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Small alternator for my Savonius prototype


By RobD, Section Homebrewed Electricity
Posted on Thu Apr 29th, 2004 at 05:26:21 PM MST
Air core alternator pics

Here's the alternator for the small Savonius I posted a few days ago. I made the coil form from fiberglass reinforced body filler. After I made it I noticed one of the ingredients was a traces of metal that cut my final power slightly. To bad the body filler worked really well,was cheap and is quite strong. I'll have to see if I can find one without metal.


Everything can be made on a Sherline size lathe I believe although my lathe is larger. I did wind the coils on the Sherline though.

To get the coil form accurate and allow the gap to be as small as possible I cast small mounting posts in the core(you can just see them in the photo). This permitted me to have a core exactly .180"(4.5mm) thick as the posts keep the plate at the right thickness when the weight is placed on them while curing. The slight ripple in the core is from waxpaper. The hubs are ABS and contain 1/4"(6.35mm) ball bearings. To mount the small round magnets I machine the aluminum plate in the picture and placed a steel plate behind it. The steel plate keeps the magnets in and the aluminum front plate keeps them from flying off.The steel plate also adds to the power. There is no adhesive on the magnets.
Power is about 4 watts.
RobD

Small alternator for my Savonius prototype | 14 comments (14 topical, 0 editorial)

Re: Small alternator for my Savonius prototype (none / 0) (#1)
by jared on Thu Apr 29th, 2004 at 05:55:33 PM MST
(User Info)

what size magnets are those?



Re: Small alternator for my Savonius prototype (none / 0) (#3)
by RobD on Thu Apr 29th, 2004 at 06:35:23 PM MST
(User Info) http://www.dsgnspec.com

Magnets are 1/4" diameter x.2" thick. The magnet radius is 1.06". Coils wound with #30 wire about 225 turns each. Resistance is 28.376 ohms. 24 magnets total. Gap +/- .015". Single phase.
Rob

[ Parent ]


Re: Small alternator for my Savonius prototype (none / 0) (#13)
by JohnnieBumchin (johnniebumchin@hotmail.com) on Sun May 2nd, 2004 at 09:51:46 AM MST
(User Info)

How tall do you think the savonius would have to be to produce a decent amount of power.

Johnnie B.
--Remember what Johnnie Bumchin says kids, it could save your life................
[ Parent ]



Re: Small alternator for my Savonius prototype (none / 0) (#2)
by windstuffnow (elenz(at)windstuffnow(dot)com) on Thu Apr 29th, 2004 at 06:14:42 PM MST
(User Info) http://www.windstuffnow.com/main

   Very nice work Rob !

Windstuff Ed
Have Fun! Windstuff Ed



Re: Small alternator for my Savonius prototype (none / 0) (#4)
by Radomike on Thu Apr 29th, 2004 at 09:31:45 PM MST
(User Info)

  Very sweet little alt!
Four watts at what speed?
Mike




Re: Small alternator for my Savonius prototype (none / 0) (#5)
by stop4stuff on Thu Apr 29th, 2004 at 11:09:20 PM MST
(User Info) http://www.stop4stuff.com

nice work Rob,
if only my efforts were as fruitful.
what diameter plates are you using for the rotors?



Re: Small alternator for my Savonius prototype (none / 0) (#6)
by RobD on Fri Apr 30th, 2004 at 07:16:25 AM MST
(User Info) http://www.dsgnspec.com

The plates are 2.120" (53.8mm). Don't be dismayed. I'm impressed you did such a great job with Legos. Remember I have precision lathes and test equipment here to refine things.
I did not test the rpms but the test wind was in the range of 23 mph (10 meter/sec or a little more). I'm guessing but I'd say around 1500 hundred rpms.
Rob

[ Parent ]


Re: Small alternator for my Savonius prototype (none / 0) (#7)
by stop4stuff on Fri Apr 30th, 2004 at 11:51:27 AM MST
(User Info) http://www.stop4stuff.com

cheers Rob,

i just cracked 1/4 watt off 1 coil, 200 turns 28 SWG, 9v @ 0.03 A.... more later :)

Do you know what sort of rpm the sandia blade design can get to?

paul

[ Parent ]



Re: Small alternator for my Savonius prototype (none / 0) (#14)
by RobD on Sun May 2nd, 2004 at 10:30:37 AM MST
(User Info) http://www.dsgnspec.com

I just did a crazy thing and stuck it out my car window at 55 mph to see if it would blow apart. It didn't but got really loud and fast.
Rob

[ Parent ]


Re: Small alternator for my Savonius prototype (none / 0) (#8)
by wayne (wayne.jones@sait.ab.ca) on Fri Apr 30th, 2004 at 03:02:47 PM MST
(User Info)

Hi Rob
Nice job and looks good. Did you use 24 coils? I was thinking of using body filler for my first one. How did it flow into your jig. How did you know it had metal mixed with it. Is there such a thing body filler without. Everyone says to use resin because its the best. did you have to lathe yours at all. I have a 12" lenz turbine just trying to find the best way to make a coil with magnetics. I thought os using a large PCV cap and do a resin pour or body filler. Must look around more.

Thanks
Wayne



Re: Small alternator for my Savonius prototype (none / 0) (#10)
by RobD on Sat May 1st, 2004 at 09:11:35 PM MST
(User Info) http://www.dsgnspec.com

Hi Wayne,
I like the body filler. There is a minute amount of metal somewhere in there but I contacted the company and they said no but I didn't talk to a chemist because they are wrong or not considering the minute amount enough to be effective.
Here's a simple test: take some out of the can and spread a small amount about 1/8" thick about an inch from one edge on a half sheet of paper. Now suspend the paper from a paper clip by the other end and place a really strong magnet on the other side of the paper without the filler and see if it attracts, chances are it will. There is one that may work and it's called "Cat Wiskers", it seems to not have all the ingredients of the other fillers but I haven't tried it yet.
I'm very happy with the body filler and from the tests I've done it isn't making any significant difference because of its magnetic properties.
Here's how I formed it. I made a simple aluminum template out of thin flashing (.010")
then I cut a ring from PVC pipe that I machined to the exact diameter I wanted and the exact thickness too. I places the template on the bottom of the ring and set all my coils in it just the way I wanted them. I then cut three posts to the same exact thickness and placed them in the registering holes in the template. When this was all set up I placed it on a sheet of wax paper and placed it on a granite layout table but you can use a piece of glass if you don't have the layout table.
Now i mixed my filler and filled the ring, placed another piece of wax paper over it and worked all the excess filler out of the mold. Then I placed a piece of glass over the whole thing and put a weight on it.
When it was dry I pried the aluminum template off the bottom of the mold and filled the area with a thin layer of filler, put waxed paper over it, glass and a weight. When it cured I cut through the ring on one side and removed it, put it on my lathe and bored a hole through the middle but you can just drill a hole for the drive shaft.
Because of the posts the wafer thickness was uniform and excellent which allowed me to place the magnets closer to it.
Sounds harder that it is.

[ Parent ]


Re: Small alternator for my Savonius prototype (none / 0) (#11)
by RobD on Sat May 1st, 2004 at 09:48:22 PM MST
(User Info) http://www.dsgnspec.com


Basically the coils and posts fit into the aluminum plate to keep them registered. The posts are used to align the coil form with the alternator housing and is held in place with spacers set to give .015" magnet spacing. Everything is 'sandwiched' between two pieces of glass and weighted.
Rob

[ Parent ]



Re: Small alternator for my Savonius prototype (none / 0) (#12)
by wayne (wayne.jones@sait.ab.ca) on Sun May 2nd, 2004 at 09:15:25 AM MST
(User Info)

Hi Rob

Thanks for all your help and will try this. You should try a Lenz turbine with your same size and see which works the best. I have a little 6" lenz on my fence post with good bearing and this is always spinning. Now built a 12 " and change Ed's numbers on the winglets and seems to spin very good. I don't have a lathe so its harder for to get everything perfect. I will post a pic soon on mine. I really like VAWT and would to build 12v charger for low wind conditions. If you want to tack it just get a bike speed tach for $15.00 cheap and easy.

Thks
Wayne

[ Parent ]



Re: Small alternator for my Savonius prototype (none / 0) (#9)
by hvirtane (hannu_markus_virtanen(at)yahoo(dot)com) on Sat May 1st, 2004 at 03:18:17 PM MST
(User Info) http://web.archive.org/web/20050404022706/www.cc.jyu.fi/~hvirtane/cooker/

Really nice!

What about making the
same 100 times bigger?

- Hannu



Small alternator for my Savonius prototype | 14 comments (14 topical, 0 editorial)
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