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how to determine the right voltage for led lamp?

Discussion in 'Troubleshooting and Repair' started by pharaon, Jun 3, 2019.

  1. pharaon

    pharaon

    234
    3
    Oct 28, 2014
    ok today i tried with 0.04 current and 2.6 voltage for 5 leds
    1- connected for only one led and the 5 light up together
    [​IMG]

    2- connect the first and last led and the 5 light up
    [​IMG]

    then i tried to light up 10 leds same current at 0.04 but i had to rise up the voltage to 5 V
    [​IMG]
     
  2. Alec_t

    Alec_t

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    686
    Jul 7, 2015
    That's a much clearer image and points to the LEDs being arranged as a series of 18 groups, each group having 5 LEDs in parallel. So I reckon you'd be looking at a power supply of at least 18 x 3V = 54V, capable of supplying a constant current up to 5 x 60mA = 300mA.
     
  3. BobK

    BobK

    7,572
    1,633
    Jan 5, 2010
    Ah, this finally makes sense. At least I was right before I was wrong!

    Bob
     
    bushtech and Martaine2005 like this.
  4. Martaine2005

    Martaine2005

    2,229
    603
    May 12, 2015
    Yes Bob, you guessed about 60v ages ago!. So you were right!.

    Martin
     
  5. pharaon

    pharaon

    234
    3
    Oct 28, 2014
    how did you calculate this part?
     
  6. Alec_t

    Alec_t

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    Jul 7, 2015
    See posts 10 and 12. If 66mA is the maximum rated current, it is always advisable to run things at less than maximum to prolong their life, so 60mA per LED seems reasonable.
    I'm still puzzled by your assertion that "they all share the positive line but the negative is every 5 leds". If 18 groups of 5-parallel are indeed in series then they can't all share the positive line.
     
    Last edited: Jun 11, 2019 at 11:37 AM
  7. pharaon

    pharaon

    234
    3
    Oct 28, 2014
    yeah sorry about that, it's the opposite
     
  8. Alec_t

    Alec_t

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    Jul 7, 2015
    You mean they all share the negative line? That still leaves the puzzle.
     
  9. pharaon

    pharaon

    234
    3
    Oct 28, 2014
    [​IMG]

    see that top thin line that all each group of leds share
     
  10. Alec_t

    Alec_t

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    Jul 7, 2015
    I think you'll find that the light-coloured line is an insulating strip, not a power rail, and the darker areas are conducting paths connecting the groups in series. Can you confirm with a meter?
     
    Last edited: Jun 12, 2019 at 11:52 AM
    Harald Kapp likes this.
  11. pharaon

    pharaon

    234
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    Oct 28, 2014
    yes that's true
     
  12. Harald Kapp

    Harald Kapp Moderator Moderator

    9,034
    1,810
    Nov 17, 2011
    This is what the circuit looks like (the polarity of the diodes may be reversed, I can't see that from your photos):
    upload_2019-6-14_12-36-36.png
    Each of these meandered sections has 5 LEDs in parallel. The sections themselves are in series.
    All else has been said.
     
  13. Alec_t

    Alec_t

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    Jul 7, 2015
    Conclusion: you'll need a ~300mA constant-current ~60VDC supply.
     
  14. pharaon

    pharaon

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    Oct 28, 2014
    thanks every one
     
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