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Stubby
10-22-2009, 03:11 AM
Odd question.
Is there a way to modify a chainsaw clutch to make the clutch engage at a lower rpm?
I fabricate wind generator components and I was to experiment on using a clutch. This should allow the blades spool up in sooner then engage when the blades have develop enough torque to continue spinning.

Ideas?:confused:

darryl
10-22-2009, 03:39 AM
Is there a reason to need a clutch? I would think that any generator could be 'hard wired', or direct coupled, and when there's more than enough speed available it would either start to generate more voltage than the battery it's charging, if a permanent magnet design, or a relay would cut in to supply the field winding, if it was an alternator. In the case of an alternator, a circuit of some kind would have to sense the rpm and operate a relay to supply the field winding at the point where it could generate more power than the field would take.
A chain saw clutch, or any similar one, is going to slip quite a bit at the point where it's just starting to cut in, so that might not be an optimum solution. That type of clutch is designed to respond to large increases in rpm, where the clutch action changes from not engaged to strongly engaged over a short period of time.

In the case of a windmill, it's likely that the clutch would be slipping a large part of the time, so a lot of energy would be wasted, and it would wear out early.

Ironic- lately I've been thinking of adapting a direct drive washing machine motor to a windmill. This would be direct drive, no gears or belts, etc. I figure that having a dual set of windings on it would allow me to charge a battery pack at a lower current, but sufficient voltage, when the rpm is low, then charge at a higher current from the other winding when the wind speed has picked up. A relay would operate from the higher voltage winding to switch over to the higher current winding when there's enough power in the wind to generate significant power.

figge
10-22-2009, 03:41 AM
The key is to make the weights heavier, or the feather weaker.
Often there are no space that allows bigger weights, so
i once drilled a couple of holes trough them and filled those holes with lead.

you can also try to replace the feather that holds the weights with a weaker one.

winchman
10-22-2009, 04:27 AM
I'd look at a magnetic clutch like those used on automotive AC compressors. They get full engagement with 3 amps at 12 volts, but it takes a lot less input to get enough grip to transmit significant torque. You could put in a new coil to get the torque you need at a different combination of voltage and current.

The magnetic clutch will have a superb double-row ball bearing that supports the pulley, and the clutch pulley is made of steel that machines and welds easily. You could mount a pretty large blade right on the pulley/bearing with a few easy modifications.

http://img144.imageshack.us/img144/9607/maximaaccompdw6.jpg

They're readily available in a wide range of sizes for reasonable cost, too.

You could get a junked compressor with the clutch, gut the compressor, and install the clutch mounting end of the housing right on your alternator. You could probably modify the hub of the clutch disc to fit the alternator shaft.

Roger

dr pepper
10-22-2009, 06:50 AM
I have seen auto air con compressor clutches used for other stuff too, thats a good idea.
If you guuted the comp, you could mill a slot in the side, fit a pulley on the shaft and connect a v belt to it to drive your alty.

Evan
10-22-2009, 07:54 AM
Scrap the idea of using a centrifugal clutch. They depend on the high rpm of small motors to operate. Simply modifying it by weakening the springs or similar will not work because at lower rpm it will have much lower friction and no effective grip. I know because I have tried it.

The air con clutch is the way to go. They are made to last and have the ability to transmit at least several horsepower at any rpm you will require. Here is one salvaged and ready to use for whatever I decide.

http://ixian.ca/pics6/airclutch.jpg

http://ixian.ca/pics6/airclutch1.jpg

EVguru
10-22-2009, 08:04 AM
What's the point of trying to get the wind turbine to cut in earlier if you just throw the energy away in an electromagnetic clutch?

Wind turbines have three speed ratings.

Start up speed. The wind speed at which the friction is overcome and the blades start turning.

Cut in speed. The wind speed at which the generator is turning fast enough to produce enough voltage to start pushing current into the battery.

Rated speed. The wind speed at which the trubine produces it's rated output. This may or may not be the maximum output.


Adding a clutch might improve the start-up speed, but won't do anything for the cut-in speed.

airsmith282
10-22-2009, 08:43 AM
why dont you just turn up the low idel so the cluctch will enguage sooner beats messing up the saw and its safer then messing with stuff you just shouldnt mess with...

Evan
10-22-2009, 08:47 AM
How do you turn up the low idle on a windmill????

airsmith282
10-22-2009, 08:50 AM
ya ya my bad i just woke up sorry , i miss the wind generator part lol

airsmith282
10-22-2009, 09:19 AM
use a ligher tension spring on the chain saw clutch and it will enguage faster/sooner then it normaly would,

A.K. Boomer
10-22-2009, 11:37 AM
What's the point of trying to get the wind turbine to cut in earlier if you just throw the energy away in an electromagnetic clutch?

Wind turbines have three speed ratings.

Start up speed. The wind speed at which the friction is overcome and the blades start turning.

Cut in speed. The wind speed at which the generator is turning fast enough to produce enough voltage to start pushing current into the battery.

Rated speed. The wind speed at which the trubine produces it's rated output. This may or may not be the maximum output.


Adding a clutch might improve the start-up speed, but won't do anything for the cut-in speed.


Just dragging this over to this page as it's right on the money.

There's no need to use a clutch of any sorts, If mechanical it will simply result in more complexity and possible waste precious energies, If electrical it WILL result in wasted energies.
The only complex mechanical addition is to keep the blades from over running and destroying themselves --- this can be done by feathering the blades individually or a mechanism that rotates the tail vane 90 degree's and in some cases applies a brake,

Blade feathering is the preferred method due to being able to control the individual blades from a central centrifugal mechanism that unlike braking/tail vane systems will not wear out or need adjustment, if done properly it can also aid in the lowest start up/cut in/rated/ and maximum output.

Iv been kicking around an idea since i was young and found an example yesterday while browsing windmills, The low end torque of the old water pumping windmills were generally too slow for using in an electrical generator -- until now...
I thought about doing this but was going to use the blades to drive a large ring gear and massive planets and drive the generator with the sun.
I pondered about going gearless with a huge circumference motor but quickly abandoned the thought due to weight/awkwardness and unpractical.

The cut in speed for this windmill is an amazing 2mph, Im guessing start up and cut in are either extremely close or one in the same.

http://www.popularmechanics.com/technology/upgrade/4332392.html

Carld
10-22-2009, 11:51 AM
Stubby, doesn't the pitch of the blades control the speed of the wind generator? If so then why is there a high start up load? With the blades at a high pitch the wind would start the blades and gen. turning easily and as the speed increases the pitch control would reduce the pitch so the rpm of the gen is within the rated spec.

If there is no pitch control on the blades then the gen. would over speed so it has to have some kind of speed control.

EDIT: hmm, I got interrupted by a phone call as I was posting and Boomer posted much the same thoughts as I did.

jnissen
10-22-2009, 12:17 PM
Magnetic drag will limit most turbines from starting up at low speeds. The rotor with the magnets will cog past the windings. Takes a bit of power to overcomes this then it will start to rotate. A variable air gap axial design can eliminate a lot of the early drag but then again that makes it more complex. I built an axial design alternator for a turbine a few years ago with my son for a Science fair project. We could reduce the startup speeds by just spacing the coil /magnet further apart. Of course this reduces the efficiency so yes it turns but does not generate much energy!

.ps I really like that Honeywell design. Got the old gears turning on how to build one.

Carld
10-22-2009, 02:37 PM
That's good but you still have to control the rpm of the gen. to keep from over speeding it. I suppose you could put a system to move the magnet away from the rotor when it's not rotating and then when the blades reach a certain rpm the magnets move into their charge position but you still have to control over speed.

jdunmyer
10-22-2009, 02:42 PM
It seems to me that the best setup would be an excited-field alternator, not a PM job, so as to eliminate the 'cogging' effect and allow the blades to begin spinning easier. Use a speed sensor on the alternator shaft or a seperate anemometer to engage the field circuitry. The field current would ideally be automatically adjustable so as to allow the blades to run at optimum speed, while pulling optimum current from the alternator.

Unless things have changed since I last studied wind power, there is nearly NO useful energy in winds of less than 7 Mph, so a "low startup speed" that sounds nice is really pretty useless. Those things only become kinda useful when the wind speed gets to 12 Mph or more, and most wind turbines are "rated" in a 25 Mph wind.

I had a HeathKit weather station for many years that has an anemometer as one component. You'd be amazed at how windy it 'feels' at 10 Mph, and 25 seems like a hurricane. Winds seldom reach useful levels in our area, YMMV.

Evan
10-22-2009, 02:46 PM
That's good but you still have to control the rpm of the gen. to keep from over speeding it. I suppose you could put a system to move the magnet away from the rotor when it's not rotating and then when the blades reach a certain rpm the magnets move into their charge position but you still have to control over speed.

It seems to me that the easiest way to regulate max rpm is to shunt some of the power to electromagnets as part of an eddy current brake on the rotor. Dead reliable and cheap to make.

kendall
10-22-2009, 06:06 PM
Think the AC clutch would work nicely. Think with a small generator built into the blades, or the clutch itself you could possibly tune it so it engages the primary generator at the desired RPM.

Alternatly, a smaller windmill set near the primary could provide power to the clutch, and engage it when an attached tach signals that the speed is high enough (possibly installed at the other end so it's driven from the 'exhaust' air?)

The smaller low power windmill's output could also be used to provide a maintenance charge to batteries if the wind isn't strong enough to run the larger mill.

Ken.

Carld
10-22-2009, 08:40 PM
Evan, that may work as it would be a variable brake but would take energy from the system and may generate to much heat. Why not just use a centrifugal controlled blade pitch change system. It would not take energy or build heat and be nearly bullet proof.

darryl
10-22-2009, 10:33 PM
Sure are a lot of variables to wind power. At one point I wondered whether a pumped fluid system would be valuable- it could take the form of an over-speed brake by driving fluid through small diameter tubing which is immersed in a tank of water. Somewhere around the point where the generator is outputting maximum, a parallel driven fluid pump would begin to operate, dumping excess energy in the form of heat into the water tank, and putting some brakes on the windmill. The heat in the water would be drawn off to heat the building, which is a need that pretty much goes hand in hand with high wind speeds. This fluid braking system could also stall the blades by closing a valve, which would prevent the pump (and the blades) from turning. Before this point, the fluid bypass would be closed, which causes the fluid to go through the heat exchanger in the water tank. At low wind speeds, the bypass would be open, so the pump wouldn't restrict the windmill and the generator would get all the input energy, minus some losses of course.

I've always figured that in high winds, there is so much more than the average amount of power output available that you'd want to take advantage of that somehow. Having to stall the windmill to avoid having it fly apart is kind of wasting its potential.

Of course, everything you do to make it more useful also makes it more complex. A variable pitch blade system would work to keep the speeds within limits, but it also bypasses a lot of the potential power that would be available from it, if you had the means to extract it. The generator is only going to be capable of so much, and what do you do with its output anyway if your battery bank is already topped up- seems wrong somehow to waste it- but it could also be sent to the water tank or resistance heating.

Imagine your house getting warmer instead of colder when high winds are blowing-

The Artful Bodger
10-22-2009, 10:33 PM
How do you turn up the low idle on a windmill????

Change the pitch of the blades.

The Artful Bodger
10-22-2009, 10:38 PM
Look at this site http://www.thebackshed.com/Windmill/FORUM1/forum_topics.asp?FID=2&PN=1 if you are interested in direct drive washing machine motors as wind mill generators. These guys have been doing it for years and have all the information you need, wiring, voltage, fitting more powerful magnets, making blades, furling, cogging. Everything.

"F&P" and "smartdrive" are names of the machines they use.

Carld
10-22-2009, 10:45 PM
darryl, many of the wind generators put unused current into the power lines so with that condition you could be generating near full output as long as the wind will do it. Some systems have a battery bank and they still put unused current into the power lines.

Where there are no power lines and the wind gen. is the only source of power and the battery bank is fully charged then you could feather the blades to cut down on wear and tear of the system.

Evan
10-22-2009, 10:52 PM
This is my design for a relatively cheap and very simple variable pitch wind turbine blade. I would have built this long ago but we have too many trees to use wind power. I thought this up over 30 years ago.

http://ixian.ca/pics6/windblade.jpg

Black_Moons
10-23-2009, 03:24 PM
If you use an alternator insted, they have 0 cogging untill you apply a rotar field current, also the torque they require to turn while outputing a charging voltage will depend entirely on how much field current you apply.

Only problem is car alternators are usally like 3000~10000rpm so you'll likey need a custom one. it is rather efficent to supply a field coil however because you can do regulation by it, so power that would of been lost with regulation is used to power the field coil insted.

darryl
10-24-2009, 05:03 AM
Black Moon has raised some good points about alternators. It definitely is handy to be able to regulate output by varying the field current, and within reasonable operational limits they are quite efficient. A typical car alternator might draw 3 amps for the field (the rotor), so that represents about 40 watts or so of 'wasted' power. That could be for a 50 amp unit, and that represents about 600 watts. Ignoring other losses for now, that's about 93% efficient. Who's gonna complain about the other 7% when the input power (wind) is free, and not easily quantifiable anyway for its power density. You don't really need a permanent magnet generator in order for wind power to be efficient- it's largely a choice of how you want to regulate the output, and in what way you want to use the output.

If you want the most from the least rpm, permanent magnet is probably the way to go, and in that regard these pancake style direct drive washing machine motors look pretty good. If you could find an old or abandoned multi-kilowatt standby generator or similar, you could probably make up your own alternator which would work similarly to the permanent magnet motor, except you'd have control of output via the field current, and freedom from cogging or stalling at low speeds as Black Moons pointed out. If you found something with a rotor a foot or more in diameter, you could salvage say an inch or two of the length of the rotor and field, which might be fifty or so laminations, to make your pancake alternator out of.

The whole premise here is that you might want to avoid gears and belts and pulleys, and complex power electronics, etc to keep things simple and reliable. Because the speeds expected are so slow, you'd go as large in diameter for the alternator as you can.

QSIMDO
10-24-2009, 12:48 PM
Gentlemen.
Stubby left hours ago.