DIY Wind Turbine - Is this a Hoax?

[Rhythmtech]

Checking this blog this morning I came across this Wind Turbine
project.  On closer inspection of the motor they were using I noticed it did not appear to be an "Old DC Motor" as they claim. Not to mention that in some of the pics you can see a rectifier attached and the cap leads going to a plastic box.  I would think if they had come up with an excitation voltage scheme to generate the back EMF they need to make the inductive motor act as a generator it would be the most interesting part of the build.  Anybody else think this is not on the level?

[Simon]

there is a website that deals exclusively with home builds of wind turbines, it's feasible but there will always be hoaxsters

[Rhythmtech]

EMF - Electromotive Force.  Basically means electrons get moved around in moving magnetic field.  Like the inductive flashlights you shake to charge. Back EMF in the application of a generator presents itself as the magnetic field in the stator or rotor, depending on design, countering the magnetic fields on the rotating stator or rotor inducing electrons to move around. If you don't have a permanent magnet motor, you must create the magnetic field electrically.  This is very often done on alternators for cars, so it is not uncommon, however it requires some sort of circuit to induce the field until the motor begins to generate enough current to supply its own field then whatever surplus energy that is generated charges the battery.

A motor and a generator are quite similar in operation and design but opposite in function. Like anything involving electrons, ideal is generally only on paper. Since you have rotating magnetic fields you actually end up with both a generator and a motor. The function (motor/generator) is determined basically by which one is done most efficiently. I am sure I've over simplified it and I probably have an error in there somewhere, hopefully it is helpful.

[tecman]

I do quite a bit with the wind and renewable energy business.  Any standard polyphase induction motor will also function as a generator.  You can read lots on induction generators on the web.  The biggest issue is energizing it.  If you apply power when it is stopped it will just spin as a motor.  If it is spinning near its nominal RPM when you apply the power, as you increase the speed to synchronous speed and above it will start to generate power.  Spinning faster than the synchronous speed is akin to the "slip" that a motor runs below synchronous speed.  Basically as you try to increase the speed it will generate power.  More speed, more power, just like a normal generator, but always within 10% or so of synchronous speed..

In commercial wind turbines, nearly all use induction machines (as they are called).  Lowest cost and very reliable.  In those applications, reduced voltages are applied as they come up to speed and this brings on the field and power quickly without any surge on power up.  The trend, being tested by some, is to have a large polyphase synchronous machine with permanent magnets or excited rotor, rectified and fed to an inverter to power the grid.  This scheme has advantages that they can provide better power (better control of voltage, frequency and reactance) which will be mandated by FERC for the grid.  But many obstacles exist in making variable speed, high efficiency synchronous machines of this size (1 MW on up), so the market is currently developing.

Paul

[tecman]

What you have drawn will not work.  An induction machine (generator) will not generate power on its own as you have drawn.  Only a "synchronous" machine (one with some sort of permanent magnet or equivalent).  An induction machine will generate power if energized, ie hooked up the the power line, and spun faster than its normal speed.  If you spin an induction machine as you have drawn, it will just freewheel.

http://en.wikipedia.org/wiki/Induction_generator

http://www.electrodynamics.net/documents/electrodynamics_power_gen2002.pdf

http://www.usmotors.com/products/profacts/1-204.htm

paul

[rf-loop]

Example normal asynchronous 3-phase AC motor can use as generator(of course also 1-phase) Tecman is also partially right.  If it go as motor it take power from powerline (it take active power and also it take reactive power component (inductive). It run littlebit mor slow as synchron speed. If you start help motor... you start running it with mechanical power. With synchron speed it take very little power (in theory only this reactive power). What if you start running it more fast... you need put more power for turn it more fast but same time it start pushing electric power out (to electric powerline) but same time there is still this reactive power what it "take" from this powerline. But this is also why it get this magnetic field what it need...as motor and as generator.

But then. If no powerline but still it need start to generate electric power with asynchronous motor. (using it as asynchronous gnerator)

It is simple. Normal (older) ac-motor have many times some small remanence magnetic and it can wake up with it. But how to make magnetic field enough strong. Here is solution.. (it is just this reactive power... inductive - capacitive. Just opposite. We can use capacitor for source. Now it give this reactive power for generator magnetic field. (good new ac motors may have less remanence and need small help for wakeup in generator use)




But if there is no remanence magnetic in motor (as generator) metal parts and system is not connected to powered powerline. It need make this magnetic field... example short pulse from battery to one motor coil just as it is running and it start (and then system itself make it more strong as it is loaded becouse current and reactive power... (yes this time all systems need olso be good designed for take all this momentarily stress) Only very weak magnetig field can "wakeup" this system. (also you can see that in this picture capacitors are in delta connection but depending situation (motor/generator type) it may also be Y connection. (capacitance values need be calculated so they are compatible for individual system). Today normal motors metals are so good that there is less remanence magnetic fields so mostly they need some wakeup magnetic. (and to powerline connected generator may take it from powerline but it is also danger... becouse what you do in fail situations... you loose magnetic field if system can not serve this reactive power. It may be very labile system and difficult to control and worst case - and you need put smoke back to system if it comes out accidentally.. . Also there is not very good to draw lot of reactice power from powerline. And also this is inductive so there is heavy inductive reactive power "draw" from power lines.. (if big enough.. and powerline breaks ... have you never seen selfmade thunderstorm... now you maybe can. So it is better to serve generator magnetic field with local reactive power as in picture, and specially if it is use as stand alone generator without need to push power to allready powered powerlines.


This capacitance method is very common and widely used. Specially in fuelmotor generators becouse speed servo control is easy to make..  (becouse real generators are much more expensive if look this mechanical reliability class what have normal 3-phase motors (and always good AC generator need good speed and voltage control.
In wind turbine need very tight and fast speed control if want normal AC directly (nearly impossible) and  small "stand alone" systems it is nice to load battery and make AC for use with inverter.

If load accumulator it is not so difficult as making good AC to power lines network. (home system (separated from commercial power lines)
Generator (what ever type) --> battery* --> use DC. ---> inverter (sine) --> use AC

*this can serve also magnetic field wakeup "start" pulse power in self (reactive power) magnetized system.

[Mechatrommer]

so much the complexity of the technology. i'd rather learn from this school dropout guy http://williamkamkwamba.typepad.com/williamkamkwamba/2007/06/from-november-2.html. enuf for my need and knowledge and think i can start from there. and later to create multi mega million dollar windmill from info provided here. thanx guys

[rf-loop]

That young boy's story is amazing and wonderful. I read the news a few months ago. Deep respect for him.

[Rhythmtech]

Here's another good Back EMF article detailing how they use it to measure speed from operservo - http://www.acroname.com/robotics/info/articles/back-emf/back-emf.html


I also got a response to my comment on the site.  They will be publishing their circuit soon - http://carlitoscontraptions.com/2010/05/the-wind-turbine-part-2-desing-and-materials/   bottom of the page

[tecman]

Back EMF is often misused as a term.  The classical use, that I stick by, is, as described in the first article, when a DC generator is spun, or freewheels, generates voltage (and power).  I personally would not use the term for power generated by an induction motor.  Others disagree and use it freely.

In any case, an induction motor will generate power when properly "energized".

Paul

[Rhythmtech]

ah yes! i knew it! i just got confused with the terminology, induced vs inductive. i was confused when discussing about inductive and capacitive loading etc. but this is different. the induced means generated in my "layman's" term.

...If it is spinning near its nominal RPM when you apply the power, as you increase the speed to synchronous speed and above it will start to generate power.

huh?! u apply power to a motor, and u get back power (EMF ) in return? at higher than synchronous speed? well that sounds strange?

well, if i want to build my own wind turbine... cant i just do the following (my own sketch)? am i missing something?

Only if the motor is a permanent magnet motor, otherwise you need some sort of control (Regenerative Drive usually) to "manage" exciting the windings and regeneration. There is no flux where their is no field and there is no field unless there are magnets or electromagnets.

[Mechatrommer]

now i get it. induction motor need power to create electromagnetic field, right? is that what you mean guys? so why use induction motor if it needs power to excite it? more efficiency (wattage output) compared to permanent magnet? (which no hassle no need to inject power to it)

[tecman]

Once you excite it and it generates power, it is self sufficient.

Induction generators are used in large wind turbines primarily for cost, reliability, ease of "control" and simplicity.  Any "normal" alternator needs either permanent magnets or an excited field.  Magnets are not an option in big alternators (too big to be able to create flux from PM), and separately exciting means another component (exciter) with slip rings, or even more complex as a brushless design.  In terms of reliability, no brushes or wound rotating field, no exciter controls so fewer parts.  Control is easier since you are not synchronous and do not need a precise speed input and lastly an induction machine is considerably cheaper to build than a synchronous machine.

The biggest downside is that they only work well into a grid of established frequency.  As a standalone, not as good.

paul

[Rhythmtech]

now i get it. induction motor need power to create electromagnetic field, right? is that what you mean guys?

Yes

so why use induction motor if it needs power to excite it? more efficiency (wattage output) compared to permanent magnet? (which no hassle no need to inject power to it)

My opinion - Magnets that are really strong and large enough are not as cheap or reasonably feasible as copper windings. Most large inverter duty type motor designs with years of proven reliability that are on the market are induction based designs, add a smart electronic drive for a lot less money than a redesign can turn them in to a regenerative motor or generator.

[Rhythmtech]

The authors of the original blog post responded to a comment regarding the lack of documentation saying they would follow up with a description. So I guess, we're waiting.  - http://carlitoscontraptions.com/2010/05/the-wind-turbine-part-2-desing-and-materials/

[Zero999]

EDIT:
Deleted, sorry wrong thread.