electronic resistor Furling

[Disaster Transport]

Im in the process of my first wind genny and Im still researching furling techniques. I believe variable pitched blades with centrifical force as the drive is the best method. I am a machinist and the machanisms needed to create such a device would not be so diffucult. Although I would like to explore the resistor method. How does it work?  Explain as if it were a 12 foot machine please...

[Flux]

What on earth are you on about?

A wind generator left to its own devices will have an output proportional to the cube of the wind speed, at some point it will produce more power than it can deal with and will run into trouble.

Very small machines may be robust enough to survive normal high winds without taking precautions but larger ones just will not survive. In every case the method of survival is the same, you reduce the energy captured by the blades.

As you say the best method is to alter the blade pitch either to reduce the lift causing the power out to stay constant or by bringing the blades into stall to reduce the efficiency ( again it reduces lift indirectly). This is not normally considered as furling but I suppose the effect is the same.

Furling strictly is reducing the effective area of the blades, as was done on sail windmills directly on the covered sail area. With modern blades it reduces the effective area by making the wind rotor turn at an angle to the wind so that the projected area is reduced ( cosine law).

The only other method I can think of is stall loading of the blades which may be what you mean by resistive furling. If the blades are loaded to slow the rotation drastically the effective wind direction ( a vector of the actual wind speed and blade tip speed) moves round to bring the angle of attack into the stall region and again destroys the lift. This requires an alternator that is much more powerful than the power output of the blades at the point you want to control the thing.

The classic case is the grid connected induction generator where the alternator is confined to effectively constant speed. If you try to use this approach with any other loading scheme you have to force the load to be so great as to prevent the blade speed rising. For battery charging it requires an expensive and heavy alternator to keep the load up to where you want without the speed rising or burning it out.

Now you have me completely baffled when yo talk about the resistive method, does that mean you are using a heating load or are you planning to add a dump resistor before the rectifier on a battery charging scheme?. In every case it will need a special controller, an excessively large and costly alternator and if you loose load and it comes out of stall you loose the machine unless you have a back up mechanical shut down.

Flux

[dinges]

I think he has mixed up 'dump loading' with 'furling'. There's a clear distinction between the two.

Furling protects the windmill against too high wind conditions, the dumpload provides a constant load on the windmill so it won't overspeed when the battery is full.

Both have very distinct functions. Furling is a mechanical process, dumploading is electronic.

http://www.otherpower.com/glossary.html

Or read from the link below the parts on 'furling and shutdown systems' and 'regulation':

http://www.otherpower.com/otherpower_wind_tips.html

[Disaster Transport]

I was planning on useing a centrifical varriable pitch mechanism in the blade hub. Where the centrifical forces actually pull the blades out an inch to two inches, and a follower turns the blades along a slotted cover plate..Shaft moves out and turns at same time. Wont this be effective enough to not have to furl the machine.?In theory, I will have over speeding controlled by blade pitch ,if the mechanism works properly ,and be able to have a great startup pitch aswell..Right? I thaught elect. resistors allowed only so much output and held the machine back in overload ,wich wont actually slow the machine, it will only regulate the output ,is that right.? Its all new to me at this point. But if designed right I know it would work. Thanks for your help.

[Flux]

With a pitch control you have no problem with overspeed, there is no need for any other form of furling.

There is no real need to have any form of resistive loading as far as the mill is concerned. You do still need to prevent your battery from over charging or if you are using it for direct heating then you need to alter the resistive load with wind speed to make best use of the output but you have none of the runaway problems of a furling machine with loss of load or the wrong resistive loading for heating.

If you want to use a blade activated pitch control why not copy the Jacobs rather than play around with slides in slots that may work fine but more likely will jam or not stay synchronised.

Flux