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Farm windmill

PostPosted: Thu Apr 08, 2010 12:45 pm
by marshdog
Can a conventional 10 foot farm windmill be converted to generate electric power?

Re: Farm windmill

PostPosted: Thu Apr 08, 2010 10:52 pm
by bellboyrsa
Hi there Marsh. Most definetly yes! I spoke to a guy a few months ago that do maintenance on windmills and he told me it is allready been done.

As a windmill allready has a gearbox in it should be to difficult to replace the up and down motion with something that can turn around at the desired speed by replacing one or 2 gears.

Re: Farm windmill

PostPosted: Thu Apr 08, 2010 11:31 pm
by windgat
I have also heard of people who have added a belt drive at the top of the tower, and bolted on a car alternator. It needs to be geared up a lot, as the alternator needs to turn fast to generate enough voltage.

Re: Farm windmill

PostPosted: Sun Apr 11, 2010 9:54 pm
by bellboyrsa
Windgat I pondered about this this afternoon. If I'm correct a altinator needs about 1000 rpm's to start charging. If a windmill is giving you 1 turn per second it means 60 rpm's.
To up this to more than 1000 rpm you will have toget a gearing connecting in 1 or more stages that will up the speed. To do this in 1 stage 1 might need a weel or gear of about 1500mm in radius on the windmill. On the alternator side you then needs a weel or gear of about 75mm radius.

If I remember correctly from school maths the formula for the surcumfere of a circle is 2 x phi x r.

This means on the winmill side with 1500mm radius with 1 revolution the length is 2 x 22 x 1500 all divided by 7 = 9428.57 mm
On the Altinator side 1 revolution is 2 x 22 x 75 all divided by 7 = 471.43 mm

If I divide this into 9428.57 I comes to a value of 19.999999 or 20. This means that for every 1 revolution on the windmill I get 20 revolutions on the altenator and therefore if the windmill does less than 1 turn per second resulting in 50 rpm's x 20 on the altenator I will have 1000 rpm's on the altenator. On 60 rpm's it will be 1200 rpm's.

I'm not sure how practically a 3m diameter wheel or gear will be on a windmill and I will think apart from aditional losses due to gearin a multiple gearing aproach might be better to get up to the desired rpm's.

200 mm - 50 mm ratio is 1-4. If I repeat it 3 times it will be 4 x 4 x4 = 64 time!
64 x 40 rpm's = 2560 rpm's that should be a nice save speed to run a altinator on.

Myself will also install a shunt resistor inline with the output of the altinator to limit the amount of currnent that can be drawn from the altinator to prevent the altinator to brake the windmill completly due to execive current being drawn from the altinator by the load or batteries.

Re: Farm windmill

PostPosted: Tue Apr 13, 2010 10:46 am
by windgat
Perhaps 2 stage is the way to go, to minimise losses? A ratio of 8 x 8 = 64 as well.

Re: Farm windmill

PostPosted: Thu May 26, 2011 10:44 pm
by bdean
If anyone has done this with any success, I would be most interested in some photographs - etc. I have a 12 ft farm windmill available. I have been considering this for some time. These windmills generate a HUGE amount of torque --- but, they don't turn very fast. You also have to control the tail to set it off-axis when it does start to over-spin a bit. What is that rate??

As I have considered this, it seems that it makes the most sense to somehow transfer the spinning power to the ground below the tower somehow. Maybe you use the traditional up-and-down pumping rod to connect a coorisponding cam and flywheel on the ground. Or, maybe you install a low RPM high volume hydraulic pump at the top, and then use a hydraulic motor to spin the flywheel on the ground.

The flywheel would serve as a speed stabilizer, and would also provide a large circumference surface against which to power the generators/alternators. For a consistently windy environment, it seems you could pull a fair amount of power from such an arrangement. You just have to be very careful to gaurd against losses in each stage (oversized hydraulic hoses, etc.), smooth bearings, etc.

My primary interest is to retain the classic "look" of the rural windmill -- while turning it into a productive player on the ranch.


Re: Farm windmill

PostPosted: Thu Jun 02, 2011 7:03 pm
by windgat
You could just use a car-type regulator to avoid overcharging the battery. The windmill can work as it usually does, and the regulator will cut current to the battery when necessary. Its not an RPM rate that should trigger the cut - its the voltage as measured across the battery.

Re: Farm windmill

PostPosted: Mon Jun 06, 2011 5:57 pm
by dawie
Most car alternators are connected in delta, and changing to star gives a slightly higher output voltage. Then it is useable from slightly lower rpm's.

Typical Lundell type car alternators only have about 50% efficiency or even less at max output. If rotor is about 3 ohms, then at 14V and low rpm's it needs 42 Watts before it starts giving any output.

Most are not self-exciting, and needs a bias current via the warning light and ignition switch of the car.

Some have modified the rotor to use neodymium permanent magnets. Then it provides an output from much lower rpm's.

One way is to retain the rotor's "claws", remove the wiring inside, and fit the magnets there. A stainless steel shaft then has to be used, (which is non-magnetic).

The other way is to replace the "claws" with neodymium magnets. Could be a problem to keep the magnets secured at high rpm's/ (centrifugal forces).

Modified permanent magnet rotors are for sale in the US, but may only fit Delco-Remy alternators (from those huge US cars). Think it is for the Delco 10si and 12si alternators...

A special regulator will obviously be required. Large motorcycle-alternators have permanent magnets and use a different type of regulator.

Re: Farm windmill

PostPosted: Sat Jun 11, 2011 8:53 am
by windgat
Yes it can. If you use an alternator, then a gearing system is needed to turn the very low rpm of the blades into a fast enough RPM to generate the required voltage. Or you can build a low RPM generator, as described on the main site, and connect it via a belt or gear system.