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Ash Small

Sun Mar 17 2013, 05:18PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

OK, point taken. I've watched the part of the video where you remove the coil from the jig now.

I appreciate you are developing a method that is easy for others to use, and that electro-polishing and 'shocking' aren't that straightforward without the correct equipment and experience. My point was that the bond between a highly polished metal surface and epoxy is muchweaker than the epoxy-epoxy bond, and will easily shear or pull apart with much less force than it takes for the epoxy to fail. (It was quite easy to scrape off using a knife)

One other point that came to mind is that if you are going to place washers at each side of the coil when it is installed in the CG (I understand this can increase efficiency), you could place the washers in the jig before winding, then it wouldn't matter if they get stuck, it will save adding them later.

I maybe should have watched your video first, but I pay for internet by the gigabyte, so don't generally watch lots of ~15 minute videos.

I'm sure that if you placed the jig in a vice (vise), and placed a wrench on the other 'nut', it would shear (the more highly polished the washer, the easier it would be to do), but I'm experiened at 'tricks' like that, which, I admit, aren't easy unless you know what you are doing.

While not that cheap, I think the high-temperature mold release wax here:

should be ideal for your requirements.

There are some further suggestions here:

You'd still want as good a finish as possible on the parts of the jig that come into contact with the epoxy, though.

Yandersen

Mon Mar 18 2013, 05:49AM

Registered Member #6944 Joined: Fri Sept 28 2012, 04:54PM
Location: Canada
Posts: 340

There are no metal parts come in contact with epoxy in the video - washers are covered with transparent scotch tape (it is not mentioned in second video - sorry - it is explained in first part only), while the central part has oiled paper ring over it rolled over with scotch tape, once again. So "jig" is completely insulated from epoxy by a scotch tape everywhere. Paper rings on sides are not epoxy-protection - those are just a physical barriers protecting the wire from hard surfaces coil will push during shots. Those are electrical insulators from steel washers I use to put on sides. You can include steel washers into the coil module (in fact my first recoup was done like that), but I found that for high stages induction currents are so big, that parasitics got higher then benefits. So I decided to not include washers into the coil. But if you do, cut washers first and epoxy-glue paper rings as insulators to them prior to work with wire. Here is some pictures for this approach:
1) Get two washers:

2) Cut them:

3) Sand the surface which will be covered with paper to ensure good epoxy bond:

4) Apply epoxy and glue washers to the paper (plastic underneath!):

5) Insulate the gap too:

6) After epoxy hardened (5min epoxy is good enough), remove all excess paper:

7) Here is an example of coil made with those washers:

BigBad

Mon Mar 18 2013, 06:18AM

Registered Member #2529 Joined: Thu Dec 10 2009, 02:43AM
Location:
Posts: 600

Actually I just wound a coil a few weeks ago, before I read this, but it wasn't nearly as nice as yours. 250 turns of 0.3 odd mm magnet wire.

One thing, I potted it in polyester, it set off in just 20 minutes.

I didn't think it would, but it penetrated incredibly well in fact, the polyester I used was a car bodywork fiberglass plastic. Clearly it's intended to wet stuff out thoroughly anyway, as it turned out I didn't even get a single bubble, it sucked it all up.

The downside of polyester is that it contracts a good few percent, much more than epoxy but the copper seemed to stop it. I'll let you know if it shrinks later, it can take a few weeks. The copper wire will tend to stop it shrinking though, wires are pretty good fiber reinforcement.

Not saying I recommend it, but it was dirt cheap (about $10) and seemed to work, at least this once.

Ash Small

Mon Mar 18 2013, 10:38AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Yandersen wrote ...

There are no metal parts come in contact with epoxy in the video - washers are covered with transparent scotch tape (it is not mentioned in second video - sorry - it is explained in first part only),

I did watch the first part, then skipped to the end.

Did you find the links in my previous post useful? If you keep the curing temp. to below 110F you can use car wax and hairspray as a release agent.

Yandersen

Mon Mar 18 2013, 11:15PM

Registered Member #6944 Joined: Fri Sept 28 2012, 04:54PM
Location: Canada
Posts: 340

Would you like to try it and show the results? :)

Sulaiman

Tue Mar 19 2013, 12:59PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

There is the option of self-bonding wire

You can also get 'square' cross-section copper wire for maximum current density.

Ash Small

Tue Mar 19 2013, 02:35PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Yandersen wrote ...

Would you like to try it and show the results? :)

There are plenty of online resources that explain in detail how to apply a release agent to a mold, it's not difficult to do.

,or.r_qf.&bvm=bv.43828540,d.d2k&fp=4e753e884ed8bf3 6&biw=1366&bih=663

ElectronicBob

Tue Aug 13 2013, 09:40AM

Registered Member #2973 Joined: Tue Jul 06 2010, 01:13PM
Location: Leeds UK
Posts: 9

Hey Yanderson

The coils you have produced are really impressive and you have given me some great ideas for my own coil winding process.

I am going to adopt the use of a "prodder" to get my windings nice and regular and ensure they bend in one place (like yours). Also I have done a test wind and used superglue to impregnate the coil. But your use of epoxy has got me thinking...which is best? I am thinking that epoxy might be better if the coil gets to higher temperatures. Does anyone have any thoughts?

Ash Small

Thu Aug 15 2013, 12:32PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

ElectronicBob wrote ...

Also I have done a test wind and used superglue to impregnate the coil. But your use of epoxy has got me thinking...which is best? I am thinking that epoxy might be better if the coil gets to higher temperatures. Does anyone have any thoughts?

Even so called 'high temperature' epoxies are only good for ~100 degrees C.

klugesmith

Thu Aug 15 2013, 05:36PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

1. I had not seen this thread before this week. Hats off to Yandersen for his outstanding coilcraft and teaching skills.

2. @EB: What temperature are you planning for? You can figure the temperature rise per shot from the electrical energy and mass of copper. There are many good epoxies.

3. @Ash: where did you get that 100 degree figure? That isn't very hot for most electronic materials and components. Glass-epoxy multilayer circuit boards are lead-free soldered at over 220 degrees C. What do you think IC packages are made of? A quick Internet search turns up this slow-curing potting compound rated for service at 275 degrees C.

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