Max length of running a dmx daisy chain.

[stonehedge99]

Hi,

I want to run a single length 360' feet (120 meters) of dmx cable (actually high quality mic cable with a dmx terminator which i will be using at the end) for a season run install, it wont be permanant, just for a month and then ill have to store them till the next season at maybe a different venue.

This line of 360' is ofcourse made of certain lengths to accomodate 10 moving heads and 10 scrollers on the line. Will my line be reliable with 20 fixtures spread out over a length of 360' ?

Or is it better to split the signal (http://www.ebay.com/itm/XLR-cannon-...485?pt=LH_DefaultDomain_0&hash=item3a635bc005) at the beginning and then send one run for the backdrop trusses and one for the foreground lighting. This method reduces 70' on my 360' cable run so it will only be 290'. Would this make any difference at all ?

Regards

 

[BillESC]

First, welcome to Control Booth.

Second, you will need REAL DMX cable for this application since the run it long and connections are many.

Third, you can NOT split a DMX signal using an XLR twofer. It can only be done using an opto-isolator.

 

[derekleffew]

...Or is it better to split the signal (XLR(cannon)female to 2 XLR male y splitter adapter 10cm | eBay) at the beginning and then send one run for the backdrop trusses and one for the foreground lighting. This method reduces 70' on my 360' cable run so it will only be 290'. Would this make any difference at all ?

...Third, you can NOT split a DMX signal using an XLR twofer. It can only be done using an opto-isolator.

And, even if you could use a two-fer (again, emphatically stating that you cannot), the one you cited is going the wrong way. You'd need one with one male and two females.

The suggested limit of a DMX512 run, using proper DMX cable, is 1000'-1500', so your set-up, with 20 devices over 360', is not an issue. I have done several runs over 500' of mic cable with 20+ fixtures. Be sure to use a terminator, DMX. See also the rather lengthy recent thread http://www.controlbooth.com/forums/lighting-electrics/27615-ongoing-debate-mic-cable-dmx.html .

 

[porkchop]

You shouldn't use mic cable, but if that's what you've got then try and and make sure you use a terminator. Whether or not it will work reliably is going to depend on just how accurate you need it. If you're ok with a little bit of inconsistency and the possibility of seeing the lights wobble a little in cue then you ought to be fine. If you're not ok with that you might be calling up a rental house and getting some real DMX cable. Either way don't use a Y-cable to split the signal.

 

[stonehedge99]

Hi Bill,

Thanks for the warm welcome. Much appreciated.

Derek > Yes. I had no other option because the guys on my side of the globe dont sell technically specific DMX cable. So i had no other option but to buy high quality mic cable. I asked him which costliest variety he had and picked up that. I read the dmx debate, and it scares me more now . But im keeping my fingers crossed. I have not much time to R&D for the particular project im doing and so cannot locate the exact kind of cable. And here people who deal are like just traders who know nothing technically about the lights. The guy who sold me the moving heads doesnt know what a dmx terminator is. He doesnt know what kind of cable he has but he has cable that people use to control heads. Thats all they know.

I will DEFINTELY be using a terminator by making one myself. Thats why i mentioned ill be using one in my original post/question. Its not worth risking it for the price of a 120 ohms resistor.

But i have no option but to use this cable now. The ones on ebay are five times costlier. How much do you think i should pay for a 10 meter cable with connectors ? If you guys know any ebay item that ships worlwide do post in an item number or two that i can consider importing. But thats going to take time to reach me too.

Also to explain my plan a little more. From my control desk the signal first goes (thru this XLR cable that ive already got) for a distance of 70 feet after that it hooks up to the 10 moving heads and each head links to the next one using the cable set that came with the heads respectively. Then finally the 10th moving head sends the signal out via another 70 feet of the XLR cable in question which then links to the front lighting which are all daisy chained to each other using the cable bits that came with them originally. So the mic cable that ive bought is esentially 70' + 70' in this 360' feet run. I dont know if this pattern of usage matters but just thought ill mention it.

Brett > Like you said, at this moment i have nothing else but this option Brett. Ill still look out for some import options. Its very expensive to import these to my country. And if customs gets it they'd slap on another 50% duty fee as they've done to me before. Heavy and large sized boxes attract their attention. Imagine paying $200 for 50' of dmx cable.

Thanks

 

[icewolf08]

There are many online dealers that sell theatrical products who would probably be happy to ship them to you. Going to eBay for theatre products often results in overpriced items. There are plenty of US and European based dealers who would be happy to help you out, and I am sure there are probably dealers closer to you as well.

Just food for thought.

 

[josh88]

There are many online dealers that sell theatrical products who would probably be happy to ship them to you. Going to eBay for theatre products often results in overpriced items. There are plenty of US and European based dealers who would be happy to help you out, and I am sure there are probably dealers closer to you as well.

Just food for thought.

What ice wolf says is true, and even amongst dealers one needs to remember that just because a product is the most expensive it isn't necessarily the
Highest quality. Don't use that as a judge of quality.


Sent from my iPod touch using Tapatalk

 

[stonehedge99]

I agree that just because its costly doesnt mean its good quality. Similarly the same applies the other way too. Just because its very cheap doesnt neccesarily mean its bad. In my industry ive purchased very expensive equipment pertaining to other industries / line of work etc and there have been instances when cheap non-brand items have exceeded the qaulity of the branded version or been designed better. Ive also bought expensive stuff that never even worked.

Any ideas which dealer in asia or USA would be able to internationally ship proper dmx cable at reasonable prices ?

I only found a lot of Chinese suppliers and they dont know squat about quality, they just know to replicate and sell, and they can replicate high quality or even low quality. But not all of them are that way maybe. But most of them ive dealt with are that way. They can hardly speak english if at all. And they will sell you standard mic cable and if you asked if its real DMX cable you'd get a shrill hi pitched voice yelling "yeah yeah" without even understanding what you asked.

Thanks

 

[n1ist]

Two other ideas come to mind:

- Do you have cat-5 cable available? Shielded stranded cat-5 works fine for DMX and may be easier to get
- Sticking an opto-splitter half way (say at one of the movers) will regenerate your signal.

/mike

 

[JD]

Do you know the impedance of the cable? (would be in the manufacturer's spec sheet.) For DMX, that is a more important factor then the cost. High quality mic cable usually has very low capacitance, so that is good, but look for that number. If it is 50 to 60 ohms, you may have problems. If it is 100 to 120 ohms, then you are good to go.

Note: Impedance can not be measured with a common meter. It is a factor of the inductive and capacitive loading of a line used as a transmission line.

 

[stonehedge99]

Hi,

I actually just located a dealer in CAT5 cable (He said it has a 150 ohms rating) as i was seriously considering it as an option since many suggest it to be a good alternate.

How good is it ? Equal in performance to original DMX cable ? I also understand its the same thing used in LAN cabling. Plz do let me know. Also will this 150 ohms class be useful for DMX ?

Finally CAT5 has so many strands and i dont know how to get it soldered at the male and female connectors, any links or images that could point me to a clue would be useful when getting them soldered.

Thanks

 

[derekleffew]

See the video in this post.

For the proper pin-out of DMX over Category cable, see Pathway Connectivity Inc. - Cat5 Pinout for DMX :

Category wire is not recommended for loose or temporary cabling. The use of RJ45 connectors for DMX equipment should be restricted to patch bays in access controlled rooms and should not be used for the direct connection of portable equipment.

Same/similar information at ETC KnowledgeBase: DMX over CAT5 .

In my opinion, CAT5+ cable is not the magic solution to DMX transmission, for a variety of reasons:
1. If used outside of metal conduit, it must be STP rather than UTP, which is as rare as proper DMX cable.
2. For durability in portable use, must be stranded rather than solid. Again, rarer than DMX cable.
3. The RJ45 connector was never meant to be used on a daily basis. Terminating connectors other than IDC is problematic.

-----

It looks like The Lighthouse (Facebook page link) is the largest lighting company in Sri Lanka. Have you contacted them?

 

[stonehedge99]

OK so now even CAT5 is not good enough . Why does dmx happen to be so rare ?
Ive located a guy offering CAT5e STP. They told me they have the stranded type. Will this help ? Will these cables be easy to solder onto 3 pin dmx xlr connectors ?

Regards

 

[FMEng]

Shielded Cat 5 would be preferable, but I see no reason why unshielded Cat 5 wouldn't work. The balancing of the data signal is whan eliminates most electrical noise, not the shield. The impedance of Cat 5 is close enough to work well with DMX, especially compared to mic cable.

If you make a DMX cable with Cat 5, simply use the orange/white twisted pair for pins 2&3 and cut off the others. It'll solder in an XLR just fine. Pre-made Cat 5 jumpers are readily available and they are stranded conductors. Buy them and cut off the RJ-45 plugs. Bulk cable for installation is solid conductor, and should be considered a throw away after a use or two as repeated handling will damage it.

 

[stonehedge99]

Hi FM,

Ive found someone offering stranded type. I think what you mean by bulk cable is that the copper wire is a solid thick single wire right ? So they are good for permanant installs if im understanding right.

The stranded looks like typical braided hair or crossed type ? I also see some CAT5 cables listed as twisted or straight. Are they referring to the solid and stranded types ? When you say premade Cat5 jumpers are available and they are stranded conductors, are you basically reffering to the readymade computer RJ45 jack, and ur suggesting i buy the 10 mtr units and cut off the plugs right ?

Thanks

 

[JD]

I always take the other six conductors and solder them to pin 1. (Kind of a wee bit like a funky braided partial shield.) The impedance works fine. It is fully acceptable to use it in conduit. It is not recommended to use it out of conduit on it's own, but many do. The solid conductors have a limited amount of flexing they can do before they break. Stranded is better, but as said above, harder to find in bulk. Use ONLY one pair for the 2/3 data line, do not parallel. I'll let the 3 pin XLR connector part slide as I am guilty of this as well. (DMX is 5 pin only! Despite the fact that pins 4 and 5 are not used.)

I think what you mean by bulk cable is that the copper wire is a solid thick single wire right ?

Just means a continuous length on a roll (Like 250, 500, or 1000 feet)

 

[stonehedge99]

Everywhere i read it says CAT5 is not to be used for portable installs. Im needing this for a touring show. But not often. Now i have a one month season run coming up. Next after that will be 3 months later and so on. But ill have to reuse my cables.

Also on a sidenote, i just noticed the printing on my existing dmx cables and it says AVVR 300/300 V. Does that mean its compatibile for DMX ?

Thanks

 

[stonehedge99]

I think CAT isnt for me because ill be taking down this setup and putting it back together at different locations for different seasons. So im thiking about buying something like this..can you guys give it a look and tell me what you feel. Secondly i think they dont ship internationally. So if any of you can tell me where i can buy this with international shipping and if preferably at a lesser cost ? Ill be buying about 10 nos of 25' packs.

Accu-Cable AC3PDMX25 3-Pin DMX Cable, 25 Feet

Any ideas about this brand and is it technically specific for a 120 meter run or say 140 meters allowing room for future proof addition of some fixtures. ANy sources that would offer this a little cheaper and with maybe reasonable shipping costs ?

Thanks

 

[techieman33]

That would work. But instead of just buying 25' pieces you need to think about your spacing. Your probably going to want a longer cable to get from the lighting console to backstage, having to attach lots of 25' pieces is just begging for problems in my opinion. 250'-300' is pretty standard length for something like that but it all depends on the kinds of venues you'll be playing in. You'll also probably want some 25'-50' lengths in case you need to go further than that, and for the longer gaps between fixtures. And also some 5'-10' lengths for the shorter gaps between fixtures. It all depends on what you need for your specific show and the venues that your going into.

 

[church]

Do you know the impedance of the cable? (would be in the manufacturer's spec sheet.) For DMX, that is a more important factor then the cost. High quality mic cable usually has very low capacitance, so that is good, but look for that number. If it is 50 to 60 ohms, you may have problems. If it is 100 to 120 ohms, then you are good to go.

Note: Impedance can not be measured with a common meter. It is a factor of the inductive and capacitive loading of a line used as a transmission line.

JD is correct the impedance is a factor of capacitance and inductance and the impedance of both of these is a function of the frequency of the signal. becomes interesting for data signals because a 100kHz square wave needs a cable that can easily handle the eleventh harmonic without the cable impedance changing dramatically. Cable construction can result in changes in inductance and capacitance at higher frequencies which appears as a significant impedance change to the higher frequencies resulting in an impedance mismatch. This results in signal reflections which appear as rounding of the slope and corners producing errors in the receivers which is why the impedance issue and the need for good quality cable becomes an issue.