Explanation and help please. :-)

Discussion in 'The Projects Forum' started by Shanspau, Oct 29, 2012.

  1. Shanspau

    Thread Starter New Member

    Oct 29, 2012
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    I need a little help figuring some things out.

    My idea is as follows...
    3x50w 35vdc HO LED's wired in series and dimmable using Arduino microcontroller. I want to know if there's a way to use 110vac converted to DC and safely sustain 35vdc for the 3 high power LED's. This post I read on here at...

    http://forum.allaboutcircuits.com/showthread.php?t=19462

    was along the lines I'm looking at but i think someone's pide took over and the post wasn't answered but rather ignored. Any proactive help is appreciated.

    I'd rather not spend hundreds of dollars on several LED ac/dc dimmable controllers..

    Thanks Dave
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,103
    3,038
    Mains-direct projects like that one violate the terms of service here, for safety reasons, so this thread will likely be closed just like that one was.

    If you're willing to use an isolation transformer, you'll find help here.
     
  3. Shanspau

    Thread Starter New Member

    Oct 29, 2012
    6
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    I'm not sure what that is to be honest. An isolation transformer sounds all fine and dandy but I'm sill not sure what to do with that or how to build it etc... That's why I'm here. I'm not trying to be unsafe just gain safe knowledge and implement it in my project.
     
  4. Shanspau

    Thread Starter New Member

    Oct 29, 2012
    6
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    Okay so I read a bit on the isolation transformer and it said " Isolation transformers block transmission of DC signals from one circuit to the other, but allow AC signals to pass." Now DC signal is what led's require right? If that transformer blocks dc signal then I'm stuck right?
     
  5. MrChips

    Moderator

    Oct 2, 2009
    12,440
    3,361
    No, you're not stuck. What you need is a step-down transformer followed by a bridge rectifier to produce the appropriate DC voltage.

    If you don't know how to do this and what components to acquire keep asking questions and someone here will be glad to help.
     
  6. wayneh

    Expert

    Sep 9, 2010
    12,103
    3,038
    Putting your LEDs in parallel instead of series would allow you to get your voltage down to a safer, more workable level. Do you have the specs for your LEDs, in particular the voltage and current requirements? You said 35V, but that's a bit odd. It makes me wonder if there is internal circuitry that you need to know about in planning to control them.

    You mentioned controlling the brightness. Have you worked out how you plan to do that?
     
  7. Shanspau

    Thread Starter New Member

    Oct 29, 2012
    6
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    The specs on the LED are 50 watts and 35 volts for a single module. It has 50 1 watt led's all on one chip.
     
  8. Shanspau

    Thread Starter New Member

    Oct 29, 2012
    6
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    Okay here's a brief overview of my project. I will have a total of 9 of these 50 watt LED's. 3 6500k 50 watt 35 vdc 4900lm and 6 royal blue 470nm 50 watt 35vdc. The blues and whites will need to dim in and out in their color groups. I'll be using an Arduino mega programmed with java to provide complete automation for my aquarium. As far as i can see, the arduino will control the light dimming values in the code.
     
  9. wayneh

    Expert

    Sep 9, 2010
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    It's not quite that simple. I assume the plan is PWM control by the Arduino. The PWM signal from the Arduino will need to drive a MOSFET to control the power to the LEDs. Since you're talking about a lot of power for DIY project, this will need to be carefully designed for the right components and a robust drive system. Those LEDs aren't cheap.

    One thing you need is a 35VDC, minimum 500 watt (15A) power supply, or multiple supplies with lower capacity. Not trivial. I see a single 1.5A supply for one of these LEDs is about $25. You'd need 9 of those. :eek:
     
  10. Shanspau

    Thread Starter New Member

    Oct 29, 2012
    6
    0
    That's precisely what I'm wanting to accomplish and the exact reason I've contacted this forum. I appreciate all your help. You're not kidding about the price tag on all those drivers. I've found another driver but I'm not sure if this is safe or not. You can google this ( 100W Watts High Power LED Driver Boost / Step up Topology ) as the power supply, couldn't i get an atx supply with say 500-700 watts? If this method is deemed unsafe then please excuse my ignorance of what's safe or not. I can tell you what a safe distance/kill radius is from an explosive device or what is the best charge to take down something in your way. As for electronics, i'd rather take your word for it. :)
     
  11. wayneh

    Expert

    Sep 9, 2010
    12,103
    3,038
    The problem is the 35V. A computer PSU is a cheap and handy way to supply power to many projects, but they don't put out 35V.

    Oh, I see, you're thinking of powering that LED driver - which is meant for a 12-24V DC supply - with a PSU? That could work although I don't see how you'd insert your control signal. And you'd still need several of those drivers.

    An end-to-end solution - where the power supply itself is controlled by your Arduino - would be more elegant but would require some skilled help from experts here, if they're available and willing.

    Short of that, if you can find the right DC power supply, adding the PWM control circuit is not too complex.
     
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