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## Wind energy => Wind energy generators => Topic started by: irethedo on November 17, 2008, 11:48:33 PM

Title: Finding the right generator
Post by: irethedo on November 17, 2008, 11:48:33 PM
I am helping my son with a science project and attempting to build a very efficient small wind generator.

We have a very efficient rotor design which can spin (without load) in 1.5 MPH wind but now we need  to
find a very inexpensive generator which can be spun easily and with as powerful of an output as possible.

I have read aboout people using tape drive motors but from what I have read, these are typically yield lower output
levels less than 10 W.

I have heard of people that use car alternators but these require too high of an RPM for substantial
power. Someone also mentioned to me that the older police cars and emergency vehicles had higher output
alternators which had a full output at idle but I have not been able to find much on these.

We would like to rectify the output and pass it through an inverter for ~ 120V AC @ 60Hz and perhaps we are dreaming but
we would also like to get 100 W if possible...

I was playing around with a flywheel off a briggs and the coil but didn't get very far...Not sure if there are any overunity configurations
out there that might be retorfitted for this task or not but thought I might ask on this board to see if anyone had any suggestions...

Can anyone recomend a relatively inexpensive generator that we might use for this project?

Title: Re: Finding the right generator
Post by: capthook on November 18, 2008, 12:58:28 AM
irethedo -

The power you can generate is directly related to the wind resource.  There are a number of formulas you can look up to give the potential energy related to wind speed.

As such - trying to extract 100W from 1.5 MPH is impossible.  You could generate a tiny amount of power given such low wind speeds - but it's not practical.  A min. wind speed of 7mph, while still quite low, is kind of a min. rule of thumb for practical (tiny) generation.

As far as generator designs - you have a number of options.  The current DIY that offers the best output with the least amount of losses while being relatively easy to construct is the axial flux dual rotor design by Hugh Piggott.
It uses air coils surrounded by two rotors of magnets allowing for a large flux to the coils without the large losses associated with iron core/stator designs.

Hear are some links to get you started.  The 1st site has a .pdf you can download with details of an early model: http://www.scoraigwind.com/pmgbooklet/index.htm

http://www.scoraigwind.com/
http://www.fieldlines.com/
http://www.windstuffnow.com/main/
Title: Re: Finding the right generator
Post by: irethedo on November 18, 2008, 11:33:54 AM
thanks Capthook-

I will check these out...
Title: Re: Finding the right generator
Post by: khabe on November 18, 2008, 01:36:57 PM
It is difficult to advice any generator when given info about rotor is just only:  <i>very efficient rotor design which can spin (without load) in 1.5 MPH wind</i>
Iron core or ironless ... there I have seen also many misunderstandings about.
Efficency could be higher than 90% for both - iron core or iron-less brushless motor/generator.
Ironless design has no cogging but well designed iron-core generator could have near zero cogging as well.
Iron-less generator need to have at least twice bigger magnets as iron-core brother. Art least! In reality all the mass of Stator need to be added for rotor magnets ...
Most of ironless generators made by "masters" are made totally unprofessionally - they are speaking about "coils" as well as design based on the "coils" - forgotten about
basic physics laws about left/right hand rules (moving_magnetic_field_wire_current) wheres "coil" need to meet two magnet poles at the same time - N-left and S-right side of "coil" and conversely.
And only part of "coil" is useful when we are speaking about ironless machine - only wires what crossways to moving direction of magnet poles.
Iron core generator is bit easier to build for first-timer, especially when low rpm and low power. There is several ways for reduce cogging torque near to zero:
Choice number of stator slots versus number of rotor poles - Pole-Slot Combinations
Skewing rotor poles or stator slots.
Unequal tooth width - influence of pole number
Unequal distance between rotor magnets ...
etc ...
And combination of mentioned above
There are a lot of perfect styles and designs worldwide - it will take full year to expand upon even part of more precise ...
The best choice is some older brushless servo motor from ebay - older because cheaper. Usually you can find out unique Pole-Slot Combinations like 39 slots / 12 poles ... + skewd rotor poles or skewed stator slots ... Nominal power and KV (rpm/volt) gives enough info about is it useful or not for your project.
When you like to choice axial flux ironless desigh anyway - then do not use too weak (thin) magnets and too large airgap between. Airgap (between magnets or between magnet and return iron) must to not exceed 1/2 of thickness of magnet when one-side magnets or 1 thickness of magnet when two-side magnet design.  Less airgap = less "turns of coils" for the same Voltage ... well wound you can use larger total cross area of wire ...
You have to think about Eddy losses - do not use thicker wire than 0,5mm. When higher current then stranded wire. Litz wire is the best choice when airgap machine (ironless generator).
Hereby one good PDF file how its look correctly made windings for slotless generator. Please look at only like "coils" must to be placed. Please note - 6 pole machine, but actual magnets are too weak ... and just 6 poles - requests higher rpm ...
http://www.windstuffnow.com/3phasekit.pdf
But you can see how windings need to look like - and that there are no "coils" literally - just wires between magnetic flux!
Regards,
khabe
Title: Re: Finding the right generator
Post by: irethedo on November 27, 2008, 08:09:50 AM
Are there any other motors out there used in other applications which are low RPM
and require little force to turn them that can be used for a reasonable output generator?

Perhaps a washing machine or dryer motor or a treadmill or electric scooter type motor???

Not sure if these would work or not or if they are difficult to turn or not...

Any ideas?

thanks
Title: Re: Finding the right generator
Post by: khabe on November 28, 2008, 12:53:19 PM
Are there any other motors out there used in other applications which are low RPM
and require little force to turn them that can be used for a reasonable output generator?

Perhaps a washing machine or dryer motor or a treadmill or electric scooter type motor???

Not sure if these would work or not or if they are difficult to turn or not...

Any ideas?

thanks

No ideas until you have not gave more info about turbine(blades) you planned to use. Is it 3m diameter ... or half meter ... or you have no ideas at all >:(
cheers,
khabe
Title: Re: Finding the right generator
Post by: gyulasun on November 28, 2008, 02:18:51 PM
Are there any other motors out there used in other applications which are low RPM
and require little force to turn them that can be used for a reasonable output generator?

Perhaps a washing machine or dryer motor or a treadmill or electric scooter type motor???

Not sure if these would work or not or if they are difficult to turn or not...

Any ideas?

thanks

Hi,

Just come across this link on a generator,  maybe useful for you: http://www.fieldlines.com/story/2008/11/27/211427/37

The video link is here:  http://www.youtube.com/watch?v=Axo8v37beM0   And he tests the output current when rotates the rotor by his hand: http://uk.youtube.com/watch?v=CzsD6iaLE0c

And see the same generator working as a pulse motor, pulsed by hand from an AA 1.5V dry battery:

Title: Re: Finding the right generator
Post by: khabe on November 28, 2008, 09:55:23 PM
Yes - this is by principle correct made generator. You can see you dont need any "coils" - just WIREs between  magnetic field.
Right hand and left hand rules ... motor and generator effect ...
http://waowen.screaming.net/Maghandrules.htm
Faraday law - iron core motor
Lorentz Law - air core motor (ironless ...).
cheers,
khabe

PS:
NewmanÂ´s motor uses also  Lorentz Law, right hand rule  - but ... he does not use closed magnetic cheme, flux of rotor magnet stays "on the air" - there is no outer side magnets or flux returning ring (rotating steel or laminated stationary ...)
Title: Re: Finding the right generator
Post by: pese on November 28, 2008, 10:50:09 PM
. Please look at only like "coils" must to be placed. Please note - 6 pole machine, but actual magnets are too weak ... and just 6 poles - requests higher rpm ...
http://www.windstuffnow.com/3phasekit.pdf
But you can see how windings need to look like - and that there are no "coils" literally - just wires between magnetic flux!
Regards,
khabe

Attention (above PDF)
Correct the drawling on page 10.
The star rectifiering is wrong designed.
Gustav Pese
Title: Re: Finding the right generator
Post by: khabe on November 28, 2008, 11:47:38 PM
Attention (above PDF)
Correct the drawling on page 10.
The star rectifiering is wrong designed.
Gustav Pese
Hm? There is no different in rectifiers in principle when star or delta connected 3ph generator windings.
This guy just trying to show how to use two one phase full bridge rectifiers for three phase ...
Usually people dont use this kind of temporary means - ast least I do never and even do not heed attention ... correct or wrong ...
When now you forced me to look at ... by my opinion it works - it uses three pairs of diodes  +  -I<- ~ -I<- -  of total 4 pairs.
regards,
khabe
Title: Re: Finding the right generator
Post by: TinselKoala on November 29, 2008, 12:31:56 AM
Never mind.

Getting back to the science fair, I hope you and your kid have a great time.
Title: Re: Finding the right generator
Post by: khabe on November 29, 2008, 01:01:44 AM
Yeah, but when you need bit bigger generator than spoken above and  buying 6 small diodes does not kill you as well as assembling ::) - then I can recommend well built brushless servo motor from ebay:
http://cgi.ebay.com/BLDC-servo-motor-robot-lathe-mill-cnc-encoder_W0QQitemZ260303719487QQcmdZViewItemQQptZLH_DefaultDomain_0?_trksid=p3286.m20.l1116
\$5 + shipping  ::) Encoder from back side you just take apart and throw away. It has hollow shaft OD 1/2" and id 1/4", well made motor, four poles rotor, 24 slot stator - scewed rotor segment magnets - special shape + vintage overlapped winding cheme gives brilliant coggingless run. Rotor OD ca  43.5mm, Total OD ca 102mm x ca 60mm, bearings are rubber sealed 9R8 made in Japan.
Good and cheap found for several projects.
regards,
khabe
Title: Re: Finding the right generator
Post by: pese on November 29, 2008, 01:07:35 AM
see the last of 3 bridge rectifiers.
the 2.AC  is not connected.
so that cant work
Pese

P.S.
I controlled again.
It is roght so - as designed.
(sorry, I was to fast .. and not seen my error)
Pese
Title: Re: Finding the right generator
Post by: Yucca on November 29, 2008, 01:18:34 AM
For a small wind genny you could use a brushless outrunner motor similar to what Khabe is recommending.

(http://i8.ebayimg.com/03/i/000/ff/d7/428e_1.JPG)

They are small motors for model cars and planes that have moving neo mags and stationary coils. They are VERY efficient motors and make quite efficient gennys. (Might have to gear your turbine output up a little though?)

They come in all sorts of sizes from tiny to large so you should find one to match your turbine. They are also quite cheap on ebay:

http://shop.ebay.com/?&_nkw=brushless+outrunner

They will generate 3 phase AC when cranked. With bridge rectifiers feeding a cap you get rough DC, can then use efficient regulator for proper DC.
Title: Re: Finding the right generator
Post by: Yucca on November 29, 2008, 01:28:55 AM
Yeah, but when you need bit bigger generator than spoken above and  buying 6 small diodes does not kill you as well as assembling ::) - then I can recommend well built brushless servo motor from ebay:
http://cgi.ebay.com/BLDC-servo-motor-robot-lathe-mill-cnc-encoder_W0QQitemZ260303719487QQcmdZViewItemQQptZLH_DefaultDomain_0?_trksid=p3286.m20.l1116
\$5 + shipping  ::) Encoder from back side you just take apart and throw away. It has hollow shaft OD 1/2" and id 1/4", well made motor, four poles rotor, 24 slot stator - scewed rotor segment magnets - special shape + vintage overlapped winding cheme gives brilliant coggingless run. Rotor OD ca  43.5mm, Total OD ca 102mm x ca 60mm, bearings are rubber sealed 9R8 made in Japan.
Good and cheap found for several projects.
regards,
khabe

Now thatÂ´s a good bang for the buck! Shame the international shipping is too high for me or I would go for a couple of those!
Title: Re: Finding the right generator
Post by: khabe on November 29, 2008, 01:28:58 AM
For a small wind genny you could use a brushless outrunner motor.

They are small motors for model cars and planes that have moving neo mags and stationary coils. They are VERY efficient motors and make quite efficient gennys.

They come in all sorts of sizes from tiny to large so you should find one to match your turbine. They are also quite cheap on ebay:

http://shop.ebay.com/?&_nkw=brushless+outrunner

They will generate 3 phase AC when cranked. With three bridge rectifiers feeding a cap you get rough DC, can then use efficient regulator for proper DC.

Yes, but even low cogging outerrunner brushless RC motors  (12 tooth/10 or 14 pole and 9/8 ... 9/10 ... 18/16 ... 18/20 ...)  have cogging too much for small windmill - it will not self-start. And those motors are cheap but not very cheap ---. \$30 for tiny ones and up to \$300 for larges. Tiny ones has tiny bearings and thin shaft as well. At that kV of these motors is at 500 to 3500.  When kV is 1000 then you need 1000 rpm for get one Volt !!!!!!!!!!!!!!!!!!!!!!!!!!!!!! And this is NO LOAD VOLT !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!  :o  :'(  >:(
regards,
khabe
Title: Re: Finding the right generator
Post by: Yucca on November 29, 2008, 01:53:07 AM
Yes, but even low cogging outerrunner brushless RC motors  (12 tooth/10 or 14 pole and 9/8 ... 9/10 ... 18/16 ... 18/20 ...)  have cogging too much for small windmill - it will not self-start. And those motors are cheap but not very cheap ---. \$30 for tiny ones and up to \$300 for larges. Tiny ones has tiny bearings and thin shaft as well. At that kV of these motors is at 500 to 3500.  When kV is 1000 then you need 1000 rpm for get one Volt !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
regards,
khabe

I have a small outrunner from Hong Kong about \$15 on ebay and yes I notice it has noticable no load cogging even though it has different number of poles to mags? I think a wind turbine of a couple feet diam would start one running though.

YouÂ´re right the kV on the normal model motors is too high for direct to turbine and cogging will amplify through gearing. :(

I suppose a rewind with finer wire for lower kV would help but then thatÂ´s a fiddly long winded job.

Yucca.
Title: Re: Finding the right generator
Post by: khabe on November 29, 2008, 02:13:55 AM
My bread-and-butter comes from generators Im developing and building past 10 years, even longer,
Those are very specifics, but el.machines anyway, at that sui generis and ... devilishly good (they are speaking, the customers ;)
As more specific - as higher price :)
regards,
khabe
Title: Re: Finding the right generator
Post by: TinselKoala on November 29, 2008, 05:16:57 AM
I guess I paid about 2 dollars for this little motor that makes a pretty good demonstrator generator.
We're not trying to save the world from the tyranny of oil, here, we're just trying to help a kid do a science fair project, and I have a hunch he's not (yet) attending MIT, so it doesn't have to be too complicated.
Neither does it have to be the most efficient generator, or the fanciest technology.
A mechanically commutated DC motor won't require rectification, and if the right type of motor is chosen it won't exhibit "cogging" or excessive bearing drag, and so will be easy to turn with a wind turbine or water wheel or even a hamster in a cage, without complicated transmissions or gearing.
And a demonstration using this kind of motor will give the presenter ample opportunity to discuss issues of overall efficiency, ease of construction and maintenance, environmental impact, not to mention the physics of electromagnetism.
Title: Re: Finding the right generator
Post by: Thaelin on December 04, 2008, 11:26:49 PM
Very simple setup would be to take the 12 mag 9 coil and make it smaller. Use grade 8 magnets from the hardware shop and smaller wire. Since its a concept show and not a off the grid system, many options. Not to mention he will learn the ins and outs of construction.

And now, Uber thanks to all here that have posted as you have given me the final piece to my long sought puzzle of the coil make up. I have yet to find out the turns or ohm rateing  for a standard system. All I could find was let us sell you a kit or a video of how they made them but no specs. So now I build. I have to have 12v @ 25A output at a fairly low speed and this will do it. Less than 300rpm.

thaelin
Title: Re: Finding the right generator
Post by: pese on December 04, 2008, 11:32:38 PM
and drive your car with this

http://www.brasschecktv.com/page/456.html
Source BBC-News Car 120km/h speed !

Gustav Pese

Title: Re: Finding the right generator
Post by: khabe on December 05, 2008, 08:48:07 AM
I have seen one compressed air car - was surprisingly noisy.
cheers,
khabe
Title: Re: Finding the right generator
Post by: pese on December 05, 2008, 09:38:01 AM
All energy that make noise, have to mutch losses. Regardless of whether piston or turbine propulsion. Similarly, it is certainly possible with a  sound insulation to build. Some Honda generators show the possibility as there is. Certainly, it is possible to progress. Pese

P.S. I  womder that nobody have think about to reduce the coists and losses -for- compression the air. I look for contact to figure that out.

Title: Re: Finding the right generator
Post by: khabe on December 05, 2008, 12:32:01 PM
Perhaps take up with compressed air is not prestige enough - there is no orotund sounding therms and words - no ether ... fusion ... scalar ... essential ...  >:(
Is it too commonplace, cheap and bathetic ??? At that it needs attend school ...  and it needs much more precise work - no fluttering wheels, no crooked shafts  ::)
when making compressed air. And pressure is dangerous ... especially when education has been poor 8)
gruss,
khabe
Title: Re: Finding the right generator
Post by: pese on December 05, 2008, 06:29:01 PM
Perhaps take up with compressed air is not prestige enough - there is no orotund sounding therms and words - no ether ... fusion ... scalar ... essential ...  >:(
Is it too commonplace, cheap and bathetic ??? At that it needs attend school ...  and it needs much more precise work - no fluttering wheels, no crooked shafts  ::)
when making compressed air. And pressure is dangerous ... especially when education has been poor 8)
gruss,
khabe

education for poor folks

GP

http://rexresearch.com/negre/negre.htm

PS.
If you can handle
butan/propan camping gas (12 bar)
than you can handle , lower pressured air....

Title: Re: Finding the right generator
Post by: Thaelin on December 21, 2008, 09:02:11 PM
Concerning Gen heads for wind, there are many makeups to choose from. I have settled
in on the 12mag/9 coil setup. To reach fair output, it seems to be necessary to hit 700 rpm
with it.
Now what would happen if you had a wheel with 24 magnets on it and two sets of 9 coils
in two arcs on both sides? If both sets were wired seperate but outputs together for double
the amps, still mean the wheel would have to only travel one half the speed?
That would make the wheel bigger, but it would only have to go 350 instead. I have a bike
wheel that had 48 slots between the spokes I am thinking of mounting two metal rings on
so as to put 24 magnets on both sides for a total of 48 and run the coils in a half circle mounted
on both sides and running in the middle of the mags.

thaelin
Title: Re: Finding the right generator
Post by: capthook on December 21, 2008, 09:57:55 PM
Hi Thaelin -

One implementation of the  12mag - 9 coil setup is in the axial flux dual rotor design.
The idea of the dual rotor is eliminate iron in the stator and then maximize the flux in the airgap between two rotors of magnets.
If iron is used (should always be so) as a backing for each rotor, the 'magnetic circuit' is completed - boosting flux.  (the flux from the backside of each magnet is 'channeled' to flow back through the adjacent magnet and back through the stator)

The problem with a single rotor/dual stator design is the incomplete magnetic circuit.
One would think that putting coils next to BOTH faces of the magnet would offer superior performance - but that is not the case.

I have just completed my first axial flux dual rotor build. (Hugh Piggot style design)
1. 12 mags 9 coils
2. .75" x .5" N42 mags  :  1/4" steel rotors
3. 500 turns #24 AWG coils .75" ID x 2" OD x 7/16"
4. airgap from each rotor to stator 1/8"

The magnets were taken from a build I did 2 months ago of a single rotor/dual stator design like you describe.  The coils had an iron core.

Comparing the two:
1. The dual ROTOR generated TWICE the power
2. The dual ROTOR resulted in around FOUR TIMES (or more) LESS drag. (no iron in coils)
(so at least 8x better performance)

For a long time I was of the notion that putting coils on BOTH sides of the magnets would be best - even though I'd been told it was not so as the 'magnetic circuit' was incomplete and thus inefficient.

Having now built BOTH designs - I can say that a DUAL ROTOR is SUPERIOR in many ways over the dual stator.

My next build of this design will use larger magnets (2" x 1" x 1/2") , 16 mags 12 coils with larger wire (#18 AWG?) and 1/2" steel rotors.
Title: Re: Finding the right generator
Post by: Thaelin on December 22, 2008, 10:14:09 AM
I see I was incomplete with what I was trying to say. I am looking to put
two metal rings, one for both sides of the stator. The magnets will be placed
on the inside of both rings so that they face the stator.
I see tho that the two rings will have to be joined somewhere for the flow
to happen. Guess I could put small metal pieces across the back of the rings
so to complete it.

As I am not going to be powering this by wind prop, I need to maximize the
low speed output as much as I can. That is the reason I am considering this. I
just wished I had drawing software that I could put down what I see in the head.
It frustrates me to no end when I cant put my thoughts to action.

The beat goes on.

thaelin
Title: Re: Finding the right generator
Post by: terry1094 on December 22, 2008, 04:56:17 PM
The Fisher Paykel washing machine motor makes a good generator.  Here is a complete detail plan for a windmill from downunder:

http://www.thebackshed.com/windmill/fp2a.asp

Elsewhere,

http://www.watchtv.net/~rburmeister/smart.html

others recommend grinding the edges of the cores of the electromagnets to reduce cogging.

Terry
Title: Re: Finding the right generator
Post by: Thaelin on December 22, 2008, 05:48:55 PM
Thanks Terry:
I believe I saw that vid of one hooked up. I must stress again tho that this will not be
a windmill setup. It will be a Gravity Wheel that is running it. The only kick back I have
is it must be a low speed unit. My latest test shows I have ample torque and can most
likely do  a six to one gear up to the head.
I have to get another pair of weights yet and a drive belt that is the correct length. I
really only need to generate 60watts over the needs of the wheel to charge up the batt
stack.

thaelin
Title: Re: Finding the right generator
Post by: irethedo on January 12, 2009, 08:58:07 PM
Would the motor out of a washing machine, clothes dryer, or dish washer work as a generator?

These are relatively low RPM but I am not sure how much torque might be required to spin these at a rate
that couldt create some sort of usable energy...

Is there any appliance motor that can be salvaged for use as a generator like this?