High power LED array dimming

Discussion in 'The Projects Forum' started by knnrdvrmrn, Jun 3, 2015.

  1. knnrdvrmrn

    Thread Starter New Member

    Jun 3, 2015
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    Hello,

    I'm currently planning to build a high power LED array that can be dimmed using an arduino. The LEDs will be used to light an aquarium. This project is on a budget so I'm looking to buy some cheap LEDs on ebay, as well as a constant current LED driver that supports PWM.
    I think I have that all figured out. I just have to make sure that the combined forward voltages of the LEDs don't exceed the output voltage of the driver?

    The one thing I'm a bit stuck on now is what power supply I should choose. The LED driver accepts input between 5-35V.
    So I'm guessing I need an AC-DC converter that doesn't output more than 35V? Also, does the amount of output amps matter?

    Thanks in advance!
     
  2. wayneh

    Expert

    Sep 9, 2010
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    Amperage definitely matters and will be determined by the LEDs you choose. Or you might say the power required is dictated by how much lighting you want to achieve.

    You'll want to choose an LED driver rated to output more than the current required for the LED. The online specifications may be a bit generous, or outright exaggerated. Likewise, don't run your LEDs too close to their rated max current. They'll last longer.

    Each controller will drive the needed current through a few LEDs in series. The output voltage of the controller will dictate how many LEDs can be in series.

    Be sure to consider heat sinking for the LEDs.
     
  3. knnrdvrmrn

    Thread Starter New Member

    Jun 3, 2015
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    I know amps matter, for 3W LEDs I can use a 700mA constant current driver. But you're saying I could also use a 1000mA driver?

    I think I might have phrased the most important part of my question a bit messy. What I mean is this. I can't just connect the constant current LED driver to AC coming from the wall. How should I do this? :)
     
  4. wayneh

    Expert

    Sep 9, 2010
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    You can if you get the right driver. Check out Mean Well drivers.
     
  5. knnrdvrmrn

    Thread Starter New Member

    Jun 3, 2015
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    Thanks for your suggestion! I think I found a suitable driver, the LDD-700.. link here. Now I still have one problem.
    I want to use 1 PSU to power multiple drivers.
    I browsed some forums and some people are saying that the amps do not matter for this driver. It handles it all by itself by converting exces volts to amps, while others say the amount of amps the PSU supplies must be bigger than the amps all the LDDs combined need.

    The data sheet of the driver says it needs 650mA input. I'm confused on what to believe now.. so how should I choose my PSU? o_O
     
  6. wayneh

    Expert

    Sep 9, 2010
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    Just curious - were you not able to find one that runs from AC mains? This would eliminate the need for a separate PSU but I'm sure it adds cost, too.

    One thing you can be sure of is these things cannot create energy, so the energy out can be no more than ~90% of the energy in. So if your LEDs need 12V and 1A, that's 12W. The DC-DC converter will need at least 13W input (and will burn off the excess as heat). If the converter can handle only 650mA, you'll need at least about 13W/0.65A=20V at the supply.
     
  7. knnrdvrmrn

    Thread Starter New Member

    Jun 3, 2015
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    Hey, first I want to say thanks for your help so far! The meanwell drivers were a really good tip.

    I was able to find find drivers that run from AC, but most of them didn't support PWM.
    Because some strings of LEDs need to be dimmed different than other strings, I need multple drivers. I did find AC-DC drivers that support PWM but they were fairly expensive, and multiple of those drivers were way more expensive than setup I will use now.
    (If I recall correctly, been a while since I researched those before deciding to take a different approach).



    That's what I thought! But since I came across so many forum posts stating that it would work and that the driver would "magically" create current I started to doubt myself :). Thanks for your clarification!

    I think I got everything planned out now. So to summarize an example:

    • 10 3W LEDs connected in series to an LDD-500 (underpowering them)
    • I will be using 3 of these drivers, parallel connected to PSU
    • LEDs have Vf of 3.8V, so the PSU has to output at least 38V + some margin
    • 3 LDD-500 drivers = 1.5A, so the PSU must output atleast 1.5A + some margin
    Is this correct?
     
  8. wayneh

    Expert

    Sep 9, 2010
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    That sounds all about right. I had to look at the documentation regarding point 3, but the LDD-500 is referred to as a buck converter, so the input voltage does indeed need to exceed the output.

    Regarding point 4, the "some margin" should be healthy, in my opinion. For instance I'd feel better about a 2A rating when using a continuous 1.5A draw.

    I don't have experience with this kind of set up so it'd be nice if someone can chime in here.

    One thing I wonder about is supply the LDD-500 from a SMPS power supply, and any potential issues with that, whether each parallel line drawing on the PSU should have a bit of filtering. Perhaps the LDD-500 documentation addresses this issue.

    Oh, and I said it before but it's worth repeating - you need a heat sink plan.
     
  9. knnrdvrmrn

    Thread Starter New Member

    Jun 3, 2015
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    Alright, thanks for your advice then.
    I will get heatsinks, just didn't mention it before :).
    So I have to make sure I don't buy an SMPS power supply as long as I don't know if it causes issues or not? The SMPS power supply is better for my energy bill according to a quick google search?
     
  10. wayneh

    Expert

    Sep 9, 2010
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    Oh I'd want an SMPS no matter what. I doubt you could find what you need otherwise. It's just a question of making sure there isn't a problem requiring a little attention.
     
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