to use individual wires so I can match up the motor colours all the way through to the drivers. Or, use a 4 core wire to the control box and individual wires within.
    So my question is what size wire do I require? I can find suitable rated amp wire but I then get confused with the 0.5,0.75, 1.0 etc.
    I have read different things about wire size in respect of using 18awg or 22awg, but most listings for wire I have seen refer to the 0.5 etc.
    Is automotive wire ok?
    I know I will be using proper rated cable for the actual power supply. I just need to sort out motors and peripherals.
    Thanks in advance
    Mick

  2. #2
    0.75mm 4 core CY cable, you need CY normal 4 core is a big No due to interference. Wire colour is irrelevant and you'll find CY you get 3 blacks wires and an earth. It's very easy to work the wiring out it doesn;t matter how you wire it to the motor the end you wire to the drivers twist 2 wires and try to turn you ballscrew if you feel resistence you have matched pair if not try a different combination. When you have a matched pair the other pair must be matched wire them to the drivers. If the motors go the worng way invert the pin in Mach3/linuxcnc.

    https://www.ebay.co.uk/itm/ALL-CY-CA...EdeT991FfFPUNw

    Search for companies local to you it's not hard to source cheaper than this.
    Last edited by Desertboy; 25-01-2018 at 12:17 PM.
    http://www.mycncuk.com/threads/10880...60cm-work-area My first CNC build WIP 120cm*80cm

    If you didn't buy it from China the company you bought it from did ;)

  3. #3
    The CY cable I have used has the three black cores numbered along their length so you can identify which core is which at both ends. The third core could be used for an earth but it works fine as one of the four connections for the steppers - electricity doesn't care what colour wire it runs in!

    Talking about awg and oz-in motors suggests that you have been looking at US sites. Europe and European suppliers tend to talk about cross-sectional area (0.75, etc) and Nm. It doesn't really matter which system you use but that's why some people use one set of units and some another.

  4. #4
    Thanks guys, it seems to make a bit more sense.
    In my research, I've just watched a video of a guy wiring his steppers with
    Cy cable. He used a 4 core plus earth and didn't use the earth. He did however expose the wires in his control box and connected them to the side of the metal box to earth them. I'm planning on building a Perspex box, so do I still need to earth the cable or can I just use the 3core and earth as my 4 wires?
    Thanks
    Mick

  5. #5
    Quote Originally Posted by Cobey3289 View Post
    Thanks guys, it seems to make a bit more sense.
    In my research, I've just watched a video of a guy wiring his steppers with
    Cy cable. He used a 4 core plus earth and didn't use the earth. He did however expose the wires in his control box and connected them to the side of the metal box to earth them. I'm planning on building a Perspex box, so do I still need to earth the cable or can I just use the 3core and earth as my 4 wires?
    Thanks
    Mick
    You need 4 cores to connect the motor to the driver in the control box and use use the screen to connect to the ground star point. Also a plastic box is not suitable it is better with a metal box that can be earthed as it will help with the screening.

    You will also need CY cable for the spindle
    Last edited by Clive S; 25-01-2018 at 10:21 PM.
    ..Clive
    The more you know, The better you know, How little you know

  6. The Following User Says Thank You to Clive S For This Useful Post:


  7. #6
    Quite agree, it seems the more you research, the more questions that end up needing answers!

  8. #7
    Quote Originally Posted by Cobey3289 View Post
    Quite agree, it seems the more you research, the more questions that end up needing answers!
    Which is exactly why you should never buy anything until you know 100% it's correct for your needs. So don't be afraid to ask.

    Regards wiring then it basicly boils down to this for CNC.

    Anything which carries signals Ie: Motor wires, Control signal wires, Limit switch, E-stop, require shielded or twisted pair cables. With the Shield going back to Single Earth point " Star point".

    Other wires which carry power to components Ie: From PSU to drives, power for control, power fro relays etc can all use normal single core cable often called Tri-rated cable. The cable must be sized according to load it will carry but often people will use one size, that being rated for highest load they'll use. 1.5mm/2 will work for most things.

    If using VFD for the spindle then they require special treatment in that shielded cable must be used between VFD and spindle even thou not carrying signals. This is because of the high frequencys they use which can creat lots of electrical interference(noise).

  9. #8
    Thanks for that jazz.
    Stepper drivers and psu's.
    I'm going to be running nema 23's 425oz 3amp. What stepper driver should I use? Some are rated up to 3amp and some more and then they are rated voltage wise. Until I decide on steppers I'm assuming I should hold off on psu's.
    I see some people use 2 psu's driving two motors each. Can I just use one for the motors and a 5v supply, or is it best to use one for motors, another lower rated for fans etc and a 5v for the board?

    Mick

  10. #9
    Quote Originally Posted by Cobey3289 View Post
    Thanks for that jazz.
    Stepper drivers and psu's.
    I'm going to be running nema 23's 425oz 3amp. What stepper driver should I use? Some are rated up to 3amp and some more and then they are rated voltage wise. Until I decide on steppers I'm assuming I should hold off on psu's.
    I see some people use 2 psu's driving two motors each. Can I just use one for the motors and a 5v supply, or is it best to use one for motors, another lower rated for fans etc and a 5v for the board?

    Mick
    Well it's little more complex than just amps.?
    Not all steppers are equal and even thou may be rated same size doesn't mean they will perform the same. Inductance rating of the motor is very important to how well stepper will perform with a given voltage.

    For instance, motor with high inductance will spin much slower than one with low inductance using the same voltage.
    So if the steppers you buy have high inductance it will mean you'll need to run them with much higher voltage to get the same speed as Low inductance motor.

    Then you have how the motor phases are wired. Steppers tend to come in two flavors. 4 wire and 8 wire.
    4 Wire motors are less flexible because their phases are predefined at the factory. Often their phases will be series wired.
    This means they will require much more voltage to achieve high speeds. Parallel wired motors, on the other hand, will reach same speeds with less voltage.
    Often you'll find Series wired motors on Mills or machines which require high torque but less speed. This is because they produce higher torque lower down the rpm range but quickly lose torque as RPM's rise.

    Parallel wired phases, on the other hand, give less low down torque but carry more torque higher up the rpm range. This is why parallel is preferred for routers.

    8 wire motors allow Either series or parallel phases so again are preferred and easier to find than 4 wire parallel wound motors.

    Voltage is the key to getting speed from stepper but at same time too much voltage can lead to over heating and resonance issues.
    So this brings us back to inductance and why it's important. Lower inductance means higher speeds can be got with less volts and less volts equals less motor heating, less resonance etc.

    So to answer your question about Drives and PSU will require knowing more about the motors. Would also help to know more about the machine spec and what you intend to do with it.

    However if you want proven setup which works with most small to medium sized routers then the spec below works great.

    Nema 23 3.1Nm 4.2Amp 8 wire motor wired parallel. Ideally with Inductance around 3mh or less.
    Digital drives with voltage between 70-80V. Leadshine AM882 are great drive.
    PSU with 60-68Vdc output depending on drive voltage. Current will depend on #motors and PSU type.

    Now the Psu is little more involved because several types but the best solution by far is unregulated Toroidal PSU. It's gets little involved to why best but trust me this is the best setup for stepper motors. If really want to know why I will explain.

    The reason you have probably seen people use 2 psu's is because they have bought off the shelf units which have limited current output so not enough to power 4 motors.
    However the best solution is to build your own PSU which is very easy to do and doesn't require degree in electronics. We can help you with whats needed and will say if you can't wire this then you can't wire any of the machine it's that simple.
    This way you get exactly what you need in terms of voltage and current in one setup and will work out cheaper than buying off the shelf units.

    You will need a separate linear PSU for the Control etc and these are best bought off the shelf and cheap enough not bother building.

    Hope this helps.

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  12. #10
    Regulated or Unregulated Power Supply
    Both regulated and unregulated power supplies can be used to supply the drive. However,
    unregulated power supplies are preferred due to their ability to withstand current surge. If regulated
    power supplies (such as most switching supplies.) are indeed used, it is important to have large
    current output rating to avoid problems like current clamp, for example using 4A supply for 3A
    motor-drive operation. On the other hand, if unregulated supply is used, one may use a power supply
    of lower current rating than that of motor (typically 50%~70% of motor current). The reason is that
    the drive draws current from the power supply capacitor of the unregulated supply only during the
    ON duration of the PWM cycle, but not during the OFF duration. Therefore, the average current
    withdrawn from power supply is considerably less than motor current. For example, two 3A motors
    can be well supplied by one power supply of 4A rating.
    Multiple Drives
    It is recommended to have multiple drives to share one power supply to reduce cost, if the supply has
    enough capacity. To avoid cross interference, DO NOT daisy-chain the power supply input pins of
    the drives. Instead, please connect them to power supply separately.

    Selecting Supply Voltage
    The power MOSFETS inside the AM882 can actually operate within +20 ~ +80VDC, including
    power input fluctuation and back EMF voltage generated by motor coils during motor shaft
    deceleration. Higher supply voltage can increase motor torque at higher speeds, thus helpful for
    avoiding losing steps. However, higher voltage may cause bigger motor vibration at lower speed, and
    it may also cause over-voltage protection or even drive damage. Therefore, it is suggested to choose
    only sufficiently high supply voltage for intended applications, and it is suggested to use power
    supplies with theoretical output voltage of +20 ~ +72VDC, leaving room for power fluctuation and
    back-EMF.
    http://www.leadshine.com/UploadFile/Down/AM882m.pdf
    Last edited by Desertboy; 27-01-2018 at 09:27 AM.
    http://www.mycncuk.com/threads/10880...60cm-work-area My first CNC build WIP 120cm*80cm

    If you didn't buy it from China the company you bought it from did ;)

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