shutting down

[windspeed]

we have over 30 knots on the west coast of Ireland regularly

I can't shut down my 10ft with the shorting switch,

I am making a mechanical shutdown but the weather is too rough to set it up

my question is

by loading the three phases before the rectifier would it shut down easier

Windspeed  

[TomW]

speed;

I would suggest you only short it before the rectifiers.

No need to load the rectifiers plus the issues of shorting it at the battery. Not sure how you would short it "after" the rectifiers anyway?

Also be aware that, even fully shorted, you get some rotation. It has to do with only getting braking action if there is movement between coils and magnets. My 10 foot Danbilt will rotate about 20 to 30 rpm even shorted in higher winds, for instance.

Hope that all makes sense?

Good luck with it.

Tom

[Dave B]

 If your blades are similar to the plans and what most here are flying and the rest of your alternator is the same also you will most likely be as successful as others shorting out the phases as a shut down mode.

 Higher torque blades can start up in high winds completely shorted and go into run away burning out your stator and then possibly worse as the machine free wheels. Been there done that and learned from it. Also, if you have an open circuit on any or all phases your shorting switch will be less effective or possibly useless.  

 I now have a mechanical brake cable operated from the base of the tower. I would never again put up any machine without this or another mechanical means as well as shorting it out to keep the machine in the no-run mode. It is a great piece of mind.  Dave B.

[Flux]

You have to have a very powerful alternator to shut down in a storm. You don't say exactly what the alternator is but if it is based on the 2 x 1 x 1/2 rectangular magnets then I suspect it will not stop in very high winds. If you catch a lull in the wind you may get it stopped and with a bit of luck it will hold stopped but even that is doubtful in your wind area.

If it is furling correctly and holding the alternator current safe it is far safer to let it run. If as I suspect it is one of many that don't furl safely then you have a dilemma. Let it run and take a chance or try to stop it. Unless it stops in 30 seconds you would be best not try to stop it. Either catch a drop in the wind or try adding some resistance to the phases ahead of the shorting switch and see if you can extract more power from the prop and slow it to a point where the brake switch will stop it.

With the alternator efficiency down below 40% you may never be able to stop it unless the wind gives you a chance.

Brake switches are simple and convenient for modest wind areas but leave something to be desired in high wind areas. Either make it furl safely so that you can leave it running or devise some alternative shut down method. I like Dave would never risk not having a backup. I prefer to turn the tail at right angles and pull it at right angles to the wind but a really effective brake will do the job but in your wet climate you may need to maintain it well and test it often or it will fail when you need it.

Flux

[imsmooth]

I know you have seen this link, but for others who haven't:

If you go to http://www.mindchallenger.com/wind/wgpage14.html you can see the mechanical braking system I have come up with that works very well, and in very strong winds.

[windspeed]

thanks to all

yes Flux this is what my query was about

"adding some resistance to the phases ahead of the shorting switch and see if you can extract more power from the prop and slow it to a point where the brake switch will stop it."

would a rheostat where the load could be varied be helpful

thanks

windspeed

[dlenox]

Here is another design that I used on my 17' wind turbine.

It uses a manual go-cart caliper coupled with a 12v dc actuator to engage.

The page is: http://www.briery.com/wind_turbine/build_log3.html

go to the portion dated 10/18/07

Dan Lenox

[Flux]

If you have 3 low value rheostats that you can add in series with the line then give it a try. It is a grey area as far as I am concerned, I have not generally had any desire to use brake switches to stop these things.

If your machine is operating towards stall then I assume that any resistive volt drop that you introduce must be lower with the brake switch closed than the alternator produces into the rectifier when charging the battery. If not then it will move away from stall and get completely out of control.

You are aiming to produce a loss greater than that from the internal resistance of the alternator to gain more braking torque but the ac line voltage into the resistors will have to be lower than the normal rectifier input voltage to load it more than the battery.

The series resistors will be low. As  a rough guide take your full input line current ( dc value will be near enough) and choose resistors that will produce nominal ac line voltage at this current. If using rheos you can leave them set to zero resistance and leave them in circuit. Close the brake switch and increase resistance to get the blades to slow to the lowest speed then try reducing the resistors to see if you can get it to stop. Try to use times of the lowest wind speed to do this.

Basically you are relying on the loading into resistors maintaining as the speed falls to get you stalled down to stopping point. The battery holds stall at working volts but the load vanishes below cut in and that is the bit you are trying to maintain down to stop.

If the alternator can't hold it stopped when completely shorted ( no resistors then this is a non starter, but often the thing will hold even if it won't stop it.

It will never stop, it will crawl round at a low speed but that should be fine as long as the short circuit current is below the stator rating.If it gets away from the crawl then you will soon destroy the stator and it would be safer to let it go and run into the battery.

Whether this will help at all may depend on the line resistance. If you have long ac lines it may not help at all. In which case trying the short on the ac lines at the base of the tower may be worth a try.

Flux

[Chris OC]

On the subject of mechanical brakes has anyone ever tried a scooter clutch assembly?

Its just an idea not something I have tried: The clutch friction part could be fitted to the turbine spindle with the clutch bell fixed to the turbine. When the RPM reaches a certain level the clutch will engage slowing {but not stopping} the turbine. Different weight springs are used to make RPM adjustment. I know this is not as good as a well designed furling system but could be retro fitted to most turbines and used as a last resort!!

Regards

[Shelly]

I am new to wind generators but have an ARI 750 12v to supplement the solar panels I have. This is braked electronically with an over-ride switch at the controller. Last night the blades broke in a storm because the generator was braked because the controller overcharges in a high wind. A discussion is now in progress with ARI. Having spent a few hours thinking about it, I wonder if a possible solution is not to completely brake the generator but allow it to spin slowly. I know that a dump load can be used but I wonder if anyone has come up with an "intelligent" dump load that is able to alter its load thereby altering the prop speed. Just an idea.