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"1.5V AA" 3 months continuously night lamp

Discussion in 'General Electronics Chat' started by TDA2030, Nov 5, 2009.

  1. madhippiescientist

    madhippiescientist New Member

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    It was simply another suggestion, and
    those "camera" type batteries, I believe,
    are NiMH and have a pretty good AH, for
    their size.
     
  2. audioguru

    audioguru Well-Known Member Most Helpful Member

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    We are talking about primary alkaline battery cells that have the same capacity as a charged Ni-MH cell.

    I don't think anybody uses an old carbon-zinc or a low capacity Ni-Cad battery anymore.
     
  3. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi again,


    I am still in favor of using two or three batteries rather than one with a converter.
    I have done lots of tests with white LEDs and batteries and have found that there
    are two ratings for a battery (this has been known for some time however)...
    one rating for when the battery is used 'normally' under more typical uses like
    flashlights and medium to high current draw, and another rating for VERY low
    draw applications like what you would see with a white LED running with very
    little current. The capacity actually comes out much higher when the current draw
    is much much lower than 'normal' so the run time actually goes up again because
    of that factor alone. That can get us more hours with the same battery.

    If the LED is to be turned on and off in order to save even more power, then
    another idea is to simply use three batteries in series and a circuit that is designed
    just to turn it on and off rather than a converter. This can be made EXTREMELY
    efficient, using a mosfet as the switch element of course and mosfet or lower power
    microcontroller circuitry.
    As an example, i have a temperature monitor using a uC chip and LED that can
    run two years on two AA cells.
     
  4. dave

    Dave New Member

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  5. mneary

    mneary New Member

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    I agree with MrAl. Circuits which rely on parts to work properly at half their minimum voltage are curiosities. Maybe you build one and it sort of works but reproducing it is another matter.

    Putting it on the web, to trap newbies and make them struggle, is just plain cruel.
     
  6. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Nearly all solar garden lights use a single 1.25V Ni-Cad cell, a simple cheap voltage stepup circuit and a low voltage cheap solar panel.

    Instead if they used three fairly expensive Ni-Cad cells and a much higher voltage solar panel then their cost would be too high.
     
  7. mneary

    mneary New Member

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    That's not my point. They don't use a 2 volt 555.
     
  8. audioguru

    audioguru Well-Known Member Most Helpful Member

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    National Semi guarantees that their LMC555 will work with a supply as low as 1.5V.

    I made some LED chasers with 74HC4017 ICs that are guaranteed to work when their supply is as low as 2.0V. They all work perfectly when their supply is only 1.4V (but the red LEDs are very dim).
     
  9. karthiks

    karthiks New Member

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    current drawing is 500 micro amp

    HELLO. Hey you say that the circuit consumes about 500 micro amps how did you come up with that number? well the led draws 20mA of current right? then how 500 micro amps
     
  10. karthiks

    karthiks New Member

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    Audioguru, would please help me out
     
  11. karthiks

    karthiks New Member

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    HELLO. Hey you say that the circuit consumes about 500 micro amps how did you come up with that number? well the led draws 20mA of current right? then how 500 micro amps
     
  12. karthiks

    karthiks New Member

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    HELLO. Hey you say that the circuit consumes about 500 micro amps how did you come up with that number? well the led draws 20mA of current right? then how 500 micro amps
     
  13. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The LED is turned off for most of the time. The Cmos 555 charges the capacitor slowly with an extremely low current then connects the capacitor in series with the battery to blink the LED with maybe 5mA for a moment until the capacitor has drained. Then the LED turns off and the capacitor charges slowly again.

    The average current from the battery is 500uA.

    My LED chasers blink each LED at a very bright 25mA for a moment. Their average battery current is about 200uA. The AA alkaline cells battery lasts for months.
     

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