Using Air to Recharge Your Cell Phone 346
sanspeak writes "Now you do not have to look for a power outlet to charge your cell phones. Department of Industrial Design at Indian Institute of Technology, Delhi have come up with a mobile turbine which generates around 3 to 4 watts of energy - sufficient to charge a mobile phone. It costs around $4, fits in your pocket and runs on air ;-). What else do you want ?"
We want truth in summaries... (Score:2, Informative)
Summaries that are closer to the reality of the article.
It costs around $4.
"The technique is not yet commercialised but the department has sent a proposal to the ministry of science and technology to help manufacture the turbine on a large scale, Das said."
RTFA (Score:3, Informative)
Instead, they're expecting that typical environmental wind, especially that found on coasts, will work well enough. The idea is to ease communications access to areas without convenient electricity. (Mountain climbing, anyone?)
Re:compressed air (Score:5, Informative)
There's also a compressed-air car [theaircar.com].
Re:Alternatives (Score:1, Informative)
Or, better yet, buy one of those cables... (Score:4, Informative)
Paul B.
Re:Blow or run really fast (Score:3, Informative)
Re:Alternatives (Score:2, Informative)
I envision this, and I think they do to, as a turbine at the end of a long thin cable, probably with a magnetic mount. You'd stick it to the top of your car or the side of a bus, close the window, and be good to go. Assumedly, you could also stick it to the side of a house on a windy day.
Re:A better idea! (Score:2, Informative)
Warning: They suck according to engadget [engadget.com] .
Re:Ok then... (Score:4, Informative)
Tell me why if this model produces 3 - 4 watts of energy why they can't cover the blades of larger windmills with these things or better yet design the blades so they have edge holes with these things inside.
There is no such thing as a free lunch (1st law of thermodynamics). The drag produced by the turbines extracting energy slows the speed of the windmill blades reducing the power delivered to the main generator so you gain nothing by adding those (more likely you will lose since the main generator is less efficient at slower speeds).
Coincidently, this is the same problem with charging the cell phone by clipping this device to the outside of the window while riding in a bus, train, or car. The vehicles engine needs to consume more energy to offset the drag produced by the turbine. Granted it is small compared to the amount of energy used to move the vehicle in the first place but it would be more energy efficient to connect the phone to the vehicles alternator than to convert the engines rotory motion to motion induced "wind flow" and then the wind flow back to rotary motion.
Now could you make a windmill with no main generator and use a large number of small turbines instead? Yes but it probably would not work well at all. In fact, it would probably work less well than just pointing the turbines into the wind which in turn would not work very well at all. The problem is a serious impedance mismatch. Turbines want high pressure/high airflow. A windmill blade tip will be travelling at a lower linear velocity than the air that turns it.
Incidently, power from wind is proporional to the cube of the wind velocity. Generators are inefficient at low speeds. Modern windmills adjust to different wind velocities by feathering the blades to try to run the generator at a relatively constant speed. In really high winds they turn the blades parallel to the airflow to avoid destroying the generator and gear train.
Note that since it was described as a turbine and not a "wind turbine" (which is normally a very different beast) and described it as fitting in a pocket, I am imagining a device with multiple disks with the edge shaped into blades inside a tube like you might find in a jet engine or gas fired power plant (every other disk is stationary or counter rotates to restore longitudinal airflow). A friend built an toilet paper roll cardboard tube sized device out of sheet metal in this topology that was demonstrated with the air from a shop vac that would be about the right size for a cell phone charger. If that is not the topology used., then some of what I have said will not apply but much of it still will.
Whatever turbine topology you use on your windmill blades, you are converting from wind to rotary motion twice and therefore are reducing the efficiency by around 60% compared to doing so once even if it is well designed and operating at optimal wind speed. And poor performance at low speeds will be made even worse by being being run twice through the innefficent portion of a non-linear transfer function.
Back to the original article, the usefulness of this is likely to be very limited since people in India who don't have electricity aren't likely to spend a lot of time running around in vehicles every day to charge their phones. A small roof mounted windmill would probably be a lot more practical. It may have some use as a travel charger for people who will be traveling to distant points but not be staying for very long (such as tourists).
The little generators that run headlights on a bicycle might be another alternative for charging a cell phone. With a stand, pedal power can even be used while stationary. Someone built a generator stand for a bicycle [erols.com] that was capable of generating as much as 260W (100W seems more likely for an extended period of time).
A small solar panel with built in battery (so you don't need to leave your cell phone on char
Re:RTFA (Score:2, Informative)
The idea is to ease communications access to areas without convenient electricity
Problem being that most places without electricity don't have coverage anyway (at least in Australia)
Re:compressed air (Score:3, Informative)
See more about energy density here [tinaja.com].
Personally I would think a hand squeezer device like this [thinkgeek.com] would be ideal. It's a very natural motion.
Compressed air IS useful if you need to deliver a lot of force at once, like with compressed air tools, or if you want to avoid using electrical devices for some reason.
Re:uhh... (Score:3, Informative)
(That was a joke. Laugh. Or don't, it wasn't all that funny, I won't feel hurt. But I have to say, I think you aren't laughing because I'm Jewish. Fucking anti-semite.)
Re:Blow or run really fast (Score:1, Informative)
Actually, the mythbusters show covered this one. They took two SUV's with the same amount of fuel in them and ran one with the A/C turned on and one with the windows down. The one with the A/C ran out of fuel first by a good margin. I suppose that if a vehicle had a significant number of windows, as in the bus example, it might be the other way around.