Diy Ring light. Help?

Discussion in 'General Electronics Chat' started by Austin Shelton, Aug 3, 2016.

  1. Austin Shelton

    Thread Starter Member

    Aug 3, 2016
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    Ok at the moment i'm working on a Diy Ring Light.
    I will try to be as detailed as possible.
    The light source i'm using is from an old LED light box that has over 204 leds in a array 17x12 matrix
    I am using a Old circle fan outer shell for the ring shape and i already made the outer casing.

    My problem is i am trying to wire these leds off of the matrix and in separate rows.

    My plan is wire these leds in a circle and connect the ends to the LED light box controller.

    Basically take the box led shape and make it into a circle. At the moment the leds are attached to the board. I have desoldered all of them almost and i have figured out the positive led and negative led. As long as i wire the positive leds in a row and negative in its own row with paper clips and then connect it back up to the positive wire and negative wire on the controller i should have it working?


    Is there something else i need to do? It will be powered by the wall because the controller has its own dc input and i have the correct power supply for it.

    I will provide pictures if needed. i hope this is enough info to help you guys help me. Thanks.
     
  2. #12

    Expert

    Nov 30, 2010
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    You said nothing about resistors or current limiting, so I say this:
    The problem with LEDs is that they are not like light bulbs. They need a resistor to limit their current or they will pop like a fuse.
    We need you to show us how any resistors are wired into this circuit, what amount of resistance they have, and what the voltage supply is.
     
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  3. Austin Shelton

    Thread Starter Member

    Aug 3, 2016
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    The leds are wired into a led light that controls all that. The voltage. The limiter. Its all handled by the controller the leds were orignally connected to.
    All i'm doing is taking the leds and making them into a circle then reconnecting them back up into the controller but in a different shape.

    but you might be right on that.

    ok im going to upload all the pictures i can. hold on.

    Ok here are pictures of led controller board and the led matrix along with what I'm doing wiring them up.


    I hope thats enough for you.
     
    Last edited by a moderator: Aug 6, 2016
  4. #12

    Expert

    Nov 30, 2010
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    One problem is that 204 LEDs can be arranged in many ways. It seems you have exactly 2 wires connected to the light board. True or false? If all the LEDs are in series, your fast switching power supply can hit them with as much as 600 volts at 0.02 amps. If they are wired in parallel, the voltage is around 2v to 4 v and the current will be about 4 amps. If they are all in parallel, they need resistors on the board with the LEDs, but I can't see how the board is wired. Can you see how the copper traces are arranged? If you don't know about series and parallel, can you do a better photo?

    Just some guessing here: The inductor and the wires look compatible with low voltage, high current, but you can't place 200 LEDs in parallel with no resistors because the weakest LED will hog the current and they will start a cascade failure.
     
  5. Austin Shelton

    Thread Starter Member

    Aug 3, 2016
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    Yes i noticed my self how the leds were soldered on. There were traces on it. All the positives had their own traces and so did the negatives.
    So + were going to the red and -went to the black wire. The thing about the resistor part is i dont see any on the led board it's self so it makes me wonder do i even need them? Maybe its the way i'm trying to wire it that makes it need new parts?

    So after double checking i have come to the sound conclusion that they were indeed in parallel NOT series.
     
    Last edited by a moderator: Aug 6, 2016
  6. #12

    Expert

    Nov 30, 2010
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    If the manufacturer matched those LEDs so accurately that they can all be in parallel without starting to pop a few, more power to him! Apparently you have 204 matched LEDs.:confused:
    Continue as planned.
     
  7. Austin Shelton

    Thread Starter Member

    Aug 3, 2016
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    Maybe i was not clear. All these parts were in one product before that worked. The leds. The controller. I'm basically reusing the whole light.

    Now you got me scared :/ I'm now worried that ill ruin it.

    Here i found the product if that helps
    https://www.amazon.com/dp/B019E79GGI?psc=1

    operating voltage for the light ranges from 4 to 10V DC
     
    Last edited by a moderator: Aug 6, 2016
  8. Sensacell

    Well-Known Member

    Jun 19, 2012
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    If that one photo of LED's soldered on one side is your ring light- you are in trouble already.

    As #12 states, you cannot wire the LED's in parallel, LED's have a fixed forward voltage that varies from unit to unit.
    The one that has the lowest forward voltage will hog the majority of current and fail.

    To get even brightness, the LED's must share current equally. LED's in series all share identical current, but the voltage required adds up to dangerous and impractical levels quickly. In all cases, there needs to be a current regulating system external to the LEDs, they do not regulate current themselves.

    Large arrays of LED are tricky to drive.
     
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  9. Austin Shelton

    Thread Starter Member

    Aug 3, 2016
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    Alright. So what should i do then?

    The control board should handle all that by its self considering it was working before and could get very bright with a wheel on the back. I really want to complete this project.

    if i need a vo

    i checked the traces YET again. IT seems right in the middle the + and - do connect and then they go back to not connecting for the rest of the traces. I think i will draw it out for you guys on photoshop. Brb.

    It will be awhile guys but i hope this will help

    OK this is the traces on the back. Hope this helps. took me a bit.

    I added where the positive wire went and the negative.
    The leds postive went on the postive lines and the neg like wise.

    The only place they meet is in the middle.
     
    Last edited by a moderator: Aug 6, 2016
  10. Sensacell

    Well-Known Member

    Jun 19, 2012
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    Freaky.

    Looks like they are wired in parallel, this looks very odd to me.

    There must be something else going on to make this work in a reliable way.

    Since LED's have a negative temperature coefficient, (Vf goes down as they heat up) the tendency for thermal runaway is problematic.
    If one LED starts hogging current and heating up, the same led will tend to hog more current in a runaway cycle leading to smoke.

    You need to figure out what prevents this- otherwise it will happen.

    Can you take more photos of the PCB showing details? Maybe they make the traces of the PCB thin in areas to add balancing resistance?
    Are there ANY other parts on the LED board?
     
  11. #12

    Expert

    Nov 30, 2010
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    I see half the LEDs in parallel and that group feeding the other half of the LEDs. That makes 102 LEDs in parallel and the current from them feeding another group of 102 LEDs. Two in series and 102 in parallel. That makes the feed voltage from the converter 6.6 volts @ an average of 2.04 amps, and it's obviously pulsed because that's how switching regulators work.

    204 LEDs times 0.02 amps is 4.08 amps. You can't get 4 amps out of a AA battery (or 6 of them in series). Maybe that is the current limiting resistance. Any attempt to get 4 amps out of those batteries will cause the voltage to collapse.

    Let's run some math and some measurements.
    Assuming 3.3v for a white LED. 3.3v x .02A x 204 LEDs = 13.64 watts.
    with a 90% efficient switching regulator you need 14.96 watts.
    15 watts out of 9 volts uses 1.66 amps.
    I just placed 1 ohm across a new alkaline AA battery (Coppertop) and the voltage dropped to 1.3 volts in 2 seconds.
    1.16 volts after 10 seconds.
    My old Radio Shack battery book shows 0.68 amp hours out of an alkaline AA with a 1 ohm load. They did that in 15 second bursts and took 145 bursts to get to 0.75 volts at the battery terminals. Total: 36.25 minutes. That's down to 1/2 the original voltage to get 0.68 amp hours out of the battery at an average draw of 1&1/8 amp.

    1.125v (average) times 1.125A (average) times .604 hours = 0.765 watt hours per battery.
    0.765 watt hours times 6 batteries = 4.587 watt hours.
    4.587 w-h/15 watts = 18.35 minutes.
    That's a pretty short video.

    I can imagine a switching regulator working in the range of 9 volts to 4.5 volts, but at the same time, the necessary current draw will double to 3.3 amps, which the batteries can't do. Summary: you can't get 18 minutes out of this machine with the batteries they recommend.

    Now, back to the 102 LEDs in parallel: You can't do that with a random batch of LEDs. Somebody is going to hog the current. Therefore, these LEDs must be matched sets. You can do that if you're sorting a million LEDs. The best advice I can give you is to keep your wiring nice and neat. Try to use equal lengths of wire. Use fairly fat wire. 10 gauge is the mathematically correct size, but you'll never get that to work unless you're using the wire for the mechanical support for the LEDs. (That's not a bad idea!)

    Place two LEDs in series for every circuit and make lots of parallel circuits. If it takes 14 inches of feed wire to get to the farthest group, use 14 inches for every group and make little coils to use up the extra length.

    So it goes: two points where the power wires arrive from the regulator. A bunch of long red wires which are equal to each other. A bunch of long black wires which are equal to each other. A bunch of groups with 2 LEDs in series. Connect each group with a red and a black.

    The only other way is to redesign this with some resistance in series with each pair in series. I think 102 resistors of about 33 ohms. I also think AA batteries are a miserable power supply. You need something like a 9 volt wall wart good for at least 1&2/3 amps.
     
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  12. Austin Shelton

    Thread Starter Member

    Aug 3, 2016
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    OK here is what i have planned. I used red leds in this drawing so you can see it better. They are going to be WHITE.
    The ring is the ring light. I made the leds big so you can see it in general. I used red for positive wire and black for neg.

    The green board is what the leds were originally running off. It has a coil some capacitors and on the back a chip or two and tiny smds.

    Keep in mind this is just a mock up. I know its shit but i wanted to convey and hopefully have you guys guide me on this.

    Btw none of this is running off battery's. I used a power supply that connected on the back before i took it apart to repurpose the leds
     
  13. #12

    Expert

    Nov 30, 2010
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    You need 2 LEDs in series in every place where you show a red LED.
     
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  14. Austin Shelton

    Thread Starter Member

    Aug 3, 2016
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    I am new to electronics. What you said was extremely useful but from my point of view alien. I have limited resources in terms of parts but i do have some resistors but i dont have 102. I am hoping that all i have to do is wire these leds as i remove them from the led board and attach them to the perimeter of the casing i made and use paper clips to solder the negative first then the positive and then proceed to hook the + to the + wire on the board and the neg to - wire. Power it up by plugging in the power supply. Done.


    But it seems its not going to be that simple sadly


    alright perfect. So two leds in a kind of group instead of single wiring that i had plan?

    Any way you could show an example
     
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  15. #12

    Expert

    Nov 30, 2010
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    No. I'm on my Linux computer and I don't know how to do drawings yet.
    Red to positive leg of an LED. The other leg of the LED to the positive leg on another LED. The last LED leg to the negative power line.
     
  16. Austin Shelton

    Thread Starter Member

    Aug 3, 2016
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    Like this then? just repeated?
     
  17. #12

    Expert

    Nov 30, 2010
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    Yep. That's two in series.
     
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  18. Austin Shelton

    Thread Starter Member

    Aug 3, 2016
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    Ok its going to be a little confusing as the way i have the leds set in the case is weird but basically Instead of a complete run around of paper clips on the positive leds and like wise for neg. I should wire one leg + or - does not matter i think but - to a + leg and then basically consider TWO fo them as ONE in a sense and just use solder them in GROUPS.

    So this is what needs to be done in order for it to work like i want. Great.

    ugh its already confusing. Lets say i take two leds and i take the negative terminal of one and hook that up to the positive. They are now one.

    But that still leaves the other terminals. Do i continue hooking up the negative terminals to ALL the negative terminals of the other like originally plan but have cross sections every other set of leds ? Or do i skip some on the sets ? idk
     
    Last edited by a moderator: Aug 6, 2016
  19. dannyf

    Well-Known Member

    Sep 13, 2015
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    Nothing freaky at all.

    This "parallel leds don't work" talk is theoretical in that it assumes imperfectly matched perfect leds.

    In reality, leds, particularly power leds, behave much like resistors at high levels of current. So a little bit of mis match in their forward voltage isn't nothing go worry about.

    As a matter of fact, that's just how most lighting (power) leds are constructed.
     
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  20. Austin Shelton

    Thread Starter Member

    Aug 3, 2016
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    plus do i still need resistors ??


    So now you are kinda saying that my original plan is ok to go with? Just hook up the leds in parallel?

    0-0
     
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