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'When' do I decide to inject power

Discussion in 'Power Supplies' started by Greg.Ca, Feb 23, 2013.

  1. Greg.Ca

    Greg.Ca Apprentice Elf

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    I currently have a few of both 12VDC AND 5VDC strips of 2811 strips and experimenting with both of them. If I decide to use 5DVC strips (2811's) is it necessary to power up both ends of a 5V 5 meter strip with power at both ends? I would MUCH prefer to NOT run wires up to the top end if I don't have to.

    The advantage of using 5VDC strips is that I possibly do not need to wire up the 'other' end at the top of the tree. Therefore I would only have wires at the bottom of the tree where maintenance is more practical. The disadvantage is that I need to purchase more P12R's as each 5VDC 2811 strip nearly requires one of the 12 outputs. Each of the 5VDC strips requires 150 of the 170 pixels. I am willing to purchase more P12R's as the only negative I see. 5VDC strips would have NO wires at the TOP of the strip. Easier to set up in the winter time and I would have control of each individual LED on the strip making for more beautiful and complex patterns. With 12VDC strips, I would have wires connecting strips together at the top of the tree as 12VDC strips can drive 3 strips. Wires connecting strips at the top of the tree would be a big mess. Not cool.

    My question is whether or not the 5VDC strips require 5DVC power on both ends of a 5 meter strip?
    Does this strip require power on both ends?
    http://www.aliexpress.com/store/product/5m-WS2811-LED-digital-strip-60leds-m-with-30pcs-WS2811-built-in-the-5050-smd-rgb/701799_653641294.html
    --Greg--
     
  2. AAH

    AAH I love blinky lights :) Community Project Designer

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    You don't have to inject anywhere if you really don't want to. The reason that injecting is virtually a must do is the fact that the wire used on all pixels of any type are reasonably thin and there is a appreciable voltage drop down the length of the strip. This wouldn't be a problem if the red, green and blue leds all had the same forward voltage. Because they don't the further down the strip you go the more "white" turns to pink as the red leds require less volts to turn on than the other 2. If you're willing to put up with pink bits or you aren't planning on mixing colours then you don't need to inject power. I don't know what others do but I consider the easiest thing to do is use some reasonably heavy duty figure 8 cable from 1 end of a "50 strip" to the other.
     
  3. AAH

    AAH I love blinky lights :) Community Project Designer

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    Rather than editing I'll create a new post to give it a bump.
    After re-reading I'm guessing that you had planned on using 1 50 pixel strip per output of a P12. That is under utilising the P12 massively. I'm not sure if there has been any software changes lately but the P12 is at least capable of running a full universe or 170 pixels on each of the outputs. What is usually done is string 150 pixels together for instance and just inject power at the beginning and end of each 50 which for your tree sounds like it would be top and bottom.
     
  4. fasteddy

    fasteddy I have C.L.A.P Global Moderator Generous Elf

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    5vdc can be powered from one end only, what you have to consider is the distance from the power supply to the pixels and the guage of the cable and current being drawn down it. Because if you dont use a decent guage cable or have a longer distance, then the voltage drop occuring in just the supply cable will then create a situation where the voltage at the end of the strip/string will be below that of what is required for the chip to drive the LED at it rated current and thus show as dimming lights because you may have already lost 1/2 a volt just in the supply cable. So this is important if you want to supply power to just one end.
     
  5. dpavisic

    dpavisic Full Time Elf

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    So would it be preferable to simply use thicker gauge cable (leaving cost consideration aside for the moment) to run from the PS to the lights wherever possible to minimise voltage drop in long runs? I'm thinking something like the green cable used for garden lighting.
     
  6. fasteddy

    fasteddy I have C.L.A.P Global Moderator Generous Elf

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    Yes one way to minimise voltage drop is by using a thicker guage cable as thicker cable has a lower resistance value per metre which in turn means less voltage drop over the same distance as that with using a thinner guage cable.
     
  7. OP
    OP
    Greg.Ca

    Greg.Ca Apprentice Elf

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    what I plan on doing is using 5VDC strips that have 150 pixels. Not using 12VDC strips that have 50 Pixels. Using 5VDC strips, I will be using 150 pixels of the allocated 170. --Greg--
     
  8. OP
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    Greg.Ca

    Greg.Ca Apprentice Elf

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    To update everybody, today I finally tested a 150 Pixel 5 meter 5VDC strip and when I commanded all white with power on one end only, the 'other' end (which had no wires attached,) the 'end') DID have some of the whites at that end looking rather 'pinkish'.

    However when I apppled 5VDC at BOTH ends, then when I commanded all white, everything WAS bright white with no evidence of pink anywhere. ALL BRIGHT WHITE.

    So to answer my own question, Yes, it is important to provide power at BOTH ends if you wish for 'bright whites' throughout the strip. --Greg--
     
  9. fasteddy

    fasteddy I have C.L.A.P Global Moderator Generous Elf

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    Can you provide a bit more info on your test, what was the guage cable supplying the power to the strip and how long was it because these 2 factors are very important when using this strip. I would be curious as to what volts you are actually getting at the start of the strip.
     
  10. OP
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    Greg.Ca

    Greg.Ca Apprentice Elf

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    The guage wire was 18 guage but the power supply was just 1/2 meter at most from the strip. Very short length wire. The voltage drop was actually 'inside' the strip and that's why when I powered it from BOTH ends, then, the 'pinkish' whites at the 'end' dissapeared. See 2nd post from 'AAH', he actually was very correct. --Greg--
     

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