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Forum Index : Windmills : emergency stop mechanism
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imsmooth Senior Member  Joined: 07/02/2008 Location: United StatesPosts: 214 |
I plan to have a short switch for an electrical brake. However, if the blades are two big for the generator I will need a mechanical brake. What have people done here? Would a bicycle brake work which I could pull with a rope? Any better suggestions? |
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| KiwiJohn Guru  Joined: 01/12/2005 Location: New ZealandPosts: 691 |
I think a bicycle brake would be too small for any but a really small mill. How about a trailer brake mechanism? |
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| imsmooth Senior Member Joined: 07/02/2008 Location: United StatesPosts: 214 |
what does a trailor brake mechanism look like? How would one tell if the electrical braking is sufficient for the rotor diameter other than the "real world" test? I know how many watts the rotor is theoretically suppose to make for a given wind, but how many watts does a shorted unit need to get it moving? |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5116 |
I think Bruce has used a bike brake in the past. You can buy a disc brake conversion for push bikes, includes the disc, caliper, etc. Not cheap, over $50 from memory. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691 |
Trailer brakes are what you have on your caravan, boat trailer or whatever. There are various kinds mostly using a steel disc with some device to grip it actuated by hydraulic, electric or cable. Similar things are used for the 'hand brake' or emergency brake on cars where they are usually cable operated. I assume a cable mechanism would be best for a windmill. If I understand correctly a F&P once over-reving stops producting significant power (due to flux saturtion?) so the shorted circuit brake will under extreme conditions stop working. A simple pulley brake is not hard to make, this is a simple 'V' belt pulley on the shaft and a length of matching belt. One end of the belt is attached to the frame and the belt is draped over the pulley with some lever attachment to tension the other end. In normal operation the lever is up so that the belt just lies loosely in the pulley groove but pulling down the lever tensions the belt and the action of the turning pulley pulls it even harder into the groove. 
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wind-pirate Senior Member Joined: 01/02/2007 Location: CanadaPosts: 101 |
A trailer brake will work. But draws mega amps. And It will get very hot quickly.(The drag Mags) I think you might be better off looking at a brake from a motor cycle. Something hydrulic that can be left on during a strom. Ron THE Pirate. stealing wind & solar energy is fun |
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Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
Ron, its not mega Amps really. I measured the current that my trailers electric brakes draw at 5A max per wheel. So they could be used to bring the shaft to a stop, it would be best if there was some other positive locking mechanism that takes over then to avoid over heating. Electric brakes do have a slight drag when not energized which may be undesirable. Any type of brake that does not completely lock the shaft to a standstill will generate heat, I would try a solenoid operated shaft locking bolt for that. Tinker Klaus |
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| KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691 |
I guess one could get really cute and use the electric trailer brakes as a dump load!  Mill starts to over rev, voltage goes up, excess voltage diverted to trailer brake and mill slows down. |
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| imsmooth Senior Member Joined: 07/02/2008 Location: United StatesPosts: 214 |
KiwiJ, Your method with the belt and lever seems simple enough. If high winds were coming I could lock it down. What material should I use for the belt? Leather? Synthetic? Metal strip? |
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| KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691 |
Imsmooth, I think the best thing to use would be a 'V' section pulley and of course the belt to match it. The bigger diameter pulley the more effective the brake will be. I dont think synthetic would work as most materials would melt and weaken at the worst possible moment, leather would be OK on a smooth metal or wooden pulley and steel strip would be good for really heavy duty but you would need a lot of tension to make it work. |
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