LED strip questions

Discussion in 'General Electronics Chat' started by majhi, Jan 1, 2015.

  1. majhi

    Thread Starter Member

    Jul 2, 2014
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    I'm building a lighting system that will use a 3m length of 5630 LED strips at 60 LEDs per meter (generic Chinese eBay LED strips). In my personal research, 3m will have a 72W/6A draw. I'll be using a potentiometer or PWM to dim the lights as needed (I'll figure that out later). If I get a 12v 6A transformer, will that be adequate or should I get something rated higher as a precaution?

    Next question: I'm lighting my studio apartment. My current light source is a single 3-way light bulb with a max brightness of 1750 lumens. However I'm seeing that a single 5630 is 45 lumens. That means that this strip will get up to 8100 lumens, which seems way too bright. Are those numbers correct? Would I be better off using 5050's (or even 2x 3528's)?

    Thanks in advance.
     
  2. cmartinez

    AAC Fanatic!

    Jan 17, 2007
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    If your numbers are correct then I'd suggest the following:
    • Never use a transformer at 100% its capacity (12V x 6A = 72W), you'd be stressing it too much... my advice would be to never use it above 60% or 70% tops... you could use two of those 12V @ 6A transformers in parallel and be much better off
    • If you're planning on dimming the thing, I'd suggest an nFet-driven PWM circuit and certainly NOT a potentiometer, since your pot would need to be of a capacity way too high for it to be practical.
    • The amount of lumens needed to light up your place properly depends on the way the light will be spread out, color temperature and source spectrum, so more information would be needed in that regard to give you a precise answer. I'd suggest you go on trial an error on this one and not to bother too much doing calculations... buy a strip, light it up and see what happens
     
  3. majhi

    Thread Starter Member

    Jul 2, 2014
    49
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    Thanks for the info about the transformer, that's definitely good to know. Also good to know that I'll need to build a PWM (can you recommend any easy schematics?) instead of just a pot.

    As for the lighting itself, I'm wanting warm white and it will be lining the edge of my bed (lofted) which I hope will illuminate my entire room adequately. Trial and error works for me since LED strips are pretty cheap. It's not so much wanting to know how many lumens I'll need, it's more of "what is going to be overkill?" My current light bulb is 1750 lumens and I'd like something brighter.

    Also as a side note, can I just use frosted scotch tape as a makeshift light diffuser or is there a better solution? I'd prefer to cover the LEDs so they're not quite so pinpoint.
     
  4. cmartinez

    AAC Fanatic!

    Jan 17, 2007
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    PWM circuits are rather easy to google. I'd suggest you try first, get back with the results and then I'll be more than happy to share my humble opinion with you
    I wouldn't use scotch tape to as a diffuser, things would get a little too gummy after a while... Instead, I'd probably use acrylic or mica and frost them using fine-grade sandpaper. On the other hand, most LEDs have a lens at their tips that focuses the beam, turning them into tiny spotlights, I've seen people cut off the tips with a hobby hacksaw and then smooth them out with sandpaper... it's kind of laborious work, but definitely worth it..
     
  5. majhi

    Thread Starter Member

    Jul 2, 2014
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    Hmmm... it seems like it would just be more cost-effective to buy a rotary dimmer switch at the hardware store. Aren't those only like $5? I mean sure, I'd love to build my own, but I can always do that later.
     
  6. cmartinez

    AAC Fanatic!

    Jan 17, 2007
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    Commercial dimmers suck at this sort of thing... They work through phase-angle control triacs, and are normally good enough for incandescent lamps. But in this case this are LEDs, which work at DC, so you'd have to place the dimmer before the power supply, at the AC side of the circuit... and using a dimmer before a transformer (a highly inductive load) is usually not recommended, for efficiency reasons and also it might cause a lot of undesirable flicker in the LEDs
    I'd stick to PWM at the DC side of the circuit, if I were you... but then again, you can always try and see what happens...
     
  7. majhi

    Thread Starter Member

    Jul 2, 2014
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    So I think I might actually go the Arduino route. I've wanted a reason to get one for a while and the parts would be just as cheap as a DC dimmer. It would be pretty cool to have the capability to add voice activation at some point in the future, as well as the pot PWM dimmer.
     
  8. cmartinez

    AAC Fanatic!

    Jan 17, 2007
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    Kudos... if you wanted a good excuse to learn electronics, have fun and obtain something useful in the end, then this is as good as it gets... Just make sure you choose the appropriate mosfet and driver for your circuit, and protect the mosftet from transients with a good tvs diode.
    Not a big Arduino fan myself... I'm more like an 8051 junkie ... assembly programming only ...
    Then again, you don't need an MCU for PWM, a simple 555 circuit will do the trick, unless you want to do some other more interesting stuff later on, of course.
     
  9. majhi

    Thread Starter Member

    Jul 2, 2014
    49
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    ... what? Haha. If that's in regards to the PWM part, I was looking at just picking up a little dimmer module kit. Again, very cheap on eBay. I know nothing about Arduinos, but I definitely want to learn. And the parts are just so cheap!

    I have another Arduino project for the future that's far more complicated, but that's a story for another time...
     
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