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I'm slowly collecting parts to convert my Sieg X2 to CNC.
I've ordered the stepper motors and controllers from Zapp, so no matching problems. The question is - is screened cable necessary to connect the motors to the controllers (4 core bipolar parallel). Working in the electronics industry, I know (a little) about noise in electronics. What I've seen on the you-tube sites, this is not used, or is it taken for granted? Has anyone got views, or experience on this?
I think the amount of current being supplied to the motors, the voltage swings and the speed of signal switching means that screened cable is not really required.
If you were to do high-frequency, low voltage signals then you would need it.
Some sites recommend it. A lot depends on the length of the cables, the motor current in use and the sensitivity of the electronics around it. For home/hobby use with <2m or cable and typically 2-4A motor current I can't see it being necessary. For longer runs/higher currents I might consider it.Quote:
Originally Posted by pequod
BTW if you do used screened cable, only ground it to the protective ground (mains earth) at one end, to avoid creating ground loops (which can be worse than no screening at all)
I asked the same quesion to Roy at DIYCNC when i collected my parts, he looked at me like I was one of the main characters from dumb and dumber.
This was from a chap that knows his stuff and he said for short lengths of cable that I would be using then no need at all.
Got to admit Roy can weigh people up well.....................Quote:
Originally Posted by HiltonSteve
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I would alllways suggest to use shielded cable for the motor phases, even though for a home/hobby setup it may not be required.
Why? becasue it is standard engineering practice to shield cables.
From my point of view, it is easier to suggest using shielded cables than spend time on the phone trying to fault find a customers application.
Thanks for the replies. I'll be running 4.2A approx 1.5 metres through 3 axis, so maybe it's not necessary. At £3 +VAT per metre, it needs more consideration, or if I can get it cheaper, maybe I might as well.
I don't have record of how many conversion we have done but it's quite a few, none have used screened cable and we have had no issues.
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As a lower cost way to shield cables you can use Knited Wire mesh wrap.
10 meters of it is about £15.
you can get it from RS.
http://uk.rs-online.com/web/search/s...duct&R=2649196
yes they do, but in reels of 50 meters.
so that will work out a lot more expensive for just a few meters of cable.
Quote:
Originally Posted by Lee Roberts
12 and a bit quid for 10 metres of screened MiL spec, post paid.
http://cgi.ebay.co.uk/Cable-Screened...mZ330339933966
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Thats 4 cores of 7/0.2, equivalent to 24AWG/CSA0.23mm2... its good for 3.5A max in signal usage, but no more 0.6A for power transmission over any distance.Quote:
Originally Posted by John S
My preference would be http://cgi.ebay.co.uk/FOUR-CORE-SCRE...mZ300306498039 which has twice the rating and is £9.50 for 15m (£15 inc P&P)
If you want alternate lengths, try CSE cables they sell 7/0.2 4 core screened at 42p and 16/0.2 at 53p/m plus VAT & P&P which is £15 for 10m (16/0.2)
Yup definitely a better choice and there may be even better, I didn't spend a lot of time looking.
Interesting possibilites. I wouldn't put 4.2A through 7/0.2. Even 16/0.2 is pushing it. It all depends on what temperature rise you can tolerate in the wire. I'd prefer 32/0.2 and that is the problem - with price and availability. I spotted CSE and their prices are good, but they charge £7.50 minimum delivery. With the conversion costing hundreds of pounds, is this a "ha'peth of tar"? Maybe I'll try the unscreened wire and see what happens. I can always re-wire.
Stick a meter on the cables and you'll find you are nowhere near 4.2 amps PER CABLE
Drivers are rated per phase, not per wire.
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Quote:
Originally Posted by John S
I asked for that, still laughed my arse of though...:clap:
Interesting point John. I'm new to stepper motors, so don't understand this. The motor I've ordered is 2 phase, 2.73V, 4.2A, 3.2mH, wired Bipolar Parallel, Zapp SY60STH86-30. I haven't got the kit yet to measure. So does this mean I rate the cable at 2.1 A? This could be good.
Each pair of wires is a phase... so a 4.2A phase on bipolar means 4.2A is being carried in 2 wires. In full step mode only 2 of the 4 wires at any one time is carrying 4.2A and not 100% of the time, but the maximum current in any one wire is 4.2A.Quote:
Originally Posted by pequod
16/0.2 is rated for 3A continuous 6A peak in conduit, at 4A you will lose about a volt across a 1.5m length.
I can't run a test because believe it or not I only have one small CNC running and it's hard to get to the motors on this one.
I can do later in the week but it is interesting to actually check just what power is pulled on a stepper system.
Geckodrive state that 2/3 of the maximum amperage of the motors is required so if you have a 6 amp motor they recommend 4 amps of power.
i know at one stage when we were doing the prototype X3 kits we worked out that we needed 4 x 2.5 amp = 10 amp divided by 2/3 so we arrived at a 7 amp power supply.
Once built running all 4 axis absolutely flat out drew just under 5 amps ???
So someone do me a favour and stick a test meter in circuit with one of the motor leads, most of the cheap multimeters will handle 10 amp, and tell us what the driver is set to and what it pulls on a rapid move and a low speed cutting move.
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Seems to me all of the above is relevant if you are building in the wiring, in which case you may as well use whatever cable will handle the load.
If (like me) your build has the cables unpluggagble via XLR sockets then my preference is to overbuild it to buggery in terms of cable so that they are mechanically robust.
Hence will be using 4-core SY cable, 0.5 mm^2 conductors, with OD of 7.3mm which is within the 8mm max for the XLR plugs:
http://www.eland.co.uk/electrical-ca...ble-cable.html
Screening is a bit of a bonus. Current capacity is 7A per wire so should be an adequate safety margin on that front too :-)
Can't remember the cost but last time I got some from a local electrical wholesalers it was very reasonable. Anyway I figure my time is the most valuable part of any 'hobby' build so I'd rather just do it once and make it bombproof so as not to have to go back and fix it later... especially with fiddly stuff like cables, which in my experience tend to get a hard life anyway.