Misc. 10' Wind Turbine Questions - Part 2

[arwenvaughan]

I am still working on the 10 foot wind turbine from the Homebrew Wind Power book, and have another set of questions. I've finished all the welding. Now I'm getting ready to cast the rotors and stator. I am a bit paranoid about these steps because I have never worked with resins before. Thanks in advance for any responses!!

1. I have Vinyl Ester Resin with 1/8 inch fiberglass and ATH fillers for the stator. The book says use a 50:50 mix of resin to filler material. My question is if I am planning to use both ATH and fiberglass strand as fillers, what ratio of those should I use?
   
2. I was hoping to cast both rotors at the same time and did not want to build two wood molds or band the rotors. I can not find stainless banding in a small quantity and I don't have the ability to weld stainless anyway. So, has anyone tried to cast the rotors just using tape around the outside edge (and the wooden island, of course)to hold the resin in? It seems like a simple and cheap way to go.
   
   

3. Would it be ok to use the vinyl ester resin or should I really use epoxy resin for the rotors. It seems a lot of people are opting for epoxy resin for the rotors now. I am a bit nervous that the vinyl ester will not adhere well to the rotor and magnets well.
   
4. Also, what is the best way to prep the rotors for casting? One of my rotors is a bit rusty. Should I simply wire brush them, or do something more extensive to prepare the surface so the resin sticks really well.
   
   

Thanks!!!

 

[Boss]

We re-cast our stator with tape, it worked all right you can see the discussion here http://www.fieldlines.com/story/2009/1/6/154435/7727

Also we live in a dry climate and were unable to find stainless steel banding so we used regular packing bands from a refrigerator box or something which we found at the dump.

This our first turbine besides the one we built at the Other Power workshop last year so please take everything with that in mind, anyway here are our rotors

http://outfitnm.com/alt-energy/wind-power/axial-flux-alternator  

The bands make a great casting dam keeping everything level, much better than trying to keep the tape in place

[Janne]

Using normal steel band around the magnets rotors to substitute SS is a good way to short some of the magnetic flux in the magnets. Not sure how big of a problem it will be without calculating, but I would recommend using SS band for the sake of magnetic properties.

[Batdude]

In an earlier post there was a discussion about disk preparation, corrosion, epoxy, etc. Do a search.

I may have seem in the Homebrew Wind Power book where they cut strips from sheet metal and used it for the band. Check a welding shop, they should be able to make it for you. Check the book for more detail.

batdude

[arwenvaughan]

Thanks for the comments. I actually had read you posting. Good job cleaning that stator up. I couldn't tell it was tape from the pictures. I thought that was aluminum or something for the casting dam.

[arwenvaughan]

Thanks, but the only postings I found talked about using laquer thinner for removing any oil or grease. I think I will use some rust removing product, then wire brush them with my grinder, then laquer thinner.

I like your welding shop idea. The book only says to check with package strap distributors. I have found plenty but they want to sell you $100 worth or non at all.

I appreciate the comments!

[DanB]

Sorry not to have replied sooner ~ weve been away helping with Hughs seminar on Guemes Island and my internet has  been spotty.

I used to use tape that way and it orked fine I guess, but when I did I took measures to really make sure th emagnets couldnt come flying out.  It should be fine, if something goes wrong though and the magnets start rubbing the stator you may have problems.  if you do that, I would try to somehow band the rotors, even if you cannot find the stainless, either use steel.

[Flux]

If the magnets are properly stuck on with reliable adhesive then the vinyl ester should provide weather protection.

If you are relying on it for holding the magnets then I would suggest a band of some sort. If you can't get stainless then thin mild steel wouldn't have much effect on the flux, there is bound to be some loss but I can't see it being an issue with something less than 1/16" thick.

Cleaning the discs carefully with abrasive or grit blasting or something makes very good sense if you are relying on bonding the magnets to use without a band. if you use a band then just removing active rust and grease is probably adequate.

I think vinyl ester works better than polyester so for weather protection it should be perfectly adequate but I wouldn't consider it a structural glue. The better epoxies should do the job without banding.

I think even vinyl ester should be ok with a fiberglass banding round the magnets as long as you key the resin mass to stop it sliding with some holes, roll pins or screws.

Just a resin block with the magnets right up to the edge of the discs and no banding requires a structural adhesive to hold the magnets or epoxy potting to be sure, although I think the issue is much less than many think. nearly all magnet coming off issues are after some other failure such as a stator rub with heat demagnetising them.

The magnetic forces are nearly enough to hold things under normal conditions and you are mainly using the resin block to keep things from sliding. Demagnetised magnets would be really much more demanding to hold on.

Flux

[scoraigwind]

I used to run a piece of stainless steel wire rope (about 1/8" diameter) around the circumference a couple of times.  It bonds well to the resin so there is no need to tie it up.  You need a bit of extra resin outside the magnets to bed it into.

Nowadays I feel that a layer of fibreglass cloth on top of the magnets shold be sufficient.  No problems lately.

[Ungrounded Lightning Rod]

You could band it with fiberglass fabric and impregnate that with resin.  No magnetic problems that way.  (But might be difficult to get the fabric to stay where you want it.)

[arwenvaughan]

Wow! Thanks for all the great ideas. I wouldn't have come up with half of these ideas on my own.  It is funny how you can have it all planned out in your head and then after a post on fieldlines you could go any number of ways. But, listening to what worked for all of you really helps out.

I'm thinking of sticking to the book design on the rotors and spending the extra time to get the stainless bands made. I'll try the vinyl ester resin too since I have lots of it and sounds like it bonds pretty well with the steel plate. For the next turbine I'll get a bit more creative and try some of these other ideas.

Sorry if some of these question are a bit redundant on the forum, but I wanted to get the latest science from you guys. It is interesting to see how the ideas have changed over the years too.

[arwenvaughan]

Interesting. I like the idea of putting screws through the rotor to give the resin something to hold onto. Perhaps you could do this without the banding at all.