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solar garden lights improved after wintering outside

Discussion in 'Electronic Components' started by legg, May 19, 2005.

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  1. legg

    legg Guest

    There are two different brands of garden lights with differing
    internal construction, components and battery brands, sitting in the
    garden outside our kitchen window.

    In the first summer of operation, I was dissapointed to see them
    dimming after only 3 hours of post-sunset illumination, even on the
    brightest of days. I even modified one, so that the LED's schematic
    position didn't arbitrarily limit the charging voltage, without any
    noticeable improvement.

    This spring, after spending the winter entirely submerged in snow,
    they all illuminate for at least 8 hours after sundown, even after
    relatively gloomy charging days.

    Anyone care to speculate on this beneficial aging effect in the
    generic solar light product?

  2. My best guess: The LEDs are less conductive at lower temperatures.

    Try finding their associated resistors and replace the resistors with
    ones of higher value. Fair chance this does not dim the LEDs too much.
    (BEWARE - LEDs not only become less conductive or require more voltage for
    a given current draw at lower temperature, they also produce light more
    efficiently at lower temperature. Temperature sensitivity of efficiency
    of producing light is worst for red, orange, yellow and
    chartreuse-yellow-green ones, less bad but maybe significant for white
    ones, and more insignificant for ones that are non-yellowish green or

    - Don Klipstein ()
  3. I've been playing, er, experimenting with the old Weston light meter and
    measuring the light of the LEDs I put on the PS 24/7 on May 1. I've
    already noticed the decline in light output over just a few weeks, even
    tho I couldn't tell this with the naked eye.

    The reason why I bring this up is that your garden lights may be putting
    out less light, and this may be the reason why it is lasting longer than
    before. The way to know this is to measure the current drain during
    discharge. If it's substantially less than before, then your garden
    lights are really just putting out less light for longer. And you're
    not noticing the decreased light output.
  4. "Watson A.Name - \"Watt Sun, the Dark Remover\""
    Did the current drop over time as the light output decreased?
  5. We went thru a good discussion here on what circuit to use for such a
    mockup, and I settled on a constant voltage source of 5.1V for the bases
    of all 5 transistors, and a 220 ohm resistor in the emitter of each
    transistor, which has 4.44V across it, giving 20mA. The LEDs are the
    collector loads of each transistor, so each LED has 20mA current thru

    BTW, each 220 ohm resistor measured about 4.44VDC at the beginning, and
    they still measure that now.
  6. "Watson A.Name - \"Watt Sun, the Dark Remover\""
    I'm not sure you answered the question, though maybe this hint at the
    end tells us something.

    The OP asked why his lights last longer, you responded that light
    output may decline, but unless the current drain declines as well, the
    runtime isn't going to change, is it?
  7. I guess what I was referring to was as clear as mud. :p The OP may
    not notice with the naked eye that the LED brightness is less than when
    the lights were originally installed. So a reduction in current and
    brightness may not be apparent to his eye, and may be the reason for the
    longer runtime.
  8. legg

    legg Guest

    Don, this is a permanent (~) change, present even now that spring is

  9. legg

    legg Guest

    I agree.

    Either the current drain in the circuit is noticeably reduced or we've
    found a new reason to stick NIMH batteries in the freezer, to 'form'
    Cold is traditionally the bugbear of electrochemical devices. Solar
    cells don't like it either, while it is present.
    The circuit uses no other parts that are permanently affected by low

    I guess I'll pull the modified unit, to see if any recorded operating
    data has changed.

  10. I would say that other parts can be permanently affected by changes in
    temperature, especially temp swings that are greater. One change, even
    tho it may take a long time to occur, is when temperature changes cause
    semiconductors to creep internally due to uneven expansion and
    contraction, which can cause bond wires to separate, or chips to crack
    or pull away from their heatsink.

    And according to the bathtub curve theory, many of those early failures
    are supposed to be caught during production burn-in. But some companies
    may not do a proper burn-in, or do any burn-in at all. So the customer
    ends up as the burn-in guinea pig. :-(
  11. ehsjr

    ehsjr Guest

    legg wrote:

    Another possibility that hasn't been mentioned, probably
    because it is so remote: the solar cells are now putting
    out more energy because the snow washed something off the
    sun facing surface.

  12. legg

    legg Guest

    The components are are all two or three-wire. Construction of the two
    device types is completely different. The phenomina is identical and
    is exibited in all devices.

    If this is a guinea pigs reward for abusing the device, its an
    atypical one.

  13. Check these out.
  14. Chris Jones

    Chris Jones Guest

    Actually the maximum power point on the I-V curve of a solar cell occurs at
    a higher voltage when the temperature is low and so the efficiency is
    better when the solar cells are cold.
  15. legg

    legg Guest


    It's midsummer, and they are back to their usual performance, lasting
    less than three hours from sundown.

    I suspect that there's just less light to collect out there, once the
    neighbourhood trees are fleshed out with leaves. Though a signifigant
    proportion of those nearby are evergreen, these have greater blocking
    characteristic for a northernly oriented sun's path.

  16. ehsjr

    ehsjr Guest

    Try washing the lens to see if that improves things.
    Doubtful, but worth a try.

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