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Power Supply to Controller - What Cable

Discussion in 'Computers, Cabling & Other Miscellaneous Hardware' started by Charger, Nov 16, 2016.

  1. Charger

    Charger Apprentice Elf

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    With my newly purchased RGB's this year I am also noticing a much greater current draw. When the lights are on white (Full RGB) they draw about 8 amps per 3 (RGB) channels. So when running 2 sets of 3 channels I am looking at 16 amps and at 3 sets - 24 amps. While this is within the tolerance for my controller zones (rated at 35 amps per zone) it does seem extreme for a cable to be carrying this load from the power supply to the controller zone.


    Just wondering if this is normal and what would be the best solution ie what cable should I be using that will carry that load?


    Thanks
     
  2. Fing

    Fing Full Time Elf Generous Elf

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    Hi Charger


    a very rough, back of the envelope type, rule of thumb is 10A per 1mm2 cable. And you also have to account for voltage drop which inceases with current....the bigger the cable the less voltage drop..


    Cheers
    Fing
     
  3. scamper

    scamper Senior Elf

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    I actually by accident stumbled across a couple of handy apps when I was looking for all my old ones after upgrading my phone.


    1 is called simply wire gauge calculator. you punch in the variables such as voltage, current, distance and allowable voltage drop in % and it will give you the size cable you require.
    the other, while not that hard to research, is called pinout. It gives you all of the standard pinouts for many of the common plugs that you would come across. Including rj45 network which is the one I often need to do, yet not often enough to remember it.
     
  4. OP
    OP
    Charger

    Charger Apprentice Elf

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    Thanks Fing for the advice. I think I will use this cable from Jaycar rated at 25 amps, so it should cover what I need. I took a look at that gauge calculator app scamper, it looks like good stuff. Thanks for that.


    Just looking at my numbers again, the multimeter indicates that I am drawing about 8 amps for 200 lights. That's 40mA per light. Looking at Ray's info page for my lights and it says that the max draw is 20mA (presumably per light). Am I missing something obvious here, as my current seems to have doubled?
     
  5. Fing

    Fing Full Time Elf Generous Elf

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    some of my reply seems to have fallen off... you can parallel up wires to achieve an equivalent larger size, so two 1mm2 equals one 2mm2 or there abouts....maybe...


    what kind of LEDs are you using? dumb strip or pixel nodes? usually the rule of thumb is 20mA per Colour. so a RGB LED would pull 60 mA on white. In practice these values could be as low as say 15mA or so, and of course you must take into account that the chinese mA is smaller than the Au one ;)
    cheers
    Fing
     
  6. i13

    i13 Senior Elf

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    If it is WS2811 or WS2812B, it will be limited to 18.5mA per colour. It could be less but it won't be more due to a limitation of the WS2811 chip.
     
  7. fasteddy

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

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    What type of multimeter are you using as they do vary greatly and the low end cheap versions have a lot of tolerance, so it may be your multimeter that may not be giving the correct readings

    But

    If you are using the non intelligent 12vdc RGB strip and if this being the case then the current of the LED is controlled by the resistor value with 3 LEDs in series. As the load of the lights along the strip take current the voltage will drop the further along the strip you go, thus reducing the current drawn from the LEDs towards the end of the strip. This would be why you would see a variation in the amount of current not matching the 60mA per LED (20mA per colour) that you would expect and is the reason we see a colour shift in the LEDs along a long run because the LEDs are using much less current at the end, the same rule applies for non intelligent RGB strings

    Its all about Ohms law and the relationship between voltage, current and resistance. The more load (current), the higher the voltage drop is and the resistance gets higher the longer the strip or string is, thus effecting the expected readings

    Now lets just confuse you a little more, When we talk about the current draw on a LED circuit then LEDs in series will draw the same current. so 1 LED will draw the same current as 5 LEDs in series, so when we talk about the current draw then its not per LED that needs to be considered, but instead the number of series LED circuits. So for the 12vdc 3 LED per section strip then each section of 3 LEDs we count or if you are using a string then its each individual LED we count.

    But to help confirm my thoughts then we do need to know what type of lights you are using as this determines many things. RGB is a very broad term and there are many variations
     
  8. OP
    OP
    Charger

    Charger Apprentice Elf

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  9. fasteddy

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

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    So being non intelligent RGB LEDs then what I stated previously would be the reason your current reading may not meet the specified value, its voltage drop along the string that lowers the current draw of each LED the further down the string you go.

    Now if you increased your voltage from your power supply to 12.5v then you would see an increase in current draw.

    Unfortunately the 12vdc non intelligent string is not efficient at all as the resistor for each LED has to bring the voltage down from 12vdc to approx. 2.3 volts for red and 3,2 volts for green and blue, so that's a lot of energy being wasted through the resistor, Im sure these must get a bit warm when on
     
  10. OP
    OP
    Charger

    Charger Apprentice Elf

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    Thanks all for the advice. I think I understand most of what you are saying eddy, although it took a few reads.


    I guess I more or less wanted reassurance that the current reading for my lights was relatively normal. Judging from your explanation, it does sound about right.


    Obviously I was concerned about overloading my hardware. I am comfortable with my Power Supply, Controller and now the cable from PS to Controller. Should I be concerned about my cable from controller to the lights, or even the cable joining each light. The cable is 14/020, which according to the 101 carries 4.5amps. If the current drawn is 8 amps, would that likely to cause issues? Should I be doubling up my cable?


    Sorry for the stupid questions, just don't want to create a potential safety hazzard.


    Thanks.
     
  11. fasteddy

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

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    Yes if you are using cable that is 4 amps with something that is drawing 8 amps then this can actually be dangerous because you will be heating up the cable as its underrated for the current you need to run through it.

    If you are running 8 amps using the security cable then I would at very least double up and would even consider tripling up because even if you connect 2 together then you have 9 amps current capacity through the cable with 8 amps current draw.
    You will see a much higher degree of voltage drop the closer you get to the rated current capacity of the cable, so by tripling up the cable you then have 8 amps going through 3 cables that combined can take 13.5 amps (4.5amp x 3) so the more headroom between the max rating of the cable and the actual current ran through the cable will reduce the amount of voltage drop before it gets to the string.
     
  12. OP
    OP
    Charger

    Charger Apprentice Elf

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    Thanks eddy. Exactly the kind of advice I was after.


    Just out of curiosity how does the cable that joins each of the lights (you know the one that comes with the lights) handle the load.
     
  13. fasteddy

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

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    The cable is short and the size is large enough to handle the load of the lights on the string itself, now if you decide to connect a second length of lights then I would believe that the cable would not be suitable and then this is where power injection comes in to play as this will then divide the load up
     
  14. OP
    OP
    Charger

    Charger Apprentice Elf

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    Gotcha! I have injected power between the two, so this should be fine. Thanks eddy for your excellent advice.
     

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