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Chris Elston

Stage Lighting retractable or coiled power cord?

20 posts in this topic

I am doing a church project where I have to hang a light bar. I am using triangle trusses and we are hanging our light bar on a winch. The winch will allow us to winch the light bar up to the ceiling and bring it down for the stage production. Also winch it down to the floor. The total winch distance is about 30 feet. It's at the top of a gym. I am looking for a power cord or something for my lights. My light bar has 3 dimmer packs on it. Each dimmer pack is 20AMPS. Since the light bar goes up and down 30 feet, I am having problems finding something that will recoil or retract the power cords from the ceiling to my light bar. Does anyone have any suggestions? I will have 3 power cords, 20 amps each, and a data cable for the DMX signal.

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We use Lapp USA (Oflex) for festooning applications. They offer a lot of different coil cables. See the attached link for Industrial Coil Cables. http://www.lappusa.com/sect11contents.htm We also use Gleason for hose reels but they also make cable reels. See the attached link for Industrial Cable Reels. http://www.hubbell-gleason.com/PreEng/CableReels.html Bud

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You mention winching it up and down. Is the winch permanant? Make two spools to attach to the shaft? Also look at air line retractable coils. I think they stop at 20' but it is possible to tie wires to them. I have a machine that has this in a horizontal application. I don't know how it would do in a vertical application

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You mention all the details of the "Z" axis but very little of what is happening in the "X" or "Y" direction. Seems to me you need 30 excess feet of cable to drop from roof to floor. If you run it around a set of pulleys with a spring to keep the tension you could hold the excess in the ceiling when the bar is up. I estimate the distance between pulleys would need to be 15 feet if you used one set or better use 2 sets about 8 feet apart. Hope I make the idea clear.

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Be careful if you decide to use any kind of drum as in operation you are likely to have 50% of the cable still on the drum. The inductance could easily melt your cables!

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I agree, festoons would be too expensive. Would you have room to hide the take up pulleys?

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The take up pulleys sounds like a good idea. But I am not mechcanially minded, and having a hard time seeing that in my head. Can anyone provide a picture or more of an explaination of how pulleys take up the cable slack? BobO, There is no movement in the X,Y direction. Just up and down. Raise the light bar to the ceiling when not using it, bring it down about 15 feet when the show is going one, lower it down almost 30 feet, or maybe 20 feet (could be within step ladder range). The light bar is 3 sections of traingle truss 8 feet long. So the total distance is 24 feet long. The bar will be held with 4 cables and one winch mounted on the wall. With the pulley idea, if we crank the lights to the ceiling, I don't know if there would be enough room to cram the pulleys inbetween the top of the light bar and bottom of ceiling. We could leave it not cranked up so high. Depending on what the pulleys look like.

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It is in my head but unfortunately I can't draw. Here is my best shot

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Hey, not a bad idea. Thanks!

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Here's another option.... http://www.cablescience.com/retractile_cords.html

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Simple may be best, a basket fitted to the lighting rig with the cables routed so that they drop down towards centre of basket. You would just have to take your time lowering the rig to ensure the cable comes out smoothly. Hopefully the random way the cable is stored in the basket will help prevent induction problems.

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Good Picture. Just watch the bend radius spec. on your cables. Oleflex makes some nice multi-conductor intended for flexing operations and power. I'd add some definition to TW's picture. You'll need cam followers mounted on either side of your pulley and a capture rail for the cam to ride in. Just a spring and pulley will allow it to twist and this would wind the top and bottom cables together not a good idea. Also I'm attaching two drawings one shows how to use the winch to keep tension on power cables and the other shows construction of the pulley. You might need two additional bearings at the cable attachement points. Hope this helps. Please note if done this way you'll need 60 extra feet of powers cable and 30 feet between pulleys. If you run lift off a seperate but geared winch. You'll need a 2 to 1 gear ratio between lift winch and cable winch, but only 15 feet or maybe 20 between power cable pulleys. Hope I am being clear. I just re-read the post. Chako if you are worried about ceiling space consumed by the pulleys remember this. You can run cable from Z Axis to X/Y Plane around pulley A, redesign the sliding pulley B so it is laying on the X/Y plane and travels along the X axis. Run the Cable back to the Z Axis from the X/Y plane over Pulley C. Pulleys A & C can then be mounted co-linear consuming half the vertical space. Hope I am speaking a dialect of English you can follow. Edited by BobLfoot

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I had a another idea. If I got FLAT CABLE, and fabricated clips to clip between two hang points, the flat cable would zig-zag up and down with the light bar, like a festoon. What do you guys think about this idea? I looked at this option, but the "at rest" length of this cable compared to the required 30 feet of stretched length I need would cause a big droop in the cable I think. Am I envisioning that correctly? -

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Some Simple Math is in order. If you use a clip every 3 feet and it is 8 feet horizontal between the clips then A squared plus B Squared = C squared tells us that the distance is 8.544 feet between each clip when fully extended. You'll need 86 feet minimum of flat cable. When fully up the 4 inch clip would give you a clip to clip distance of 8.006 feet. That means 6.5 inches of droop in each section. If you can tolerate the extra 50 feet of cable and the droop's don't snap then it sounds kewl.

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Simple is better. I like it except I am worried about snagging. I have seen this many times on cranes in horizontal applications but I can't place a time I have seen it in a vertical application. Anyone think of any examples?

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Does the cable HAVE to come down from the roof? If it could come sideways (about 15' down) then you dont need to worry about coiling / decoiling - it would just be a striaght run wherever the beam is placed? (looks like a lever arm - you could even use a metal 'stabiliser' arm and run the cables on it, lighting rigs can swing a bit & they often have guy lines or arms). Or for a cheapo system, use elastic bungee cords, with clever placement and some sliding rings you could have the cable pulled up fairly neatly.

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Are we making this too hard? http://www.grainger.com/Grainger/wwg/itemD...emId=1611725813 http://www.grainger.com/Grainger/wwg/itemD...emId=1613502087 You could defeat the reel lock so the reel is always in retraction. We have something similar on one of our overhead cranes. ------------------------------------------------------------------------------------------------------------------- Edit: Another thought. What about a cable carrier or at least something along the same idea, where the bar itself helps guide the cable carrier as it raises up and down. http://www.igus.com/echain.asp Edited by Alaric

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Good Point Alaric, Keep it Simple!! Like Alaric said what about Cable Carriers (Cat Track). Igus can also be found at Mc Master Carr. See link. http://www.mcmaster.com/nav/enter.asp?pagenum=1388 What about just using inexpensive String Balancer(s) to raise (pull up like a bungee cord) a normal cable? See link. http://www.mcmaster.com/nav/enter.asp?pagenum=2431

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Well, I ended up going with this idea. I had to use TWO of them so they would push against each other. I don't have it quite done yet, as you can see once I got the wires on the one side it's unbalanced again, but on the other bar I am going to add some cables, communications and such and might have to add some dead weights to even it out again.

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Looks good

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