numberwrong Posted February 5, 2011 Share Posted February 5, 2011 So being digital DMX can be coiled and not loose anything right? or am I just being stupid Link to comment Share on other sites More sharing options...
DrummerJonny Posted February 5, 2011 Share Posted February 5, 2011 Sorry, can you expand on what you mean? If you mean "Can I coil a DMX Cable without damaging it" then yes.If you mean, "can I make a coil of DMX that has signal running through it without it creating unwanted interference", then also yes. Link to comment Share on other sites More sharing options...
paulears Posted February 5, 2011 Share Posted February 5, 2011 Sorry? It's not supposed to leak out of the cable in some way? The general rule most of us follow is to coil shorter cables because this works. Figure 8 thicker and longer ones that mechanically can't be coiled properly. Digital or analogue, sound or lighting - doesn't matter. There's a train of thought that coiling fragile cable - like normal solid conductor CAT5 type isn't good if the bend radius is too small because repeated winding/unwinding will accelerate the time before it fractures. Mind you - figure of eighting might be just as bad. Foil screened audio cables can also have the screening compromised by too coiling too small. Other than that, coils for me all the way. Fig-8 multicore if it's 16 or more core. Link to comment Share on other sites More sharing options...
numberwrong Posted February 5, 2011 Author Share Posted February 5, 2011 Sorry, yes I mean will coiling interfear with the signal. I thought that all analogue signal is better fig8 then coiled including VGA, 50/75 ohm coaxle BNC, standard MIC, the lot? Obviously power cables heat up when coiled adding unwanted current. Link to comment Share on other sites More sharing options...
boswell Posted February 5, 2011 Share Posted February 5, 2011 Is this a wind up? Link to comment Share on other sites More sharing options...
paulears Posted February 5, 2011 Share Posted February 5, 2011 If the cable is particularly 'leaky' then yes, it's possible. For audio, the levels are so low and delay so minuscule it's not worth worrying about. After all - plenty of multicore systems live on a drum, unwound to the correct length - makes no difference. The physics says that digital systems would be affected by delays - but reflections from unterminated ends are more likely to be trouble, than very weak spurious signals leaking out of one turn, into another. In TV work it's common to uncoil cables off the drum and figure 8 them on the floor - but this just allows extra length to be pulled out while connected. If you look at figure 8 cable on the floor turns still lay together. The idea that cables leak, and this leakage could then leak into another is perfectly possible - but the levels would be very low. We've always recommended in the books not to lay cables next to each other and cross them at right angles, but in practice it's very common for audio multicore/digital audio/mains/video and DMX to be taped to each other getting from stage to FOH, and I've never come across any examples of problems with crosstalk. Power cables left coiled do heat up, especially on metal drum formers, and I've seen PVC Arctic cable melted into a solid lump. Is this just interest, or do you have a real problem you're trying to solve. Link to comment Share on other sites More sharing options...
numberwrong Posted February 5, 2011 Author Share Posted February 5, 2011 No problems, just wanted to know the answer just so I can look big and clever on site ;) Link to comment Share on other sites More sharing options...
DrummerJonny Posted February 5, 2011 Share Posted February 5, 2011 No problems, just wanted to know the answer just so I can look big and clever on site ;) I'd rather (think I) look like an idiot and ask questions of the people I am working with on site to ensure I get it right, rather than go in thinking I know it all and making myself look a bigger idiot later on. Nothing wrong with asking questions, it shows willingness to learn and work hard far better than researching everything from the internet, getting to site, blindly setting up and doing it all wrong. Different companies have different approaches, so learn to ask and adapt :) Link to comment Share on other sites More sharing options...
revbobuk Posted February 5, 2011 Share Posted February 5, 2011 Personally, I'm a fan of over/under coiling, especially when it comes to the cheap DMX cable I've got - coiling all one way tends to mean that the cable doesn't lay flat, where over/under coiled cable has no net twist, and sits flatter. Not so much of an issue with better cables. Knowing how the particular crew you are working with likes cables coiled is a really important bit of information to avoid getting into trouble! Link to comment Share on other sites More sharing options...
Brian Posted February 5, 2011 Share Posted February 5, 2011 Obviously power cables heat up when coiled adding unwanted current.Obviously. Although where does this current which gets 'added' come from? Link to comment Share on other sites More sharing options...
DrummerJonny Posted February 5, 2011 Share Posted February 5, 2011 Personally, I'm a fan of over/under coiling, especially when it comes to the cheap DMX cable I've got - coiling all one way tends to mean that the cable doesn't lay flat, where over/under coiled cable has no net twist, and sits flatter. Not so much of an issue with better cables. Knowing how the particular crew you are working with likes cables coiled is a really important bit of information to avoid getting into trouble! Revbob, can you clarify this method for me(over/under coiling)? Not sure I've seen this done / called this... Thanks Link to comment Share on other sites More sharing options...
Jess-- Posted February 5, 2011 Share Posted February 5, 2011 the added current (although it should strictly be called added load) is caused by the coiled cable acting as a transformer with each coil inducing current into its neighbours (the more coils the more this effect is amplified), this shows up as heat and can melt extension leads quite easily. the heat problem is compounded by the fact that the wire is coiled closely together giving the heat nowhere to escape as a (very) rough rule of thumb you should derate cables according to how much you have removed from the spool so if you have a cable specified to carry 30 amps but you have only removed 1/3rd of the cable from the spool you should only trust the cable to carry 10 amps without problems (in an ideal world all of the cable would be removed from the spool and snaked backwards and forward) Link to comment Share on other sites More sharing options...
Brian Posted February 5, 2011 Share Posted February 5, 2011 the added current (although it should strictly be called added load) is caused by the coiled cable acting as a transformer with each coil inducing current into its neighbours (the more coils the more this effect is amplified),...But what effect does having the return line (aka Neutral) running alongside have? Surely the return current, which is flowing in the opposite direction, will cause an equal and opposite magnetic field which will cancel out the one produced by the outgoing current flow? Link to comment Share on other sites More sharing options...
Ynot Posted February 5, 2011 Share Posted February 5, 2011 Revbob, can you clarify this method for me(over/under coiling)? Not sure I've seen this done / called this...There are several Youtube vids which show this - a quick search gives this near the top... http://www.youtube.com/watch?v=lLwwB29uQRg Link to comment Share on other sites More sharing options...
Matthew Robinson Posted February 5, 2011 Share Posted February 5, 2011 In the suggestions that come up on Youtube with YNot's link, there's . Ouch. OT, but what size do people make their coils? I make mine about 1' in diameter when laid down on the floor in a circle and use the over/under coiling method. Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.