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Design fix on a battery powered COB LED

Discussion in 'General Electronics Discussion' started by Richmrf, Jun 13, 2020.

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  1. Richmrf

    Richmrf

    10
    0
    Jun 13, 2020
    PROBLEM:
    24 SMD COB LED has too much illumination drop off over 3 hours. Currently powered by four 3V button batteries.

    PREFERRED SOLUTION:
    Get this battery powered LED to perform more consistently over a few hours.

    THE STORY:
    I’m working on a little project at home for a custom show car I built. I’m trying to get my interior lights to work independently with a small power source.
    I have a few COB LED’s placed inside the car and can not run wiring without destroying my interior.
    I thought I designed a perfect fix using four 3volt button batteries ran in series. The small batteries allow me to hide the power source without running more permanent wiring. It only needs to last a couple hours for the final judging.
    Currently, they are lasting much longer then needed but the drop off is very dramatic. From over 100 LUX when first switched on, to 30 LUX after 10 minutes, 17 after 20 minutes, 15 after 30 minutes, then it starts to stabilize and remain around 13 LUX with very little drop off.
    These lights do not need to be over 30 LUX. They are only decorative lights but the drop off can’t be so drastic that a judge can notice the difference over a 20 minute period.
    QUESTION:
    What are my options to get a more stable output with much less drop off in illumination?
     
  2. Martaine2005

    Martaine2005

    2,751
    742
    May 12, 2015
    Show us a picture or schematic of your project including data on the LEDs.
    You only gave two bits of information. 24 LEDs and 4x3v button cells in series.
    I’ll say straight away that button cells are not the way to go. Use a minimum of AAs cells.
    Curious how you measured LUX ?.

    Martin
     
  3. bertus

    bertus Moderator

    689
    240
    Nov 8, 2019
    Hello,

    What kind of button cells are you using?
    There are so many different types.
    On this page of the wiki, you will find a list:
    https://en.wikipedia.org/wiki/List_of_battery_sizes
    There are also the dimentions given on the page for all types.

    Bertus
     
  4. Richmrf

    Richmrf

    10
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    Jun 13, 2020
    3 volt, CR 2032’s. I have been using 4 of them.
    I’m an electrician/instrument tech by trade with zero experience with small electronics. Sorry for the lack of information I provided.
    The reason I have tried button batteries is because I need to keep it as small as possible. I need all these components to be as small as possible to remain hidden.
    I measured LUX with a handheld LUX meter in a dark bathroom. The measurement I’m taking is only to see the drop off. I only tested so I would be able to compare a few different LED’s. Unfortunately all 6 I tried, tested very similar.
    I only learned yesterday about step up converters. That May make 2 AAA’s feasible without taking up too much space.
    I was hoping one of you would say to put a capacitor or some other component. ‍♂️ I am familiar with capacitors. I know they store energy but that’s about where my knowledge ends.

    What kind of button cells are you using?
    There are so many different types.
    On this page of the wiki, you will find a list:
    https://en.wikipedia.org/wiki/List_of_battery_sizes
    There are also the dimentions given on the page for all types.

    Bertus[/QUOTE]
     
  5. Richmrf

    Richmrf

    10
    0
    Jun 13, 2020
    I’ll have a picture posted shortly. Unfortunately, I don’t believe I have enough space for 2 AA’s. If I were able to make them fit, it would be very tight.

    Show us a picture or schematic of your project including data on the LEDs.
    You only gave two bits of information. 24 LEDs and 4x3v button cells in series.
    I’ll say straight away that button cells are not the way to go. Use a minimum of AAs cells.
    Curious how you measured LUX ?.

    Martin[/QUOTE]
     
  6. Martaine2005

    Martaine2005

    2,751
    742
    May 12, 2015
    Without the LED details, it’s difficult to say. But you are supplying 12v @ max of about 200mA for brand new batteries. The LEDs are obviously wired in series/parallel. Whether 6xseries and 4xparalleled for example. If each series string is 30mA, that’s 120mA straight away. As we don’t have the data on the LEDs, we can only guess.
    Put your DMM in series with the LEDs and measure their current. Lets start there.

    Martin
     
  7. Audioguru

    Audioguru

    2,832
    634
    Sep 24, 2016
    You have nothing in series to limit the LED current so of course that are too bright with new batteries which kills the batteries and dims the LEDs before you want. An LED needs its current limited by a series resistor or a constant current circuit.

    We need to know the voltage (color) of the LEDs and how they are wired. Then we can simply calculate the value of a current-limiting resistor so that the LEDs brightness and their battery current is not too high with new batteries allowing the batteries to lase longer at almost the same brightness.
     
  8. Richmrf

    Richmrf

    10
    0
    Jun 13, 2020
    1CE6D534-B071-4837-90BF-3D74DE36DA0E.jpeg C280CD90-195C-474F-A002-DEF67E19C30E.jpeg
    [/QUOTE]
     
  9. Richmrf

    Richmrf

    10
    0
    Jun 13, 2020
    Thank you all for the help. I figured if you all are kind enough to help me out, I had better not make you wait, so I ran out and grabbed another Fluke.
    I tested the old batteries from last nights test (about 12 hours on them) and it read 9.5mA. Then I switched out the old batteries with another 4 new batteries. With the new bats, it read 35.5mAmps at first.
    Both current tests showed the current to be dropping significantly. It was counting down the same as the LUX meter does when I run a test.
    As for the color of the LEDs, they are Advertised as full spectrum. I can’t say I trust the China manufacturer to tell the truth. I’ll attach a couple pictures of the different LEDs I have been testing. All have been giving me similar results.
     
  10. Richmrf

    Richmrf

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    Jun 13, 2020
    This is the style I gave you the amp readings for. I have used 3 different styles with very similar results.
     

    Attached Files:

  11. Richmrf

    Richmrf

    10
    0
    Jun 13, 2020
    This is a pic of the chart I made. It just shows the drop off. On the left is LUX (The number isn’t very relevant. It just shows the drastic drop off) and in the bottom is length of time in 10minute intervals.
     

    Attached Files:

  12. Richmrf

    Richmrf

    10
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    Jun 13, 2020
    This is another one if the LED’s I tested. Maybe this one will have better information needed.
    Should I order some components? If someone told me the sizes on various resistors or other components that may be useful, i’m sure they don’t cost that much and I can order them so they’ll be here in a couple days.
     

    Attached Files:

  13. Audioguru

    Audioguru

    2,832
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    Sep 24, 2016
    Did you measure the battery voltage as the LEDs were slowly dimming?
    The dimming was caused by the small overloaded batteries dying.
     
  14. bertus

    bertus Moderator

    689
    240
    Nov 8, 2019
    Hello,

    You are clearly abusing the little CR2032 batteries:

    CR2032 data.png
    Your led can draw 170 mA, as the battery data states a maximum discharge current of 3 mA or pulse discharge of 15 mA.

    Better look for other more powerfull batteries.

    Bertus
     
    Richmrf likes this.
  15. Martaine2005

    Martaine2005

    2,751
    742
    May 12, 2015
    Those LEDs are designed for 12v and advertised to replace the interior dome light. Which is of course for illumination.
    IMHO, you will be better off using different LEDs to suit your project. You can then design them smaller and less power hungry. You do not need 12v LEDs as you are not powering them from the vehicles 12v battery.
    For the sake of simplicity, try repurposing a cheap LED torch or cheap bicycle light.
    Either way, change the batteries or LEDs.

    Martin
     
    Richmrf likes this.
  16. Richmrf

    Richmrf

    10
    0
    Jun 13, 2020
    Is their a way for me to use 2 AAA’s? If so, what else would be needed to make the 3V step up to 12V? I would imagine I could use a fixed V step up converter. I have only found variable/adjustable converters on amazon. I figured if the make a fix voltage converters they would take up less space.
    In short, could it be run off of 2 AAAs? What other components are needed?
     
  17. Richmrf

    Richmrf

    10
    0
    Jun 13, 2020
    I didn’t measure the dying voltage.
     
  18. Audioguru

    Audioguru

    2,832
    634
    Sep 24, 2016
    Two AAA batteries make 3V only when they are brand new. Their voltage begins dropping the moment you start using them.
    A voltage boost converter might not work when the battery voltage is only 2V or less and since the LEDs use Power then the battery current will be much higher then the voltage will drop much faster.

    AAA batteries are small with low capacity so you will see the LEDs dimming but a little slower than with the CR2032 batteries.
    Depending on how many LEDs you use and how long you want the LEDs to be bright, you might need eight AA alkaline batteries.
     
  19. WHONOES

    WHONOES

    887
    218
    May 20, 2017
    Perhaps a joule thief may be suitable. It is a simple circuit that will increase the voltage available from a AAA battery and could be used to drive you LED string. I think the joule thief has been dealt with a number of times on this forum. You could also use a small LiPo battery in conjunction with the joule thief. LiPo's have a higher energy density as well as a higher terminal voltage.
     
  20. bertus

    bertus Moderator

    689
    240
    Nov 8, 2019
    Hello,

    The AAA batteries would last about 4 to times longer when you take a alkaline type.

    AA verus AAA batteries wiki.png

    When using AA you will win a factor 2 again in comparison with the AAA.

    You could use a boost converter with a MAX668.
    Have a look at the figures 2 and 5 of the datasheet.

    Bertus
     

    Attached Files:

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