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Maximum voltage from blowing through small turbine?

  1. Apr 7, 2016 #1
    If I had a turbine roughly 2 inches in diameter (4-5 blades), where the housing for the blades is about one inch wide (meaning the axle is 1"), what would be the estimated voltage I could produce if I were to use my lung power in one complete exhale through the input? That is, if there were small coils lining the housing and magnets on the tip of the blades.

    I understand that this is purely an estimation, but I'd like to eventually make something like this so I'm curious.
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  3. Apr 7, 2016 #2


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    The Voltage would depend on the design of the alternator but the Power from your blowing would probably be a few Watts. The problem would be partly because of the short time you have to blow and the Moment of Inertia of the turbine. To get to my figure of a few Watts, I use my frequent measurements of Power developed by teenage students, running up stairs and using their leg muscles. The fittest boys could develop about 1kW for a few seconds and legs are actually designed for power, whereas your chest muscles are pretty damn weak, needing only to waft just enough air in and out.
    You could perhaps manage to light an (indicator) LED for a while, if you used a suitable capacitor to store the energy and let it out over a few seconds.
    You could measure the pressure that you're capable of producing by blowing into a U tube and measure the level change. That static measurement would correspond to the short term pressure into a narrow turbine tube.
    The cross sectional area of the blades of you particular turbine is rather big, thinking of your lung capacity and the corresponding distance of movement of the column air. You might get better results by blowing through a nozzle onto a small sector of the turbine, which would match your output better.
  4. Apr 7, 2016 #3
    In your calculations did you also measure amperage and voltage separately? What did those come out to be?

    If I were to blow for a longer, less powerful period, do you think that would produce a higher or lower wattage than a single burst into the turbine? You mentioned inertia of the turbine, which I didn't consider. In light of that, an abrupt burst sounds more efficient, but as a result the charge would last for a shorter period. Either way, it can't have that much intertia, since it's so small.

    Speaking of efficiency, I thought about Tesla turbines. I wonder if those might be a better idea, as long as I can figure out how to hook up the electrical component.

    You're definitely right about the design. It needs to be rethought, but I just kinda threw together a concept that wasn't finalized.

    Out of curiosity, how exactly did you measure the power of your students' legs?
  5. Apr 7, 2016 #4
    In case any of you were wondering, I just wanted to see how fast I could get electrolysis of water to go purely out of the power of the human lung. It's an odd application, but I thought it would be cool to see. I also understand the problem of electrolyzing the water using AC. Oh, and this is also why I'm more concerned about voltage.
    Last edited by a moderator: Apr 7, 2016
  6. Apr 8, 2016 #5


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    Power is defined as rate of doing Work or rate of transfer of Energy. It doesn't need to use Volts and Current, explicitly. Many different combinations of Volts and Current will correspond to a given Power. Calculating the Power from the students involved measuring their Mass, the height of the flight of steps and how long they took.
    Power = Mass X G X height / time taken.
    Your question about Volts vs Current can only be answered when the design of the generator is known. One generator with many many turns of (thin) wire can produce many volts but the output current will be limited due to the resistance and Inductance of the coils. Another generator with fewer turns will produce fewer Volts but the available current will be more. If I were to try to use my students as a source of electrical power (they could have been useful for once - haha), they wouldn't have run up stairs; they would have worked a treadmill of wheel (hamster) but the power they could develop would be about the same.
    If you are planning to do electrolysis, the Voltage you want will probably be fairly low and so your generator would need to be designed appropriately. But that's just a detail really. Have you done any research into how much Charge you need in order to electrolyse a given amount of water (say 1gram)? That is the critical question - as with systems for charging batteries with 'harvested' energy. For your application, you are really more interested in the Energy available over a long time than the peak Power.
  7. Apr 8, 2016 #6


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    I once built several miniature steam engines . One of these was small enough to work when blown by lung pressure .

    In an improvised experiment with this engine coupled to a model boat motor used as a dynamo I managed to light a torch bulb to about normal brightness for a short time .
  8. Apr 8, 2016 #7


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    Allowing for all the inefficiencies, that's not a bad indication of usable Power. But the "short time" would produce very little electrolysis , though.
  9. Apr 8, 2016 #8
  10. Apr 9, 2016 #9


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  11. Apr 9, 2016 #10


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    Could you use breath to power a Van de Graaff generator :-)
  12. Apr 9, 2016 #11
    It says in the article this contraption uses turbines as well, but it seems as if the project never really took off, which makes me wonder why.

    I almost want to try something using the piezoelectric strip, or a number of them, like in the article I posted before. I also found this as well:


    It appears that these people used the triboelectric effect, but also rigged it to harness friction from air, or in this case breathing, to create a static charge that was able to light up several LEDS.
  13. Apr 9, 2016 #12
    Generating electricity with human power has a long history of laziness stopping it. Humans are weak, frail creatures when compared to steel and hydrocarbons.

    There is no free lunch. Producing electricity is work, no matter which muscle group you use. Other than some exercise fanatics, few are willing to do the work. (Myself included.)
  14. Apr 10, 2016 #13
    I understand, but I just wanted to know, in a relatively efficient system, if there would be enough charge to comfortably produce oxygen in a rebreather-like system. For example, if I blew through the turbine or one of the aforementioned methods, that electricity would then be used to provide the energy required for electrolysis, which would produce enough O2 to create a 21:79 environment that I would inhale, then repeat the process as long as there is a carbon dioxide scrubber. I know it's farfetched, but all of the sources I've so far found have given me anything but consistent information.

    Feel free to roast my idea as much as you want.

    I've tried to do the math, but I can't seem to grasp certain areas.
    Last edited: Apr 10, 2016
  15. Apr 10, 2016 #14


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    That sounds like a complete non-starter. The energy needed to produce the electrolysis would be more than the energy your body would need to achieve it. Better just for your lungs to do less work in the first place.
  16. Apr 11, 2016 #15
    I used to scuba dive. My lungs would ache for the next few days. It takes enough work just breathing underwater. Adding extra load would be hell.

    Your body wouldn't have enough energy for electrolysis even if you melted your fat and used it as oil. (For more than a few hours anyway.)

    My understanding is that artificial gills suck dissolved oxygen from water. But even they seem unworkable. Lots of water would need to flow, more than could be pumped. Mammals rule the ocean (whales, dolphins) because lungs work so much better than gills, that they can compete with fish simply by holding their breath.

    I wouldn't completely dismiss the idea of an artificial gill, but it would seem more of a novelty or niche item than a useful tool.
  17. Apr 11, 2016 #16
    I thought about the scuba diving rebreather as a likely application, but after some more thought, I found out that it could be used for practically any low oxygen environment. It would be lightweight, and when compared to contemporary oxygen tanks, rebreathers, etc, it would be much more convenient, such as in a building fire. However, as you've described, lung power probably isn't enough to supply a consistent amount of breathable oxygen. The best method I can think of is to line a tube with many piezoelectric strips, but even that sounds out of reality. I read in one of the previous links (the Georgia Tech one I believe) that the handheld triboelectric generator is able to charge an iPad 2, but that's its limit, but that isn't too bad considering its size. Using that generator, they modified it to use air friction from the lungs.
  18. Apr 11, 2016 #17


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    Think about it this way:
    Which generates more energy for a car;
    1. The flow of air into the engine?
    2. Burning gasoline in the engine?

    The proposition here is somewhat of a biological perpetual motion machine: humans burn fuel in oxygen to power their bodies. You want to make the fuel with a small part of the energy your body produces.
  19. Apr 11, 2016 #18


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    The energy extracted by the mask isn't free. It would cause you to expend more energy. That would require you to burn even more oxygen which has to be generated by the mask causing you to expend even more energy etc
  20. Apr 11, 2016 #19
    I fully understand that, but your car analogy doesn't really work out too well. Turbochargers both can increase the efficiency and add more power when needed by increasing the airflow into the cylinder, where the energy for the process is supplied by the gasoline. One can argue that my idea is a human turbocharger, but that's out of the question. The real question is, how efficient can it work, and is that efficiency worth it? That's the essence of this thread, and it appears that I have found my answer.

    The point about a human perpetual motion machine is completely inaccurate.

    On a side note, this thread really got me interested in piezoelectric and triboelectric generators :oldbiggrin:
    Last edited: Apr 11, 2016
  21. Apr 11, 2016 #20
    Turbochargers use the energy from the burning fuel-air to provide more burning fuel-air. The power comes from the compression of burned fuel-air taking up more "space" than unburned fuel-air.

    In your question the power to compress the air comes from lung muscles.

    If you are looking for concentrated oxygen, there are chemical solutions. Oxygen generators exist and are popular solutions. (Ex. Airline oxygen masks are frequently chemically based.)
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