Doubling up on the USB supercap flashlight

[Antoine] wrote in to let us know that he soldiers on with his flashlight project. He’s doubled up on the supercaps and tripled the LEDs (translated).

The core concept has stayed the same since the original version. He wanted a flashlight that was small and used no batteries. This iteration came about as he looked at increasing the light output of the device. He’s switched to some warm-white LEDs which are easier on the eyes, but was unhappy with the charge life now that he’s using current at a faster rate. The solution, of course, is more potential from the capacitor. He’s now using two 10 Farad caps in parallel. We are a little skeptical about his capacitor theory and ended up using this lecture to defog the issue of parallel and series capacitance.

The upgraded hardware is right at home in that plastic egg like you’d find in a coin-op trinket vending machine. You’ll see there’s still a colored LED to warn when the charge is getting too low.

Comments

  1. Indyaner says:

    plastic egg like you’d find in a coin-op trinket vending machine

    In Europe we call it Kinderüberraschung. I guess you had to talk around it as they are illegal in the US?

    • RooTer says:

      https://en.wikipedia.org/wiki/Kinder_Surprise

      illegal wtf USA :F

      I wonder does that make this flashlight illegal in USA too?

      • Marshkillz says:

        Evidently our lawmakers believe the general population is incapable of discerning tasty chocolate from inedible hard plastic…
        Ive kinda wanted to build a high powered version of this with one of those 30~watt leds.

      • ScottInNH says:

        >I wonder does that make this flashlight illegal in USA too?

        You must ask this question aloud, really?

        The US regulation is about embedding non-edible items inside of an edible item.

        So.. to answer your own question, you needed only to have asked yourself if the flashlight case were made out of food. Is it?

      • Dax says:

        If you give a small child one of those things, the first thing they do is they put it in their mouth and chew on it, and they’ll keep chewing on the plastig egg as well, which contains small items that are a choking hazard. For adults too, it’s not readily apparent on the outside that there’s plastic on the inside because it’s covered in chocolate.

        I’m surprised they do allow this kind of a product in Europe. It’s like putting a rock inside a candy and then going “sike!” when someone breaks a tooth on it.

      • tehnoo says:

        …I don’t get it… pretty sure I see Kinder Surprise eggs at the grocery store all the time (I’m in the US). I got one probably a year ago, it had some monkey thing inside.

        And non-edibles inside food items? What about fortune cookies? Those are everywhere…

    • Jax184 says:

      It is clear to me that you have never seen a Kinder Surprise toy in person. We have them here in Canada and I enjoyed many of them as a child.

      First off, they’re a large thin shell of chocolate with the plastic case rattling around inside. You can hear and feel that there’s something inside when you pick it up.

      Secondly, It’s not possible for a child or even many adult to fit the entire chocolate egg into their mouth whole.

      Thirdly, you only need to squeeze it a tiny bit for the chocolate to break apart into pieces and reveal the plastic toy capsule inside.

      So there’s absolutely no risk of someone putting the chocolate in the mouth and chewing on it until they hit plastic that they didn’t know was there. It just doesn’t happen.

      • Malikaii says:

        Many people thought the same applied to people like the dumbass woman who sued McDonald’s for the hot coffee burning her. Look what happened with that. People are stupid (in general), and a lot of them are just looking for a way to make a quick buck. I can see someone just biting into this thing blindly and then suing because they didn’t read the label, or pay attention to what they were eating.

    • Elias says:

      You probably mean in Germany…

    • No One says:

      As another poster has stated, putting a toy inside an edible container is against regulations.

      However, what we do have in the US are vending machines that contain toys in plastic eggs. This is exactly what the OP referenced and is not an attempt to “talk around” anything.

  2. Dax says:

    The colored LED is there to tell that you should stop charging, because there’s no other overvoltage protection in the circuitry.

    • Dax says:

      And the reason why you need to stop charging as soon as the LED comes on is because the series resistance will eventually let 60 mA through the diode when it should be less than 20 mA, so if you forget to plug it out, the LED will burn and the capacitors will get overcharged, and the whole thing goes pop.

      • ScottInNH says:

        There’s a lot I don’t understand here, but couldn’t the same transistor logic that turns on the colored LED… instead be used to disconnect the input power?

        (If the LED’s not sufficiently accurate, then I amend my question by substituting an appropriately accurate diode in place of the LED. I’m assuming there are diodes or transistors that activate at a current level rather than voltage.)

      • Dax says:

        There is no transistor logic to turn on the LED. It’s like a hole on the side of a bucket: when the water level reaches the hole (2.2 Volts which is the treshold voltage for the LED) it starts flowing out and the level won’t rise any more.

        The problem is, that the LED can only handle about 20 mA of current before it starts to overheat, and when it does it eventually burns, which is effectively plugging the overflow hole.

        You could use a couple LEDs in parallel, but because LEDs are always slightly different, one of them is going to turn on before the other and get the full current, and they’ll just pop one by one.

      • Dax says:

        That’s also the reason why the guy’s solution with the three LEDs on the output is just going to have two of the three LEDs burning dimmer that they should, because their treshold voltage is higher.

        The design is just all sorts of messed up.

  3. Pup says:

    I see that Kinder egg toy capsule. :)

  4. EccentricElectron says:

    Why has Antoine got such a downer on batteries?

    • Dax says:

      They wear out easily in intermittent use, are always empty and take a long time to recharge just when you need them.

      Of course you could use a small 50 mAh lithium battery, but it would have a shelf life of only couple years, and if you don’t recharge it occasionally it dies.

  5. Ed says:

    The trick I use to remember how capacitors behave in series and in parallel is to recall how resistors work. Capacitors work in the opposite way from resistors, so while resistors add in series capacitors add in parallel. The math is the same for resistors in parallel as it is for capacitors in series – basically the sum of the ratios.

    • andar_b says:

      THANK YOU. I was gonna type that.

      Just had to explain it to a half-dozen of my classmates last week, AFTER the professor said it several times. :s

    • Dax says:

      Of course, if you actually understood how capacitors work you’d know it intuitively.

      Capacitance is surface area divided by distance.

      Adding them in parallel increases the surface area of the plates, while adding them in series gives you a bigger gap.

  6. LG says:

    Wow very sad that people have trouble with capacitors in parallel, im sure that’s high school stuff. Are the ease of use of arduino’s and prebuild protoboards etc causing people to skip the fundamentals?

  7. Stripe says:

    A better solution that doesn’t destroy the green LED to overcurrent: http://www.dumpt.com/img/viewer.php?file=njzoorv4xw9aybf6r0ir.png

  8. conundrum says:

    Another related trick to make a ghetto constant current.
    Locate a surplus electret microphone from a broken phone etc, remove the casing and then short the centre (gate) pin to either of the remaining pins.

    I found that this gives a constant current of between 5 and 30 mA depending on the fet used, but only works correctly in one direction.

    (test with cheap/unwanted diode first!)

  9. space says:

    Original joule thief circuit can be modified to run several LEDs connected in series. This ensures equal current on all the LEDs but does not stabilize the current, ie currnt will dorp as capacitors discharge.

  10. Roger Wilco says:

    i remember “wonder ball” in the us a ball of chocolate with a toy in plastic egg inside, dont know if they still sell it but the ones that dont have chocolate i see all the time in supermarkets and other stores.

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