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Homework Help: How to wire an emergency flashlight?

  1. Dec 14, 2017 #1
    1. The problem statement, all variables and given/known data
    I plan on wiring an emergency flashlight to power an led. It must be able to store charge without batteries, generate charge and create a light.

    2. Relevant equations
    None, at least for now

    3. The attempt at a solution
    I was planning on following this diagram and modifying it to follow the following instructable
    chargeCapacitortolightLEDschematic.jpg
    http://www.instructables.com/id/Rechargeable-flashlight-without-batteries/

    The reason I was planning on following that diagram is because the intsructable does not explain the steps as well as I would like nor the end resulting circuit. I am gonna get the parts from scrap electronics so I do not know what the capacitance and such will be, so lets assume I get parts that work together if wired correctly. Could I add in a several capacitors in place of the single capacitor in the diagram and get the same result, and replace the 9 volt with a stepper motor and use a rectifier diode between the capacitor and the resistor. Also could I add mini solar panels into the circuit to charge the capacitors while the led is off or on and how complicated would that be.

    Also if it is not clear I know virtually nothing about circuit diagrams and electronics so please try to dumb it down for me, and spell out what parts are what if you create a circuit diagram to show me what I could do.
     
  2. jcsd
  3. Dec 14, 2017 #2

    mfb

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    Even a 1 F capacitor will discharge within minutes. If you want to store energy in the capacitor for a longer time you'll need a switch at the LED as well.
    If you are willing to put in many large capacitors, you could equally put in a battery. That lasts much longer.
     
  4. Dec 14, 2017 #3
    I know capacitors can't store charge as long as a battery but I'm not allowed to use batteries, which is the only reason I plan on using capacitors. So other than what you mentioned is there anything else I should know?
     
  5. Dec 14, 2017 #4

    mfb

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    At least to me it is unclear how this thing is supposed to be used.
     
  6. Dec 14, 2017 #5

    Nidum

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    The article is about a flashlight which uses power stored in a bank of capacitors . The capacitors are charged as often as needed by hand cranking a small built in dynamo .
     
  7. Dec 14, 2017 #6

    Nidum

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    In the diagram given in #1 above the 9V battery should be replaced by the dynamo .

    The article suggests using a salvaged stepper motor but really many types of small permanent magnet motor could be used . Ones sold for model boats etc would be suitable .

    Circuit would ideally have more protection for the LED's .
     
  8. Dec 14, 2017 #7
    Alright I was thinking I could salvage a stepper motor from a printer as well as capacitors from pcs and rectifier diodes from power supplies. And how would I wire a mini solar panel to it, could I just wire in parallel just after the motor in the diagram?
     
  9. Dec 14, 2017 #8

    mfb

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    Then the power of the solar panel would discharge via the motor. With a diode it might work, but you have to check the voltage of the solar panel.
     
  10. Dec 14, 2017 #9
    Alright, thanks
     
  11. Dec 16, 2017 #10

    Nidum

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    One of the problems of designing this type of flashlight is going to be how to make the selected motor work effectively as a dynamo . We'll come back to the electrics later - the basic difficulty is going to be making it turn fast enough to generate anything when you only have a relatively slow turning hand crank to drive it .
     
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