Getting Piezo Elements to Charge a Battery

Discussion in 'The Projects Forum' started by foreverfree, May 19, 2008.

  1. foreverfree

    Thread Starter New Member

    May 19, 2008
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    Hello,

    As part of my chemistry class, I am experimenting with using piezoelectric elements (the kind inside piezo buzzers) to charge a rechargeable battery (very very slowly). I have successfully been able to feed one of these elements' output through a rectifier and into a battery, and I'm wondering how I could most effectively hook a bunch of these elements together to get the maximum power output. Also, would I need a separate rectifier for each element or can I get by with feeding them all into the same rectifier? Thanks a lot!
     
  2. hgmjr

    Moderator

    Jan 28, 2005
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    Are you under the impression that these piezoelectric elements are able to output a voltage without any mechanical stimulation?

    hgmjr
     
  3. SgtWookie

    Expert

    Jul 17, 2007
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    hgmjr,
    this seems to be a popular topic recently since it was brought up on EDN.

    If people are in a noisy neighborhood, they can capitalize on that noise by generating electricity from it.

    Charging a battery may prove problematic, but charging a supercapacitor is relatively easy. Just use a Schottkey diode to rectify the current. Once the supercapacitor is charged up enough, you'll need someplace to dump the stored charge.

    So what do you want to do with the pent-up energy?

    This could be interesting.
     
  4. roddefig

    Active Member

    Apr 29, 2008
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    Just how big a capacitor are we talking about here? o.0
     
  5. hgmjr

    Moderator

    Jan 28, 2005
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    I see. So this is a novel approach to recycling noise polution.

    Very interesting.

    hgmjr
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    Big. Let's say, a Farad. Let's say we're talking about lots of piezos charging up lots of caps that are of around 1 Farad capacity.

    What are you going to do with all of that energy?

    You could be saving it.

    Heck, I might take some Piezo generators along with me on my next trip to the rifle range ;)
     
  7. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
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    Rock concerts could light themselves!:D

    Have a look at US Patent number 7365455
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    Absolutely!

    Search EDN for this exact title:
    "Harvest energy using a piezoelectric buzzer"
    It's in one of their latest PDF files (March 20, 2008) #6541376, available for free download. You don't even have to register. It's a small energy source, but it's worth considering.
    Here's a link to the article:
    http://www.edn.com/article/CA6541379.html?spacedesc=designideas&industryid=44217
     
    Last edited: May 20, 2008
  9. nanovate

    Distinguished Member

    May 7, 2007
    665
    1
    You can hook up elements in parallel also
     
  10. foreverfree

    Thread Starter New Member

    May 19, 2008
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    0
    Hi,
    Thanks for the link to the article. That's kinda what I'm thinking of doing, but just to clarify I'm planning on hooking up several of these piezo elements together in a place where they will experience mechanical force... What I'm wondering is what is the most efficient way to get energy from the element and/or if I can hook them together (like nanovate suggested.) What I'm not sure about is if the piezo elements are hooked together if they will cancel each other out somewhat. I've already experimented with using one and two elements to charge a battery, and I've seen that it takes quite a while to charge a single battery. However, if I could hook together say, twenty or forty of these elements, I believe I could achieve a reasonable charge time. I would like to find a way to use a single rectifier effectively for all the elements, and also if I'm charging a battery what additional circuitry would I need? I can also charge a capacitor, I have a few 10 Farad ones, if that is more feasible.
    Thanks!
     
  11. SgtWookie

    Expert

    Jul 17, 2007
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    As far as the most efficient way to get energy from the piezo elements - consider a sound-focusing element. If your noise source is coming from one particular direction, make a parabolic reflector, or perhaps a corner reflector.

    If you hook them directly together, the may fight each other unless they're all perfectly aligned. Use Schottkey diodes to rectify each one's output.

    Charging a capacitor is easy; you don't have to worry so much about the charging rate, as long as you don't get too outlandish with it. Large electrolytics will start leaking current when you charge them up more than half their voltage rating.

    There have been very large volumes written on battery charging. Different battery technologies require different charging methods. What's good for a lead-acid battery might kill a different technology battery quickly.

    But basically, you'd need a buck/boost circuit to get the voltage high or low enough to provide the proper charging rate for the battery you have in mind, and then taper the current off as the battery becomes nearly charged. Some types you need to monitor the temperature to ensure you don't overheat them.
     
  12. foreverfree

    Thread Starter New Member

    May 19, 2008
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    Hey,
    Thanks for the link to the article and schematic diagram, I have designed and tested a circuit based on the one in the article. This is really an obscure question, but for a given amount of mechanical stress what element will produce the highest amount of electrical energy? (I know that all elements have a characteristic capacitance, frequency, impedance, size, etc.) What should I look for in selecting an element to produce the most electrical energy?
     
  13. SgtWookie

    Expert

    Jul 17, 2007
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    Select an element which has a natural resonance of the frequency of the noise source.
     
  14. DC_Kid

    Distinguished Member

    Feb 25, 2008
    638
    9
    what about grabbing all that free RF energy from radio, tv, and private generators? but hold on, when you go to sell the energy someone will claim that the energy obtained was obtained from licensed bandwidth, sparking a big congress investigation and the fcc will be involved..... more regulation.. arrrggghhhhh.
    :)
     
  15. Externet

    AAC Fanatic!

    Nov 29, 2005
    761
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    I would say the piezoelectric elements can be connected in parallel to a single rectifier bridge IF they are all subjected to the same vibration and in phase. Otherwise, one's electrical output will 'deform' another in parallel.

    10 Farads capacitors will leak more than what a piezo can recharge.
    :)
     
  16. aashishkoshta76

    New Member

    Apr 10, 2013
    1
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    foreverfree this has been quite old. By this time you must have made your project. Please tell the details to me as i am also making the same project.
     
  17. Brownout

    Well-Known Member

    Jan 10, 2012
    2,375
    998
    Foreverfree is probably long gone. Too bad members don't share their acquired knowledge, especially after they've received help.
     
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