DMX, Cat 5 cable, and power injection

Bill Ellick

Bill Ellick

Full time elf
Joined
Dec 31, 2011
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My appologies if this has been discussed before.
I have spent the last hour and a half digging around and can't find anything specific so I will ask here.
When using Cat 5 cable for hookup with the various RGB pixel nodes and strings and using power injection along the line is there any standard that most folks in the DIY section have adopted for a pin out to use.
I understand that pins 1 and 2 are the DMX signal lines and it appears that Dave from Holiday Coro makes his cables up so that the remaining 6 wires in a Cat 5 cable are used for the power injection by using the 3 solid colors twisted together as either + or - and the other 3 striped pairs twisted together as the other side (- or +).
Is this a fairly constant way to do the cat 5 cable for most folks or is there another way?
Just curious as the DMX signal also has a ground on most cables that I have seen so far, then I "assume" that most folks don't worry about using the ground line? Or am I missing something here (which is entirely possible since I have spent the last week reading and studying this stuff and feel like my head is overloaded about now - LOL) or is this true?
OR do you not use all 6 wires in a cat cable for power and 'reserve" say one pair for ground or some other function that I am missing?
I'm sure that this will become a lot more fun once the information sinks in a little and my brain sorts it out into some better organized fashion! Yea right, like that is going to happen anytime soon!
So can one of you nice folks steer me in the direction of a reasonable answer or is this something that really has no set definition of yet?
I just hate to build a bunch of things and then find out that everybody else uses some other standard. Especially if the folks who are designing some of the newer devices are using the RJ-45 jacks into things with power injection figured for certain pins on the jacks.
Thanks
Bill
 
Personally im not a big fan of power over ethernet, i like to keep them seperate. ethernet cable is officially rated at 1 amp per core so if your using a 5 metre strip of 12vdc 30 LED/M strip then you will require 6 cores, so yes that leaves 2 cores and no ground. this is where is can be a hit a miss thing, it will work for many not having the ground but then ive seen others where it wont work without a ground.

The other issue is that a lot of people use solid core CAT5 due to being cheap, this in itself is problamatic as our installations are only temporay and the CAT5 cable can easily break a core and then become overloaded especially if this is a return common core, then this can heat up and melt the insulation then putting 12vdc or whatever voltage into the data line and causing damage.
Another potential issue is mixing the cores around and accidently injecting power into the data line and causing damage as you are finding that there are not any decent standards that are followed within the hobby.

For me its not much more cost to buy cheap 4 core security cable which is rated at 4.4 amps and use that for your power and keep the CAT5 seperate. But then thats only my opinion. many others do it with power over ethernet and have no issues.
 
Thank You Eddy
This is the answer that I was actually expecting to see (as well as somewhat hoping to see) from a person of "reasonable responsiblity, intelligence, and experience" in this hobby.
I was pretty sure that there was no standard for it but I did have a doubt after seeing the Aus listing showing the DMX connector listings for T-568, P-DMX, LOR, and JEC/wjohn:
http://auschristmaslighting.com/wiki/Connector_Pinouts#RJ45
which made me question as to whether an actual standard had been developed for this.
I actually agree with you on NOT using the Cat cable for power and data and am planning on going with seperate cabling myself as well.
I just figured that it does not hurt to ask when you have any doubts about something.
I am still in the planning stages for my incorporation of RGB into my display and wanted to "get the facts" on some things to make my set up plans.
While I can see where the use of the cat cable for things like the Holiday Coro stars and such is a nice simple way to hook them together, my 40+ years of electrical experience also tells me that it "just doesn't feel right" to do it. The problem with Cat cable with the solid core plus it being too small a guage just seem to glare out as a warning to me as "a problem waiting to happen".
While it can be done and be done safely as long as one takes the care to watch it closely and take the precautions, it can also be a hazard for those less experienced with electricity.
I was glad to see someone with the "credibility" in this hobby say so as well.
I also can not see where it will ever be a reasonable thing to do at this point. I can see where there will come to light a need to incorporate another connector into the mix of things possibly later on for this but there is already plenty of ways around the problem without any extra parts.
It doesn't take much to make a power supply in an encloser with multiple outputs for 5V, 12v, 24V, or whatever extra power that your display items may require or even to take a small supply and make some leads off it to run short distances to controllers, strips, nodes, whatever with better safety and cable management in mind.
While this is a "hobby" and people have the right to do as they please, it does behove people who understand the underlying principles of things to speak out and bring things to light for those who are not as knowledgeable especially in light of the number of people who are jumping into this in the last year or so. I see so many who have no knowledge of electricity getting into this field and there is a need to show them the hazards as well as the fun side of things in my opinion.
No one wants to be told that something is dangerous but is is way too easy to fail to "see the forest for the trees" with things and is becoming more so with the increasingly rapid developement of technology.
Also with the advancements in ethernet, LOR, DIY, E1.31, and other things on the horizon, I see the upcoming problems when someone plugs one of these POE "style" cables into a SansDevice board or an LOR board and lets out the magic smoke. That could be a costly error and a very easy thing to do if you happen to have a person or kid helping you set up your display and they inadvertently connect a cable wrong.
Perhaps it is time to take a look at this practice and make a standard up for "Christmas Lighting Power Distribution" for smaller scale devices out in the yard?
Maybe call it "Dedicated Electrical Auxiliary Devices" or DEAD for short? That might get their attention?
Reallky not a thing to make humor out of but you get my drift I'm sure.
I have no problem with people making up their own electrical items, but we need to remember that while WE understand this, not all the folks who are wanting to make a display are as knowledgeable nor will understand. They depend on the folks who do this to help them make it happen for their displays.
Bill
 
The P-DMX pinout and voltages we came up with last year are perfectly fine for their intended use. The current in the CAT5 is limited to 2 Amps and protected by a fuse at the source.

Also, with P-DMX, the voltage on the cable is not necessarily the same as what the final circuit uses. Step down converters at the load are the key. In this regard it's the equivalent to PoE (Power over Ethernet) but for RS485 / DMX connections.

Yes it's bad to plug things into each other that weren't meant to be. In the case of P-DMX and Ethernet, as far as I'm aware, no damage should occur however. We did go through many scenarios when we arrived at the solution.

So, in a nutshell, there's no reason you can't send power down the same cable as data. Would you power a whopping big light or controller with it? No, of course not.

There are many ways to achieve a suitable result. Separate power and data suits some things, whilst schemes such as P-DMX suit others. That's the great thing about this hobby - choice! :)
 
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