RGB strip and 4 core wire question

[theadar]

Hi there. Finally jumping in with both feet after several months reading the forums here and over at ACL. I'd like to add some dumb RGB stip lighting to accent the lines of my second story but I am still a little unclear on the best way to actually wire the strips up.

Here is what I'd like to do (you'll have to excuse the ASCII art). I'd like to have 6 sections of RGB strip which are independently addressable (each section has its own 3 DMX channels). I haven't done the measurements yet but each section should be between 8-10 feet.



/i
3 / 4
/
/
/
| |
2| |5
1 | | 6
______| |_______



I'm planning on using four core 18AWG wire with the waterproof pigtails. From what I've gathered two options are:


1. Use the four core wire to carry power and DMX signal. The four core wire would serve as a 'backbone' and then feed DMX controllers which then go into the strips.




Strip 1 Strip 2
| |
| |
12V+ $8 DMX contr. $8 DMX contr.
12V- | |
DMX+ / ------|----------------|----------- ....
DMX- /



Pro - Seems like less cabling
Con - I'm worried the 'backbone' cable may end up carrying too much current. Is this a valid concern?



2. Use the four core wire to carry RGB and 12V+. This would be a more centralized approach:


12+ Centralized RGB+12V+ -------------- Strip 1
12- DMX RGB+12V+ -------------- Strip 2
DMX+ / Controller .
DMX-/ (e.g. CMB16D) .
.

Pro - Seems to be more examples of ppl doing it this way.
Con - I was planning to keep most of the components in my garage so it seems like I'd have more cable to run. Would I have to worry about voltage drop with the long runs of cable?


For reference, here are the components I was going to use.

$8 DMX controller - http://www.holidaycoro.com/3-Channel-DMX-RGB-Controller-p/26.htm

18AWG 4 core cable - http://www.monoprice.com/products/product.asp?c_id=102&cp_id=10239&cs_id=1023904&p_id=4043&seq=1&format=2

Dumb RGB stip - http://www.aliexpress.com/fm-store/701799/209843764-329544925/5m-one-roll-5050-SMD-30LEDs-m-led-strip-waterproof-by-silicon-tubing-and-coating-RGB.html

Waterproof pigtails - http://www.aliexpress.com/fm-store/701799/210128048-532156471/10-pairs-4-Core-White-Waterproof-cable-45cm-long-each-male-and-female.html

Any comments/help/guidance would be greatly appreciated!

[WilliamS]

they both seem like your on the right track. Although you do not carry signal out of the CMB16D all you carry out is 4 wires, the common and the r,g,b wires. The 16d can run 5 strips in total. Im not a fan of the Power over DMX, but it works for many here I just dont want something that can end up sending power back to something that shouldnt.

Go with the 4 core cable, you can still carry DMX and power. Once again I would go with the centralized approach with a DC board. All the connections in one area going out to your strips.

If you are up to it you can also adjust the power output a tad to compensate for the power drop across the lines. At full load test your voltage at the end of the wire leading into the RGB strip. Adjust to get to 12v. This can be very bad as it doesnt take much to get too much power and smoke a LED.

[flogger7]

My personal preference and what I'm doing for 2012:

Cat5 to run the DMX signal daisy-chained from one $8 controller to the next. Power injection on the Cat5 (unused 6 wires; 3 +12v, 3 ground) for fixtures that draw minimal current.

12v power over 2 wire SPT-1 home-run to the 12v DC power supply enclosures for the fixtures that need more power than can safely run on cat5.

[theadar]

Thanks for the replies....makes sense. I hadn't thought of using SPT for the 12V. From what I've read SPT-1 is rated for 7 amps and SPT-2 is rated for 10 amps. Seems like this will allow for 2 or 3 strips to be powered if I go with the backbone approach. Still undecided ... but that's just how I am.

[Steven]

Let's say the strips you are using are 150 LEDs / meter. At 100% white, 10 feet would take about 2A.

18-gauge wire is about .65Ω per 100 feet. Your wire probably won't be than long, so let's assume 50 feet. This would be a voltage drop of .65 volts on the common (positive) wire and .22 volts on each of the 3 colors, or .87 volts. This is a minor voltage drop and says that running a bunch of 4-conductor cables from the ribbons to a DC controller mounted 50 feet away would work fine.

If you attempt to run all your ribbon (~50 feet) through one 18-gauge cable, this would be 10A, or 1.3 volts drop for every 10 feet of 18-gauge, 2-conductor supply cable.

The resistance of Cat5 cable is calculated from the resistance of an individual 24-gauge conductor, which is 2.567 Ω per 100 feet. If we multiply this by 2 (for the positive and negative conductors), then divide by 3 (since you'll put 3 wires in series), we get 1.71 Ω per 100 feet. If we attempt to power all 10A through this (which is a bad idea, as according to http://www.powerstream.com/Wire_Size.htm , you can put a maximum of 10.5 A through 3 conductors of 24-gauge wire), then we'd lose 1.7 volts in 10 feet.

One way to avoid voltage drop problem is to use multiple power supplies, distributed throughout your display.

[rmturner54]

We are not actually running power over DMX. Using 4 core wire, 2 for power and 2 for DMX.

[Robert Burton]

Your doing exactly what I want to do with some "Dumb" rgb strips. Just ordered;
http://www.diyledexpress.com/index.php?main_page=product_info&cPath=10&products_id=78
Am splitting these up just as you are and am wanting to either inject the 3 channel dmx OR use the 27 channel dmx controller. Just not sure yet would work over the longer hauls. Not sure either if the power adjustments to make it reach the ends of the lines would harm the rgb strip lights.

[rmturner54]

Here is the post I put up on converting my NP lights to DMX. There is also a video and wiring schmatic
http://forums.lightorama.com/forum75/33239.html