# Wind Turbines have little torque?

Registered Users Posts: 1
Hello Forum,

I am a Boy Scout leader and wanted to try an experiment with the kids. I want to explain perpetual motion and why it does not work. Here is my idea, which needs some input. I have a 12 ft long, 3 ft diameter concrete form tube. These tubes are a thick cardboard. I want to cut the length of the tube to 6 ft. I want to put a powered fan at the end, blowing air into the tube. Then I want to place another fan 3 ft deeper into the tube, facing the powered fan. I want to turn on the powered fan and measure the electricity used, then measure the power generated from the fan facing the powered fan, measuring the electricity created. Then we can discuss the differences.

I don't know much about electricity, generators, or turbines, but I think it would be fun anyway. Watching vids on many different generators, I see that once a load is put onto the generator, the shaft torque increases. I'm betting this will slow or stop my facing fan. However, I saw an interesting vid on a wind turbine that was producing power and putting it back onto the power grid, turning back the power meter. It seemed to have little or no torque. I think I am confused about this. I get that power generated can flow into a battery bank or back onto the grid, but doesn't that also put a load on the wind turbine? If you were to run the wiring directly to something like a flood light, would that create a different torque on the turbine than just feeding it back onto the power grid?

I hope this makes sense. If it does, and using a wind turbine head, or something similar, do you think we could produce 80% of the power from the electric fan blowing into the tube?

Thanks,

Jeff

• Super Moderators, Administrators Posts: 32,924 admin
Re: Wind Turbines have little torque?

Welcome to the forum Jeff!

An optimal coupling of a wind turbine to wind (open field) is something like 35% in the best of turbines and can be as low as 10% (really closer to average efficiency in average conditions).

https://en.wikipedia.org/wiki/Betz%27s_law

With a ducted fan (blades inside a tube/shroud, it will be more efficient.

However, the next issue becomes matching the turbine blades with the alternator/generator. Right wind speed, RPM of blades, correct airfoil, torque/RPM of the alternator, etc. is pretty difficult.

I would suggest for scouts, something like this may be a bit easier and more interesting:

Hamster-Powered Night Light

Replace the hamster with blades, the DIY alternator (magnets and copper coils) do not "cog" like many permanent magnet alternators--Which makes it difficult to "start" a turbine in low wind/low torque design.

Add an LED and a couple diodes--And you should have a very workable and simple turbine setup--Probably don't even need the tube (LEDs are very efficient, 50 mWatts or 0.05 watt RED led or other high efficiency color should be very obvious).

You could also put a pulley on the turbine and run a string "belt" to some outside devices (grain mill model, trip hammer, etc.).

I don't think you really want to get into the efficiency of wind--It is a pretty complex subject to start with--And building an efficient system is not an evening task. Here are some links to read: