New LEDS and power/data distribution

neilric99

neilric99

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May 20, 2010
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Irvine, the OC, CA
Has anyone come up with a modular distribution design for their power and data requirements for the new 24v/ 5v led circuits.

What makes sense in terms of distributing power, running 100/240V to key areas and running power supplies for the displays in that area or keeping the high voltage away from the display area.

Data circuits today would revolve around DMX (via ACN/E1.31 or usbdmx dongles), LOR networks and possibley wireless LOR or DMX receivers.

Neil
 
David, this is great, you go into a lot of detail on the construction of the data and power distribution for the stars which could easily be applied elsewhere.
 
If you are not constrained by the limits of CAT5 current carry ability, then it works well and it's modular. Need power? Just plug in a power injector.
 
I have been thinking of using 7 pin (5 Amp) waterproof plugs and sockets, wired as such:
  1. DMX Shield
  2. DMX -
  3. DMX +
  4. Power Ground
  5. +5V
  6. Power Ground
  7. +24V

I'd locate a number of these outlets around the perimeter of the house. Each DMX controller would plug into those sockets and use either the 24V or 5V power.

By using separate pins for the different voltages, the danger of plugging a 5V controller into 24V power would be eliminated. I think the 5 Amp per pin limit is reasonable considering the low current draw of LED based displays.

As for exactly where to mount the actual 5V & 24V power supplies, I'm undecided. Home running the power cables could result in an unacceptable voltage drop, especially on the 5V line.

Both male and female line (cable) connectors are available, so (DMX + DC) extension leads would be easy enough to make up. There are plastic caps available to seal off the panel sockets when not in use, lest the spiders and hornets build nests in them!

Anyway, that's my thoughts so far. :)
 
David_AVD said:
I have been thinking of using 7 pin (5 Amp) waterproof plugs and sockets, wired as such:

  • DMX Shield
  • DMX -
  • DMX +
  • Power Ground
  • +5V
  • Power Ground
  • +24V
I'd locate a number of these outlets around the perimeter of the house. Each DMX controller would plug into those sockets and use either the 24V or 5V power.

By using separate pins for the different voltages, the danger of plugging a 5V controller into 24V power would be eliminated. I think the 5 Amp per pin limit is reasonable considering the low current draw of LED based displays.

As for exactly where to mount the actual 5V & 24V power supplies, I'm undecided. Home running the power cables could result in an unacceptable voltage drop, especially on the 5V line.

Both male and female line (cable) connectors are available, so (DMX + DC) extension leads would be easy enough to make up. There are plastic caps available to seal off the panel sockets when not in use, lest the spiders and hornets build nests in them!

Anyway, that's my thoughts so far. :)
Click to expand...

How would the other end of the DMX lines be connected? Are you looking at a DMX splitter versus multiple dongles?
 
budude said:
How would the other end of the DMX lines be connected? Are you looking at a DMX splitter versus multiple dongles?
Click to expand...
Yes, I'd run the DMX lines back to a central point and use an isolated DMX splitter. You could also feed the DMX lines from the ECG (name?) 4/8 way boards.
 
That splitter certainly is cheap! I'd use an isolated type though to avoid ground loops.

As for the 32 node limit, simply changing to a "1/4 load unit" chip extends that to 128 nodes.
 
Back to the Power Discussion

Warning Techo talk

Glad someone raised this, power distribution for 5V stuff is going to be critical to get right with significant voltage drops that happen at higher currents. Dropping 2v across 20 feet of power cable at 110v means nothing, doing the same thing at 5v means the lights go out!

Now an example of the ubiquious Cat5 and lets be generous and use a 26 gauge version.
From this page http://www.mwswire.com/barecu6.htm 26AWG has a resistance of 41 Ohms/1000feet. So 20 feet has a resistance of (41/1000)*20 equals 0.82 Ohms - now double that for the loop resistance (pos and neg sides) = 1.64 Ohms. Sounds pretty low, so lets draw 400ma through the cable for 20 feet. Ohms laws say V=IR so V=0.4A x 1.64 = 0.656V DROP. Now at 12v you get 11.344V, not a real issue, but at 5V you would be down to 4.344V, this will be an issue.

Now an example for 18AWG cable suppling a string of 100 RBG Pixels.
From http://www.mwswire.com/barecu5.htm
18AWG Resistance = 6.386 Ohms /1000 feet or 0.006386 per foot (just a little better than Cat5)
Current draw for 100 RGB Pixels all white = 100 x 60mA = 6A
So at 6A current draw (using V=IR) 18AWG will drop 0.038316V per foot ( 0.114948/metre).
As you need to take the loop distance into account a 20 foot run = 40foot loop will drop 2.3V at 6A..... yes 2.3V... more than enough to cause issues.
What's this mean... well either THICK cables to reduce voltage drops or move the power conversion out to the point of demand, that is right at your pixels.

All of the above apply to any high current load, think about 16A-20A feeds to DC controllers at 24-28V, again many volts can be lost on even thicker cables.

Cheers
Phil
 
Thanks for the information Phil, this is really what I was thinking about without knowing the real detail behind it.

So I will be pretty much plugging in my strings into the PSU (or within 6ft If I need to run power half way up my tree)
 
Where distribution of 230v is not really fesible, i'm usign 48VDC, and a DC/DC converter down to 5VDC.. The national semi conductor "smart switchers" are really simple to use and they have a great design tool online, littlerally put your parameters in and it will spit out a design.. A well regulated DC/DC converter can run anywhere between 12 and 60VDC in, putting out a nice solid 5V
 
On the 5V switched PSU there is an output voltage adjustment that will allow it to be tweaked, is this a valid way to increase the output voltage to account for the expected voltage drop on the node extension cables?
 
Yes, its quite fesible to adjust the output voltage of the PSU to go higher than 5V.. Be careful however, not to exceed VCC max at the first node on the string..

And, also remember that the voltage drop on the wire will not remain constant.. ( nb: this is not a violation of ohms law )...

When you strings are turned on full ( #FF FF FF ) and drawing the max current, the voltage drop will be at its maximum, when they are off, voltage drop will be at a mimimum..

Make sure you consider both the minimum and maximum current conditions.. If you set the output voltage too high, you could fry your pixels when they are off, by exceeding Vcc.
 
mrpackethead said:
When you strings are turned on full ( #FF FF FF ) and drawing the max current, the voltage drop will be at its maximum, when they are off, voltage drop will be at a mimimum..

Make sure you consider both the minimum and maximum current conditions.. If you set the output voltage too high, you could fry your pixels when they are off, by exceeding Vcc.
Click to expand...

Must reinforce this forcefully.... NEVER adjust the voltage above the max voltage for whatever you are running.

Under no load or light load the voltage will be whatever you set and can blow things if too high.

Phil
 
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