How to turn a TEG output into something I could use?

Discussion in 'Power Electronics' started by Matienzo, Jul 6, 2016.

  1. Matienzo

    Thread Starter New Member

    Jul 6, 2016
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    0
    Hello there,
    I'm working on a project that uses a Peltier device (TEG) as the power source. The conditions under which it is used allow me to harvest about 1V and 130mA. The motor I want to power on a cycle - off and on with intervals of about 30' or a minute- works using a minimum of 1.5V and ~100mA under the load.

    I think that if I could store the electrical energy in something like a capacitor and then release it with the desired voltage and current it could work.

    My questions are:
    How do I tell the capacitor to release the energy once it is full?
    How do I transform the stored energy into a useful, constant output? 1.5v ~100mA


    The main constrain: the only power I can use is the power coming from the peltier.

    I'm a ME and my knowledge about circuits is rather rustic so I would appreciate if you guys/gals keep your explanations or instructions as basic as you can :). Any resources, references, suggestions, ideas or schematics are welcome.

    Thank you in advance!
    Paulo
     
  2. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,671
    898
    The voltage of a single capacitor charged with 1V will never be more than 1 V. You can charge 2 capacitors in parallel to 0.8V and then put them in series to get a higher voltage. They will need to be quite high capacitance to run the motor very long. Such switched capacitor voltage reglators/converters are available as IC's. The ICL7660 is just one of several examples. They are quite limited in current capability, but the idea is there. How long do you want to run the motor?

    You might also consider what is called a boost regulator. You would have to search for one that would work to up 1 volt. Of course, as you increase the voltage, the current available from your source will decrease, as V*C input = (V*C output)*efficiency. Efficiency is always <1. HOwever, a boost regulator could be used to charge a battery and then the battery could run your motor. You will lose efficiency, but if the TEG works 24/7 and you only need the motor to work 30' per day, you may get by with it.

    A third option is to remove some windings from the motor to make it operate at 1 V. That will increase its current needs. Can you find a small, 1-V motor?

    John
     
  3. Papabravo

    Expert

    Feb 24, 2006
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    You could also put two TEG devices in series and use a resistor in series with the motors to adjust the voltage. The resistor will only need to dissipate 65 mW, which for 0.5V drop would be about 4 Ω.
     
  4. Matienzo

    Thread Starter New Member

    Jul 6, 2016
    3
    0
    jpanhalt thank you for your suggestion and taking the time to ponder about this. The motor should run for 20 seconds in intervals of 1 minute

    So lets say I have 1 TEG. Directly connect the capacitor/s, then a battery and from the battery I should bring the voltage down with a buck to a constant voltage (all of this was a suggestion from someone from another forum) and I see you are thinking very similarly.

    How would this look on a schematic? Are there any IC you could think that I could use besides ICL7660?

    Here is a drawing of what I'm trying to do.

    Thanks for the help!
     
  5. Matienzo

    Thread Starter New Member

    Jul 6, 2016
    3
    0
    Papabravo, I'm limited to only one TEG because of the cost but that is a good idea. Thank you!
     
  6. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,671
    898
    Capacitors would make lousy battery chargers because their voltage varies so much during discharge. For the same reason, they will not be good for running your motor. You need to think in terms of watts for a defined period. 1 V at 100 mA is 0.1W.

    Yes. Search on capacitor switching regulators or voltage converters (many are designed for converting positive voltages to negative voltages, but it is a small jump to make them into voltage doublers).

    Why is the heat source only available when/while the milk is stirred? With that constraint, your TEG will probably not develop enough power, based on the information you have given.

    John
     
  7. Papabravo

    Expert

    Feb 24, 2006
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    Then I'm afraid you're hosed.
     
  8. crutschow

    Expert

    Mar 14, 2008
    12,973
    3,219
    Here is a energy harvesting DC-DC converter designed for low voltage sources.
    You might be able to use that to charge a 1.5V Li rechargeable battery, which could then power the motor.
     
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