Thermoeletric Energy Harvesting problem?? URGENT.

Discussion in 'The Projects Forum' started by Theinsainepops, Oct 25, 2015.

  1. Theinsainepops

    Thread Starter New Member

    Nov 22, 2013
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    Hey Fourm
    My name is Elliott I am a senior in highschool and im currently working on a science fair project in which I will be representing my Highschool in state and national competitions. My project encompasses around the use of Thermoeletric Generators and energy harvesters and how they can harvest energy and take little amounts of energy and essentially boost it. But im running into a small problem with my circuit and im coming to this fourm for both help and guidance for the continuation of my project. Because as of right now im stuck and time is one of the things I dont have on my side. First and foremost my main question is... Is it possible to wire 2 energy harvesters in parallel to one another in order to produce a higher power rating. Basically harvesting the TEG power and that harvested power is being doubled by another harvester. What Ive tried is wiring my TEGs to a ltc3108 demo board harvester that I ordered from DIGIkey, now the harvester works to a degree. It seems to boost my power but it has no form of storage so I attached a 16v 450uf capacitor from its output VCC 3.3v and Gnd and the capacitor seems to store 3.3v continuously but doesn't seem to charge up more than that. Then I try to take that power and revert it into another energy harvester, that can supposedly take .80v-5v and harvest it to 5v. I treid wiring this all together and nothing happens. This is about 1 of 3 problems i currently have and I just want to get one solved at a time and go from there. Baisically what im asking is can anyone help me re configure my circuit so I can add the additional energy harvester!!?
    By the way im a newbie and taking on a topic that im trying to learn as much as i can about. So i apologize for the lack of know how and intellect as im currently teaching myself to the best of my ability.
     
  2. strantor

    AAC Fanatic!

    Oct 3, 2010
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    What is this you're calling a TEG? Can you provide a link?
     
  3. Theinsainepops

    Thread Starter New Member

    Nov 22, 2013
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    Yes!
    Link: http://tetech.com/product/hp-127-1-0-1-3-71/

    Uses temperature differentials to create power. Power fluctuates between 20-35mV im using that power to harvest.
     
  4. #12

    Expert

    Nov 30, 2010
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    I would suggest you use the words, energy, power, voltage, and current carefully in order to minimize confusion in the conversation.
     
  5. strantor

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    Ok that's a Peltier module. That's what I thought you were referring to but wanted to confirm.

    You should know that what you are trying to achieve is the holy grail of alternative energy. Nobody has a good solution for harvesting low grade heat.

    Peltier devices have pathetic efficiency when used as heating/cooling devices, and even worse when used as thermoelectric generators.

    This document has a lot of info that might be helpful to you. Here's some efficiency figures for you from that doc:

    I point this out not to discourage you, but to inform you what you're into. Still a perfectly viable HS science fair gig, but maybe worth mentioning at your presentation rather than making it sound like the solution to the world's problems.

    That document also mentions some series/parallel options but it's pretty vague. You might just need to play around with it and see.
     
  6. wayneh

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    Sep 9, 2010
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    I think parallel connection will be a problem unless you can ensure very similar conditions for both modules. Otherwise one will be driving current through the other and you'll lose a lot of efficiency.

    Putting them in serial would be more effective, in my opinion, especially since you need more voltage for the later stages of your harvest. You'll still want the modules to see similar conditions.
     
  7. Theinsainepops

    Thread Starter New Member

    Nov 22, 2013
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    I was thinking... And please correct me if this isn't possible.
    To give yall a better idea of what im working with. I currently have 3 TEGS wired in series that is then wired to my LTC3108 demo board. This board has a 3.3 Vout, thats what im using, with this circuit and my multimeter set to 2V. I see a wide fluctuation in voltage, anywhere from .400-2.1V. This is expected due to temperature gradients and thermal matching. Anyway I was looking into voltage regulators. More specifically the shunt regulator (thanks to the article Strantor posted in this discussion) I am curious to know whether or not it is possible to build a shunt voltage regulator that has a fixed output of 1.25V so I can easily wire another energy harvester into my circuit that can take lets say 1v and harvest it to 5v! Ive been doing some research on these types of regulators but from what it seems, I will need a higher input voltage than output voltage in order to regulate my output? Also when researching these types of regulators they seem to be using realitviley high voltages so I would like to know if its possible to basically build a circuit that can give me a fixed output of 1.25v?
     
  8. Kermit2

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  9. tcmtech

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    Nov 4, 2013
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    I'm not following the logic here at all being you want a 5 volt DC output and you have a TEG unit with a rating of 16 volt 36 watts capacity at a ~27 C temperature differential but say you are only getting a few tens of millivolts from it.

    What am I and everyone else missing here? Do you have any applied temperature differences between one side of the TEG unit and the other and if so how much?
     
    Last edited: Oct 26, 2015
  10. blocco a spirale

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    Jun 18, 2008
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    I think you are making the, all too common, mistake of assuming that power can somehow be stepped-up or "boosted", it cannot. Every conversion wastes some of the power that you're trying to preserve. If you step-up 1V to 5V you will have even less power available than you started with and it's power that you need to do anything useful.

    The questions you should be asking are; how much power do you need and how much power does the TEG deliver?
    If you find that the TEG falls short, and you will, no amount of clever electronics will fix that.
     
  11. blocco a spirale

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    Aren't those the input figures for heating/cooling? This thing is only 3cm square.
     
  12. tcmtech

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    That also holds true if you are not applying any temperature differential across the TEG unit as well which makes the practice about as useful as saying, 'How many dead batteries do I have to stack together to get X amount of power out or how many solar cells in a dark basement room at 2 AM do I need to make X amount of power?':rolleyes:
     
  13. tcmtech

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    Nov 4, 2013
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    Oops. Your right. I was thinking they were TEG's not TEC's and did not look at the dimensions given.

    Still my experience with using TEC's as power cells has been that they can typically put out at least 10% of their rated input power as output power while working with similar hot to cold side temperature differentials.
     
  14. Theinsainepops

    Thread Starter New Member

    Nov 22, 2013
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    Hey guys sorry things got very busy with school and football so I havnt had too much free time, that and shipping took a very long time. Anyway, what I want to get too. SOOO you can call me uneducated, stupid, noob whatever you want because truly in this field im all three. But ive basically came to another road block.

    I ordered the X0122 Voltage regulator for my circuit design. As of right now i have 3, 30x30cm TEGs in series that is wired to an ltc3108 demoboard. With a temperature differential applied my voltage starts to rise, from 0.00 on up to 1.8V if i keep my hand on the ceramic chips long enough. This X0122 regulator can take anywhere from 400mV to 5.1V and regulate it to select outputs. In this case my output is 1.8V. My problem is when I wire the ltc3108 energy harvester to the X0122 voltage regulator nothing happens. My voltage goes to -.03V. I cant seem to get this regulator starting up and I need help with doing So! Can someone please point me in the right direction please.. Ill post some pics/ videos if needed to get a better understanding of what im talking about!!
     
  15. tcmtech

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    Nov 4, 2013
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    So are you using anything to create an actual temperature differential across the thermal generator as in creating a deliberate hot side and cool side with the units or not?

    Also as far as the second regulator unit in series with the first not working I suspect you simply do not have enough available current for it to start up and run on.

    As the first unit steps up the voltage the available current on its output goes down which is why your original unit can not step up the TEG output to over 3.3 volts. It simply does not have enough input current available to trade off for higher output voltage.

    Basically if you want a 5 volt 1 milliamp output from a 50 millivolt input you need to have at least 100 milliamps of current available behind the 50 milliamps on the input side or the output will either not reach the 5 volt set point or it will not be able to sustain anywhere near the 1 milliamp current.

    Power out equals power in minus conversion losses so if you do not have enough input power available you cant get more from the output than what you put in which is what I think your whole problem is based on.
     
  16. strantor

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    Oct 3, 2010
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    Delusions of persecution?
    How much untapped potential energy do you think exists in the temperature difference between your hand and the atmosphere?
    The datasheet for X0122 is pretty retarded; There is no table of specs and quiescent current isn't divulged. But rest assured, every electronic device has quiescent current (that is, the current required to operate the thing, with no load on the output). They say it's 90% efficient, and capable of outputting 100mA, so let's assume the quiescent current is 11mA. You want to output 1.8V, so to give you that, at a minimum the X0122 needs to consume (1.8V * .011A) = 19.8mW. That's about what a 5MM LED consumes.

    Do you think there is enough untapped potential energy in the temperature difference between your hand and the atmosphere, to light an LED? I highly doubt it. And that is just the power required to produce a voltage at the output. If you wanted to use that voltage for something, like lighting an LED, then it will need even more juice.

    Try creating a higher temp difference across the plates and see if you can get an output.
     
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  17. Theinsainepops

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    Nov 22, 2013
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    Well this is where things get interesting, because ive used a few energy harvesters in the past that had the ability to take one TEG and power an green led with the harvested power. The problem with that circuit was the led would eventually dim out as the ambient temperature between both sides of the chip evened out. I guess my digital Multimeter doesnt work all to well because when I try to read out my mA the output is always changing. EX: jumps from 80mA to 5mA then back up to 30mA. I think im going to invest in an amp meter
     
  18. Theinsainepops

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    Nov 22, 2013
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    Is there any way around this issue. Since my power output from the 3108 is constently flucutating, is there some other type of regulator I could use in order to sustain just 400mV or at best 1V?

    What I really want to accomplish is taking a TEG and regulate its voltage, thats what my project has basically turned into. Because If i can obtain a constant output I can harvest that energy or hopefully raise the current using ohms law. Because as of right now ohms law cant come into play beause I dont have a constant power output.
     
  19. Theinsainepops

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    Nov 22, 2013
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  20. blocco a spirale

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    You need to go back and read the replies to this post! Ohm's law isn't optional in electronics and you can't get more power out of a system than you put in, try to understand this, otherwise you will forever be going round in circles.
     
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