Connect with us

Power From Sterling Engine

Discussion in 'General Electronics Discussion' started by teego, Sep 25, 2016.

  1. teego

    teego

    4
    0
    Sep 25, 2016
    Hey,

    I would like to get the power from a small (hand held) sterling engine to output some electricity. Since it is pretty weak but has good rpm, what would be a good way to tap it? The easiest cheapest way.

    Basically I would like to make a radio. I can build a board to do the radio but not sure the power requirements.

    Any suggestions?
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,173
    2,689
    Jan 21, 2010
    Have it spin a dc motor and use a MPPT type controller to maximise the power. Use it to charge a battery (lithium or lead-acid are the easiest) and use the battery to power a load.

    The major problems are:

    1) ensuring the regulator doesn't consume more power than that being generated.
    2) ensuring you don't over-discharge the battery
     
  3. Bluejets

    Bluejets

    3,432
    697
    Oct 5, 2014
    There are numerous ways and motor types but as already mentioned, not much power.

    I have built a couple of these engines myself (not with generator though) in the past and just out of interest I did a Google and came up with many, this being just one.

    Maybe give some direction and you could expand your search from info provided there.

    They quote 3v output @1600rpm but no idea of current so no real idea of power except they drive a few LEDs.

    http://diystirlingengine.com/stirling-engine-generator/

    As an example, they used a CD rom motor and searching on from there quoting CDrom motor, it gave other links of interest.
     
  4. teego

    teego

    4
    0
    Sep 25, 2016
    hey thanks for the response.

    Spinning a dc motor makes sense. Would it make sense doing it via belt or directly from the center of the spinning wheel?

    I dont care about the stability of the radios output. I just dont want it to blow up, and I can pretty much calculate the max output.

    What about if we exclude the battery.

    Can we run it dependent on the power being generated? And I am assuming volume would be the biggest suck, not the receiver. So volume being dependent on output is fine.

    I would like to make a candle powered radio for 10-20$ in parts. Just curious if it is possible and I would like to try it as a test.

    I have a decent sized candle beside me and it outputs crazy heat that could totally be harnessed.
     
  5. teego

    teego

    4
    0
    Sep 25, 2016
    Hey yeah I was just going to buy a cheap sterling engine on ebay. Like 50$ cad. The real test is just seeing if it outputs enough to output radio to some degree.

    Im not sure the power behind the spin (torque?). Could using magnets increase its power?
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,173
    2,689
    Jan 21, 2010
    If you remove the battery then you need to ensure that your load is compatible with the power being generated. This typically means you need excess power generation capacity.

    Replacing the batteries with a bank of capacitors and using a zener diode to limit the max voltage is a reasonable alternative.

    A candle puts out quite a lot of power. Allowing for the various inefficiencies you should still be able to extract some useable power.

    Whether you drive the motor directly (probably the most efficient) or use a belt depends on the speed your Stirling engine runs at. it is quite likely that the Stirling engine runs nowhere near as fast as the motor when it is being powered.

    The way you extract the power is key. MPPT requires a microcontroller, and you'll want something pretty low powered -- however the power output probably won't change rapidly so processing speed is not important and this allows you to (perhaps) have the microcontroller sleeping most of the time.

    And how do you supply power to the microcontroller from a cold start?

    This could be a fun project, but it could be as complex as you desire it to be!
     
  7. teego

    teego

    4
    0
    Sep 25, 2016
    a microcontroller sounds like a big added chunk. A bank of capacitors is what I was thinking exactly.

    The consistency of the output isnt important at all. So for example, if sound fades out because the engine stops or slows down, fine. As long as it does not destroy itself in the process.

    Direct drive makes sense vs belt so I dont lose energy in the band. But what about gears? Should it use gears to alter the speed for the dc motor. Does the dc motor have a special efficient point it should run at (a sweet spot?)?
     
  8. Bluejets

    Bluejets

    3,432
    697
    Oct 5, 2014
    If you look at the link I provided you will see they drive the load directly from the sterling engine.
    They quote 1600rpm but the engine shown is NOT a 50c puppy. I'm guessing the output there would be around 150mW to the electrics with fractional horses to spare.
     
  9. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,173
    2,689
    Jan 21, 2010
    An MPPT controller ensures that things are operating in the "sweet spot" at all times.

    Otherwise it's a bit of a lottery and you have to do a lot more work to ensure it reaches equilibrium somewhere near it.

    The one thing in your favour is the constant (or near constant) heat input. However, the differential temperature will fall over time. The load (ignoring that to charge the caps) is likely to be fairly constant, and as long as it I well behaved (I.e. that the current demanded drops with voltage) then you should have fairly stable operation.

    But remember that you've asked on an electronics forum, and you're likely to be given a good solution rather than one which might work if you're lucky.

    Without any form of electronic voltage boosting, the motor may need to spin quite quickly. The problem with belts (and even more of an issue with gears) is the extra losses which will accumulate. The best solution would be a motor which operates from a relatively high dc voltage (I.e. 12V rather than 1.5V) and has good bearings.

    But just try it with what you have.

    Once it is connected, measure the open circuit voltage and the short circuit current (be careful if you have caps connected). Maximising both of these will ensure you're in a reasonable place.

    Note that if you get 2V and 25mA, it DOES NOT mean you can power a load requiring 2V at 25mA. But you may be able to get 1.5V at 20mA.

    If you connect the motor via a diode ( preferably a schottky diode) to a capacitor of a known capacitance and measure the voltage at regular intervals it would be possible to calculate an optimal load (for the current conditions, ignoring heating effects).
     
  10. hevans1944

    hevans1944 Hop - AC8NS

    4,158
    1,970
    Jun 21, 2012
    If all you want is an "emergency radio" that operates from a heat source, a Stirling engine would not be my first choice. Delicate and expensive to build, inefficient, and too many moving parts to wear out or otherwise fail.

    During the Cold War, the Russians developed a multi-band radio that operated from the heat generated by a kerosene lamp for use in rural, isolated, areas of the Soviet Union. They used a few hundred thermocouples arranged radially and series-connected, the "cold" outer ends of the TC junctions being convection cooled by ambient air and the central TC junctions being heated directly by the lamp.

    Such a thermopile is easy to construct, involves no moving parts, and is a reliable source of electricity. Variations on this theme use radio-isotopes (plutonium mainly) to power remotely operated space craft, but so far civilians have zero access to the technology. Kerosene lamps, however, are still available for purchase.

    IIRC, a variation on the Stirling engine is used for cryogenic cooling with helium gas as the working fluid. Gets down near 10 to 12 K after a few hours. Gotta wonder why no one hooks a Stirling engine to the Stirling cooler. Might be a way to make iced tea in the outback. :D
     
  11. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    4,960
    648
    May 8, 2012
    Yeah, it's the weakling of the motor world.

    It's a little known fact that the U.S. Navy's Mark 1,2 & 3 torpedoes of WW2 were driven by miniature piston steam engines. I've always loved steam power. It's real power. So if I were doing this that would be my choice. They'll run off compressed air too!

    Chris
     
    (*steve*) and hevans1944 like this.
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-