Hand Cranked Rechargeable Flashlight

Discussion in 'The Projects Forum' started by VA101301, Aug 16, 2016.

  1. VA101301

    Thread Starter New Member

    Aug 16, 2016
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    I need some help in constructing this device. I am a beginner in electronics and I have a lot of questions in my mind. I am planning to construct this using a bike dynamo and 4 AA rechargeable batteries. How will I be able to charge the batteries using the dynamo? Is it possible? How will I connect the dynamo, batteries and bulb all in one circuit? If anyone can answer it, it would really help. Thanks!
     
  2. wayneh

    Expert

    Sep 9, 2010
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    The first task is to determine the performance properties of the components. For instance what is the voltage and current capacity of the dynamo? Is it DC or AC? What do the light bulbs require? What is the battery chemistry?
     
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  3. VA101301

    Thread Starter New Member

    Aug 16, 2016
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    My dynamo produces 9V and the Batteries are 1.2 V NiCad AA Batteries. The dynamo is really built to power up bike lights so I thought that I can use it to power flashlights.
     
  4. hp1729

    Well-Known Member

    Nov 23, 2015
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    https://www.amazon.com/Powered-Flas...71410683&sr=8-4&keywords=survival+flashlights
    If the link works, here is what you can buy.

    How fast does your generator have to turn to get the voltage you want out of it?
     
  5. VA101301

    Thread Starter New Member

    Aug 16, 2016
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    I tried connecting a LED Diode to the dynamo. Cranking it with my hands produces enough light to power the LED diode. I do think it can produce the voltage that I wanted if I will be able to use gears or make a crank for the dynamo itself.
     
  6. hp1729

    Well-Known Member

    Nov 23, 2015
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    Super!
    Batteries or supercapacitors?How long do you need it to last on one charge?
     
  7. VA101301

    Thread Starter New Member

    Aug 16, 2016
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    Batteries. I need it to last for 20 mins of charge
     
  8. hp1729

    Well-Known Member

    Nov 23, 2015
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    Yep, batteries. Crank a lot. How much amperage does the generator put our. AA's? Maybe 2,300 mAhr, divided by the current the generator puts out ... may be 24 to 48 hours of cranking for a full charge. :)
    Super caps may not last you any where near as long for a charge but won't require that much cranking.
    Do you have room for a flywheel?
     
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  9. VA101301

    Thread Starter New Member

    Aug 16, 2016
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    That's a lot of hours of cranking maybe I'll just try to use
     
  10. VA101301

    Thread Starter New Member

    Aug 16, 2016
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    Super caps. Thanks for the help everyone! Really appreciate it.
     
  11. BobTPH

    Active Member

    Jun 5, 2013
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    Supercaps will not reduce the amount of cranking needed. The same energy is produced no matter where you put it.

    Bob
     
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  12. wayneh

    Expert

    Sep 9, 2010
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    And supercaps won't hold a steady voltage as they discharge. Forget 'em. You need a battery.
     
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  13. wayneh

    Expert

    Sep 9, 2010
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    That probably means it's a 6W dynamo. That level has long been used a compromise. It gives a decent amount of light without too large a drag on the rider. You feel it, but it's not excessive. Making 6W at 9V means you're making 2/3 of an amp.

    That 6W level was established before LEDs. If the dynamo was designed to a deliver a lower wattage to an LED system, it might not make nearly so much current.

    How many lights do you want to light? A single LED would give you the longest run time. If you want 2 or more incandescents, it will be a much shorter run time for a given amount of cranking.

    I'd consider using an LED landscape light circuit with a single AA. Charge with the crank dynamo, and you'll get a fairly long run time out of it. The boost circuit in the light will run the LED off the single AA battery. (AAA would be OK, too.) The single battery has more than enough capacity to store the cranking energy.

    Or, you might use an LED flashlight. I have a lot of those cheapo ones that use 3 AAA batteries and have something like 9 LEDs in parallel. Again, just put the dynamo in parallel with the batter pack to charge them up. You could even add another LED "head" to it, to get more light. Of course every LED you add reduces the run-time:crank time ratio.
     
    Last edited: Aug 17, 2016
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  14. hp1729

    Well-Known Member

    Nov 23, 2015
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    Super! Thanks. We will go with 9 V, 0.66 Amps. AA 2,400 mAh batteries only means 3.6 hours of cranking for a full charge. Still a lot of "hand exercises". He ought to look like Popeye in no time. :)
     
  15. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    And you guy's are forgetting the gear ratio that the bicycle generator is turning at. The small generator hub riding against the edge of a bike tire. You'd be hard pressed to turn a hand crank the same speed the generator turns in it's real application.
     
  16. wayneh

    Expert

    Sep 9, 2010
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    I was assuming a gearbox like they use in commercial crank flashlights.
     
  17. wayneh

    Expert

    Sep 9, 2010
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    The AA batteries in a solar light are often as little as 300mAh. But capacity is moot. He doesn't need to ever get to a full charge for it to work. With just a bit of charge, the voltage will come up to a workable level.
     
  18. Tonyr1084

    Active Member

    Sep 24, 2015
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    It's been years since I used one of those bicycle generators. Mine was AC. The hub (friction wheel) was about 3/4 inch diameter. Riding a bicycle at about 10 MPH would produce an RPM on the generator with a 3/4 inch drive wheel of about 4,480 RPM. At 10 MPH the light (incandescent) would be bright enough to be seen but not be stunningly bright. So if you're going to be hand cranking that generator using a gear ratio of 10:1 (ten rev's for every one turn of the crank) you'll have to turn that crank at 448 RPM. That's turning the crank 7.47 RPS (revs per second).

    Does that give you a little perspective on what to expect?

    Below are some numbers I used to calculate my figures. I'm fairly confident I got it right. But just in case I got it all screwed up (as I do from time to time) someone will be quick to point out my error. I welcome such pointers.

    2.3562 inch circumference of a 3/4 inch diameter drum (generator)
    63,360 inch per mile (5280 feet per mile multiplied by 12)
    26,891 revs per mile (rounded out)
    268,907.5 (revs per hour at 10 mph)
    4,481.8 RPM @ 10 mph (268907.5 ÷ 60)

    I'm also keeping in mind that using LED's is not going to require as much power as an incandescent bulb. Still, the TS wants to generate power to charge batteries. There - a whole lot of variables come into play, and I don't know the specifics to be able to calculate how much power will be needed and what efficiencies (or lack there-of) will come into play.

    Personally I think this is just going to be one heck of an exercise machine. Popeye forearms for sure. Or dashed dreams of creating something from scrap parts laying around.

    You might get better results from building your own generator. Smaller hub, higher RPM and voltages. Power - you can't get around that one. It takes so much power to produce so much power. No free rides.
     
  19. wayneh

    Expert

    Sep 9, 2010
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    It's pretty easy to just assume a 50% loss of power end-to-end going into and out of a battery. I'm sure folks like Tesla can do better than that, but just about any DIY system will likely be in that range. For instance even charging a capacitor at constant voltage loses half the energy.

    Now, the lights will also be powered directly by the cranking and so much of the lighting energy will not be lost in the charge/discharge process.
     
  20. BR-549

    Well-Known Member

    Sep 22, 2013
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    Throw away the crank. Buy a solar panel. Have a beer.

    No one is gonna charge a battery with a hand crank.
     
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