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Topic: Will 20 moving lights run on a single dmx cable ?
Message: Posted by: plainman007 (Feb 16, 2006 11:22AM)
Any idea if 20 dmx fixtures can be run on a single line of dmx cable?

The dmx line is 100 meters long and the fixtures are evenly spread across the 100 meters. Each fixture is a 15 channels unit. The controller is a PC based software controller with an interface running out of the USB. Will I need a splitter or booster anywhere down the line?

Or will 20 fixtures running on 100 meters work fine?
Message: Posted by: Kevin Ridgeway (Feb 16, 2006 11:41AM)
In theory it should work. However, you may want to buy a DMX splitter. These are special units and are powered. I'm sure you know this but for others reading this...you cant just "split" the DMX with a Y adaptor.

Keep us updated on how it turns out. Especially post some pictures of the rig in action.

Message: Posted by: plainman007 (Feb 17, 2006 11:45AM)
Sure I will post some pics once I get it running. Bye.
Message: Posted by: Grandillusionsmagic (Feb 17, 2006 02:28PM)
I have about 300 channels all around the room there are about 14 heads some scanners and some full heads. I also have dimmer packs, LED lighting and more and they all run no problem on one line from my compu-pro powered by my USB drive in my laptop.
Message: Posted by: muzicman (Feb 17, 2006 06:59PM)
I easily ran 20 DMX fixtures on a 300 ft cable. Not all were moving head but I had no problem. I was using Elations Compu Ware Pro software and DMX interface. It's important to have a termination plug in the last fixture.

My laptop wouldn't run the software properly. The processor speed was just under the manufacturers specs. I now run on a desktop that has a 3.25 Pentium 4 HT running XP Media Edition and it will run all my lights and foggers with no problem over great distances.

I believe there is a limitation on distances but I have never exceeded whatever that number is. Technically speaking, there are 512 channels on a single DMX cable. As long as you do not exceed that channel limitation, you should have no problems. Each fixture will take up between 1 and 8 channels (some may take more). Moving heads typically are 6-8 channels. Assuming you have 20 fixtures and each is 8 channels that equals 160 channels so you have plenty of room to spare. Some fixtures can be programmed for the same channel so the fixture will "mirror" another fixture. I have never done this but it is possible.
Message: Posted by: plainman007 (Feb 19, 2006 03:07AM)
HI grand illusions and muzicman,

I'm aware of the dmx multiplexing method and the channel separations etc. The key point of what I was doubtful about was the maximum distance. I am more worried about the fade level of the signal after it passes thru 20 fixtures. And so with 20 fixtures what kind of safe distance I could expect. So both of you have never used a splitter or booster and have run the rigs you have described ?

Also tell me, is it OK to extend a dmx line for further distance by simply connection another dmx female in to the end socket so that we get extra length ? I mean using bits of dmx cable with male female ends to stretch out a cable for reach.
Message: Posted by: Grandillusionsmagic (Feb 19, 2006 09:20AM)
I have never used a splitter or booster.

I know a guy who has foot and 10 foot cables and that is all he uses, when he needs to go 35 feet he pulls 3 10 foot and a five foot and link them together. I have linked cables together when I didn't have one long enough. I do use a termination plug in the last fixture.

I heard you can run about 1000 feet without a problem, I don't know if that is true but even if it is 800 feet that is a long distance.
Message: Posted by: Kevin Ridgeway (Feb 19, 2006 10:23AM)
It is not just the length...it is connections also. These are where you can start to "lose" signal as connectors may not be very good, worn out, not making good contact, etc.

For the lengths and amount of fixtures that have been described, most will be fine with one run of DMX. The best thing to do is get a DMX tester, so you know you are good when it comes to showtime.

Message: Posted by: silverking (Feb 19, 2006 01:26PM)
As Kevin has pointed out, a tester is the ultimate DMX accesory.

Here's the ultimate tester. (IMHO)
With a Lil' DMXter, you will never encounter a DMX problem that you can't track down and fix,.

Message: Posted by: Kline (Mar 2, 2006 08:40AM)
Connections do wear ! We usually do at least two seperate links to our computer ( we run Martin LJ) its rather simple, the upper 17 fixtures are on the same link the lower (on the deck) 4 fixtures are on another link. and then the effects (fog and Haze ) are usually on a third link if not at the end of link 2.
This saves a bit of cable as well as having to string a data line from the flies to the deck.
Message: Posted by: Fitz (Mar 2, 2006 08:09PM)
You should have no problems with your set up. You should be able to run up to 512 channels in one universe. Yes you can link more cables (2-25' to make a 50' run) but like the others have said this could create problems... but most likely it wont. If problems exist check your cables first. As far as I know your fixture will send a signal through it bumping up the strength.

What kind of fixtures are you useing?