Putting the brakes on!

[alibro]

Has anyone ever come up with a successful system for slowing down a wind turbine during a storm using brakes? I only ask as I have painful knowledge of what happens when a shorting switch is thrown when the wind is blowing too hard. It seems a shame that we can't, especially as many turbines are made using car disk brakes.

If a third brake disk was fitted the brake could be activated mechanically when the tail starts to furl. Or it could be activated electronically using the rpm of the blades as a trigger, or voltage/current monitoring.

I have no idea how this could be done in reality but thought it might be an interesting question to throw out

Cheers

AliBro

[thirteen]

depending on any extra space they make a small disk brakes that may be used if machine in correctly. they are on remote cars but may not be heavey enough. Look in a robot construction Not sure of the magazine. I believe it has to do with centirficl(sp)force. Just an idea.

[racingbrett]

just an idea but why not use a motorbike caliper and disk, there small sized and lightweight and should provide enough stopping power, just a case of fitting it into the machine somewhere.

[nanotech]

The only part about putting a mechanical brake on the hub that would scare the crap out of me would be the momentum in the blades.  

I'd be terrified of stopping the hubs and have the tip portion of the blades try to keep going.....

I think I'd rather go with a mechanical override on the furling system so that you can completely turn the blades out of the wind with the tail.

[DanB]

I've never had a problem shorting the machine no matter what the speed.  While it certainly puts great torque on the stator if you do it while output is high... I've still never had a problem.

That said - some other redundant system surely couldn't hurt - but I still think that with the air core alternator, if the alternator is not under sized - it will stop the machine instantly if you short it.

[seanchan00]

Hi Alibro,

Here's my mechanical brakes.

You can see on the lower part of the back magnet rotor my mechanical brake which will come to play when it furls fully. The stronger the wind the harder the brake force applied by the furling tail. A spring between the two plunger rods releases the brake pad contact when the tail unfurls. The brake pad is made from tire thread samples, which is flat.

See 2nd picture here in my post.

http://www.fieldlines.com/story/2006/2/26/21156/5171

SeanChan.

[zubbly]

hi nanotech,

i think if your blades are well made and the hub construction is strong (i always use steel hubs for the blades) shorting your machine out at high rpm should not be a problem.

just torturing my new 7.5hp unit with 12 foot prop lately, allowing it to hit 450 rpm free wheeling and throwing the shorting switch, stops it in 2 seconds or less. the tower shakes and the guy wires bounce, but all stays together. in my twisted way of thinking, if you can't do this, the machine shouldn't be flying.

lol!

zubbly

[inode buddha]

Here is a mechanical idea, Why not use a hydraulic cylinder connected to the tail? As the tail furls it shoves on the hydraulic cylinder, causing it to pump brake fluid into a caliper/dic. This way you get both a furling action and a braking action.

[Flux]

If you want an independent mechanical brake, then make it a good one capable of stopping the machine at all times.

I can't see any point of adding a brake to a furling system, it will not survive long and what is the point. Furling should hold the machine at the maximum power you choose for the safety of the alternator. If it can't do this it is not working ( there are many that don't but that is another matter).

If you want it to shut down above a certain wind then have some positive way to engage the brake and stop it.

A progressive brake load works at low power for gramophone governors and telephone dials but it will not survive a big windmill for any length of time.

Flux

[disaray1]

 You wouldn't want to try to regulate blade speed with brakes...too much wear on the brake, too much heat generated and transfered to other gen parts, and unless you use carbon fiber rotors and pads, WAY too much organic/metal grit around your delicate magnets, stators and such...just look at the dust on front wheels of your car.

  The only reason anyone would use a brake on a mill, would be to stop the machine IF your stator had already burned out, and your furler had bit the dust allowing total freewheeling...this would be a triple redundant..but could be done...I'd use racing go-cart disc brake system (cheap, easy and very lightweight) or motorcycle front disc setup.

 disaray1

[BruceDownunder]

Hi there,

I've fitted a bicycle brake disc to my 11 foot mill and yesterday applied the brake while the mill was going so fast you could hardly see it. The mill slowed and came to a complete stop within a few seconds.

The brake is featured in my irc  Picture album .

All the talk of this sort of control being useless is ignorance,or just the usual theory sprookers. I'd done it and it works !!!

Bruce

[Ungrounded Lightning Rod]

If shutting it down by shorting it in a high wind is an issue, add a manual furling control (for instance, a pull cord) to force it to furl all the way to 90 degrees to the wind when you want to shut it down - either for protection or to work on it.

At that point it will be going slowly enough and have little enough torque, even in a high wind, that the genny braking should be within reach of even an badly undersized alternator.

Once the mill is stopped stopped a mechanical brake to KEEP it stopped makes sense.  (But why bother when you can lasso a blade and tie it down?)  Trying to use a mechanical brake to STOP a mill is asking for trouble when it wears out, corrodes, or gets dust in the works.

[alibro]

Phew!

Looks like I opened a right old can of worms here.

The problem I had with shorting out the stator was it blew up one very windy night! I ended up with a very black and nasty smelling mess. However I must admit to having made quite a few errors during the building of my wind turbine which I documented in my diary.

I was thinking along the lines of having a shaft running backwards away from the alternator and mounting a brake disk on it. Because it is behind and up wind from the gennie, brake dust should not be a problem. Because it is on a shaft and not belt driven there would be no losses when the brake is not engaged. I guess this would be easier to achieve if the wind turbine was reversed, i.e. the blades are behind the tower and there is no tail as some comercial wind turbines are. I wouldn't think activating a brake should cause the blades any problem. Not unless it was so severe that it stopped the genie instantly. After all shorting out the coils does pretty much the same thing. The main question is how to activate the brake and is furling required. If I was really clever I would make an electronic trigger to activate it when the blades reached a certain rpm. Pity I'm not that clever.

I'd love to hear more thoughts.

Cheers all

AliBro

[seanchan00]

Yes Alibro,

Right now my mechanical brake system is the cause of all my troubles. First the spring which disengages the brake when I used to raised it worked but the other day a week back it didn't open due to time wear of the spring and the brand new 12 feet diameter blades which I just fitted won't budge. When lowered it again to find out why it was late and my friend helping me had to leave. In raising the tower again I lost control and smashed my new set of blades. Lucky for me the alternater is ok. 2 days ago I fitted back the old blades and used a long spring to pull the brake open when the tail unfurls on raising the tower. Again the damn mill won't budge. the cause this time is the spring not only pulled the brake open, it also put enough tension on the stator frame to twist the stator till it touches the magnet. Now I have to lower it again to sort it out. The most frustrating point for me is I don't have enough wind to even hope to see my genny furl let alone depend on the brake to stop it when the winds is too strong. This I found out only after I made the genny.

The moral of this story is anything you add on has the potential to cause trouble, when you least expect it. It costed me big time. I am wishing I can just dismantle the brake system but it is welded on.

SeanChan. (:<)

[jimjjnn]

Sean, Time to get the cutting torch out. Sorry for the misery that you are having. I know you will get her up and running and reap some good power there

[jimjjnn]

I love that design of your brake, Bruce. Looks simple and clean. I like the way that some fellas use a cable to furl the mills as it seems simpler.