Emergency Torch Runs Without Batteries

It’s always good to have a torch on hand for emergencies. Unfortunately, sometimes these torches can be forgotten, and wind up with dead batteries when you need them most. For those cases, this build from [techrallyofficial] is just the ticket.

Instead of a battery, the torch relies on a 1.5 farad supercapacitor to store energy. The body of the torch is constructed out of PVC pipe and fittings, and packs strong neodymium magnets inside. A coil of wire wrapped is formed around an old solder spool, which, when shaken past the magnets, generates a current. This is rectified with a series of diodes and charges the supercapacitor, powering the light.

It’s a classic design that is available commercially, but it’s one easily replicated in the home shop, too. It would make a great educational project, particularly as students would be left with a useful device to take home at the end of the lesson. We’ve seen others resurrect commercial builds with upgrades, too. Video after the break.

29 thoughts on “Emergency Torch Runs Without Batteries

  1. If you’ve got a sanding drum set, you might wanna check if one jams into the middle of the bobbin/reel you’re using before you bother making the bit for it. Also if you made that RPM counter from the other day it would probably just take a simple mod to the code to use it as a turn counter, if you want to know how many turns you’ve got on your coil.

    1. More thoughts (I wish you could just edit and add) … if you want this to be useful for longer than the learning experience, put heatshrink over that coil or mummify it in insulating tape, it doesn’t take much to chafe and snag them when they’re unprotected.

      Alternative ideas for the reflector would be the foil cups off mini fruit or mincemeat pies, or moritz icy choc cups or something. Or cut out of a larger pie tin. You could glob those in with hot glue, don’t really need the self adhesive stuff. But in that version, you’d want to leave the edge of the plastic showing to glue the lens to. Speaking of the lens, you might try a cheapy plastic magnifier on it… if you find another sleeve that slides over the end of the flashlight in a close fit, like a pill bottle or something, cut the bottom out, put the lens in that, then you’ve got an adjustable beam.

      I know the old hands can find a billion ways to mod it to their tastes and preferences, just like to drop some additional hints for the less experienced on these simpler projects.

      1. @RW ver 0.0.1 said: “I wish you could just edit and add”. Hah! This is Hackaday, you’ll die waiting for a comment editor. Heck, it took them YEARS just to allow posters to use CAPITAL LETTERS here.

  2. Shake lights were a big thing like 10 or more years ago. They fell out of favor fast because they are a pain to charge. I have both decent and low quality squeeze flashlights that are much nicer. Somebody could take one of them apart and mod the basic design to be 3D printed. It would still be old tech but it would be more useful old tech. The next thing will be putting an LED and an LM3909 on the flashlight so you can quickly find it in the dark… Oh, wait, that is more like 40 year old tech…

    1. While I don’t disagree on shake lights as such they do have their uses same as any other human powered light. Not everyone has the grip strength, co-ordintation etc to make use of every variety of them effectively, for accessibility this design is probably the king. My personal favorite is the hand cranked gearbox dynamo versions seems to be for me the best way to get high charge in short time, though the few I’ve had have all got the gearbox teeth shredded pretty fast (they were cheap though).

      Can’t say I think a huge amount of this build though, its a great demonstration of the concepts – all very visible. But that makes it a mediocre torch in practice, exposed coils being probably my biggest dislike of this design., followed by the switch fitting bound to get broken both of them.

        1. Indeed, though if you can get commodity motor/generators that work for similarly fast charge power without a gearbox is the question, not if it works at all. Better off just making some decent metal geared version if not as you want the charge phase to be pretty quick within the normal human range for cranking speed and force.

          I suspect the rare-earth magnet boom in small quad motors and the like means backdriven directly motors would work pretty well now, but I’ve not run the numbers at all. Even if it does work well I suspect you would want to add a gearbox because its easier to apply more force than spin a crank faster by hand. Especially as the force needed to backdrive one of those motors isn’t going to be that high so once you add in the crank handles mechanical advantage…

      1. I have some of the fold out crank ilk as well, the thing I like about the squeeze ones is you can use them when the batteries are dead. It is not hard to squeeze them and point them at the same time. The crank ones charge up pretty quickly but they do require you to stop what you are doing to crank them. The shake lights were IMHO just a novelty unless you could come up with a way to holster them to you such as they shook every time you took a step. I think having it strapped on to you all the time would get old and a lot of people don’t do all that much walking anyway.

        1. Hmm that’s an interesting point. I always liked the cranked ones because a short blast of cranking gives lots of power and therfore long light duration.. But if you are not putting it down to use both hands I guess the constant squeeze type does make alot of sense.

          I wonder what an LED one would be like now anyway, the incandescent bulbs faded nice and gradually giving you time to go back to it as it ran out.. LED tend to just stop illuminating suddenly, that would be annoying trying to find your light source in the dark so you can get it going again..

      1. Yus there were some really crappy ones around with barely any coil and a weak magnet. Also well intentioned designs could suffer from the magnet having all the magnetism pounded out of it if the stops were too hard and it was the wrong kind of magnet.

      2. Yes, I got a counterfeit one myself, that seemed to be always charged….and shaking didn’t change anything. So I took it apart and found a hidden coin cell in it..the magnet wasn’t, the coil wasn’t wired to anything useful, it was all dummy “mechanical sample” parts, and it was just a battery/led light.

        I also had one of those squeeze-cranked ones. It was real but used an incandescent bulb, and the plastic gears quickly went south.

        Since I had no need for either…

    1. Blowtorch. Blow lamp is an old name, not heard it in ages.
      Propane torch if we want to be really specific that it’s not MAAP.
      And with the weather we’ve had round here recently, they also get called “cigarette lighters”…

  3. Sales may have been affected by the joke-stigma of charging it.
    I hope that the pipe has thin walls and the spool (or wind direct on tube) could be very thin such as using glue soaked cardboard or sheet plastic glue coated coil winding. The thinner the space between magnet and coil the more charge current. A way to use a smaller cheaper magnet or less wire.

    1. I have one that just has a full wave bridge rectifier connected directly to a tiny NiCd battery. For the LED there’s a resistor in series with it and a switch.

      The magnet in it is pretty powerful. Tip the light up on end and the magnet *hovers* inside the coil. I’ve though about making a mount for it in my car that holds it like that so all the jostling that happens while driving will wiggle the magnet up and down to keep it charged.

      1. >it’ll empty most of the energy from the capacitor. Even when the capacitor’s voltage falls below the LED’s forward voltage.

        Is that what they do? I thought they played piano man over and over with out paying royalties.

        Oh, never mind, that’s a joel thief I am thinking of…

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