Ive read many use Cat5 shielded cable for wiring the Keling 381oz motors. I noticed the motor wires are 20ga. Cat5 is 24 gauge. In the Handbook of Electronics, 3.5A should use 16 gauge(3.7A) for Power. And what is called Chassis uses 24ga(3.5A). I have a feeling the manual uses conservative ratings.
No problems using Cat5 24ga for the motors?
btw-PS is 48v-7.5A
How long a run of wire are you talking about? With "long" runs, the concern would be with voltage drop (and secondarily with heating), but typical hobby installations that I have seen only use a few feet of cable to the motors.
The current carrying capacity tables do make some conservative assumptions which might not be relevant for the application that you are considering.
If I were hooking up those motors, I would probably use #20 or #18 wire. In fact, I just ordered four of them from Keling, and that is what I expect to be using. I personally would avoid using #24 wire for that application, although for short runs you could probably get away with it without ill effect. Since there are four pairs of #24 inside a cat5 cable, and the 381 oz-in motors have four wires, you could double-up the conductors.
The problem that I have with using typical cat5 cabling intended for in-wall (or in-plenum) use is that it uses solid copper conductors, which have a nasty tendency to break if the cable end is subject to vibration or movement. Some cat5 cables (such as those used in patch cords) use stranded wire which is less of a worry in that regard.
I was planning to do a mockup of components this wknd, but all my Cat5 cables(I cut the ends off) are solid, non-shielded.
Is all Cat5e solid? If not, is there a way to tell? The crossover cable Ive seen for purchase online doesnt say shielded. See RiteAV.
The motor cable run will only be 5-7'. The computer box(SFF) and controller enclosure are going inside one of the lathe cabinet stands. Mounted on silicone gel or foam pads w/an exhaust fan built into the cabinet.
Know anything about VGA cable, is this shielded & stranded?
How will you shield the separate 18ga wires and what will you use as a cable cover?
You can probably tell the difference between solid wire and stranded wire cable simply by handling it - if it is somewhat stiff then it is probably solid wire, whereas if it is flexible then it is probably stranded.
I have not decided whether or not to use shielding for the motor wires. I may just go with individual wires held inside some "split-loom" tubing (such as 1/4" x 14 Ft. Protective Wire Wrap).
I will probably use shielding for sensitive wiring such as the limit switch cabling.
The VGA cables that I have used are shielded and they use stranded wire, however I do not recall what wire gauge was used. VGA cables do not normally carry high current, however.
You brought up a misconception about shielding I have. I thought it was to prevent the electrical interference coming from the cable wires, not the other way around.
That said, I can change my approach and need only to be concerned w/current capacity of the stepper wires.
Cat5 cable was not designed for that application in mind, for servo's or steppers you are better off going to a larger gauge cable that consists of twisted pairs, there is a natural cancellation of the EMI when using twisted conductor pairs.
Also it often comes with at least foil shield.
Al.
CNC, Mechatronics Integration and Custom Machine Design (Skype Avail).
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.
The question of whether to use shielding to protect the wires from induced signals or whether to prevent or reduce radiation of EMI is an interesting one. It can be used for both applications.
For example, VFD power wiring is notorious for putting out extreme EMI, and shielding is a wise precaution. Stepper motor wiring can put out some EMI as well, especially if the motors are connected to a chopper-type drive. But then you need to consider what it is that you want to protect from the EMI. In my case, since I will use shielding on the limit switch wiring, the main concern that I would have about EMI from the stepper wiring would be interference with AM radio or shortwave (I'm a ham radio operator), however I'm unlikely to be using either when I'm running the CNC equipment, so I'm not particularly concerned about the EMI from the stepper wiring. But YMMV.
(Edited to add: Yes, it is good engineering practice to reduce radiated EMI by shielding cables, such as the stepper wiring, that could be carrying high-frequency currents which could be radiating signals. Yes, it is even possible that the radiated signals could carry for a significant distance, and so it is even possible that they could cause interference to services such as aircraft communication. The twisted-pair technique that Al_The_Man mentioned above is certainly a good thing to consider if no shielding is used. That said, I still have not decided whether or not I will use shielding for my motor wiring.)
Last edited by doorknob; 02-05-2012 at 11:49 AM.
While on this topic of shielded, when wiring to a connector, does the foil shield need to be attached to the connector? Need to be "drained or grounded" ?
It needs to be connected to earth ground, If grounding one end, I find it easier to ground at the drive end as it can be connected at or close to the star earth ground point.
Al.
CNC, Mechatronics Integration and Custom Machine Design (Skype Avail).
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.
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