Dynamo > Battery, Battery > Bulb

Discussion in 'The Projects Forum' started by Thewildman, Sep 17, 2013.

  1. Thewildman

    Thread Starter New Member

    Sep 17, 2013
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    Hello people!
    I must confess this is the first time I have ever posted anything on this, or even posted anything on any kind of forum.

    I want to change my shed into a little workshop. But first, I need a source of light. I had an idea- we have a solar powered light that would work fine in the evenings, but it is near winter- the days will be short and gloomy. So, I plan to hook up a dynamo to a battery, charge it, then connect it to the light when the solar power is done.

    I know how to make a basic dynamo, and i know how to hook up a battery to a bulb that was not intended to be hooked up to a battery, but i am unsure and afraid of charging the battery with the (basic, cardboard-and-nail) dynamo- will it take years to charge, or will it melt the battery?

    A little help on how-to and what-to will be extremely appreciated by a hopeful future mechatronics student.

    Cheers guys!
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    There are many posts here on wind generation here and other sites.
    I assume you want to charge the battery this way, or do you have other means or rotating the dynamo in mind?
    Max.
     
  3. Thewildman

    Thread Starter New Member

    Sep 17, 2013
    2
    0
    Hello max, thanks for the reply. I'm hoping to simply hand crank it, so it would charge a battery or two that could power a small bulb for a while. Its more the connection between the battery and the dynamo that i'd like to know- do i need any resistors or capacitors to prevent my worktop being covered in acid?
    Cheers!
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    You would have to take some test to find out what your hand cranking resulted in?
    If working with 12v battery you should not go over ~14.5 - 15v Maximum.
    The other way is to get into regulation, is this a simple unregulated Dynamo?
    From what source?
    Max.
     
  5. wayneh

    Expert

    Sep 9, 2010
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    It's worth noting that even 100W of output by a human on a bicycle is getting in to the "athlete" range of power. Half of what the human delivers will be lost in charging and other inefficiencies. So it'll take a lot of cranking to give a reasonable amount of light for any time. Could be a good aerobics program.

    Where's the wildman? He's out in the shed cranking one out!
     
  6. #12

    Expert

    Nov 30, 2010
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    Start with, "How big". How big is the light (in watts). How long do you want it to run on battery power? How efficient is your dynamo?
     
  7. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Here's some numbers. I just installed some spotlights (Home Depot and others) that run on a 12 volts solar system. Each light takes about .2 amps. They are each very bright so let's assume you can use just one and point it where need be.

    12V is also convenient for batteries as you can get common and fairly inexpensive lead acid batteries to power this. So say you want to spend just one hour each night in your man cave. How long do you have to pump before you can play?

    The current capacity is simple: just .2 amps for 1 hour or .2 amp-hours (abbreviated AH). Power is 12V x .2 amps or 2.4 watts.

    Accepting wayneh's numbers a human is good for 50 watts (remember half gets lost to efficiency). At 12V that implies a current of 50W / 12V = 4.2 amps.

    To get .2AH from 4.2 amps you need to run it for just .2AH/4.2A = .48 hours = under 3 minutes

    So unless my math is off (and that's happened) you should be able to get this to work.

    Do keep in mind batteries do NOT like running on empty.
     
  8. wayneh

    Expert

    Sep 9, 2010
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    Hmmm, yes if you can live with a ~1W light, human power is quite practical.

    I'm getting to be an old geezer and can sustain ~200 watts for over an hour (on a bike, which is very efficient). A hand crank is much harder but if you only need to crank for a few minutes, it shouldn't be too bad.

    Now the question is, what are you cranking? I believe the standard bicycle bottle dynamo is 6W. Note how this is a few percent of the energy expended by the rider, ie. noticeable but not too big a drag.
     
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