Help with RGB Leds

Discussion in 'General Electronics Chat' started by adamski07, Sep 24, 2012.

  1. adamski07

    Thread Starter New Member

    Sep 24, 2012
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    Hi good day to all. I'm new here and this is actually my first post. I'm new to these leds or any electrical stuffs, but I want to learn how I am going to use it. I Mod computer cases and wanted to use RGB leds for it. So basically, I will buy a RGB controller and RGB Leds. The RGB 4pins Common anode Leds came in today, but I'm not sure how I am gonna connect all of those? I was searching the net and it says that I couldn't wire it in series. What could possibly the best way to wire the leds? Also, do I still need resistors for it even I am going to use a led controller? If yes, what resistor for 12v rail of a computer PSU? If somebody can give me instruction on how I am going to connect the to controller then I would be so glad. Please avoid using electrical language, I might not get it. :confused: Thank you.

    These are the leds that I bought : http://www.ebay.com/itm/110937592873?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649
     
  2. Audioguru

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    Dec 20, 2007
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    We don't know anything about the "RGB Controller" so we don't know if it can drive these common-anode LEDs and we don't know if it limits the output current.

    The LED is common-anode so the anode goes to the positive supply for the Controller and each output of the controller must limit the current to ground through the LEDs.

    The spec's for the LED shows 25mA for each colour. Will it overheat if all 3 colours are at 25mA? The Chinese datasheet does not say.
     
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  3. Tealc

    Member

    Jun 30, 2011
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    Maybe a link to the RGB controller would be helpful.

    If the RGB controller is like the cheap ones that come with generic RGB LED strips then you'll need resistors in your circuit in series with each colour. RGB strips tend to have 3 RGB LEDs in series with 3 resistors to minimise power consumption and wasted heat.

    If the controller is current controlled then things are different.
     
  4. adamski07

    Thread Starter New Member

    Sep 24, 2012
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    I'ts actually this controller http://www.amazon.com/gp/product/B008RWT2IY/ref=oh_details_o00_s00_i00

    I am going to modify it as well. I'm not sure if this would work tho. It has led strips included on it already, but I wanted to add more LEDS on it. What do you think? Will this controller work? I'm guessing I would still need resistors for the RGB Leds I have right now.
     
  5. adamski07

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    Sep 24, 2012
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  6. Audioguru

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    You must test the RGB controller to see if the outputs go high or go low to turn on an LED. Also see if the LED strips have current-limiting resistors on them.
     
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  7. Tealc

    Member

    Jun 30, 2011
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    In this review...

    http://hexus.net/tech/reviews/chassis/43289-nzxt-hue-rgb-led-controller/

    ...the Hue already comes with a LED strip but it's unclear if it can handle much more than the initial 2 Metres of LEDs.

    For things like this it's often easier, cheaper and simpler just to buy a pre-made LED strip and if necessary change the connectors to suit the application. Wiring up RGB LEDs, all the resistors is a fiddly task and will be even more tricky with SMD LEDs. That is unless you are planning to build them onto a PCB of some kind.
     
  8. adamski07

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    Sep 24, 2012
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    I'm going to use the LED strip that comes with it and add more leds that i'll be placing in random place. Another Led strips won't work for what I am gonna do with my current project. Time isn't a problem as long as I can do it safely and it will work.
     
  9. Audioguru

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    When you overload it I wonder if it will invisibly burn out or make a little smoke when it burns out. Try it to see and let us know what happens.
     
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  10. adamski07

    Thread Starter New Member

    Sep 24, 2012
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    Okay, but as I see on the led strips it has resistors on it.

    Please correct me If I'm wrong. On the data sheet of the SMD RGB LED, the information are these.

    Red = 20mA | 1.8-2.2v
    Blue = 20mA | 3.0-3.4v
    Green = 20 mA | 3.0-3.4v

    So this means that if my power supply is 12v

    12 - 3.4 = 8.6
    8.6 / 20mA = 0.43

    So based on led resistor calculator, I need 470 Ohm resistors for blue and green led connection. Is that right?

    12 - 2.2 = 9.8
    9.8 / 20 = 0.49

    For red led, the led resistor calculated that I need 560 Ohm resistors.

    Also, if this is correct can you guys please recommend me a good resistor. I could buy it online. Probably on ebay since it's cheap. I am not rushing it. Thank you for all the responses guys.
     
  11. Audioguru

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    Dec 20, 2007
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    Why are you using only a single LED? Why not connect a few LEDs in series and they all share one resistor?

    The max voltage for your blue and green LEDs is 3.4V so you can connect 3 in series. Their total voltage is 10.2V. If the LEDs are all actually 3.0V then their total voltage is only 9V so use that to calculate the series resistor. (12V - 9V)/20mA= 150 ohms. If all LEDs are actually 3.4V then their current is (12V - 10.2V)/150 ohms= 12mA which is almost as bright as 20mA.

    The max voltage for your red LEDs is 2.2V so you can connect 4 in series. The resistor is calculated with the minimum voltage which is 1.8V and 4 in series have a total voltage of 7.2V. The resistor is (12V - 7.2V)/20mA= 240 ohms. If all red LEDs are actually 2.2V then their current is 13.3mA which is almost as bright as 20mA.

    Use 1/4W carbon film 5% resistors.
     
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  12. adamski07

    Thread Starter New Member

    Sep 24, 2012
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    Wow thanks. I just actually seen this led resistor calculator online, http://ledcalculator.net/ and I found out that I can do it in series. I just need to put how many leds i'll be using for one supply of 12v. Tho, I am still confused on how you gonna connect it on a RGB Led. If I am right, I just need to treat each connection on a rgb as 3 different LEDs with one positive connection or the annode.
     
  13. Audioguru

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    Leave about the same voltage as one LED for the current-limiting resistor.
    Don't use an internet program, calculate it yourself using Ohm's Law.

    You cannot use your original LEDs that have a common anode in series. You can use the SMD LEDs that have all 3 LEDs completely separate.

    The absolute maximum continuous current in each of the SMD LEDs is 60mA so calculate the resistor for 50mA to be safe.
    Again, the Chinese datasheet does not say if all 3 LEDs can be turned on bright without it getting too hot. 3.9V x 50mA x 3= 0.59W which makes a lot of heat.
    Do you know how to solder to an SMD LED that has its solder pads underneath? You might be able to tack solder on the sides.
     
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  14. adamski07

    Thread Starter New Member

    Sep 24, 2012
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    I'm totally new on this. Will you be able to make me a diagram of 5 SMD leds connected together. I can't tell how many SMD leds I am going to connect for the project as I haven't started it and I am still on design phase. If you can also please include the calculations and what resistors I would need. Also, please don't use electrical languages or symbols, I might not get it. If you could make it as simple as you could then that would be perfect for me. ;)
     
  15. Audioguru

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    Each blue or green LED in the SMD LEDs has a maximum forward voltage of 3.6V so 5 in series might be 18V plus another 3.6V for the current-limiting resistor. Then "IF" the unknown output of the controller saturates well then the total power supply voltage must be 21.6V.

    But before we talked about using a 12V supply which can power only 2 blue or green SMD LEDs in series and in series with a current-limiting resistor.

    Since we don't know anything about the details of the controller then we can't show how to connect the LEDs to it.
    Here is a schematic showing the SMD LEDs and two in series:
     
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  16. adamski07

    Thread Starter New Member

    Sep 24, 2012
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    For the controller I am not sure how this works but I used multimeter to get the voltage each connection outputs.

    Green - 3.3v
    Blue - 3.3v
    Red - 3.5v


    I'm thinking now of just using different controller for this smd leds and keep the controller i have and the led strip as it is.
     
  17. Tealc

    Member

    Jun 30, 2011
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    Or you could have 2,3 or 4 LEDs in series with a resistor which will produce less heat and waste less energy.
     
  18. adamski07

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    Sep 24, 2012
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  19. Audioguru

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    You cannot use your 4-wire LEDs in series.

    The maximum forward voltage of the blue and green SMD LEDs is 3.6V. Three in series use 10.8V so the 12V supply feeding the LEDs will be fine. The minimum voltage of those LEDs is 2.9V so three will use 8.7V and the current-limiting resistor will have a voltage across it of 3.3V. The 91 ohm resistor limits the current to 36mA which might be fairly low since 50mA is safe (60mA maximum allowed forward current). Use 68 ohms.

    I do not believe the spec'd 3.6V maximum forward voltage of those SMD red LEDs. If it is true then some cannot be used as 5 in series with a 12V supply.
    My Luxeon SuperFlux (American, not Chinese) red LEDs have a voltage range of 2.19V to 3.15V at 70mA.
     
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