Mike, can you explain the power transmission rating for me? I am versed in commercial wiring. That I need to go to 13ga to run 6.3 amps is hard to understand. especially when the motor leads appear almost threadlike. Any insight would be appreciated.

Well, Chuck, you see all wires aren't created equal. If you use special gold-platinum-titanium ... Whoops, I seem to have turned into a monster.

Actually, the rated current capacity of a wire of a given size is largely a function of controlling the heating or potential heating of the wire. You want to avoid having the wire heat up to the point that it has a detrimental effect on its environment, its insulation, or itself. The intended use of the wire has a lot to do with this. In the case of a traditional incandescent light bulb, we are quite happy to pump a lot of amps through a very small uninsulated wire, because the heating is acceptable in this context.

For commercial wiring, heating that causes the insulation to deteriorate over time is unacceptable, as is heating that might trigger a fire. So the amperage ratings are very conservative, for good reason. From a commercial wiring perspective, you want to be able to draw the full rated current continuously forever without any significant heating.

Now, our stepper motors actually have wires inside that are even smaller than the motor leads. However, they are assembled into windings with heat tolerant insulation (varnish), and the assembly itself acts as a heat sink within reason. This is why the motors have temperature ratings; if allowed to go to high, a insulation or a wire will melt somewhere, short, and set off a cascading failure.

But when you look at how a stepper motor is driven, it doesn't draw the full amperage continuously. It's varying all the time. So it doesn't heat the wire as much, and you can use smaller gauges than you might normally. This shows up as those threadlike motor leads.

This brings us to the last point, which is that the wires on a CNC machine undergo a fair amount of physical stress as they are dragged back and forth, and they can be fairly long. This calls for upsizing a bit to compensate for wear and resistance. 13ga for 6.3a seems a bit more than necessary, but it's consistent with Mike's engineering principles; he likes to run his motors and electronics as cool as possible, and use large wires in order to build systems that will not have failures. There is a lot of wisdom in that.

I think you would be fine with 16 or 18ga wire. Geckodrive recommends 14 or 16 gauge wire from the power supply to the drivers, and 22ga wire afterwards.

So, there ya go, 13ga at one end of the spectrum, and 22ga at the other. Pick your poison. I use 18ga.

Thanks Brad and also Mike Richards, you both are my electronic teachers. The way you both explain these mathers are awesome and make perfectly sense to me. I'm learning and learning.

Polder

My first thought was "that can't be right. Mike is just going gold standard or something". So I google'd the question and came up with a chart that matched Mikes' numbers exactly. OK, this seems to be a known value. Better have someone explain this to me. Thanks Brad, you done good.

Its like selecting pipe size when you lay your plumbing... when you need a certain flow rate, (current), you don't normally choose the pipe size that is just right or smaller than it is required. a slight oversize give some guarantee on the reliability & longevity.

wire gauge / voltage drop
 

I'm about to place my cable order, and having difficulty making up my mind on the 4-conductor motor cables.

With my size of table and control box location, I'm looking at a 50-foot run for the the Y and Z motors.

I looked up voltage drop for DC power wiring in the technical standards published by the American Boat and Yacht Council (ABYC). They have tables for 12V, 24V and 32VDC (the most common sizes found on recreational boats).

Taking the 32VDC table, a 100 foot cable run (to the motor, and back) carrying 5 amps, for a 10% allowed voltage drop, is specified at 16 gauge. For a 3% voltage drop, the requirement is 12 gauge.

So playing a bit loose with the numbers, I'm running 35VDC to the motors, so with 16 gauge I'm already down to 31.5VDC at the motor. The tables don't specify anything smaller than 18 gauge. But I'm wondering... with 20 gauge, what's actually showing up at the farthest motors?

Michel, have you considered moving the control box closer to, or underneath the table? It might be more straightforward to have a long cable from the computer than to have long cables to the motors, spindle, sensors, and switches.

If you do go with the 50' run, I'd upsize one gauge (lower number).

Ah, there's the rub. I've already decided to mount the computer (mini-ITX) in the control box. So I'd now have to decide where to locate the keyboard, mouse, and monitor.

Hmm, there may be merit in this approach, using a KVM extender.

So, in looking at McMaster Carr's site, I found this...

9700T41
Cable-Tray Rated Continuous-Flex Multi Cable Shielded, 18/4 AWG, 600 VAC
Quantity Per Ft.
1-99 Ft. $2.27
100 or more 1.82

This seems to be comparable or lower than some of the other prices being listed. Is this the right wire for the motors? Is there a cheaper source for it? I just got some stuff from McMaster (2 days after I ordered it) and am really happy with their shipping and products at this point. So if its a reasonable price, I'm perfectly happy with going with them. Thoughts?

Is there a particular reason not to include the 2 core E-stop wiring with the 7-core signal wires? Is it just industry standard that it is a separate wire, dedicated to the task? It seems more economical to go with a 9/10 core wire than to have a 7 plus a 2. Am I missing something really obvious? It seems like, for the most part, they go to roughly the same spots if you position your boxes opposite the sensors for the e-stops.

Am I missing something really obvious here?

One of the e-stop circuits has a mains voltage (to open the contactor). You don't normally mix mains voltage and low signal voltage within the same cable over a long distance.

That would be the obvious part that I was missing...

Thanks. :)

Eric are you using the 126 BOB on your build?

Yes, I will be. Downloaded the manual a couple of days ago, am still working my way through it. Going to order that and 4 geckos 203Vs in the next day or two.

Hey mates,

I got in contact today with the distrubutor for Lapp kabels Croatia, and they sent me over their catalouge to check which cables i need to order.. i checked for the ölflex classic 115c in the catalouge but found only ölflex classic 115cy which by reading the product description doesnt seem to fit our needs... Now i dont know if they changed something in their brandings or the product does fit our needs, but they dont tell it to us in their data sheet because they got something "more" specialized for this purpose..

Now, im gonna copy the link to the catalouge (43 mb) its in english, so if anybody could check this i would really aprecciate it. Also, why doesnt the cables have 8 cores , but 3,4,5,7 and then 12?? I must admit that my knowledge of electicity comes down to lights on/lights off but on the other hand a man told me sometime ago that there are no dumb questions, just dumb answers :-)

I also talked with a forum member who mentioned that LiYCY cables should be my choice, i checked them out (gonna copy that link too) and by reading the description they seemed to my unknowing eye more appropriate... This data sheet is in croatian :-( but maybe you guys can figure it out by the technichal terms, they should be readable to a broader audience..

Ok here are the links:
Lapp kabel catalouge
http://www.tim-kabel.hr/images/stori...l/APPENDIX.pdf

LIYCY data sheet
http://www.tim-kabel.hr/images/stori...1101_LiYCY.pdf

Thanks in advance for the incoming wisdom ;-)

Greeting from finally a little rain but mostly hot as hell Croatia

You can use 4 cores wire. No need for 8. I had that available that is why I used it.
I got that LIYCY cable on 2 machines working 2 years now.

Just reading and learning about half coil/full coil setup... Why not 8 wires full coil? Sorry if offtopic...

Because if you looked at your drives Branko you have only 4 outputs to motors?
Bipolar drives have only that much, A and B phase. So you can lay 4 core wire to the motors and make the combination of wires at your wish there .

Still learning.. :-)

What does anyone think of the Lapp Olflex 190cy products? Are these acceptable? The current pricing seems to be less than the Olflex FD-855 and FD-855p.

Had a quick look at the spec and the Lapp Olflex 190cy looks quite good.

Thanks Gerald. It seems to be readily available (7 local suppliers) and cost is 20 to 30% less than some of the others.

Where in SA do you get your Lapp cabling from Gerald? I am also in ct.

Google is your friend!!!...http://lappsouthernafrica.lappgroup.com/

WIRE 18-4 non shield
 

hello how about this? is not shielded, but cheap and easy to buy,

I have spent a lot of money, and it is only for a while. until you have money to spare XD

http://www.ebay.com/itm/CNC-Stepper-...60393170662%26

Table 3000x2200
34HS9801
PMDX 122
G203V
PS-63NPR12

worth the risk?

Non shielded wire is just asking for trouble. Do you want to spend a lot of time tracking down random glitching and problems?

I wouldn't go unshielded for the motors. You will get loss of steps, and twitching in the motors and other random things when running the machine.

Use the extra Money, and get shielded cables from the start... Anything else is not worth the trouble.

U can try with unshield cable, you might get away with it fi you had done you EMI RFI protection well but are you ready for the complication?

You can add shielding to any wire. I made all my wire from single wires ( stranded wire from a overhead crane I had). I twisted the wires together as needed then added the shielding , looks like the Chinese finger game you can't your fingers out of then added a jacketing that looks like the same over that. have had on trouble at all since my machine has been running.

Al

eby cable
 

Can anyone tell me if this cable is any good.
thanks paul.
http://www.ebay.com/itm/Shielded-Cab...-/160632659191