[Jkountz]

Hoping someone can clear up a few things that have me a little confused and in the process help me fix a huge problem Im having.
I have a DIY CNC, a Momus 2.1 to be exact that Ive built and Im having some real issues with the wiring. First a quick rundown of what Im working with here.
Motors Nema 24 400 oz/in 3.5A
Drivers are the Longs/Leadshine/Keling type that are common.
PSU is 36V 15A
BOB is a standard C10
All that works fine, I have smooth motion in all axis and have them tuned to a nice conservative speed of 100IPM. No problems.
The trouble starts when I tried connecting some limit and home switches. I have an Estop switch on pin 10 of the BOB and it functions just fine.
I connected a lead to pin 15 and another to the 5V terminal next to it on the BOB and all hell broke loose. Motors starting making a grinding noise and erratically moving axis, shaking and all kinds of nastiness. On the Diagnostics screen the proper led's are lighting however indicating the switch is making contact.
Soooooo If I disconnect the wires to pins 15 and 5v, everything returns to normal. Same happened with other inputs I tried, 13, 11, etc.
So Im thinking I have some serious EMI going on here and that I may have to re-route some of my cabling.
All my cables are shielded throughout the machine but I did not connect the drains to anything because I wasnt sure where they went.
This im sure is at least part of my problem.
So to make a short story long...........Where do the drain wires connect for the various wires?
Ex: the power wires FROM the PSU to the Drivers. Do I connect the drain wire to the GND terminal of the PSU?
How about the signal wires FROM the BOB to the Drivers. Where does that drain wire go?
How about the wires FROM the Motors to the Drivers. Should those drain wires be connected somewhere as well?
Finally the wires Im using to connect the limit switches themselves also are shielded with drain, where does that go?

I appreciate any help!!

Thanks!!

Jim

[matth]

Usually shields on limits and the like would only be connected to Gnd at one end.
Make sure you are tying all your Gnds back to a central point (star earthing).

[Jkountz]

Ok when you say connected to ground, where exactly are you talking? And are you meaning the drain wire inside the shielded cables?

[matth]

I don't understand "drain". The shield itself usually at the controller end needs to be connected to earth/Ground/0volts.

I usually put a bolt in the case somewhere and connect all earths and 0 volt lines to this (you don't want to do this if any of the power supplies have a floating Ground, but they usually don't).

This will make sure all the different supply Grounds at at the same 0v potential and any induced noise in the shields will be grounded out.

[Jkountz]

My shielded cables have a small wire running between the shield and the conductors called a drain wire. This is what I assumed you used to make your connections to the shield itself.
I guess Im a complete moron or cant see the forest for trees but what do you mean by 0v lines? Also when you say the shield needs to be connected to earth ground, how is this done, where do the shields connect exactly?

[matth]

Ok, Ground, Earth and 0 volts (as in the Gnd connection on your power supply) are all the same thing (in this scenario). I think a lot of people look at a power supply with + and - symbols and think positive and negative, but there is no negative. This is 0 volts or Gnd.
The key with an Earthing strategy is to tie everything together so that it is all at or as close to as possible, 0v.

The shield itself would usually be soldered to a tab in your connector which in turn would be earthed through contact with the metal chassis of your case. If you are using plastic bodied connectors and or case then you can't do this. You might have a spare pin in your connector, if so connect the shield to this and then on the chassis side run a cable from this pin to your star earthing point.
I just work the braid of the shield into a tight plate/bundle and then solder that like any normal conductor.

[hjl4]

Are you using twisted pair cables? If so, you don't need to ground the shield. By having the wires twisted together you null the EMI effects.
I'm also having a hard time making sense of what you are describing.
Typically you would use twisted pair of wires for the signal wires to your drive. It doesn't hurt to do the same for the power cables to the motors. EMI is always present when two or more wires are run parallel to each other, like it does when wires are bunched together inside a cable sheath. Yes, even if you have a foil shield wrapped around the bunched up wires in the cable.
Relays are great for the problem you are describing if you don't use a fly-back diode.
Ground is or should be the whole machine(chassis). The ground is or should be directly wired from your breaker or fuse panel to a common stud or terminal on the machine or to a separate ground rod. All other grounds ie: from the drives and computer, BOB, technically all share the same ground. Some directly, and others like the computer, usually have their own ground pins from the PSU. But never the less, in the end, it all goes back to machine ground.

[Jkountz]

Thanks guys I get it now I think. I just grounded my psu, bob, and incoming receptacle to a screw inside my metal control cabinet. Problem solved! My inputs are all functioning properly now and I'm ecstatic! I really appreciate the sound advise!

Sent from my DROID RAZR using Tapatalk 4

[Al_The_Man]

Many previous posts on this issue.
http://www.cnczone.com/forums/phase_...se_issues.html
Also read about equi-potential bonding and the latest practice about grounding both ends of shields. ch. 6.
http://www.automation.siemens.com/do.../emv_r.pdf?p=1
Al.

[Jkountz]

Thanks Al, I have a better understanding of it all now I think. Im in the middle of that article now from automation.siemens.com Good reading there for sure!!