Retail Joule Thief available

Discussion in 'Off-Topic' started by #12, Mar 23, 2014.

  1. #12

    Thread Starter Expert

    Nov 30, 2010
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    This probably isn't news to most of the people here, but I find this retail Joule Thief so convenient and effective that I carry it in my pocket at all times, and you have to be something special to get a dedicated space in my pocket.

    I'm not advertising any particular brand, just posting public notice that this design is available and effective. It is bright enough to see small hazards where you are walking at night or to look inside a computer case to find the screws. I can't tell how long the AA battery lasts because I have not used one up in 4 months, and that's about being my first line of defense against dark spaces up to about 15 feet away.

    Pleas don't laugh at me. Some people might find this informative.
     
  2. Mickster

    Member

    Jan 10, 2010
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    That's kinda neat and compact, roughly half the length of the one I made for a friend, a few years ago......wonder if he is still using it?
    Mine had a tact switch at the opposite end from the LED and the whole body was made from Polymorph. The battery was held in a single AA ABS housing, in the middle and the Joule Thief circuit was just behind the LED, forward of the battery housing.

    For a personal pocket light, I have a Coast 7831, which is pretty small and convenient.

    What's the retail price on the one you have in the picture?

    Regards,
    Mick.
     
  3. #12

    Thread Starter Expert

    Nov 30, 2010
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    $6
    The switch is in it's butt, as yours was.
    Wonderful aluminum case with an o-ring for, "waterproof".
    The circuitry is just behind the LED, as yours was.
     
  4. Mickster

    Member

    Jan 10, 2010
    25
    11
    That's a pretty good price, considering the sleek design and waterproofing.

    My friend had very young children at the time and was talking (whining) about batteries going flat, from toys being left switched on. He'd stopped buying the branded batteries for the toys and used the cheaper ones, keeping the better ones for remotes and other things the kids were less likely to mess with and leave switched on.

    He had no electronic experience and was wide-eyed when the conversation turned to a use for his 'dead' batteries..... and thus his Frankenstein flashlight was born.

    I haven't seen him for quite a few years as he moved jobs and I moved countries. I should contact him and see how things are going. Thanks for the reminder #12!

    Regards,
    Mick.
     
  5. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    A joule thief will work down to a fraction of a volt. Have you checked the circuit or tested that?

    If you have a variable power supply you could try it at 1.5v then reduce the voltage and see where it stops working.

    (And my motorcycle toolbox has had a tiny waterproof 1 cell AA torch with grain of wheat bulb in it for about 15 years. ;))
     
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  6. #12

    Thread Starter Expert

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    Naw, it's one of those, "round tuit" things.
    I don't think I'll ever get around to it.
    I'll just wait until it quits and measure what's left.
     
  7. #12

    Thread Starter Expert

    Nov 30, 2010
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    Just to be fair, Here's another brand. It is built entirely the same way except the threaded section is at the rear instead of the front. Today, it's noticeably brighter than the one found at a flea market, but it's years newer and so probably has a better LED.
     
  8. #12

    Thread Starter Expert

    Nov 30, 2010
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    You need about .65 volts to get the flashlight to start. After it is running, it will suck a battery down below .1 volt, but it gets dimmer as the voltage goes down. It's really about useless for brightness, running at .7 volts.
    Not what I expected. I thought a joule thief circuit would keep a constant current going until the battery fell below a certain voltage, then suddenly stop.

    Who knows how a joule thief circuit works? I mean the dimming part.
    Did I just prove this isn't a Joule Thief?

    Also consider that I had about 2 feet of wire between the power supply and the contact inside the tube. That is a lot different from the positive end of a battery at high frequencies. Maybe the switcher is unhappy about the length of wire I used? Would that explain the dimming?
     
  9. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    No that's normal. The simple 1-tran inverter circuit doesn't have any form of regulation, so it's efficiency and power output to the LED both drop as the Vin drops.

    The clever part is that it can light a 3v white LED at all, from <1v Vin. :)
     
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