I’m wondering if anyone here knows anything about twisted pairs for EMI shielding stepper motor lead wires? I’m getting ready to wire up my machine and I’m wondering if I should bother, and if so how I’d go about doing it.
I wouldn’t bother. I have always been of the opinion that unshielded twisted pairs are mainly for minimizing crosstalk in larger bundles of cable over long-ish distances.
If you want to shield the cable, get a cable with a foil shield and attach the shield to the chassis on the computer side, not the cnc machine side. I can’t say that it will help the steppers any, but your radio reception might be better.
@Steve_B_Thomas_delbr
Thanks. I’ve had noise issues with my stepper drives and their control signals in the past, but I think I have that sorted now.
@Eugene_Jones I might foil wrap my wires. I’m making my own cables up, I’m not investing in what multiconductor costs for my machine. When you go beyond 3 conductor the price can really skyrocket. Because then you’ve entered the realm of industrial supplies. I’m trying to do this build cheap, real cheap.
You can get 18-4 Shielded Stranded Security Cable wire for relatively cheap online or at your local lowes/home depot (by the foot).
This is what I am using on my CNC Plasma and I have not had any issues with noise/cross talk. Im using a C10 Bob, KL-4030 drivers, 485 in-oz steppers.
If you wanted to go really cheap you could probably find some Shielded Twisted Pair (STP) CAT6e and use that, but CAT6e is a single stranded copper per line so it will break with a lot of movement and could lead to problems later down the road.
This ebay seller seems to have a lot of it for cheap:
http://www.ebay.com/itm/18-4-awg-SHIELDED-STRANDED-SECURITY-CABLE-50-FT-INCREMENTS-ALARM-AUDIO-WIRE-CL2R-/180972717705?pt=LH_DefaultDomain_0&hash=item2a22d08689
@dom_gonzales one concern with using network cable is that PoE is only spec’d to like 15w something like 12.5V @ 1.25A 22awg wire would have pretty high resistance per foot.
All of this is just my opinion. I have no experience.
@Kyle_Kerr The PoE standard (802.3af) is 15.4w at 48v and i think the 802.3at standard varies depending on how many twisted pair are used. I am not to familiar with the 802.3at standard as I have only worked with the 802.3af standard.
You are correct about the more resistance (volatge drop) with the length of the run. I know there is online calculators that will show what the ending voltage would be at the ending device.
I personally prefer the shielded security wire due to the fact that the single strand in Ethernet cabling can be fragile if it is moved around to much. at the connection point to the connector.
@dom_gonzales so, 15.4W / 48V = .32A not really enough to push most steppers. I’m not trying to harp on this. Just trying to make sure I understand.
I should of mentioned that the 802.3af standard only utilizes a single twisted pair and the w/v are limited by the POE switch as a standard for hardware(typically VOIP, IP security Cameras, etc). The power loads are calculated based on the ethernet standard of 100 meters due to that being the maximum length that data can travel at the physical layer for a network. I found the following from wikipedia:
Category 5 cable uses 24 AWG conductors, which can safely carry 360 mA at 50 V according to the latest TIA ruling.[citation needed] The cable has eight conductors (only half of which are used for power) and therefore the absolute maximum power transmitted using direct current is 50 V × 0.360 A × 2 = 36 W. Considering the voltage drop after 100 m, a PD would be able to receive 31.6 W. The additional heat generated in the wires by PoE at this current level (4.4 watts per 100 meter cable) limits the total number of cables in a bundle to be 100 cables at 45 °C, according to the TIA. This can be somewhat alleviated by the use of Category 6 cable which uses 23 AWG conductors.
Since the POE standard only used half of the conductors, in the use of a strictly power we could run up to 72W and still be at a safe limit. But this also depends on the voltage that is used as well as the length of the run. Hopefully that clears up any confusion.
Also I still wouldn’t recommend using ethernet since 18 gauge stranded wire is so cheap to come by. Also I forgot to mention that many cnc hobby retailers offer ethernet smooth stepper boards for cnc use (http://www.cnc4pc.com/Store/osc/index.php?cPath=33_59). There should be maximum voltage rating for some of the product descriptions on that site or even automation technologies inc should have some on their site as well.
@dom_gonzales I settled on using 18 gauge stranded wire myself. I got mine out of surplus IEC power cords. Can’t beat free.
@Paul_Frederick Can not beat free lowering over all cost is always great so you can spend the money on parts that you need.
I reckon UTP is ok for steppers but you must use shielded cable for your AC spindle.
@dom_gonzales
Low cost has been my most important design feature of this project. It is my first machine, so I really don’t want to break the bank on it. I don’t even think I have $300 wrapped up into it all as of now. I’ll see how things go when a bit hits a workpiece. I’m getting close!
Was at home depot today looking for wire myself. As most times, I grabbed a few pics with my moto x because my memory sucks…
https://plus.google.com/u/0/102904770762217826123/posts/2RXhTPbf4Vr?pid=6071346430573395474&oid=102904770762217826123
@Mat_Helm
Those are some mighty long rolls of wire there. I like the 18/4 security wire, but at $162 a roll I guess I’ll have to play with the scraps I have on hand over here.