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RPi + OpenELEC Wire/cable thickness

Discussion in 'Hardware Support' started by Biggles, 28 March 2017.

  1. Biggles

    Biggles Member

    Messages:
    59
    Hardware:
    RPi1/Zero
    Hi, looking for some advice on type of wiring to use please.

    I'll be running 270ish LEDs, 4.5m of 60/m, and am mounting the Pi on the frame I'm building right next to the end of the strip to keep the data lines short. I have a 30A power supply (cheaper than the 20A version) which will need a 2m cable from it to the strip and Pi.

    What would anyone recommend for the cable from the power supply to the strip and also what is recommended to create the corner joints? Please don't just say something like 'thick <whatever> wire' as what you may consider thick may be different to what I might consider thick.

    Also, would injecting power at both ends be enough or should I be looking to add it separately to each bit of strip?

    Many thanks for any advice.
     
  2. penfold42

    penfold42 Active Member

    Messages:
    746
    Hardware:
    RPi1/Zero, RPi2, RPi3, 32/64bit, +Arduino, +nodeMCU/ESP8266
    It depends on the length, current and the allowed voltage drop.

    2m length
    16 amps
    0.5v voltage drop (at a guess) should be ok

    R = V / I
    R = 0.5 / 16
    R = .03125 ohms

    Over 2 metres this is
    0.015625 Ohms per metre

    But the current has to go there and come back so it's really 4 metres of voltage drop so you need:
    0.0078125 Ohms per meter

    From http://www.daycounter.com/Calculators/AWG.phtml

    Use AWG 13 wire

    I'd also power the strip at each corner
     
    • Like Like x 1
  3. Biggles

    Biggles Member

    Messages:
    59
    Hardware:
    RPi1/Zero
    Perfect, thank you. Must be a lot of underwired systems out there!

    Regarding the corners, would you recommend joining the power connections between strips and then piggy backing the power supply cable or just joining the data connections and keeping the power separate as I've seen on a few set ups?
     
  4. JaY_III

    JaY_III New Member

    Messages:
    11
    Hardware:
    RPi1/Zero
    You will do no harm in joining the power connectors in all corners. You are just adding another parallel path for voltage, and that's not a bad thing.

    As for a Vdroop calculator,
    http://www.nooutage.com/vdrop.htm
    This one is a little nicer IMHO. The charts that are pre done set to 75c i believe as a worst case scenario.
    yes you should plan for worst case, but its also nice to see what you will actually be using.

    I just setup a APA102 setup with 290 LEDs. Everything is being pushed from a 5v 15amp PSU with no issues.
    5V cable is maybe a foot long using 2, 14 AWG cables for power.
    Power is inserted in both ends, and it is running great.
    I though I might have had to run more power to the center, but with real world testing, it was not needed.
    So my furthest LED is no more than 2.45m form the input voltage, and I have the parallel path coming from the other direction as well.
    Calibration of my setup also ended up with me lowering my Luminace gain to 0.6, further lowering my power requirement.
     
    • Like Like x 1
  5. Biggles

    Biggles Member

    Messages:
    59
    Hardware:
    RPi1/Zero
    Very interesting, thanks Jay.

    First calculator I've seen that feels like it's designed for real world use rather than in a lab.
     
  6. penfold42

    penfold42 Active Member

    Messages:
    746
    Hardware:
    RPi1/Zero, RPi2, RPi3, 32/64bit, +Arduino, +nodeMCU/ESP8266
    Nice calculator - good to see my maths aren't wrong too !
     
  7. Biggles

    Biggles Member

    Messages:
    59
    Hardware:
    RPi1/Zero
    Sorry, meant to say it gave the same recommendation you did which gave me confidence i knew what I was doing with it. Most interesting was seeing how you could minimise the loss with a few changes, I'm thinking of double wiring it to the Pi so the cable is manageable but maximises the cross section.

    Maybe worth adding to the FAQ?
     
  8. penfold42

    penfold42 Active Member

    Messages:
    746
    Hardware:
    RPi1/Zero, RPi2, RPi3, 32/64bit, +Arduino, +nodeMCU/ESP8266
    Yep definitely a good FAQ

    Even better would be a link to it from the Hyperion.ng web interface that prepopulates some fields.

    5v, dc, copper, currrent are all known so should be easy
     
    • Like Like x 1
  9. penfold42

    penfold42 Active Member

    Messages:
    746
    Hardware:
    RPi1/Zero, RPi2, RPi3, 32/64bit, +Arduino, +nodeMCU/ESP8266
    On a related note - has anyone measured the resistance of the led strips ?
     
  10. penfold42

    penfold42 Active Member

    Messages:
    746
    Hardware:
    RPi1/Zero, RPi2, RPi3, 32/64bit, +Arduino, +nodeMCU/ESP8266
  11. Biggles

    Biggles Member

    Messages:
    59
    Hardware:
    RPi1/Zero
    One more question on a lesser scale, regarding the connections to the beginning of the strip.

    I'm thinking remove the heatshrink from the wired connector they come with, solder the power wire to the strip but leave all the original wires and plug connected. Then remove the wires and other gender plug from the other end of the strip and use that to connect the Pi/level shifter. Once plugged into the connector at the beginning of the strip it will take power to the Pi and data back to the strip.

    If that all makes sense, does it sound like a plan?
     
  12. penfold42

    penfold42 Active Member

    Messages:
    746
    Hardware:
    RPi1/Zero, RPi2, RPi3, 32/64bit, +Arduino, +nodeMCU/ESP8266
    Personally I don't like powering a Pi from the led strip.

    Yes it works - I've done it for testing but if you screw up the connection you can easily kill the Pi.
     
  13. Biggles

    Biggles Member

    Messages:
    59
    Hardware:
    RPi1/Zero
    Fair enough, thanks.
     
  14. Nikhil

    Nikhil Member

    Messages:
    30
    Hardware:
    RPi3, +Arduino, +PhilipsHue
    I'm also running into an issue with enough power. I have a 20A supply, so it's more than strong enough. However, with an all white string, the LEDs start out white, but by the end of the strip, they are pure red...a clear indication of voltage drop. A couple of things I'm going to try:

    1st: Right now voltage is only applied to the beginning of the strip. I'm going to take the add'l black/red cables that came attached to the front, and solder those to the end of the strip (5V and ground).

    2nd: If #1 doesn't work, I'm going to use higher gauge wires. I was hoping I could just solder the higher gauge wires to the wires already attached to the WS2812b, but given they are small gauge, I'm not sure this would work. Has anyone done this? Or when adding higher gauge wires, is the better approach to remove everything, and directly solder them to the pads.

    Thanks!
     
  15. penfold42

    penfold42 Active Member

    Messages:
    746
    Hardware:
    RPi1/Zero, RPi2, RPi3, 32/64bit, +Arduino, +nodeMCU/ESP8266
    #1 should fix it.

    There's a significant voltage drop across the led strips as the traces are so thin
     
  16. Nikhil

    Nikhil Member

    Messages:
    30
    Hardware:
    RPi3, +Arduino, +PhilipsHue
    Thanks! I'll give it a shot when I get home.
     
  17. Nikhil

    Nikhil Member

    Messages:
    30
    Hardware:
    RPi3, +Arduino, +PhilipsHue
    As you suggested, hooking up the power source to the other end of the strip indeed helps....but now the leds nearest the 2 ends are white, but as I move away they begin to yellow (not surprisingly).

    Do you think higher gauge wires might help? Or is the only real solution to:

    1. Apply voltage in the middle of the strip as well

    or

    2. Reduce the overall brightness so pure white doesn't require as much juice
     
  18. Nikhil

    Nikhil Member

    Messages:
    30
    Hardware:
    RPi3, +Arduino, +PhilipsHue
    So noticed that after soldering the 5v and GND connections to the other end of the strip, I was getting intermittent white flashes during playback. After removing hte wires, the flash disappeared. Admittedly, my soldering job wasn't that great, so possible that could be causing the flash?

    Have you ever seen this before?
     
  19. Nikhil

    Nikhil Member

    Messages:
    30
    Hardware:
    RPi3, +Arduino, +PhilipsHue
    And that's solved. Bad soldering it was.
     
  20. penfold42

    penfold42 Active Member

    Messages:
    746
    Hardware:
    RPi1/Zero, RPi2, RPi3, 32/64bit, +Arduino, +nodeMCU/ESP8266
    Both solved ?