Joule Thief - solar garden light

Discussion in 'General Electronics Chat' started by aaad2, Oct 20, 2012.

  1. aaad2

    Thread Starter Member

    May 30, 2012
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    I would like to make this circuit:
    [​IMG]

    the circuit diagram is from this website:
    http://www.evilmadscientist.com/2008/simple-solar-circuits/

    I can get all the parts apart from the toroid bead/core.
    I know you can probably buy it from the Internet but it is not cheap and I want to keep the price to a minimum.

    For people who do not know what a joule thief is:
    http://www.instructables.com/id/Make-a-Joule-Thief/

    So I would like to know if this would work for other things such as a nail?
    Does it have to be a magnetic core/bead? or does the core has to be made from Iron?

    Thanks in advanced and sorry for blabbering on.
     
  2. Jaguarjoe

    Active Member

    Apr 7, 2010
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  3. bug13

    Well-Known Member

    Feb 13, 2012
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    You can make one yourself easily following the instructable, or get one from old pc power supply, motherboard, energy saving light bulb or any old electronics, size is not critically important.

    Ps: do follow the safety step requirement when opening old electronics etc.
     
  4. acmefixer

    New Member

    Aug 4, 2011
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    No, the coil core can be made of air. The coil can be made from two 16 foot or 5 meter lengths of 24 AWG or 0.5mm wire wound bifilar (at the same time) onto an AA cell, which is then removed and the coil tied with wire ties, tape or even dental floss. This works okay, and is cheaper than using a toroid. But it's much larger and bulkier. You can see one here that I made from cat5 wire.

    The circuit you chose uses a 2N3906 to turn on and off the current from the AA cells, this can be more than 200 mA which is more than the maximum allowed for a 2N3906. Even a BC327 will have a difficult time. To fix this. move the top lead of the right side winding connected to the collector to the emitter (plus). This reduces the current through the 2N3906 to only the base current of the 2N3904, which turns the 2N3904 off. But the first thing you should to do is replace the anemic 2N3904 with a decent transistor such as the 2N4401, PN2222A or BC337.
     
  5. takao21203

    Distinguished Member

    Apr 28, 2012
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    Nothing beats my Joule Theifs.

    And what do you want, if you are desperate enough you can use an EMI filter.

    There are 100s of variants for these kind of circuits, including circuits which use 2 coils. Some need particular coupling or phase, while others don't.
     
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  6. BMorse

    Senior Member

    Sep 26, 2009
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  7. Wendy

    Moderator

    Mar 24, 2008
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  8. aaad2

    Thread Starter Member

    May 30, 2012
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  9. aaad2

    Thread Starter Member

    May 30, 2012
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    Hi, For the circuit that I will be making(when I get the parts together :) ), I will not be using a 4.5v solar panel, I was thinking of using about 2.4v solar panel and 1 1300mAh battery. This allows it to charge all day without problems.

    Another thing is that I will be making many of these, not just one.

    I used to have some garden lights but I broke them(lawn mower - dont ask...)

    when I opened up their circuit, it was very simple, a blob of black stuff(controls the circuit), resistors, 1 tiny solar panel, 1x AAA battery and 1 LED.

    So which transistors do you recommend me changing to now? Or should I just stay with the ones from the circuit diagram?

    Thanks
     
  10. aaad2

    Thread Starter Member

    May 30, 2012
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    Furthermore, I have noticed that some of these joule thief is made from bare wire while others have a pastic coating (normal wire without plastic coating being stripped off).

    Is there any difference(e.g. current etc...) in these techniques used?
     
  11. takao21203

    Distinguished Member

    Apr 28, 2012
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    Get a defunct CFL somewhere. Twist off the metal shielding from the socket using pliers. Pretty easy. They contain a small toroid core, which should be great for a joultheif.

    If you can't buy them inside the UK, most electronic appliances have some kind of EMI filters inside them. Even some USB cables have one! For sure most people have old USB leads that don't fit to anything anymore.

    There are many electronics people in the UK, for sure someone has extra cores and can send them to you. Maplin does not have toroid cores as such.
     
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  12. Audioguru

    New Member

    Dec 20, 2007
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    Bare wire is not used to make a transformer or an inductor. It will short the circuit. Instead the wire has an enamel coating as its insulation.
     
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  13. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    I've delved deeply into garden lights, that's not what is inside them.

    You are correct there is a 1 tiny solar panel, a battery, and a LED.

    That's not a resistor, it's an inductor.

    That blob of black stuff that controls the circuit is an IC. Should you find one with the discrete device it has 4 leads. However, I have never found a vendor for that device and I do not have any handy to read off the number.
     
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  14. Wendy

    Moderator

    Mar 24, 2008
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    Any simple low power oscillator will work, but it needs to be a square wave to generate the inductive kick (that converts voltage to current).
     
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  15. aaad2

    Thread Starter Member

    May 30, 2012
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    So for the circuit that I will be building, do you recommend me changing anything?

    One of the one person recommended me to change the transistors but I then mentioned that I will be using a lower voltage solar panel(about 2-2.4v solar panel) with only 1x 1300mAH.[Something that is similar to the normal garden lights].

    I will be using a nail(possibly a very thick one) and wrapping around it with loads wires(with the plastic coating) <-- this will then be used for my 'joule thief' part!

    I will buy the transistors from ebay but not sure if I should buy the transistors from my circuit diagram (this links back to my question - should I change the transistors or use the ones the other person on this thread has recommended?)

    Thanks in advanced.

    Btw, you guys know sooooooo much about circuits :p
     
  16. Audioguru

    New Member

    Dec 20, 2007
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    A nail is a very poor inductor. The circuit probably will not work or if it does work then the LED will be very dim.

    A solar garden light uses a 400mAh or 600mAh Ni-Cad battery cell and a real ferrite core inductor. It lights the LED at night for about 8 hours following a sunny day in summer. The solar panel is too small to fully charge a rechargeable cell with a capacity more than 600mAh so half of your 1300mAh cell will be wasted.
    But the nail will waste most of the charge from the battery cell anyway.
     
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  17. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    This old post of mine has the schematic I drew from an old garden light. I did find these inductors on EBay for a good price, though never bought any.
     
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  18. aaad2

    Thread Starter Member

    May 30, 2012
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    just to be clear, anything can be used to make the toroid part of the joule thief, but would have an effect on the intensity of the LED.

    a toroid made of air: low LED intensity
    magnets, ferrite, iron: High LED intensity

    Am i correct? :)
     
  19. bug13

    Well-Known Member

    Feb 13, 2012
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  20. Audioguru

    New Member

    Dec 20, 2007
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    No.
    A ferrite core torroid is supposed to be used because it is designed to be a good efficient inductor for the fairly high frequency. A nail is a joke, and a poor inductor.
     
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