Light Rebuild: Lots of small LEDs or fewer larger LEDs?

Discussion in 'General Electronics Chat' started by spinnaker, Dec 11, 2015.

  1. spinnaker

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    Our community bought a solar powered entry light several years ago. The controller went belly up as well as the panel. The controller was pretty much a horrible design so instead of trying to fix it, I designed a new controller. I also replaced the solar panel and battery, choosing larger sizes for both.

    It has been a huge success. It has been almost 3 years now and I have yet to replace the battery (though I think that day is coming soon). We used to replace the battery on the original design about every 6 months.

    At the time I did not replace the light. I am thinking I want to do so now. I want to keep the original housing and just replace the LED panel. The question is how to do it?

    The current light has an array of 108 LEDs . It operates on 12V @ ~640ma. There are just 2 pair of wires (12V and ground) going to the light. The light is driven by a Luxdrive buckpuck that also supplies 5V for the pic.

    I would like to keep the specs roughly the same so I can plug and play. Should I replace with another array 108+ LEDs ? Or should I move to the Cree type LEDs?

    One problem I understand is LEDs in an array should have their forward voltages match? So the more LEDs the bigger problem with matching LEDs.

    The problem with the CREE type lights is I would need to have a heat sink?

    Any ideas?

    Also any inexpensive reliable source of LEDs?


    [​IMG]


    I do have few of these around but have no specs on them at all. I am not sure what their current requirements might be.

    [​IMG]


    Some other pics from my project that is in place.

    [​IMG]

    [​IMG]

    [​IMG]
     
  2. mcgyvr

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    knowing the ~lumen output of the current light will allow a better suggestion to be made.

    you might just be able to get buy with 1 series string of 3W (or similar) Cree type LEDs and then parallel string problems go out the window.. or a single 10W or 20W chip
    I'd NEVER do parallel strings without individual current limiting for each string anyways..
     
  3. spinnaker

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    Good point. And something I have been wanting to do. I don't have a meter but I have a light meter app for my tablet. Do you think it is close enough? If so I can take some readings tomorrow night. A few ou there for Android if you care to take a look.

    I totally agree but want the new light to be compatible with the old. The benefit is that I don't need to rebuild the controller and if I do decide to build a new controller it would be a backup controller. I considered using multiple outputs when designing my original controller but did not want to rebuild the light too. It was my first major project and I already had my hands full. Now I sort of wandered down a road of no return unless I want to trash a lot of what I have done.

    Plus the added benefit is it makes hookup so much easier. I am not sure how long I will be living here and don't want to stick them with something complicated.
     
    Last edited: Dec 11, 2015
  4. Dr.killjoy

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    Not to change topic but what voltage are you using to charge
     
  5. spinnaker

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    12V. All specs are in post #1.
     
  6. Dr.killjoy

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    Lol what voltage are you charging the batteries at
     
  7. ronv

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    Might be a good idea to see how the current one is wired just in case the driver is a little different than you think it is.
     
  8. spinnaker

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    Sorry missed the charge part in your post. Been a long day.

    It is whatever the charge controller decides. Guessing anywhere from 14V to 12V. If it is charging or just float. Input to the charge controller can be anywhere from 30V down to zero, whatever mother nature decides. Light turns on at ~OV . The panel has been proven a suitable light sensor for the application.
     
  9. spinnaker

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    Sorry I don't have a full pic but you get the idea. There are 16 columns and 8 rows of LEDs total.

    [​IMG]
     
  10. spinnaker

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    Well I just dragged out the old board that regulated the current for this light previous. I don't know how I made this mistake. Just checked the sense resistor and looks like it was set to 330ma! The buckpuck I have driving the light is a 700ma adjustable and I am almost certain I set it to 640 ma. If that is right I have been driving those LEDs twice what the original board was doing. But it has been over 2 years now and the light is still going strong.

    Edit: Just checked it will be 5 years in March the light has been working with my design! And the light is probably 5 years older than that working on the original board. Same battery for almost 5 years when we used to go through 1 or 2 a year.

    What confuses me about the board is if you look at it, there are 3 LEDs in series. I wish I had a better pic at the back of the board. The front of the light appears to show 64 LEDs. That does not add up if there are 3 in series unless they have one hanging out there by itself that is not shown.

    And am I doing the math right? 63 LEDs (3 in series) = 420ma (assuming 20 ma standard for white) + 1 LED = 440

    If they were wired in pairs then I have my 640 but it looks to me like they are wired in 3s but it is way to late so maybe I am missing something?
     
    Last edited: Dec 12, 2015
  11. RRITESH KAKKAR

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    Hello Spinaker,
    Which community?
     
  12. pilko

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  13. spinnaker

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    Nice find. I remember seeing these a while back. Thanks for the reminder. Says "Built in constant current" wonder what that means?? If they are just resistors then that us a lot of wasted energy.

    The other issue I am seeing is the 10W light would consume about the same amount of power (actually a bit more) as my current light. But is awfully smaller At least if I am doing my math right?

    Oh they are AC. :( Wonder if there is a DC version.
     
  14. DickCappels

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    Minor point: The more parts you have the shorter the mean time to failure. All else being equal, a luminaire with 100 LEDs is about 100 times as likely to experience a failure as a luminaire with one LED in a given amount of time.
     
  15. mcgyvr

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  16. spinnaker

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    I am thinking of just purchasing one of the floods posted above. Best guess but how would the current light I have compare? Will try to get a light intensity reading tonight. Do lb two ten watt lights provide as much light as one twenty? Figure I would start with one then add if not bright enough and I can stand the extra power requirements.
     
  17. mcgyvr

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    per the specs from the LEDs on that site..
    10W = ~1000 lumens
    20W = ~1600 lumens
    30W = ~2600 lumens..

    Don't know how many lumens your LEDs output (should be on the datesheet for the LEDs.. probably in mcd) but I suspect a 10W (driven at your 700mA buckpuck output) will be much brighter than your current solution..
     
  18. spinnaker

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    I am thinking about eliminating the buck puck as the flood lights have their own current limitation. Any idea on the best way to measure lumens? I have an app on my tablet. Don't know how accurate it is. Any idea how far from the light I should place the tablet?
     
  19. mcgyvr

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    I thought lux measurements are measured 1 meter from the source
     
  20. spinnaker

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    Well tried to measure the light tonight. I was surprised it was even lit since it had been raining most of day and very cloudy for the past few days.

    The light meter on my tablet app would not even register! I am sure it is a limitation of the camera lens on the laptop. Then I took a look at the light. A 1/4 of those LEDs are out! :) Time for a new floodlight for sure.
     
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