Faraday Flashlight for 7th grade Science Fair

Discussion in 'The Projects Forum' started by betsypie, Oct 12, 2012.

  1. betsypie

    Thread Starter New Member

    Oct 12, 2012
    My daughter is planning to make a faraday flashlight for her science fair, and from her current research, it seems she will need a magnetic wire, neodymium magnet, a rectifier (is it the same as a diode bridge?), a capacitor and an LED. I just need specifics:
    1.what kind of magnetic wire (thickness?),
    2.size of neodymium magnet (she wants to make a pensize flashlight, if it is at all possible)
    3.what kind of rectifier and capacitor (what is a 5.5 v IF electrolytic capacitor? had seen it in one of the websites...)
    4. what kind LED

    Also, would it matter what length the tube/pipe for the magnet is?
    She was also wondering what would happen if there are 2 or 3 separate set-ups of the coiled wire in a single pipe that the magnet will pass through (i would not even know how to connect them to the capacitor!) and whether 2 or 3 magnets can be put together to increase the amount of currency produced.

    This is for a 7th grade project and it does not need to be complicated. I was hoping to buy all materials and not make any capacitors/rectifiers (any suggestions on where to get them would be appreciated!) I would probably just have someone help with the soldering of any wires if needed.
    Just remembered about the switch as well - where does it connect in this system?

    Thanks for any information. The research proposal is due this Monday and I am in a panic!
  2. MrChips


    Oct 2, 2009
    I hope I don't come across as trying to be difficult. But I always take issue with Science Fair projects.

    Why are you in a panic? Is this your project or your child's project?
    The questions you ask are somewhat complex for someone who does not know the answers. Yet they are not as complex for those who know the answers. Shouldn't it be your child who should be asking the questions?

    Sorry, but I too have children who did Science Fair projects in school. I am a scientist and engineer. I gave my kids guidance but I left it up to my kids to tackle their projects on their own and to discover the answers for themselves.
    Biff383 likes this.
  3. Dodgydave

    Distinguished Member

    Jun 22, 2012

    Looks like its a simple Dynamo principle, the circuit is just a Capacitor, single diode(half wave rectifier), magnet + coil, led,

    the working model above has omitted the diode, i would use a full wave bridge rectifier, as when the magnet passes through the coil backwards the voltage from the coil will be reversed.

    Size of capacitor would be 1 Farad 5v, resistor say 330 ohms, diodes schottky or germanium low volt drop, and the best of luck with the coil and magnet size!
    Last edited: Oct 13, 2012
    betsypie likes this.
  4. wayneh


    Sep 9, 2010
    Use the smallest gauge you can work with without breaking the wire, so you can wind more turns. In higher current situations, you have to worry about the DC resistance of a thin wire, but in this application I think you want as much emf capture as possible, and more voltage will help overcome the voltage drop in the rectifier.
    Big (and high field strength) is better, but of course it needs to fit your coil and tube. A "close" fit will help. I believe the length should exceed the diameter, for smooth motion and for maximum field.
    Just about any rectifier will work. I'd use a full wave bridge, and for simplicity and size I'd just get one pre-made instead using 4 diodes. But 4 diodes would work fine too. If you want to optimize, schottky diodes have a lower voltage drop and would thus increase efficiency. Any high capacity electrolytic capacitor will work. More is better.
    Any "standard" LED will work. I mean the typical, 3 to 5mm LED that uses up to about 20mA. Look for high brightness. The ones I found on e-bay are many fold brighter than one I bought (for much more money) at the Shack. The brightness specs are often exaggerated and result partly from focusing the LED into a narrow beam, which would be good for this application.
    This depends on the mechanics of a human arm. I think a longer coil and a longer magnet might give more juice per shake, but it probably gets uncomfortable to use.
    I have some ideas about this, but these would be excellent experiments to run as part of the project.
    betsypie likes this.
  5. wayneh


    Sep 9, 2010
    I think the best way to determine the R1 value would be experimentally, since it would be challenging to predict. You need to measure the peak voltage that the device can put on the storage capacitor, and then size R1 to protect the LED at that peak. The user might shake violently for a while with the switch off. Turning the switch on at that point will expose the LED to maximum current defined by R1.
  6. chrischrischris


    Feb 18, 2012
    MrChips, I don't know the answer to the question above myself, however I'm with you. Kids do need to get a thirst for knowledge themselves in order to excel. Having said that, I've been guilty too in helping my kids on occasion more than I should. In retrospect, the bond was priceless, however I didn't really consider the consequences as I should have. On one occasion, one of my kids came up with the best piece in the "school"! Hmmm, that was a bit embarrassing from my part (yet my daughter did come up with the idea and did alot of the finer work - it was a face mask). Stepping back and letting them go forward on their own is sometimes really hard (especially when it's a subject you like yourself).
    betsypie likes this.
  7. wayneh


    Sep 9, 2010
    Parenting is a tightrope walk, and you never reach the end of the rope.

    IMHO, staying engaged IS important and can make the learning experience so much more effective. An adult can demonstrate the value of persistence, and how fun it is to work and to create. Children are often quite creative, but don't have a good feel for the realities of their plans. The adult can apply the wisdom of age to help sort out what can actually be done, and teach the skills of doing research, developing a strategy, and making a plan. There's still plenty of room for them to try things and fail. But without guidance, there is too much frustration and failure for most kids to overcome.
  8. betsypie

    Thread Starter New Member

    Oct 12, 2012
    Thank you all for the quick replies!
    Mr. Chips: I am on board with you with regards to letting our kids be independent. When my daughter came up with this idea, I had no idea what a Faraday Flashlight (or the concept behind the shake flashlight was!) so kudos to her research and initiative. I am, however, not at all versed when it comes to electronics (my forte is biology and the natural sciences - could not convince her to work with bacteria!), so when she came up with her project proposal and materials list, I had no clue how to advise her. I chanced on this website when I was trying to understand what a rectifier/bridge was for and why the need to convert AC to DC!
    Thank you for all the posts since now I have a better idea about what materials she will need, and how the project will proceed.
    Now here's keeping my fingers crossed that the LED light will light up!!
    I am hoping these materials would be easy to find as well...
    Wayneh: I think she would love to know the answers to her other questions, so I will keep you updated if she gets to work on them.
    If she does the 2 coiled wires in a set-up, can she connect both set-ups to a single capacitor?
  9. wayneh


    Sep 9, 2010
    Yes. I think they'd have to be in series. In parallel, one coil would "short" the one the magnet is passing thru.
    betsypie likes this.
  10. Sensacell

    Well-Known Member

    Jun 19, 2012
    Don't forget to vent the tube, or make sure air can pass around the magnet, you don't want the motion damped by pneumatic resistance.

    Compression springs at the ends help too, so the magnet can bounce back instead of stopping dead.
    betsypie likes this.
  11. Bernard

    AAC Fanatic!

    Aug 7, 2008
    I was going to say " look for a different project". as my shake flachlight was mostly powered by 2 non rechargable coin cells & would not flash a LED with out batteries, but just found remains- coil & magnet. On scope measured 10 V P to P- connected white LED & it flashes. Wire, .004 in, # 38 ?, 200Ω. Coil 1 in long, form .754 in dia. wound to depth of about .854 in dia. Tube .66 in ID, 4 in long. Magnet, .59 in dia X .66 long & stoing. Might use rubber bumpers as steel will grab the magnet. Do not think a resistor is needed.
    Last edited: Oct 14, 2012