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Battery operated micro LED lights

Discussion in 'General Electronics Chat' started by jellyring46, Aug 31, 2017.

  1. jellyring46

    jellyring46 New Member

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    I am trying to marry up solar light battery and solar cell to output to a 50 string Led micro light string. After experimenting with smaller strings I tried to measure current drawn with a fluke meter however in setting up range to milli amps I could not get a reading. Is the current really that low that meter cannot percieve current drawn? How can i find the spec on this manufactured item to calculate current draw? thanks!
     
  2. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi 46,
    How many leds in your shorter test strings.?
    What colour are the leds, different colours have different forward voltage drops.
    For general purpose leds, current approx 10mA to 20mA.
    What is the rated voltage/current output of the solar cell/light battery.

    Need more info.
    E
     
  3. Reloadron

    Reloadron Well-Known Member Most Helpful Member

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    How exactly did you set the meter up? When measuring current the meter needs to be placed in series with the load. You should have seen something on the meter. Back to Eric's questions...

    Ron
     
  4. dave

    Dave New Member

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  5. audioguru

    audioguru Well-Known Member Most Helpful Member

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    A solar garden light uses one 1.2V battery to light a 2V red or a 3V white LED. Impossible? No, it uses an oscillating voltage stepup circuit so the LED pulses at the oscillation frequency. Your meter might not be able to measure the high frequency pulses.

    A colors changing LED has an IC inside that needs a fairly smooth DC voltage so a garden light with one of these LEDs also uses the voltage stepup circuit but it feeds a voltage peak detector that has an output capacitor as a smoothing filter.

    The 1.2 battery provides V x A power. When its voltage is stepped up then its current is stepped down. Then for 10mA in the LED at 3V= 30mW, the battery provides a little more than 30mW/1.2V= 25mA.
     
  6. jellyring46

    jellyring46 New Member

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    ok Thans for the responses.. here is a similiar product, https://www.wish.com/c/56220f0089f4...blu02dUPyYKGnhSGMr1pEisBc0Pp7R9gaAsneEALw_wcB
    The item I started to measure is an 18 led string 3' long powered by 2 AA batteries in series 3 V I cut wire on positive side at begining of string and set Fluke digital to measure ma scale and in series with cut lead to my surprise I did not see anything in this range which led me to question if I had my setup correct. I then tried to return side to battery holder by cutting lead and also got no measurable amount ... am I measuring incorrectly?
     
  7. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

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    With the meter in circuit, was the LEDs on or off? They had to be on or you would have said something.
    upload_2017-9-1_21-11-25.png
    Set the meter to "mA/A" and the probes in "com" and "mAuA" 200mA max.
    or
    Set the meter to "mA/A" and the probes in "com" and "A", to measure 2A
    Strange, my meter has a AC/DC button. If that is set to AC you can not see any DC current.
     
  8. audioguru

    audioguru Well-Known Member Most Helpful Member

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    18 LEDs use much more current than the single LED in a solar garden light, and AA battery cells provide much more current than the voltage-boosted AAA cell in a solar garden light.

    I have a solar garden light string sold last year at Dollarama (but not sold this year) that uses one AA Ni-MH cell, a voltage boosting circuit with high output current, a pretty large solar panel and about 12 LEDs.
    This year Costco sells a box of LED fence post lights that have 12 LEDs and a pretty large solar panel. I can't remember how many AA Ni-MH battery cells are in one and it is a nightmare to take apart and put back together.
     
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  9. jellyring46

    jellyring46 New Member

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    ahh didnt realize set to ac changed input to 10a instead of 400 ma now light and reads guess its been a while since i measured current and didnt think current draw would be so large measures .078 A 78 ma Thanks!
     
  10. audioguru

    audioguru Well-Known Member Most Helpful Member

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    78mA divided among 18 LEDs makes only 4.3mA for each LED. They will be visible in the dark but not in daylight.
    You will need a powerful solar light circuit and a pretty big solar panel. A 2300mAh AA Ni-MH cell boosting its 1.2V to 3V will light the LEDs all night long after charging in sunlight all day.
     
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