Which gauge wire should i be using?

Discussion in 'Computers, Cabling & Other Miscellaneous Hardware' started by Lampy, Mar 24, 2013.

  1. Lampy

    Lampy New Elf

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    Hi, i'm building eight led lights that i have calculated to be using 88.32 amps in total.
    They are 5v led strips. Each light might be as much 8 metres apart.
    So the question is - what gauge wire do i need to to carry the 5volts without voltage drop over them kind of distances.
    If it ends up being not very possible i could split the lights in to two groups with two psu's which will half that to 44 amps.
    cheers
     
  2. anon

    anon Apprentice Elf

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    Using V = I/R and allowing for 0.5V voltage drop at 88 amps is 0.0057 ohms allows to the first 8m. Using the resistance values in http://auschristmaslighting.com/wiki/Wire_Size this would suggest the need for 4-5AWG, not even taking into account the drop across at the next set which I assume would be 77A, 66A etc until the last light. That's a lot of copper.


    Two power supplies would be better, but better still would be finding away to minimize the power run as say even providing 11A over 64m (8 lights x 8m) with a 0.5V voltage drop would require the same size cable as above.
     
  3. OP
    OP
    Lampy

    Lampy New Elf

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    Wow! That is ridiculously big cable for the physical width of the led strip. Guess i need to re-think this setup.
    I've attached a drawing of what i'm trying to do. On some occasions i will be using just number 1,4,5 and eight therefore the cable distance between them will be longer. Any thoughts on best way to do this?
    Thanks
     

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  4. fasteddy

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

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    This is a very similar question that was asked in another thread so i will just give the excact same answer i put in that post

    You will always get voltage drop, the amount of voltage drop is determined by 3 main factors

    1: Distance of the run (Total Resistance)
    2: Guage of the cable (resistance/metre)
    3: The amount of current being drawn

    So from those values we can get our voltage.

    1: Distance of the run

    The drawing shows approx a 15 metre run but we have to add both the +V and the Ground together to calculate the total distance. This would be 15 metres x 2 = 30 metres

    2: Guage size of the cable (ohms/metre)

    All cables have a resistance value in either Ohms/metre or Ohms/foot and the larger the diameter (guage) the cable is, the lower the resistance is.

    There is a table in the ACL 101 lighting manual that can be used as a general reference for different cable resistance values.

    we will us the common 4 core security cable 14/020 (21 guage) which has a resistance value of 0.043 ohms/metre

    We then multiply this amount by our tolat distance of 30 metres

    30 metres x 0.043ohms = 1.29 ohms

    3: The amount of current being drawn

    So using your calculations for total current draw then each strip will be drawing 5.5 amps


    So now we can calculate the max voltage drop for a 5vdc with a rating of 5.5amps with a total run of 15 metres

    Calculating Voltage Drop

    Volts = current x resistance

    5.5amps x 1.29 ohms = 7.095 volts dropped

    So as you can see there is no way you can power this with 4 core security cable as the voltage drop is higher than the actual voltage


    So now lets look at 16 guage and then 12 guage cable

    16 guage cable = 0.014 ohms/m x 30 metres = 0.42 ohms x 5.5 amps = 2.31 volts dropped

    12 gauge cable = 0.0053 ohms/m x 30 metres = 0.159 ohms x 5.5 amps = 0.8745 volts dropped


    So as you can see the biggest issue with using 5vdc is voltage drop, even with using a very chuncky cable (12 guage) you will still see nearly 0.9 volts dropped just for using the one strip.


    Solution

    The only real way is to do your layout is to use multiple power supplies located at each pair of strips as if we had the power supply just 1 metre away we then dramatically reduce the voltage drop.



    14/020 security cable = 0.043 x 2 metres = 0.086 ohms x 5.5 amps = 0.473 volts

    This cable even at this distance is no good and is underated but the cores can be doubled to effectivly 1/2 the voltage drop to an acceptable level.

    16 guage = 0.014 ohms/m x 2 metres = 0.028 ohms x 5.5 amps = 0.154 volts dropped

    12 guage = 0.0053 ohms/m x 2 metres = 0.0106 ohms x 5.5 amps = 0.0583 volts dropped


    So by showing the above you can then get an idea of why its so important to have the power supply very close to the lights when using 5vdc high current strips as voltage drop is the biggest enemy.

    Thats why i prefer to use 12vdc as it is more forgiving with voltage drop as the % of voltage dropped is less than when using 5vdc.
     
  5. DanJ

    DanJ Full Time Elf

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    Good point on putting the power supplies close to the RGBs. I have probably read that elsewhere, but it just "clicked" tonight! If I have problems with my 5VDC setup, I will do just that. Thankfully I bought 2 CG-1500 enclosures "just in case", even though I only needed one this year....
     
  6. davrus

    davrus Silent Elf

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    May I ask a question .......
    Why do people go with 5V ???????
    What is the advantage over 12V ?


    Controllers and power supplies are the same, so no advantage there.
    Voltage drop is a bigger problem with 5V compared to 12V, so no advantage there.
    5V pixel strings have fewer pixels per metre, so no advantage there.


    What is the benefit of using 5V ??? Am I missing something ?
     
  7. fasteddy

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

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    Its mainly due to circuit design and efficiency.
    For individual pixels 5vdc is the correct design and more efficient for the output as the chips are 5vdc and the LEDs used have a forward voltage of approx. 2.3 volts for red and 3.2 volts for green and blue. So if running at 12vdc you then have to drop this voltage from 12 volts through a drop down resistor and if the LED driver is running at the full rated output then there is more energy wasted through the resistor than what the LED will use. So to get around this the LEDs are normally under driven to around 9.5 mA instead of the 18.5 to 20mA. To the eye there is no real perceived difference as we don't see light in a linear fashion and our eyes get saturated at the higher ends of the LED dimming. The actual light output would be lower if you took a light output reading.

    So 12vdc is a compromise with single LED control but manages the voltage drop much better and does not draw as much amps for the same wattage output so both 5vdc and 12vdc have their pros and cons, so using the advantages of each design for the right purpose is the key.
     
  8. Nodent

    Nodent Apprentice Elf

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    I'm not concerned about how much my electricity bill is going to be, but now I'm seeing I should go the 12v route before it's to late. I just started my collection and have 200 WS2801 and some unknown 100 dumb RGBs.

    Can get a Ray Wu link that is good to get me going in the 12v direction?
     
  9. arw01

    arw01 Full Time Elf

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    I will add that 5v strings can be cheaper, and in proper layouts, can more than pay for the extra power supplies.


    I went 12v, and will likely stay 12v. You can certainly run nearly all of those12v strings on less voltage as shown by the technicolor suggestion to bring down the voltage.


    I suppose the technicolor could be an example of why not to go 12v, or if you are in hotter areas. It's in the 20's where I am most of the winter show, but could be over 100 in my july show!
     
  10. ShellNZ

    ShellNZ Senior Elf

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    80% of my display is 12V.

    The only reason I did 5v for pixicles and matrix is because its the only strip that has individually controlled pixels.

    There are the 12v technicolor as others have mentioned but from what I gather you can only cut every 50cm which is no good to me.

    If I could have done 12v I definately would have, power injection drives me nuts :)
     
  11. davrus

    davrus Silent Elf

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  12. arw01

    arw01 Full Time Elf

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    The second one is three pixels per IC that all light the same, I used them extensively on my house outline and in pex arches (31 sections in 10') , for pixicles where you want individual control, they won't work out.


    The TM1809 string might work if the spacing is OK, I understand each IC is individually controlled, just cuttable in 3 led sctions.
     
  13. Wolfie

    Wolfie Full Time Elf

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    O_O 88amps!!

    Ok, for a real world example.....go lift the hood of your car and look at the battery cables. You will get the idea. Common starter currents vary between 90 and 200amps (not far removed from your 88amps).

    I agree with the above suggestions, at this amount of power, your best, heck, your only, solution is to place PSUs in close proximity to the display elements and have multiple PSUs to divide the power load thereby reducing any single amperage need. The downside is you have to run mains out to the PSUs to there is the increased danger involved with that aspect too.

    The only other alternative is to go with 12v pixels. Assuming similar wattage and losses, that will reduce your current requirement from 88amps down to under 37 amps. That would bring the wiring requirement at least in the realm of possibility.
     

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