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NeilTheCop 08-05-15 01:34 PM

Bouncing a idea around
I have been mulling an idea for a while now and wondered if anyone could give any input as to whether Iím wasting my time.
My idea is to have a turbine, vertical or horizontal, doesnít matter which but it needs to have a fair mass for a flywheel effect, geared up by pulleys and a Gates type toothed belt (97% efficient if their PR is to be believed), driving a car or truck alternator, depending on the size of the turbine.
I know all about the inefficiency of this type of alternator in turbine applications but my idea is to have no load on the alternator until the turbine gets to a specific RPM, then using PWM controlled by a micro-controller gradually apply current to the field windings, which will slow the turbine down and the pulse width would be reduced, reducing the field current, and the turbine would speed up again until it got to its set speed when the field windings would be activated again.
So the turbine will spin within a narrow RPM range all the time there is enough wind to turn the blades, no matter the wind speed, so you will generate power, however slight, whenever the turbine is turning, and it should turn at very low wind speeds with no load other than bearing friction and the belt losses.
Add to this if the turbine is generating itís maximum power and begins to over speed the micro-controller can active the dump load until it slows.


sunspot 08-05-15 02:43 PM


Originally Posted by NeilTheCop (Post 46262)
My idea is to have a turbine... geared up

That's the killer for an automotive alternator. Even a small, high speed, wind turbine only spins what? ~500 rpm? (guessing). Not nearly enough to get any real power out of your alternator. And with a small, high speed, wind turbine you'd need a tiny alternator (motorcycle?) or the 600ish watt load of a car alternator would simply stop it at cut in - barring some fancy electronics. To make this easier to visualize, would your windmill overpower and spin your tablesaw backwards?

You might have an easier time with a permanent magnet DC motor from a treadmill or similar.

Sounds like a fun project in any case. Good luck!

NeilTheCop 08-06-15 11:17 AM

That's why I would gear it up with the belt drive to about 2500 RPM. And pulse width modulation would allow the load on the alternator to be ramped up and down rather than abruptly switched on and off. The fancy electronics would be nothing more than an Arduino switching a power mosfet or IGBT. :thumbup:

sunspot 08-06-15 01:37 PM

5:1 is a lot of gearing. If you have a typical mountain bike put it in high gear (likely 3 1/2:1 so, still a far cry from 5:1). Lift the back wheel and see how hard it is to turn - after you take the pedals off and have only the drive axle to twist. A windmill with enough torque to start (without the alternator or heavy flywheel) will have a blade design limiting rpm to dozens instead of hundreds. See water pumping windmills for an example of those torquey low speed blades. Going that route requires even more gearing etc. etc.

Perhaps you could devise electronics to bring the transmission (and flywheel if you think you need it) into play after the windmill got up to speed?

You mentioned this was to be small windmill. You'd likely need close to 8' of swept diameter to utilize the potential of an average alternator. Small by many standards but a big project none the less (and the tower is an even bigger challenge - 30 ft above anything within 300 ft rule of thumb).

I've been pondering in a similar direction for some time now so I'm interested in what you come up with as your idea evolves.


gtojohn 08-06-15 11:04 PM

Even better build a constant velocity transmission. Like a snowmobile, honda helix, subaru low speed it gears down for torque as the load diminishes it gears up for speed. Of course this is much easier said than done.

mechanic 08-07-15 10:29 PM

I'm not sure on the efficiency of the automotive type cvt's but the snowmobile ones are quite inefficient. I used to tune them on a dyno (read at the track) and a sled with an 140hp engine was in the 50's at the track (there's a chain gear reduction to rob power on the way there too)... They are necessary in the snowmobile application though as it would be pretty hard to shift gears while plowing a couple feet of snow, especially with a peaky high performance two stroke that makes max power in a 300rpm window over an 8500rpm range...

mechanic 08-07-15 10:33 PM

The automotive ones I've seen apart actually look very similar to the open snowmobile type except there is a tapered chain running in oil instead of a rubber belt and the sheaves are adjusted by an ecu instead of flyweights, ramps, and springs...

NeilTheCop 08-08-15 12:32 PM


Perhaps you could devise electronics to bring the transmission (and flywheel if you think you need it) into play after the windmill got up to speed?
It's very crude, but I hope you get the idea from some simplistic pseudo code for a micro-controller.
It's far easier to change a bit of code than unsolder components :thumbup:

(Loop until true) Read the speed of the turbine until the speed is greater than the set cut in speed.

(When true) Read the speed of the turbine, store the result and activate the field windings using the shortest pulse width and move on to the main program loop

//Main program
Wait a set time for the load on the turbine to take effect (possibly 2 seconds but to be found by experimentation)

Read the speed of the turbine and compare it with the previously stored speed

If the speed is greater than the stored speed (turbine spinning faster) increase the pulse width and replace the stored speed with the new speed.

If the pulse width is at maximum and the speed still increases call the overspeed function

If the speed is less than the stored speed (turbine slowing down) decrease the pulse width and replace the stored speed with the new speed.

If the speed is less than the cut in speed deactivate the field windings and go back to the start

Else continue with the main program

Active the dump load or brake or furling

Keep reading the turbine speed until less than the set maximum speed then return to the main program

nibs 08-10-15 03:04 PM

Tossing cold water about;
As a one time manufacturer of small (200 Watt) turbines, I gotta tell you, that it is not likely that where you live (anyplace will do) gets enough wind to make a wind turbine worth having.
The number used to be 15mph average wind speed, now it may be down to 11 or so, but that is a most uncomfortable bunch of wind to be living in.
Then there is the engineering of the turbine mount, flywheel, gearing, mounting etc, followed by matching the blade to the local wind conditions and the load.
Good luck, but at $1.30 a watt the big box hardware store has a large deal on PV.

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