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Yet another Power Injection Question

Discussion in 'Computers, Cabling & Other Miscellaneous Hardware' started by Charles Belcher, Aug 11, 2015.

  1. Charles Belcher

    Charles Belcher New Elf

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    Still trying to work through the cabling for my new Mega Tree system built with 5m 5V 2812b strips with 30 led per meter.


    The potential problem I see is that the controller output port will only handle 4A 's total and the all white 5M is well over that.


    So my question is this:


    If I connect all three wires (positive negative and data) from my controller port to the first strip and inject power from an external power supply at the opposite end of the first strip, does that injection take any "burden" off of the amperage the controller port will see? The would be the same power supply that is supplying power to the controller and as I go down the tree, strip after strip and add power supplies, I will tie all the grounds together.


    Charles
     
  2. fasteddy

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

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    You raise a good point here and I do wonder how others are managing the higher current needs that are required by using 5vdc.

    For me i use 12vdc because its a good compromise and means the current needs are lower and the voltage drop is lower thus meaning i can get longer runs with lower voltage compared to that of 5vdc

    What i think some are doing is running their controller with either a 12vdc or a 24vdc power supply and then using a DC-DC converter to drop the voltage down to 5vdc at the lights, this way you reduce the overall % of voltage drop and also reduce your current needs going through the controller

    The other option is to just use the ground and the data from the controller and then inject power straight into the lights from the power supply, this way the power does not go through the controller.
     
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    Charles Belcher

    Charles Belcher New Elf

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    Eddie,


    Thank you for tracking through all of this with me. I know you are a busy man.


    Today I diagrammed the wiring required to do just this and it is messy, messy. Way too many connections just to get 5v around a tree and make them blink.
    T's up top; T's on the bottom---geez.


    So, using a 12v power supply and placing buck converters at each strip still allows Ohm's law to be applied using 12v numbers? If so, could I then connect the voltage to the controller output and just inject the other end?
    Can the buck converters go inside the controller case or do they need to live next to the strip input?


    I really don't want to have to go to 2811's and lose that individual led control, but I am not aware if anyone is even manufacturing 2812B's in a 12V configuration. It would seem that to do so, would be compromising a good design.


    Damn, every time I change a link in the chain, the chain changes.
     
  4. fasteddy

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

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    Ray does sell 12vdc individual controlled strip which has the buck converters installed on the back of the strip, so all you do is treat these like they are a 12vdc strip. this will solve your complexity issues, voltage drop issues and current draw issues because you are using 12vdc.
    So doing this means you change the Ohms law calculation so with a higher voltage you get a lower current for the same wattage used which means you can keep it simple and just plug straight into your controller.

    White strip

    http://www.aliexpress.com/store/product/5m-DC12V-WS2812B-addressable-pixel-strip-waterproof-in-silicon-tube-30pcs-WS2812B-M-with-30pixels-36W/701799_32348237310.html

    Black Strip

    http://www.aliexpress.com/store/product/5m-DC12V-WS2812B-addressable-pixel-strip-waterproof-in-silicon-tube-30pcs-WS2812B-M-with-30pixels-36W/701799_32313871852.html
     
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    Charles Belcher

    Charles Belcher New Elf

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    Eddie,


    Do you have any experience or knowledge of the dependability of these strips and in particular the dc/dc converters mounted within?
    Would it be safer to use the 5v strips and external converters? More work, I know but if those are unproven...then


    Charles
     
  6. fasteddy

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

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    I have not used these myself but i do know many members here have before, so hopefully they will chime in with their experiences
     
  7. AussiePhil

    AussiePhil Dedicated Elf Administrator

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    The answer is: Yes but with some qualifications needed.

    Also you have this risk: if different powers supplies are used for the injection and they go offline then the source will try to supply all the current.

    Power injection is a form of current sharing that balances the load naturally via the voltage drops in the cabling and strips.
    Electrical theory tells us that the PSU with the higher voltage will supplies the higher current and SMPS are often quite well regulated so natural cabling/resistance losses are actually needed for this to work.

    ALL numbers are for 60mA all white current draw.

    Your post 1 said 30L/M so lets work from that.
    Each meter will draw 30x60mA = 1.8A
    5M will be 9A
    Now a 5.0v supply at each end all things being identical will supply 4.5A into the string.

    now lets sting 3 together in this fashion

    IP1 ----5M---- IP2 -----5M---- IP3 -----5M ----- IP4

    5M = each 5M string 9A required
    IP1 to IP4 are the power injection points with IP1 being the controller

    Again are being equal voltage drops you get
    IP1 4.5A
    IP2 9A as it supplies both ways
    IP3 9A as it supplies both ways
    IP4 4.5A as it supplies one end
    total supplies 27A == total required 27A

    Now in the real world things are never equal, power supplies suffer voltage drop as load goes up etc and in the 5v world even .1v matters
    best guesses would be that IP1 and !P4 would supply between 5A and 6A due to less voltage drop from load
    Now if you factor in say 6 feet of cable from IP1(controller) to strip IP1 actually supplies less current due to the voltage drop on the cable and IP2 picks up a little bit of the load.

    Join 2 strips together and power from one end and you would expect to supply 18A.... this will not eventuate as the voltage drop on the strip will eventually mean that the leds/pixels will fail to light up or draw current, at what point this is would need to be tested but I seriously doubt you would get 10M.

    I know I've said this in a few threads over the years but I personally do not power from the controller for any pixels nodes or strips as I prefer to be in full control of what and where power is supplied.
    I try to ensure all injection points are powered by the one PSU however in the event I use multiple dc-dc convertors I take great care that any one convertor can supply the maximum expect draw in real life.
     
  8. i13

    i13 Senior Elf

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    This will work.

    When you cut the positive line in the strip half way between the controller and external supply, they each power half of the strip and half of the current draw.

    You only need the negatives to be tied together when one run of pixels (on the same controller output) is powered by more than one supply but what you're saying would still work regardless.
     
  9. plasmadrive

    plasmadrive Full Time Elf

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    I just finished building my Star Flakes and they require 5v at just over 5 amps each. I put 8amp converters on each one and feed them with 24v.

    I am using the new Pixlite 16 Long Range for these. The remote boards have 2 each 7.5 amp fuses on them. The is just enough to feed 6 Star Flakes with 24v via one of the fuses. So in this case I am using 10amp 24v supplies for each cluster of 8 Star Flakes. I only have to use 2 of the remote boards on high density but those boards supply my fusing already. If I had tried to feed them with 5v directly or even 12v to converters, there is no way I could have run them thru the boards and their on board fuses. I would have also had to use larger wire. As it is now I am using the white 4 core cables from Ray. (They are cheap and handy). The wire is small, but the current is low and the voltage drop isn't a problem.

    So the converters at the pixel strips works the best, and the higher the voltage you start with (to the max of the system) the more forgiving the voltage drop and the lower the current needed to feed them from the higher voltage source.
     
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    Charles Belcher

    Charles Belcher New Elf

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    plasmadrive,


    I just sent you an email.


    Charles
     
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    Charles Belcher

    Charles Belcher New Elf

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    Eddie,


    I looked at the link on Ray's page. It is hard to tell so I will ask. Is there one converter at the beginning of the strip or are there one little mini converter at every chip? I don't know if that is even possible, so I am asking.


    Charles
     
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    Charles Belcher

    Charles Belcher New Elf

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    Phil,


    Thank you very much for taking the time to write this very enlightening post.
    Now, I am off on a knowledge search for buck converters. This doesn't sound near as involved as running a bunch of 3 core T's and jumpers all over the place.


    Charles
     
  13. fasteddy

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

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    There is a mini buck converter on the back of the strip every metre or it may actually be every 1/2 metre, so that means if using with 12vdc then the strip can only be cut down to the length of each buck converter. The strip also can be 5vdc and then it can be cut down to the individual pixel
     
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    Charles Belcher

    Charles Belcher New Elf

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    OK, that explains why there is both a 5v and a 12v trace on the pcb. This unit may be the answer to my search. Including spares, I need to purchase 66 strips for this project and that isn't an insignificant amount of money to throw away if they are not proven reliable.


    Eddie, thank you for all your guidance. I believe I have taken this as far as I can and now it is time to make a decision between:


    1) Buying 5v 2812b strips and using buck external buck converters
    OR
    2) Buying the strips with the built in buck converters.


    Either choice will net me a way to keep individual led control and avoid a messy power injection scheme.
    Hmmmm?

    Charles
     

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