energy harvesting

Discussion in 'The Projects Forum' started by flare09, Oct 11, 2013.

  1. flare09

    Thread Starter New Member

    May 17, 2012
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    Okay before you turn off your brains this isn't a 'free energy, maaannnn' post.

    I'm looking to power 4 leds rated for 2.9v and 5mA. The power source will be these bad boys http://www.nextreme.com/pages/power_gen/eteg_hv56.shtml

    I am estimating am average temperature difference of about 30°

    Now the problem I have is boosting the average .6v up to 3v.i found some ics that can do it with just enough components for the space requirement, such as the intersil isl9111a. But the minimum start up is .7v and only works down to .5v then it shuts off. Does anyone know of a lower voltage IC? Or should I try using a transistor/inductor circuit? Such as this one here

    http://instructables.com/id/Joule-Thief-no-IC-and-no-Transformer/

    I built that one and tried messing around with it but the circuit won't respond to anything less than .9v
    That one may work because the components available will be small enough to fit where I need,but it just won't respond.

    So my next question,how do I make a transistor respond to a lower voltage?reduce the 1K resistor value on the gate pin?or do I need a specialized transistor?

    Thankyou in advance for your input!
     
  2. ronv

    AAC Fanatic!

    Nov 12, 2008
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    There in lies the problem. The base emitter drop on transistors are around .6 volts so most circuits need at least that much to do anything. I've seen some with JFETs but nothing with any current to speak of.
     
  3. gootee

    Senior Member

    Apr 24, 2007
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    Last edited: Oct 11, 2013
  4. flare09

    Thread Starter New Member

    May 17, 2012
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    Ronv, the company that produces the peltier units micropelt, have a boost circuit that uses a super large inductor and a transistor. The part is ATF-55143. But the inductor is too big.

    And gootee,I have actually looked over that part,but it's too big. Possibly if I could get a smaller bga equivalent. And I am planning on putting 2 of the peltier units together to give me more power but I don't believe they work exactly like a battery since they will Start workinglike a normal tec if a current is applied.
     
  5. ronv

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    Nov 12, 2008
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  6. flare09

    Thread Starter New Member

    May 17, 2012
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    I like that LTC3105 actually. don't need much for an inductor, I can do 0402 and 0201 on the resistors and caps. only problem, mouser doesn't sell the chips, and digikey doesn't have the dfn in stock. I can buy from linear though I think... ill have to contact linear about the recommended circuit design
     
  7. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Those thermo generator modules spec says 36mW at 50'C, you might only get 10-20mW at your 30'C.

    Each of your LEDs needs 2.9v 5mA (14.5mW) and efficiency of a very low Vin boost SMPS is probably about 50%, so you will likely need two generator modules just to power one LED.

    How much do those things cost? For such a low power output, the cost of 4 generator modules might be more than 10 years supply of AA batteries... ;)
     
  8. ronv

    AAC Fanatic!

    Nov 12, 2008
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  9. flare09

    Thread Starter New Member

    May 17, 2012
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    I could run the leds at less voltage,and get the super low power 2mA ones. .. the micropelt units are 96 each on Mouser. .. and this is going inside a ring. The bottom would house the tegs and the top and some of the sides have the boost converter, components and leds.

    I would use a battery,but I would want it rechargeable. And I would prefer everything contained.

    I checked out custom thermoelectric, but micropelt has better units for the size requirement.

    Unless anyone can think of a better place for power supply...I considered a tuned circuit to pick up a cell signal, but probably only with the ring spey close during a call...plus dealing with tuned circuit that's a no. A thermo generator just seems the best option.

    I know the leds won't stay Powered the entire time, just when it makes contact with a cold surface
     
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