Pre Built LED fixture problems

Discussion in 'The Projects Forum' started by ludejim, Apr 17, 2014.

  1. ludejim

    Thread Starter New Member

    Apr 17, 2014
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    Hello all, this is my first post here and I hope to get some help. I have a pre-built LED fixture from Build My LED. Recently part of the fixture went out, so I am not getting full use of the ridiculously expensive fixture (thankfully I am not the one who purchased this or I would be pissed). Anyways I took the fixture apart in hopes of being able to fix it.

    From what I can tell, part of the fixture is set up in parallel and part is in series. A total of 48 inches long, in 12 inch sections, each section with 15 LEDs. Each sections LEDs are in series, but each section is connected together in parallel. The section that went out has one led on it that popped, and in turn seemingly took out the rest of the section, hence it being setup in series.

    Hopefully I am making sense. So me being me, I soldered in a wire to replace the burnt out LED. This is obviously going to cause a problem, my understanding is now each LEDs voltage in this section is now higher. There are clearly some heat issues when I leave the fixture on for more than 30 seconds.

    What do I need to do to fix the rampant heat issue? I imagine a resistor is a solution? How can I determine the type of resistor? I do not know the specs on each LED except for what is provided here Build My LED "Specs" which really isn't a whole lot.

    I do have the power supply specifications:
    Input voltage 100-277VAC 50/60Hz
    Input current 0.9A @ 100VAC

    Output voltage 27-54VDC
    Output current 0.14-1.4A
    Dimming voltage 1-10VDC

    I am not running the dimmer, so its outputting at max specs. Help would make me and my fish tank occupants much happier, especially my corals :(

    If there are any other bits of information that are needed to solve this problem that I might be able to provide, let me know and I will do what I can to get it.
     
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    "IF" there is 2 series strings in parallel and they were closely matched before as to share the current equally in each string then now with 1 LED removed from one of the strings the current is no longer equally shared..
    The easiest/proper solution would be to simply replace the blown out LED with a new one. Then hope the fixture goes back to happily "sharing" the current.

    Any fuses in the unit?
    "some" people believe that including a 1 Amp fuse in each series string allows them to safely parallel LED strings. The hopes are that if they start to go into thermal runaway that the fuse will protect the one string thats pulling more current and then "pop" when needed and then the other fuse will protect the remaining string by "popping" when it starts to get the full load.

    How long have you had it? Don't they have a warranty?
     
  3. wayneh

    Expert

    Sep 9, 2010
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    Do you have a meter? You could measure the ∆V across a single working LED or even the entire string, on one of the functioning 3 strings.

    If you have any power resistors in your junk drawer (you DO have a junk drawer, don't you? ;)), I'd try values of 470Ω and less in series with your broken string, in place of your zero ohms wire jumper. If you find a resistor that gives the string a similar brightness to the other sections, measure the voltage across that resistor. That will tell you, by calculation with Ohm's law, how much current is flowing when the LEDs are operating normally.
     
  4. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Oh wonderful these are surface mounted LEDs? That's just a pain to solder your first time. Also your fiftieth.

    One easy (and cheap) way to balance both strings (assuming you don't have a resistor) is to short one LED in the good string: then at least they both have equal voltage drops. But is they are voltage driven you've just put more power into each LED then before.

    Any pictures you can take of the unit's boards and wiring can only help us help you. I am not sure if you can post pictures yet, you may need 10 posts till you can, so if not holla and some kind moderator may help.

    Good luck with the fishies and welcome to the forum!
     
  5. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    It also occures to me the LED may be what we call a "secondary failure": if the power source is failing and putting out too much voltage that may be causing this power issue, and all you are seeing is the first LED to die.

    Do you have a voltmeter to check the 10V is really 10V? Ummm... it will just read the LED voltage as long as they are connected. Damn... can't think of a good way for you to check that.

    Do you have the dimmer?
     
  6. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    What color are the LED's?
    Wild guess, Vf 2.8V @ 350 mA which might mean an equivalent R at about 8Ω @ 1W. Some volt meter readings will help.
     
  7. ludejim

    Thread Starter New Member

    Apr 17, 2014
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    Wow, an outstanding response, thank you guys. I am going to attempt to answer everyones questions so we can get all agree on an answer

    mcgyvr, the unit does not have any fuses in it unfortunately, that would have been nice. And since I am not the original owner of the fixture, Build My LED will not honor their warranty, sad day. If I could find one of these LEDs locally, that is most likely what I would do, do you know of any sources?

    wayneh, I do have a multimeter, and I'll be the first to admit that I don't now how to use it properly. Unfortunately its not possible to read each LED as the surface mounted LEDs just don't allow for it. So, I tried testing the voltage of each section. I switched it to VDC and put one lead on one end of a section and the other lead on the other end of the section. The first section read .5, the next .229, the next .154 and the last ~.078. Like I said, I don't know what the heck i'm doing. Maybe the picture that ErnieM asked for will help you guys tell me how to test each section. I dont have that cool of a junk drawer unfortunately :(

    ErnieM, I can detach the power source from the light and test it directly. It says it is outputting 55.8VDC which is a 4.8VDC above what it says on the power supply. Although, when the light is running, the voltage across the whole light drops down to 44.8VDC. I don't have the dimmer unfortunately, although I do have some pictures and some drawings of the light.

    Drawing of how I think the light is setup:
    [​IMG]

    Actual Photos:
    [​IMG]
    [​IMG]

    and finally Bernard, I did a little more research on the light and found out the exact number of lights for my setup. For each 12 inch section I have (7) 6500K Cool White, (4) 450nm Royal Blue, (2) 470nm Blue, (1) 525nm Green, (1) 660nm Deep Red. Also your guess at 350 mA seems to be correct as it is stated on this webpage under product info.
     
  8. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Dang... reality check time.

    The large blocks with the D2, D1, D15, D14... labels are the LEDs?

    If they are the LEDs, any idea what size they are?

    Any idea what the 3x4 bumps between these are? Do they light up too?
     
  9. GopherT

    AAC Fanatic!

    Nov 23, 2012
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  10. ludejim

    Thread Starter New Member

    Apr 17, 2014
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    Gopher the manufacturer will not honor their warranty as I am not the original purchaser of the product. I tried to be nice, I tried to bully, but they just wouldn't fix it for me. They wanted me to pay $150 for them to fix it. That's half the cost of a new light. No thanks!

    ErnieM, Correct the D1, D2... are the LEDS, as someone else mentioned they are surface mount LEDs. As far as size goes they are about 1/4" x 1/8". Pretty small. The 3 x 4 area of bumps in between do not light up, they are areas to solder things on to the board I think. I am not really sure to be honest, but they really do look like pin holes that you might be able to stick a different type of surface mount led into.

    Hopefully I can get this figured out soon, my corals can only go for so long with out light.
     
  11. burger2227

    Member

    Feb 3, 2014
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    It appears to me that those are 3 volt LED's with 45 volts as the supply. That's an unusual setup for solid strip lights and that's why they want you to pay through the nose for a new strip.

    You can either try to replace the LED or replace the strip or start all over with a 12 volt supply which is much more common. Here's a link to some other kinds of strips: http://www.superbrightleds.com/cat/rigid-light-bars/

    Ain't nothing cheap...
     
  12. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    These may be close to the LED part nos. just do not know which bin they were picked from: Phillips LUXEON Rebel
    Cool White LXML-PW02 VF 2.5-2.9-3.25
    Green LXML-PM01-01000 2.55-2.9-3.51
    Blue LXML-PB01-0040 2.55-2.95-3.51
    Royal Blue LXML-PR01-0425 " " "
    Deep Red LXM3-PD01 1.8-2.10-2.8
    At 350 mA Vf's closer to the averages, at 700 mA closer to high side, max pulsed about 1 A.
     
  13. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    They are "thermal vias"
     
  14. burger2227

    Member

    Feb 3, 2014
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    Another idea would be to buy a new aquarium light using actual Grow Lux bulbs for the floral. I've never seen proof that LED's, as much as I adore them, keep plants alive any better!
     
  15. SgtWookie

    Expert

    Jul 17, 2007
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    You could try temporarily replacing the bad LED with an 8.6 Ohm 2 Watt resistor; that should at least get you going, and the light levels from the remaining LEDs should be about equal.

    When the LED went bad, it basically shorted out, causing that string to pass much more current than the other strings. Replacing the single LED with a resistor that drops about the same as the LED originally did is a cheap and pretty quick solution.

    For another alternative, you could use four 1N400x (1N4001 thru 1N4007) diodes in series, which would have a forward voltage of roughly 3.2v at 350mA at room temperature. You can get a pack of 25 1A diodes from your local Radio Shack for a couple of bucks.
     
    Bernard likes this.
  16. burger2227

    Member

    Feb 3, 2014
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    I'm betting that the bad LED opened that set of series LED's. Jumping it with a resistor may restore that set. The exact resistance needed depends on the current drawn by the set assuming each LED drops about 3 volts. Series current is the same for all of the LED's.
     
    Last edited: Apr 19, 2014
  17. SgtWookie

    Expert

    Jul 17, 2007
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    The bad LED shorted, which gives it a much lower Vf than it had when new. As a result, the remaining 14 LEDs receive a much greater current flow than before, which results in the overheating our OP is seeing.

    Replacing the shorted LED with either a resistor with a value of roughly 8.5 to 10 Ohms or four standard 1A diodes wired in series should put things reasonably back to where they were. The individual string will still be about 93% as bright as it was previously; I'll bet the fish will hardly notice.
     
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  18. ludejim

    Thread Starter New Member

    Apr 17, 2014
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    I ended up finding an old circular led array that I was able to essentially replace the blown out LED with. The one section isn't as bright as it used to be, but it works, it doesn't over heat, and it cost me nothing.

    Burger, it may not keep them alive any better, but I don't have to replace the bulbs every 6 months or pay nearly as much for my electric bill! I really wonder how those Rigid LED bars hold up against the Build My LED bars. Considering how much cheaper they are i just might have to give it a go. Thanks for the link.
     
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