Adapter for led string, is this simple?

Discussion in 'The Projects Forum' started by clunker, Jan 21, 2015.

  1. clunker

    Thread Starter New Member

    Jan 21, 2015
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    Hello,

    I am a complete noob, so this may cause some eyerolls...

    I build weird illuminated sculptures out of scrap, and leds seem like an ideal lighting solution because they last a long time, don't heat up, and fit into tiny places which is essential.

    I bought this, which is a string of 10 warm white leds running off three 1.5v batteries:

    [​IMG]


    I cut the string up into three lengths of 6 leds and one length of 5 leds. I installed them where they needed to go, wired them all back together, and it works:

    [​IMG]

    So the (naive) plan was then to simply remove the battery pack and splice in a wall-wart adapter to make it permanent, since I have a bag of random ones lying around.

    I grabbed this, and selected 4.5v, and tried it out on the remaining leds that I didn't use:

    [​IMG]

    They all lit up nicely..... and then fried within one minute.

    So now I'm left with this thing with a bunch of leds painstakingly installed in tight places that I don't want to have to re-do, for example:

    [​IMG]

    I really REALLY don't want to try the wrong thing and fry these and have to fish new ones back through those pipes to the exact proper places.

    So, my question is this : Is there a simple solution to making it possible to just plug all this into an outlet?
    Is there a ready-made product for sale somewhere and I just don't know what to look for? Or does this need some sort of custom-designed circuit?

    It seems like it should be simple, but after looking around randomly online for a couple of hours, I just can't seem to find an answer that is comprehensible to a noob.

    Thanks in advance!
     
  2. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    I don't understand the math. How did you make 10 LEDs into 23 LEDs? How are they wired together?
     
  3. clunker

    Thread Starter New Member

    Jan 21, 2015
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    Ha! Sorry, 30 leds, 10ft string.
    Everything is in parallel I guess?
     
  4. clunker

    Thread Starter New Member

    Jan 21, 2015
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    All the leds look like this, so I assume that means parallel.

    [​IMG]

    I just cut and re-connected.
     
  5. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    That was more than likely relying on the internal resistance of the batteries to limit the current to the LED..
    A power supply did not have that and simply cooked the LEDs..

    Time to redo it and this time include resistor to limit the current.
     
  6. clunker

    Thread Starter New Member

    Jan 21, 2015
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    Ok.... but remember I'm a noob. I basically sort of know what a resistor is and what it does, I think I have a bunch of them and I think the color stripes = how much resistance. So....

    -What size resistor?
    -I just attach one side of the resistor to the positive wire from the adapter and the other side of the resistor to the positive wire from the led string?

    I can't be the only person who's ever wanted to run an led string off an outlet, is there really nothing out there that you just plug in and go?
     
  7. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    LEDs are current sensitive devices, and too much current burns them out. To set the current, one must know their specs, which can sometimes be inferred from their color, the supply voltage, and how they are wired.
     
  8. clunker

    Thread Starter New Member

    Jan 21, 2015
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    Ok....
    Well, color is warm white, they were powered by three 1.5v AA batteries, and the leds were all wired in parallel.

    The batteries were joined in series.
     
    Last edited: Jan 21, 2015
  9. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    And you aren't the only one thats let out the magic smoke in LEDs before not knowing that. :p
    LEDs are not like regular lightbulbs..
    If you want plug and go just buy some LED christmas lights or similar that plug right into the wall already..

    If you want to try again a 330 ohm 2 Watt or greater resistor should be ok assuming 30 LEDs in parallel.. Higher wattage is always preferred.
    Higher resistance will make them dimmer.. lower is not recommended to avoid smoking/overheating them.
    and yes just put it in series on either the positive or negative side of the circuit.
    That "should" work just fine.

    BUT (big but)..
    Its NEVER a good idea to run LEDs in parallel without current limiting for each LED. They sometimes don't "play nice together" and one ends up hogging the current.. Then burning out.. then another bully hogs it again and he goes up in smoke and on and one.
     
  10. KJ6EAD

    Senior Member

    Apr 30, 2011
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    Let us review.

    You've tried trial and error with cheap components and failed. You're asking for a simple solution, one that doesn't require you to learn enough to do your own circuit design. That leaves one obvious option; buy individual LEDs that have a built-in resistor for a given voltage. I'll suggest "12V LEDs" as a search term since you're likely to find the largest selection in that voltage and it has some advantages over lower voltages in the loading of your power supply.

    Also, for multiple points of light, all the same color and not requiring independent control, you may want to explore light pipes or fiber optics. There are art specialty suppliers online who sell these materials to artists and modelers.
     
    Last edited: Jan 21, 2015
  11. clunker

    Thread Starter New Member

    Jan 21, 2015
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    @KJ6EAD
    "Let us review.

    You've tried trial and error with cheap components and failed. You're asking for a simple solution, one that doesn't require you to learn enough to do your own circuit design."

    Yes, I am a great disappointment to my parents etc. etc... However, when almost every cheap device that uses batteries also has a jack for a wall-wart, you can see how I might jump to conclusions. If it's unavoidable, sure I'll do the circuit design, but yes, I was hoping that someone would say "Oh, you just need a " ", you can get them at Canadian Tire for 1.99$".

    I'll check out the fiber optics though, that might be workable if they're really flexible.

    @McGyver :

    All the plug-in christmas lights I saw were kind of traditionally shaped, too large to fit into the tight spaces I need them to fit....
    What you're saying about leds not playing nice together, is that because of slight variations in manufacturing? Because they came all together in a string already, so I would have thought that they're cooperative enough.... Is this something that is not a factor with batteries, but becomes a factor with an adapter+resistor?
     
  12. JWHassler

    Member

    Sep 25, 2013
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    I have several of those things: the batteries last about 6-8 hours. They have a chip-on-board controller on a small PCB in the top of the battery compartment.
    Remove the batteries, then connect a USB wall-wart (in series with a 1N4xxx diode if you're worried about the extra .5 Volts) to replace them.
    Toughest part will be hiding the battery-box.
     
  13. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    yes slight variations in LEDs can be the cause for that issue as well as packaging/mounting/heat sinking issues,etc...
    And its still a factor with batteries.. Its just a cheap led string and if/when it goes you will just throw it out and buy another.

    Sadly its done all the time in dirt cheap throw away products...
    Manufacturers of "cheap stuff" have tricks to attempt to control it.
     
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