Latest thoughts on resins

[DanB]

A while back somebody posted this link here on fieldlines: http://shopmaninc.com/polyesters.html

I ordered a few things from them.  I've had really good luck with West system epoxy especially on magnet rotors (for stators it didn't take heat as well as the normal polyester we've always used but on magnet rotors it shrinks less and it's not brittle).  But - it's very expensive stuff (About $100/gallon).

so I ordered up a couple different epoxies from US Composits.  They were cheap (<$40 gallong) but it turned out that they were quite brittle and not very suitable for casting.

I also ordered a couple gallons of vinyl ester.  From their site:

'Vinyl Ester resin is superior in every property as compared to all polyester resins. This product is used in high performance applications in which high-strength and maximum heat tolerance is necessary. This resin is extremely chemical resistant when cured. Similar in strength to epoxies with much increased stiffness.'

It shrinks less (not noticable shrinkage).  When it cures it feels more like a rock than a chunk of plastic.  It also machines nicely.  It's much less viscous (not such a thick liquid like polyester resin normally is) so air bubbles rise out of the mold quickly and the castings look better and I expect it penetrates the coils better.  It seems to stick better to the magnets/steel when we cast magnet rotors.  

I'm sold on the stuff and at $36/gallon the price is reasonable.  The service via phone/email from shopmaninc.com has also been perfect and so far they've always shipped quickly.

Just thought I'd share that stuff...

[Logyman]

Thanks for the information. I have been investigating several products for casting, and this sounds good. Anybody know if this is available to Canada? This board is a great resource, to be able to gather and collect other peoples experiences prior to making your own (read expensive!!) mistakes.

Phil

[jmk]

 Thanks Dan,

 I made my stator from polyester. The problem I had so far was it warped about an eighth of an inch. I am thinking of making another one. I have a 210' wire run at 24 volts. Three wires #6 wild ac.  If I make another stator can I ad more turns of wire to make up for loses? The stator is Hugh's 12' machine. Its wired three phase star twelve coils 50 turns of #13. Can I go like 55 turns to make up for the loses? If I do this The vinyl ester sounds like a good way to go.

[DanB]

adding more windings would probably just reduce your cutin speed - and resistance.  If it doesnt lean it more towards stalling the blades it might just result in more heat in the stator.  Hard to say for me - it would be only a small change though for better or for worse.  To me your wire run @ 24V doesn't seem that unreasonable.  If it's overheating I would lighten the tail/have it furl earlier.

[nothing to lose]

Are you suggesting using this for both stators and rotors for casting.

Using it for stators would you sugest using talc or not, like for the fiberglass as before.

[DanB]

I think using talc helps some with its thermal conductivity - but when I use it I get more air bubbles and I wonder if the thicker mixture penetrates the coils as well.  That stuff might not matter - air bubbles are mostly a cosmetic thing.  I don't normally use talc but maybe I should.

At first I thought the vinyl ester would be used for stators and Id stick with the cheaper polyester with rotors but.. after seeing a couple rotor failures and seeing things crack over time and seeing polyester lift off the magnets etc...  I think the rotors are the bigger problem - not the stator.  I prefer to use it for both now.

[Titantornado]

When I used vinyl ester for my stator, it was pretty thin like Dan said.  I added aluminum trihydrate for thermal conductivity and to thicken it up a bit.  Problem was, it didn't want to thicken.  I mixed all the way up to 50% by volume, and still it was very runny.  So, I guess I'll have one heck of a thermally conductive stator.

And also like Dan said, it is like rock.  In fact, after sanding, it looks like rock.

[jmk]

 I don't think it's getting hot. The warp in the stator was there before I raised the machine. The stator sat in the garage for six months. I have a 3/4" air gap and the blades look as if they are free wheeling. It does get to fourty amps in thirty mile an hour winds. To me it seems like they are over spinning, but It's hard to tell without a techometer. The African Wind turbine down the road seems to only run at about 1/4 the rpm. I was just thinking more wire would get a better grab on the blades to slow them down a bit. The tail is 8' as to Hugh's plans, but it only showed the chain to losen just a bit at 40 amps. Do you know what rpm you guys spun that alternator at when you were at Guams Island getting 2 k to charge the galf cart batteries for an hour? I can take one washer out of the spacers. I used 5/8" althread so the washers are almost an 1/8" thick. That should help get a grip on the blades. I might even be able to take two out, but the stator will be just about toutching than. I origanly had it set at a 5/8" gap, but after hearing stories of magnet rotors hitting stators and magnets flying off I was scared to set it that close. After watching it run it doesn't look like the blades bend the rotors at all. In fact I built my blades as compleat rotor. I glued screwed and stapled it together. The blades dont even seem to bend much. I thought I read in one of your post that you added a couple extra raps of wire for loses. That's why I was asking. If the vinyl ester would hold a straighter stator I for sure could take out two washers. My blades went on with a rubber malot untill I could get to the all thread. It was a real tight fit. anyone have any ideas as to how to get it off without bending or cracking the magnet rotors?  

[scoraigwind]

"Do you know what rpm you guys spun that alternator at when you were at Guams Island getting 2 k to charge the galf cart batteries for an hour?"

I have the data.  The coils were 200 turns and connected in star/parallel.  The skog battery was 36 volts.  Cut in was at 180 rpm.  The winding was to be used on a 48 volt system with 24 volts in lighter winds charging via a boost converter of some sort that Brian planned to make.  24 volt cut in would be around 120 rpm.

What we got:

rpm    volts    amps

340.   40   50
     
277.   39   33
     
350.   40   60
     
     

It got a bit hot and we had to stop.  It would work better on top of a pole in the wind.

Getting the blades on and off first time can be challenging.  Long levers and wedges are useful.  Try to apply the pressure near to the studs on the steel rotors.

[harrie]

Thanks Dan, I was just trying to decide what to use on my rotors, and wanted something that would self level, due to only pouring up about 1/3 on the mags. If its thin enough to self level, it will help to keep the rotors balanced, and the price is right!

Great fun, Harrie

[nothing to lose]

Thanks Dan.

I thought you were using the Talc on the older single and daul rotor genny stators but wasn't sure about now if you still used it onthe newer ones.

I think I will use the vinyl ester for everything also then. I hadn't bought the resin yet for mine so your post came at a great time, THANKS.

[nothing to lose]

That is a very nice looking stator, but how are you mounting it? I don't see any holes.

 Not sure where the coils lay in the picture or the size. Is that thicker outside area empty and just needs holes drilled?

[Flux]

JMK

I think your high speed is due to the long cable run and the wide air gap. You are likely working nearer the normal speeds than the leisurely stall loaded speeds that most people work with. Without speed readings it is all a guess but you still seem to have good power out in high wind so you can't be desperately fast for your blades.

Firstly I suspect the warping is no fault of the resin, it is the way you clamped the mould. Making a new stator that was flat would let you work with a smaller gap.

Vinyl ester would be better but it will not solve the warping if you clamp the same way.  I would not advise increasing the turns as a solution to a big air gap. The cut in will drop but the added resistance will do little to hold it at speed with weak field and you will end up with more stator heat and gain nothing from the advantage of the better vinyl ester.

With your long line you need to aim for a lower resistance stator ( or at least don't increase it) if you make changes. This implies more magnet ( or in your case use it efficiently with smaller air gap).

[Titantornado]

Your correct, mounting holes will be added once the frame is built.  Most of the coil is in the thinner section, with only the outer part in the thicker section.  The thinner inside circle is 13.25" in diameter for my 13" rotors.  I forget what the overall diameter is.

[Experimental]

   Several things I,ve noticed folks doing, is removeing the stators from the mold to soon, after casting and not storing them carefully.

Resins, take quite some time to fully cure -- they remain soft and are often warped from careless handling and exposure to hot sunlight, to soon after molding.

    On the ones I have built, I also "pack" all available open space, between the coils, espically the bolt areas, with fibreglass filiments -- simply pull apart pieces of fibreglass matt and push it into the resin, in all available places -- you will use less resin and become much stronger, with the fibreglass strands -- the long fibres help hold everything together.

   Lay your stator on flat surfaces , don,t just lay it on a pile of other objects -- cureing is a long process and that stator will be "soft" for quite some time !!

   Another source for supplys is, "Aircraft spruce and specialties"in California, and they ship world wide..

  Happy building, Bill H.

[jmk]

 Yes, I think that it was straight when it came out of the mold. I should have stored it on a flat surface and I didn't. Flux is probably write too about the blade speed. I just am not used to seeing a mill spin that fast. I think what I will do is leave it up till next year when I need to service it. Then I will pull some washers out to close the air gap up a little, and maybe even cut a foot of the tail. This is alot of fun. It's out there now pulling in 5-10 amps in light winds. I really want to thank you guys for all your help. My machine is a direct extension of you guys and is a part of you. I wouldn't have been able to make it without all your help. It made me feel so proud when I saw it spinning for the first time, and I hope you guys get a sence of an acomplishment when you see guys like me posting it's up!    

[Flux]

It's always nice to have some feedback when things work out well. Knowing that something has helped makes it worthwhile.

Flux

[DanB]

Im sure this isn't it - but it's something I've seen be a problem before - the stator mounting brackets.  They must be flat with the stator.  If they're even slightly off then you may well warp the stator when you tighten the bolts down.

[DanB]

I'm inclined to try that aluminum trihydrate -the price seems good and they suggest it does improve thermal conductivity.  I'm excited to see how that works out...

[finishitoneday]

Hi guys from the UK (first time poster)

I own a boat, and would like to make a small generator, hence my falling across these sites. Truly superb by the way.

On this issue of Resins, and I hope I don't repeat what others have said here, but if you are to use anything Resin related, then definitely go for West System or other proprietary EPOXY resin, particularly when working with Aluminium (let's not argue about spelling) or wood of any kind. Polyesters just don't work well in the long term with either of these. Using Aluminium grit alongside a low density filler will help you shape your final piece, wherease talc tends not to have too much structural integrity.

I am no qualified expert on resins, but have found that working on my own boat, trial and error and good research have led me to a happy understanding of how these chemicals work.

I will be using EPOXY on my stator, and expect the results to be superb. It might be expensive, but I couldn't imagine trying to repair something through cutting corners. Been there before.

Thanks to all those who have contributed to other posts, I have learned so much so far.

Ian

[fungus]

Aluminium in a stator would not be good as it would cause eddy currents and heat up the stator.

[bj]

    Thanks Dan--will try on next project.

    thanks. bj

[DanB]

I tested about a 50 - 50 mix by volume of aluminum powder and polyester resin and found it to be completely non-conductive.  So I disagree.

With regard to using west system epoxy for your stator - it will fail at a low temp than either polyester or vinyl ester so I wouldn't go that route (plus it will cost a lot more).  

[brian2034]

vinylester is one of the better resins used today in my opinion better than epoxy,that's from my 10 years building planes with the stuff. The only advice I can give is that any resin has no strength properties it is only used to hold the fiberglass mat or cloth.

 With any system you use epoxy, vinylester, polyester remember the resin is the glue the fiberglass cloth is the main ingredient for strength. For example gel coat on a boat is colored resin it chips easily and the thicker you make the gel coat the eaiser it will chip. If you look at the inside bottom of a boat where there is fiberglass cloth used and there is no gel coat you can hit it with a hammer and it will not chip.

 When laying up a rotor or any part you should used a quality resin and add chopped fiberglass to the mix (mill fiber) add as much as possible but don't make the resin to thick, or it won't flow around the magnets or the coil properly, this will prevent it from chipping or cracking.

Mill fibre is fine chopped fiberglass strands "buy it don't try to make it"