Question about shielding of cables

[JAZZCNC]

Hi,

Not shielding is like kicking a sleeping dog, at some point it's likely to wake up and bite you.! For the sake of a little wire, it's not worth not doing it.

The main areas to use are Stepper cables and limit/home cables or any cables that carry low voltage signal cables.

Here are a few tips to help you avoid EMI :

#1 Star grounding is a MUST DO, this means all Gnd's and shields, etc go to a single Earth point.
#2 Keep low voltage signal cables, like step/Dir, limits, etc away from Mains voltage wires.
#3 Use shielded cable and only ground one end of the cable at the control box end.
#4 Earth the frame.
#5 Use 24vdc for signals like E-stop, limits, homes, etc.

Now you say you are using a booster of the PC PSU, this is a bad idea and could cause problems because you are tieing the 24Vdc Gnd to the PC Gnd which can cause ground loops. For the sake of £10 do yourself a favor and buy a dedicated 24vdc PSU, you only need one 3a at max for the low voltage side.

[masdo]

Thank you for the excellent reply. Well, excellent except that I have more work to do...

I thought I would just clarify something about the computer PSU. I am using it because I need 5V for the controller as well as an Arduino, I want 12v for the fans and I figured it had more than enough juice to give me 24v through a boost converter. Just in case you thought I was actually using it in the PC which will feed the controller - I am not; I will be using a separate laptop. I do have a 24v PSU but I figured the controller only wanted 500ma and seemed overkill having another supply. All the grounds of 5v, 12v and 24v would therefore be the same. Does it still sound like a bad idea? Should I have separate 5v, 12v and 24v supplies?

Thank you for your input

[Doddy]

Hi,

Not shielding is like kicking a sleeping dog, at some point it's likely to wake up and bite you.!

That's a tag-line waiting to happen.

Now you say you are using a booster of the PC PSU, this is a bad idea and could cause problems because you are tieing the 24Vdc Gnd to the PC Gnd which can cause ground loops.

Generally agree - but think the OP is using a repurposed PC PSU as a stand-alone 24V supply.

OP: You're using mechanical limit swithes, into the BoB?, you don't mention the nature of the BoB, but I'm assuming the common Chinese flavour which has opto-isolated inputs. That should provide a bit of EMI resilience (noise picked up in the cabling on the machine is unlikely to have enough energy to generate a spurious trigger on the BoB input). A brushed motor is likely to generate a bit of HF noise - usually suppressed on the motor with a cap filter).

Ultimately the proofs in the pudding. You might find that your machine works well. Or you might find a spurious trip - usually half way through a job that ruins the workpiece. What Jazz says above is generally good advice.