selecting a resin for my generator

[DaveW]

I have made it to the point of selecting the resin for my coils and magnets.  The molds are made, the magnets are placed, and the coils are wound.  In reading over this board, I see generic, Bondo, and West Marine mentioned as used.  But after pricing the field, I am confused. Set up times range from 30 minutes to 30 hours.  Prices range $14 a quart to over $32 a quart.  Is the high priced spread really 4 times better? Does one wick heat away better than another? How much set up time do I need?  And should I be going for water thin, honey thick, or a paste? I don't want to ruin my work so far with a poor choice at this point. I would appreciate advice from those who have gone before.

[harrie]

Hi Dave. You use fiberglass resin, same stuff that is used to fiberglass boats,and such. You will want to use a some fiberglass cloth on each side of your stator. The resin can be mixed with talcom powder, or the like. I use sheetrock texture powder. you can also mix paint with it for color. Google for this on this site, it is covered very nicely.

great fun Harrie

[Shadow]

I've always used the cheapest I could find. In my case, Walmart 13.95 a quart. I mix maybe 25% talcom powder and have had good luck as long as I dont cheap out on the hardner.But too much hardner is not good either.You'll do fine.

[Flying Z]

Our home depot has some for about $32-$36 a gallon. I thought that was high, but i guess not.

[coldspot]

I've been researching this forum for a while now.

I used to run an Automotive Refinish Supply Store Chain,(two, untill screwed out of by EXwifes Father).

The $30 per gal range is a GOOD price.

Read instructions and use hardner as per!!!

Fiberglass "Matting" being multi-directional will made a better and stronger unit BUT,

It's use is a bit more MESSY and harder to use, when I get to that point on my own builds, I'll use one layer of each on each side, (Cloth, Matting, COILS, matting then cloth), And thinner is better. I saw/read somebody using a D/A sander on top of mold to  vibrate out bubbles, GREAT IDEA !!!

Also there is a "FiberGlass Epoxy" Resin also, mix = 1 to 1, Much better product but about twice the money.

I see you people using "filler's", tac ect... Works but will be less strong!! Serious!!

I'd use more Matting as filler, the muli-directional glass fibers will give MUCH BETTER STRENGHT.

I've never seen any PRO shops use powder fillers on Vett's and I've never done so.

Just my $0.02

l8r

[Flux]

You raise some interesting points.

Strength is not a significant issue here, a layer of glass weave or mat on either side will give enough strength. The main reason for talc or similar filler is to save cost and reduce the thermal runaway during setting it is not needed for strength.

Similarly although epoxy is far stronger, the normal grades are not as well suited to the temperature as polyester. West system and similar are excellent structurally but I have never seen a temperature rating given.

Industry uses special epoxies for impregnating windings and these are specially intended to work up to 180 deg C and maintain full strength. Most common epoxies are pretty weak at 90 deg C.

When I first saw polyester used for this job I was amazed but in real life it is cheap, stands temperatures comparable to that of the the wire and seems to be as good as anything.

The only thing you could add to the mix to make much improvement would be some form of filler that improved the thermal conductivity greatly without being an electrical conductor.

Flux

[DaveW]

Interesting comments. And yes, Flux, what I think I need is the thermal conductivity of the products used in electronics potting for years but without the aluminum oxide.  I suspect that would add more trouble to the mix. It seems that one limiting factor in wind generation is that just when the wind reaches a level to really produce power the heat rise in the stator requires furling to keep from cooking things.  I'm not trying to solve the problem but merely raise the limit with the proper selection of materials and additives.

[coldspot]

$0.02 More.

"The only thing you could add to the mix to make much improvement would be some form of filler that improved the thermal conductivity greatly without being an electrical conductor."

This is something I've been thinking about alot!

I have a plan to do something simular to what I've done with "Liquid Cooling" for my Computers, I'd like to use "Copper" tubes but we all know how well that would conduct electricity, so to stay away from Galvinectic type reactions I'll be trying plastic/rubber tubes to help as fill and for flow to and from a little Rad.

With the wind blowing hard enough to make heat an issue a Rad would get plenty flowing thru it to cool the liquid. A convection set-up is in mind.

Also the newer "SMC" resins are Temp rated way beyond anything a mill could make, if my born with RAM is still working. lol.

[kamikaze]

Hi Dave W,

My generator is based on an iron powder composite, mainly to gain the benefit of an iron core (increasing the concentration of magnetic flux over the coils). It consists of west systems epoxy resin with a high quality iron powder and combined with enough iron powder to form a thick paste. The iron powder I use is specially designed for electronics (moulded iron cores for transformers, etc), and each grain of powder comes embedded in resin, isolating it electrically, and minimizing eddy currents (magnetic drag).But what occurred to me is that the iron powder also helps to conduct heat away from the coils.

    Also, my stator does not embed the coils in resin. The coils are wound around channels in the stator and are then dipped in "varnish". This was recommended to me by a motor rewind company. They said that the copper wire vibrates as the magnets pass over the coils, and expands as it heats up during higher power operation. The varnish they use is slightly flexible, allowing some expansion and contraction. This is important to prevent metal fatigue in the wire. Also the varnish forms a relatively thin coating on the coils, allowing heat dissipation. Keeping the coils relatively cool is important because as the coils heat up, the electrical resistance increases. Best of luck, Regards..

[TDC]

Interesting comments. And yes, Flux, what I think I need is the thermal conductivity of the products used in electronics potting for years but without the aluminum oxide.  I suspect that would add more trouble to the mix.

What might these troubles be? Aluminum oxide is used in epoxies.

[hiker]

guess ile have to try a small experimental stator buried in  concrete...?????????

[Mary B]

Aluminum oxide should be fine, it is an insulator so no issues with eddy currents. But the heat problem would be better served by a more open stator design with cooling slots... but then you lose stiffness.

[electrondady1]

polyester is normally used in a lay up process. thin layers of glass and resin.   when you cast a stator use half the hardener and mix it twice as much as you think is enough. let is cure slowly  to avoid problems
if your bedding your mags in resin, epoxy is better.  it won't shrink and pull away from the mags.

[kitestrings]

After asking a lot of the same questions, based on feedback here, and researching what I could, I ended up using as a high temp potting/encapsulating epoxy.  It is supposed to be high temp, thermally conductive.  My biggest concern was the cracking that seemed to be a contributor to some of the failures reported, particularly with the vinyl ester.  It was not, however, a inexpensive alternate.  It seems like a key component.  Time will tell if it was worth it.

~ks

[Flux]

This post seems to have re-started after a long time so my opinions have changed, particularly with the magnets. In a damp climate, potting magnets in polyester is a disaster. I think epoxy may be the only option but I am not sure potting in a solid block is the best way. Sticking them on with epoxy is fine and possibly coating with a layer of epoxy may be fine if it doesn't pull away from the edges. A good coating of POR15 and a couple of good coats of paint may be as good or better.

In a dry climate there is no real problem but I would stick with epoxy, polyester is not an adhesive.

For the stator my views haven't really changed. Polyester is fine with talc, ATH or other suitable filler. Cracking is invariably due to too much catalyst or lack of filler, with a large mass you need less catalyst to stop it exotherming, but perhaps a bit of heat to start the reaction in cold weather.

High temperature epoxy is fine but the normal grades are not good for the higher temperatures, the good stuff is expensive.

Not having used Vinyl ester I reserve judgement but I would be reluctant to use it for magnets in a wet climate. It is something half way between epoxy and polyester and should be ok for stators but as polyester seems perfectly ok I wouldn't bother.

Flux

[phil b]

It seems everyone has developed their own method. Mine is using Smooth-on with one layer of fiberglass cloth on each side of the stator and mixing as much chopped fiberglass as I can get into the stator. I vibrate the stator with an electric sander to get the bubbles out while it is still liquid.

I also cast the magnet rotors in Smooth-on. The neo magnets still look like they have no corrosion after 4 years. Smooth-on has no foul odor to tolerate either.

I do intend to try POR15 in the future.