RGB LED question

Discussion in 'The Projects Forum' started by BG79, Jun 24, 2013.

  1. BG79

    Thread Starter New Member

    Apr 19, 2011
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    Hi guys,

    I´m trying to use a generic RGB controller (like this: http://www.aliexpress.com/item/Free...-Tapes-Bar-Light-DC12-24V-144W/916218297.html) to make a battery powered device with some CREE power LEDs I have. I´m using 3 simple current limiters in pararel (similar to this: http://www.instructables.com/id/Power-LED-s---simplest-light-with-constant-current/#step1 - one for each LED), in order to keep them runing at 350mA each, since the RGB controller doesn´t limit current, and 450mA is the larger current my battery can handle for this project (It´s a 6V, 4.5A).

    Here´s the problem:
    When I light the white color (R+G+B), the controller doesn´t balance each LED so that the total current stays near 350mA. Instead, all the 3 LEDs light at It´s maximum, and the device goes to 1.05A.

    My question:
    Is there any (simple) way to use 350mA for any color configuration (or at least for R, G, B and W)?
    I tryed to imagine a simple circuit with relays, or transistors as a swich and a fourth current limiter for the 3 LEDS together, but could not get anywhere.

    Any help is apreciated.
     
  2. wayneh

    Expert

    Sep 9, 2010
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    I can't quite follow. Can you post a schematic of what you actually have? I do believe the solution will be be fairly simple.
     
  3. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Are your LEDS common cathode, or are you using led bulbs?
     
  4. BG79

    Thread Starter New Member

    Apr 19, 2011
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    I´m using XP-E power LEDs from Cree.

    This is what I have.
     
  5. wayneh

    Expert

    Sep 9, 2010
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    I'm beginning to get it. You want to limit the TOTAL current of the 3 colors combined while still allowing any individual color to consume as much as 100% of the total. R+B+G ≤ 350mA AND R ≤ 350, B ≤ 350, G ≤ 350

    Do you want to run all colors at lower levels, for instance, 50mA each? Or do you want the total to be 350mA at all times?

    I believe all you need is a current-limited supply circuit after the battery but I'm not sure how that would interact with your controller.
     
  6. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    I would use three separate constant current regulators and set them at the desired currents to obtain the correct Colour/Hue and brightness.
     
  7. BG79

    Thread Starter New Member

    Apr 19, 2011
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    Hey Wayneh,

    Your explanation was a lot easier than mine...

    I need the total current to be 350mA all the time.

    I already tried to use the current limiter before the RGB controller, but the controller got crazy.
     
  8. BG79

    Thread Starter New Member

    Apr 19, 2011
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    Dodgydave, this is what I´m doing now, but when I turn all the colors on, the circuit consumes 3 times more than it should.
     
  9. wayneh

    Expert

    Sep 9, 2010
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    And you still need the controller? I'm not sure it's doing much for you.
     
  10. BG79

    Thread Starter New Member

    Apr 19, 2011
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    I´m using the controller because It has all that fancy functions and a remote.

    The other option would be to design a new controller circuit and to programe a microcontroller, andI really don´t wanna go that way.
     
  11. wayneh

    Expert

    Sep 9, 2010
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    Wild speculation: Try connecting the LEDs directly to battery + through a constant current circuit, leaving the controller also connected to the battery +.

    The controller likely provides a PWM of the connection to ground. It needs battery voltage in order to function, so it cannot be downstream of the current limiter. But the LEDs can be.
     
  12. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    The easiest solution would be to find a 1.2 to 1.5amp power supply.
     
  13. BG79

    Thread Starter New Member

    Apr 19, 2011
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    GopherT, actually that would be the harder and radical solution, because of the available space I have. It would change the whole project. This is my last option. Thanks anyway.

    I´ll try the wayneh sugestion today and bring news (hope good ones) later.
     
  14. BG79

    Thread Starter New Member

    Apr 19, 2011
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    Not good news. Conecting as wayneh said worked just like if I had conected the current regulator between the RGB controller and the battery.

    With the tests I ran today (one LED at a time), I could see that the blue LED works perfectly. The problem are the green and red.

    The green works great until the maxim current position (last step of the controller). Then it freezes the whole circuit and I´m not even able to turn it off. Sometimes the maxim position goes to 350mA, other times it goes to 170mA.
    The red LED gets crazy. It´s maxim position is about 170mA too. Sometimes it works fine, other times goes to 170mA and turns off. Some other times it freezes too.

    I,ve got intrigued with this 170mA limitation of the green and red, since when I use a regulator per color, the total output for white is the triple of this (like if each color is using 350mA).

    I don´t believe it´s a voltage neither a current issue. I ran the tests with 12V as well (it´s nominal voltage) and the results were the same, and the controller says it´s able to work with 2A for each color.

    Can you check my current regulator? Schematic attached. I believe it´s configuration, or it´s operation is the problem.
     
  15. foxfan19

    New Member

    Jun 26, 2013
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    I've been working on a similar project. From what i have encountered with my project is that those IR controllers are very easy to burn out a individual color channel. When i had burned out a channel it would light up the LEDs in a sporadic fashion and was noticeably dimmer than before the channel had blown. I also experienced the problem with not being able to use the IR remote to turn off the unit.

    Would you not be able to use a battery pack like this one - https://www.sparkfun.com/products/10470

    Seems like it should provide the 12V that the controller needs and would have enough mAh to control a decent size of LEDs for at least an hour.
     
    Last edited: Jun 26, 2013
  16. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Why dont you use an LM317 regulator for variable current like this circuit, will give upto 500mA.
     
  17. BG79

    Thread Starter New Member

    Apr 19, 2011
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    Dodgydave, I know this circuit with the LM317, but I never made it. What is it´s functional diference to the one I use? Do you believe it will work better with the RGB controller?

    foxfan19, when I return the circuit to the configuration of the firts post (3 current regulators after the RGB controller) it works fine, so I don´t believe it´s burned. I´ll try another controller anyway. About the battery, I´m working with 3 single LED´s, so using a 12V battery won´t be efficient, and I need at least 8 hours running. That´s why the 350mA.
     
  18. electrimvolts

    New Member

    Jul 7, 2013
    4
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    you can take apart one of those flashlights from walmart that shine 400 yards at 140-150 lumens. All there is to the circuit is one good size resistor...see a friend of mine has a projector he wanted it super bright, told him to get a couple of flashlight from above and i could do the rest, gutted them put it all together and had each led wafer w/ 2 pos and 2 neg so i connected them and used the resistors the leds came w/ at the begining of the hot feed for them so it went form power source to resistor to led wafer then off that wafer to another resistor to next wafer and so on....it was really bright considering they were out of fls and inside of a projector...but it wasn't bright enough so took all apart and went to walmart and grabbed the led spot light w/ a 10 watt led and put the whole circuit plus heat sink inside projector and used the power souce the spotlight came with and he said its a million times better, brighter then it was new out of the box he said msrp was 3,000 or something stupid, but idk if this helps at all in anyway what so ever but to drive each cree led was just a suitable size resistor that let the most current flow with out burning out the led...sry if this is of no help
     
  19. wayneh

    Expert

    Sep 9, 2010
    12,093
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    In a flashlight, the battery itself also acts to limit current. With a mains-powered power supply, you may need additional resistance to protect the LED from over-current. Intense brightness is great fun on the first day, but when it is severely degraded in a week, the fun will dissipate.
     
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