Power Supply help

Discussion in 'RGB Lights - Intelligent Pixels and 3-Channel RGB' started by Crazydave, Jul 4, 2012.

  1. Crazydave

    Crazydave New Elf

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    I am planning on running a total of 269 pixels (5v WS2811 ) along my eves.

    For data purposes I have the strings off 166 pixels (Lower Eve) and 103 pixels(Upper Eve)

    My plan is run an e681 to control these strings.

    Since these runs of 166 & 103 MUST be linear,I know that I will have to do some sort of power injection, and that voltage drop will be an issue. The question is how should I handle the power injection?

    Option 1
    Using seven (7) seperate 5v power supplies (say 25 watts each), individually power each 50 pixel segment
    I know that I will have to run an AC line to provide electricity to the DC power supplies.

    Concerns: Expensive... I have to buy a lot of power supplies, and I have to supply AC current along the way.

    Pros: I know that this will work.

    Option 2
    Using one (1) large power supply (350 watts) run a DC power line in parallel with the strings, and "tap" into the DC power line every 50 Pixels.

    Concerns: That the DC power line may experience too much of a voltage drop near the ends. At most the DC lines will be 70 feet in length.

    Option 3
    Using two (2) large power supply (350 watts) run a DC power line in parallel with the strings, and "tap" into the DC power line every 50 Pixels. (But this time, use one power supply for the upper eve, and the other for the lower eve)

    Concerns: That the DC power line may experience too much of a voltage drop near the ends. At most the DC lines will be 55 feet in length.


    Furthermore for options 2 and 3 I can place the dc power supply in the middle of the strings, which would reduce the maximum length to about 25-30 feet.

    Does anyone have any experience or thoughts on this?


    Typically how much of a voltage drop do you actually see from a 5v power supply using 18awg wire over say 30 feet.


    Thanks
     
  2. fasteddy

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

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    I use option 3 for my gutters, but i also use 12vdc strip for gutter outlines as this works better for this application as voltage drop is less of an issue with 12vdc over long distances using strip, plus its easy to get straight lines by just mounting the strip to electrical conduit.

    Voltage drop is determined by the current being carried by the cable, so the less current, the less voltage drop, this is why power injection is essential as this helps distribute the load over the whole length thus reducing you voltage drop over distances.

    So lets then look at your application

    18 guage wire has an approximate resistance of 0.023 Ohms per metre or 0.007 Ohms per foot.

    1 x 50 pixel string will approximatly draw 60ma x 50 pixels = 3 amps

    So if we supply power to a 50 pixel string that is 70 feet away with no injection using 18 guage wire we could expect a volatge drop of:

    (0.007 Ohms x (70 feet x 2)) x 3 amps = 2.94 volts

    * note voltage drop must include both the + and - distance so this is 70 feet x 2

    This means there is no way you could run a string 70 feet away at 5 volts with a single supply

    But if we connect all the strings on your bottom gutter together we have a total load of:

    60ma x 166 pixels = 9.96 amps

    If we inject power in this fashion

    |*********|*********|*********|***|
    PSU

    We are effectively dividing the load up and reducing the current requirements on the cables thus reducing the voltage drop along the cables.

    So with longer distance runs you are best to inject power more frequently or use a higher guage cable.

    By installing your power supply in the middle and decreasing your distance to 30 feet and using 5 injection points shown in the example above would see roughly

    9.96amps / 5 = 1.992 amps per injection

    (0.007 Ohms x (30 feet x 2)) x 1.992 amps = 0.837 volts for the longest run

    * note this is a rough calculation and assumes that power is drawn equally through each injection point which in most cases will not be the true measured current.

    So looking at the above calculations using 5 volts, option 1 or option 3 may be the best option.
    With option 3, the distance of the cable run for injection must be kept as short as possible and that you also inject at pixel 150 and then again at the end with pixel 166 as shown in the example above.


    This is why im not a big fan of 5vdc pixel strings being used for outlines of gutters as the voltage drop needs a lot more consideration than if using 12vdc strip when dealing with longer runs.
     
  3. OP
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    Crazydave

    Crazydave New Elf

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    your post was extremely helpful. Now I have the tools to do more cost benefit analysis of the 5v pixels, and explore the costs of 12v pixels by recalculting the necessary injections for 12v pixel.

    I was planning on using the ws2811 pixels as they are cheaper...but the style of pixel is not available in 12v.
     
  4. OP
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    Crazydave

    Crazydave New Elf

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    Re: Re: Power Supply help


    So each injection needs its own wire from the power supply. so If I have 4 injection points I need 4 sets of wire from the power supply
     
  5. AussiePhil

    AussiePhil Dedicated Elf Administrator

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    Dave

    A very fast post then a longer one,

    Eddy summed it up very well.

    12V pixels draw EXACTLY the same current and hence have the same actual voltage drop on cable runs from power supplies to strings, its just they can tolerate a greater drop before going pink.

    Longer post in a little while

    Phil
     
  6. AussiePhil

    AussiePhil Dedicated Elf Administrator

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    CrazyDave

    Here's the longer version :)

    I'm a fan of Point of Use Power Conversion (PUPC) to minimise as much voltage drop issues as possible for both 5V and 12V

    As you are in the USA (assumed from verizon email) Option 1 using waterproof AC-> DC convertors close to your strings makes practical sense and really is not expensive. PUPC can be even cheaper than large power supplies and large copper cables.

    let's take the the 168c string first.
    Here's how i would do it
    ONE x http://www.aliexpress.com/store/product/waterproof-led-power-supply-AC90-250V-input-5V-60W-output-IP68-CE-and-ROHS/701799_486531844.html
    Supply mounted right next to the 100 pixel point with power injected at 50/100/150 points.... no power supplied at start of string.
    this way the longest run from PSU to pixel will be say 16 feet and you only need a single PSU

    The shorter 103c string you may even get away with a single central injection at the 50 pixel point also using the same PSU above. Better would be to mount the PSU at the 25 pixel point and cable to pixel 1 and 50 for power.

    Doing it this way you can get away with 2 60W PSU's, minimun cable and you could afford to go up to say 16G.

    Anyway i vote Option 1 using the layout i described.

    Cheers
    Phil
     
  7. OP
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    Crazydave

    Crazydave New Elf

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    ******
    Update
    ******
    So based on recommendations you guys provided (thanks by the way) and in order to simplify things, I have decided to use 12v pixels for the eves. It looks like this will be the best option for me. (and because this portion of my display is not very large in terms of pixel count there are no significant cost savings in using the cheaper ws2811 5v pixels vs the ws2801 12v pixels. Perhaps if I where to build a centralized mega tree that used 1000's of pixels then the ws2811 5v might be a better where it can take advantage of centralized power and cost savings anyways I'm rambling because I am documenting my thoughts before I forget this stuff)


    I have attached a diagram:


    Does this setup make sense?



    I plan on using 2 separate power supplies, one for the the upper eve and another for the lower eve and controller.


    Here are my ideas and thoughts


    Lower Eve:
    Thought 1.) Since I am now using 12v Pixels, I can power up to 100 pixels from the ends, so I don't have to power the pixel strings from the middle. This is also preferred on the lower eve due to the location of where I have access to send wires out to the lower eve. Additionally, since they are the same length, and the connection leads will be the same length, they will both see similar loads and voltage drops (which brings up question #1 below).


    Thought 2.) Power Supply Unit #1 will provide power directly to the controller (SanDevice e681) The pixel strings 1 & 2 will be powered and controlled through the control board. (Each string should only take about 2.5 amps)


    Thought 3.) the e681 controller will have to be configured to reverse the pixels on string 1 (which brings up question #2


    Upper Eve:


    1.) Power Supply Unit #2 will power the upper eve pixels only, and therefore only Data and Clock will be connected to String #3. (which brings up question #3 see below)


    2.) The controller will be set to to have "Dummy Pixels" to span the 20-30 feet distance from the controller to the beginning of String #3


    Questions

    Question 1.) The power supply units seem to often have a voltage adjustment on them. I know that the voltage drop will be about .21 volts at max draw (0.007 ohms9 (6 feet x 2)) x 2.5 Amps = 0.21 volts.


    So, if the power supply at idle is showing 12 volts, should I adjust the power supply up by 0.21volts to 12.21v to accommodate for the potential drop of 0.21 volts along the leading segment? (I know that 0.21 volts is very small but this is merely an academic exercise for me). (which brings up question #4 see below)


    Question 2.) when using the e681, would it be too much of a demand on the e681 to "reverse" the pixels, or would it be better to do this on the software end of things, and not leave this task to e681. I am wondering if I get really crazy on the sequencing if the e681 will start to mess up? (Or is this just a simple logic thing, it dumps all 512 commands into a queue, and the pulls them off the top in which case I would me more likely for me to screw up the channel re-assignment than the e681 reversing them for me)


    Question 3.) I have the PSU #1 powering the lower eve and the controller. And PSU #2 powering only the upper eve string #3. Now technically there is still two wires connected from the controller to the String #3 and the power is separate. Does the Ground wire from the controller to pixel string #3 need to be connected so that all the devices are seeing the same ground level. Or am I over thinking this? (This brings up Question #5)


    Question 4.) What is the Pixel input voltage sensitivity for 12 volt pixels. (is it like +/- 0.5 volts or what?)


    In one of the training videos I say.. it mentioned that LED's really run on 1-3 volts or something like that. Since I see that chips are the same on 5v vs 12v devices, I assume too that these also run on a lower voltage. Is the only difference between the 5v and 12 pixels is that they add a voltage reduction circuit that reduces the voltage more on the 12volt pixel?


    Question #5) Lets say I got really crazy... and I wanted to add tons of devices that necessitate using two (2) 350 watt power supplies to power one large connected string that used say 600 watts. So I put one power supply on end of the string... and other power supply on the other end. can you do this or would the power supplies be fighting each other?


    Or would I have cut the (+) off in the middle and the leave (-) connected all the way from one power supply to the other.
     

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  8. fasteddy

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

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    This is not the best way to deal with voltage drop as voltage drop is related to current draw, so as soon as your lights are off you will then see the voltage rise


    Both the E681 and ECG Series of controllers have this feature inbuilt to reverse the order of your strings, so this shouldnt be an issue at all.

    If your data and clock is fed from another controller that has its power supply seperate to the supply for the lights then the ground must be connected together so they both have the same ground reference.

    The 2811, 2801, 6803, 3001 ect are constant current chips, the 180x series is constant voltage. Now if the voltage drops too low the constant current driver cant maintain the current required to drive that LED and thus you will see colours like white which takes the most load look more pinkish in colour.

    LEDs are current devices, so its the current that is important for the LED to function correctly, but with Ohms law, current has a relationship with voltage and once the voltage drops (usually around 2 volts) the current driver cant maintain the current required to run the LEDs and then will start to underdrive the LEDs. The reason we start seeing a pinkish colour is because the Red LEDs require a slightly less voltage than what green and blue require and so green and blue are the first colours to loose intensity due to the voltage dropping below the functional limit and thus reducing the current that is supplied to the LED.

    For an 8mm LED which is used for pixels strings, the LEDs are rated at 20ma per colour but the voltage requirements are different

    Red = 2 volts
    Green = 3.2 volts
    Blue = 3.1 volts

    So this explains why voltage drop will make your lights appear pinkish when using white


    The majority of power supplies are not designed to have their + connected together for load sharing. You can get special power supplies that allow this but you will be paying a premium price for this.

    But in saying the above if they are connected together though the load of the strip then the power supply can be connected in this fashion but you then run the risk of a power supply failing and then the other power supply taking all the load, So if you are going to take this approach, ensure both power supplies can handle the full load

    Personally i prefer to keep the + seperate so i know the load being drawn from each supply and this is just better electrical practice as you dont have to worry about ensuring both power supplies are rated to take the full load each
     
  9. OP
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    Crazydave

    Crazydave New Elf

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    OK.


    So I modified the diagram to show the ground connected from the controller to the string that has a separate power supply.


    See attachment.


    Does this configuration make sense for what I'm doing?
     

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  10. fasteddy

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

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    Looks good to me
     
  11. OP
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    Crazydave

    Crazydave New Elf

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    So I purchased the (4) of the Ray Wu WS2801 12v 100-pixel string:
    http://www.aliexpress.com/store/product/DC12-input-WS2801-IP68-led-pixel-module-256scale-gray-IP68-4wire-red-green-blue-black-100pcs/701799_545340313.html

    I got extra "in case"

    Now I need to get a 12v Powersupply(s)

    Based on my reading people on the forums swear that Meanwell is the brand to buy.

    But I noticed that the one I was looking at buying is a constant Voltage

    http://www.amazon.com/Meanwell-Switching-Power-Constant-Ledwholesalers/dp/B007K4XZPG/ref=sr_1_4?ie=UTF8&qid=1342218417&sr=8-4&keywords=meanwell+power+supply

    Would this work.. or do I need to buy a constant current power supply?


    Please let me know if I'm doing the following math correctly:

    100w/12v= 8.33 Amps

    8.33Amps / 166 pixels = 0.050 amps/pixel = 50 milliamps/pixel

    50 mAmps > the 30 mAmps that the specs say I need for the pixel. But when you back into the number .30mAmps*166pixels*12v = 59.76 watts.

    But the specs also say 0.3watts per pixel which means 0.3Watts * 166 pixels = 49.8watts which is much less than the 100watts this PS is supposed to make, and well within the 80% rule for efficiency...

    which is correct (59.76watts or 49.80 watts)?
    I guess no matter what.. they are both within the limits of the power supply...

    but the big question is ... will constant voltage PS work... or do I need to find a constant current?
     
  12. fasteddy

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

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    A power supply is constant voltage as you want your voltage to be stable over load fluctuations. The current will change depending on how many lights and what colour is being used.

    What you are getting confused with is LED drivers, which are constant current and constant voltage drivers. LEDs being current devices work more reliably with constant current. The driver is what actually powers/controls the LEDS.
    The WS2801 Chip is a Constant current driver, so you already have constant current control by using the WS2801.

    To work out your load is just multiplying the 0.3 watts per pixel to get your total load in watts
     
  13. Shubb

    Shubb But mine goes to 11!!

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    This is a older thread and may be a mute point by now but Ray might have the 2811 pixels in 12v.
    I couldnt find some strings in 12 volt and email him to see if they were available and he had them in stock, they just weren't list in his store.

    Also, I want to say thank you for all the detailed answers that the experienced users here are willing to give. I am so tired of somepne posting a question (that I am interested in the answer) and just receiving a link to a help file.

    Thanks again for all the great support.

    Scott
     
  14. OP
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    Crazydave

    Crazydave New Elf

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    I did email him about some ws2811 pixels which said 5v in the specs but 12v in the title....


    he told me they were 5v


    I figured if he had 12v, we would have given me a link to the 12v or offered to sell me 12v... he didn't So I figured he didn't have them


    my next project I will have to keep that in mind and make sure to ask him specifically for 12v ws2811 pixels.
     
  15. OP
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    Crazydave

    Crazydave New Elf

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    So I received my lights from ray Wu. I got the ws2801 12v 100 pixel stings.

    I made one string that is 158 pixels long with a 30 foot leader (made with spt-2) using 3 null pixels. With out power injection the 158 pixel string worked just fine no noticable color shifting at the end of the string. But for fun I added a power injector at pixel 79. Interestingly enough with power injector connected, the entire string turns just a tad bit brighter.

    As for pixels themselves, the wiring seemed weird to me :
    Black : +12v
    Red: clock
    Green: data
    Blue: power ground

    my next project will be to build the leader for the upper eve.
     

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