2012-08-06 16:30:46 (CET)

Hardware installation tips

Building a reliable CNC system is not just making the right connections. EMC plays an important role here. We have several components that generate a lot of EMC noise, the drivers, the power supplies if they are switched mode supplies, the VFD if we have a HF spindle. The CPU and the communication to the PC, especially USB is very sensitive for EMC and may stop functioning when we make "spaghetti" wiring and no good functional Earth. So the routing of the cabling must be done in a right way. Very important is making a good EMC functional Earth using a star point GND.



To prevent this
miss function due to EMC, the USBCNC CPU should be build in correctly according these general EMC rules:

 

  • Mount all electronics in a metal cabinet or on a metal plate in a plastic cabinet.

  • Use a mains filter.

  • Create a central GND point near the filter and connect the PE (Protective Earth) as well as the GND from all power supplies to this point.



    • Route motor cables nicely along the cabinet edge, as far as possible away from the CPU. This way the cables noise radiation can flow away to the cabinet.

    • Use shielded cables for the motor connections, both inside the cabinet and outside the cabinet. Connect the shield at one side to the central ground point, leave the other side un-connected.

    • Use a professional USB2 cable, double shielded with ferrites like this:

       

       

      • Keep all GND cables especially short and use thick flexible cable

      • If not possible to keep it short, then connect it to the metal GND plate.

         

 

 

 

 Schematic drawing of a possible good layout in the cabinet.

 

 

 

Here a picture of my own system, it contains various EMC problem makers, like 2 Switched mode power supplies and a frequency inverter for a HF spindle. Check the routing of the Motor and drive supply wires.


Also there a 4 stepper-motor drives working at 75 Volt, motor currents 4,2 Amp.