Centrifigal Clutch

[whiskeygas]

just wondering...haven't seen anything like the concept on this excellent board. I hope this gets someone with more engineering experience than I thinking about it.

cheers!

whiskeygas

[Flux]

Considered it and rejected it many years ago. You don't need the clutch to engage more generators but it may be a viable solution to removing low power generators in high wind where they overload and become inefficient. Wind them right and they don't generate until speed is high enough, the snag is the low speed ones are best got rid of in high winds

In reality clutches and other mechanical devices are rather a nightmare for wind power and best avoided unless as a an absolute last resort.

Flux

[Norm]

As Flux says 'In reality clutches and other mechanical devices are rather a nightmare for wind power and best avoided unless as a an absolute last resort.'

  IMHO should only be considered in the hobby

class like a stepper motor that cogs too much

....then a simple centrifugal clutch just the

opposite of some Yoyo's that disengage above a

certain rpm allowing them to 'sleep' until rpm

drops, but this is in the fun part where  wind

is low and expectations run high !

[whiskeygas]

my thoughts were a low-wind-tuned genny with clutched higher-power genny for higher winds. I've been reading the board and find much about winding for certain wind levels, but as I am in a lower-average windspeed area of the US I thought I might get juice in both scenarios with something like this. Guess it just shows I have a lot more to learn : )

whiskeygas

[Madscientist267]

What about a mag clutch? Centrifugal would probably have significant losses within the 'grey-zone' RPM, but a magnetic clutch could be set up to engage hard at a predefined RPM. Just a thought...

Steve

[Dave B]

Go for it, try it, help us all learn. Sure it can work and if it's you passion then don't be discouraged by others who basically state what you already know, (it's the path less traveled). Dave B.

[ghurd]

Make a 3 phase for low wind and connected Star.

Use a circuit that comes on in higher wind which switches Star to Jerry Rig.

The result would be the same idea.  Best of both worlds.  An electrical solution in place of the mechanical solution.

"Guess it just shows I have a lot more to learn".  Who doesn't!

It'll take me a while to call Jerry Rig something new, like "Individually Rectified".

G-

[tanner0441]

Hi

I tried a magnetic clutch some months ago from a car AC system.  Not impressed, slip ring didn't like being out in the weather and more wires going up the tower.

Brian.

[Ungrounded Lightning Rod]

The problem is not to get the genny to be disconnected until it's up to speed.  In a battery-charging application that happens automatically:

 - At speeds below "cut-in" the voltage generated is less than the battery voltage plus the diode drop, so no current flows.

 - Once up to speed current starts flowing.

Until the current is flowing, a core-less alternator (like our homebrew axial flux machines) puts essentially no load on the shaft, while one with a core only applies a very minor drag from eddy-current and hysteresis losses.  The main load is from the interaction between the magnetic fields from the output current in the coils and the field magnets, which steal mechanical energy from the shaft to provide electrical energy to the coil connections.  This only happens to the extent that there IS a current in the coils.

The problem is to DISconnect the low-speed alternator when the speed is too high and to gracefully REconnect it when the speed drops (so you don't "slam on the brakes" and shock the spinning mill.)

We have played around with doing that electrically, making a two-speed "gearshift" by switching between Y and delta (or Y and Jerry-rig).  Look up delta-Y switching on the board.  A two-alternator system with the low-speed alternator disconnected by a clutch at high speeds would have exactly the same issues (plus mechanical problems from the clutch and the extra bearings and activation mechanism).

[Dave B]

Might not be thinking backwards if he is planning on heating direct instead of battery charging. Unloaded for start up and kicking on the load(s) as RPM increases.  Dave B.

[Flux]

For heating a two machine approach could work and it could work with a clutch ( in theory) but it would be simpler to use a contactor to engage the second machine. Having eliminated the clutch you would be back to using a speed sensor to control the contactor.

Why use 2 machines with redundant copper and magnet for a lot of the time when one machine would do. Back to the original concept in the end. Start with no load, switch load 1 when enough wind, add a second load when the prop starts to run away. Three stages would be better.

I am not trying to discourage any original thinking, I have found from bitter experience that mechanical contraptions are a pain on a wind generator ( at least here in the UK where weather conditions make them very troublesome) A centrifugal clutch will almost certainly burn out in the transition region and magnetic clutches will be a maintenance problem for eternity. It can be done, no doubt it has been done, certainly it has been done hydraulically. For large installations where regular maintenance is available then things are different but for small scale home use it will fail sooner or later.

Flux

[SparWeb]

I can't picture a centrifugal clutch working well.  That said, many single-phase motors have built-in centrifugal clutches that switch-out the start capacitor, and this works well in my drill press.  If one of these could be fit to a small wind turbine, provided that the activation speed could be adjusted, the wires can take the current, and the switch can be made "normally-off" instead of the other way 'round, then after all that stuff was set straight you might have something you could try.

I have seen centrifugal activation of prop pitch control, however.  If you're interested in that idea, look up forum member "lforbes" who has posted pictures of his working 12 foot blades.

[Flux]

A centrifugal switch is a perfectly satisfactory device and I have used one for star/delta long ago before the frequency conversion chips were readily available.

Don't try to adapt a motor starting switch as these are designed to remove the capacitor at about 80% speed but intentionally they don't reconnect it until the motor is nearly stopped, you need a very small differential for this application.

Flux

[SparWeb]

"...and I have used one for star/delta long ago..."

How did that work out Flux?  Sounds like you didn't use a motor starting switch, so what did you use?  Something off the shelf, or built from scratch?

[Madscientist267]

I definitely like the switch idea over a mechanical design, however I would think that a simple 'fly out and make contact' type switch wouldn't be ideal either.

It would seem that there would need to be some hysteresis, but how much is too much? Nuisance cycling would be likely since the prop could slow down a bit when the wind is blowing consistently at around the turn-on speed, then immediately opening again, witht he cycle repeating, right? This would just kill the contacts on the master relay prematurely.

[Flux]

Can I reply to you and spar-web in the same post.

The switch I used was home built and was based on the type of thing that was used in those days for the speed control of universal ac motors. It was on a speed increased alternator and would have needed a large weight on the spring contact to be used with a modern direct drive alternator. It was a messy thing with slip rings and as I said it was before modern electronics. Today I would not consider using anything other than alternator frequency and a 2917 chip.

There is no need for hysteresis in the switch, that is inherent in a star/delta change.

As you go from star to delta the alternator speed rises for the same power loading and the prop speeds up. When you drop back to star the loading speed drops. The system alone gives a very significant differential and you don't want to increase it with the switch ( you have to add a tiny bit with the 2917 tacho or the relay will chatter no matter how much you try to slug it, but keep it very small).

Flux