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What's the best off-the-shelf solution for a vacuum encapsulation chamber?

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jpsmith123

Tue Oct 27 2009, 11:59PM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
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Posts: 843

I thought possibly something like this.

Or like this.

But considering that I probably won't be using it very often (maybe only once or twice), these seem too expensive.

Maybe a modified low-end pressure cooker? But then there'd be no way to see what's going on inside...unless a viewport of some sort was added, which would add to the cost in time and money.

Anybody have any other ideas?

Proud Mary

Wed Oct 28 2009, 12:46AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

You haven't said what kind of dielectric you intend to use, Mr Smith.

Anything other than oil will be extremely expensive in those large capacity containers in your illustrations.

If you intend to use eco-freindly vegetable oil dielectric, get back to me for further advice and opinion.

jpsmith123

Wed Oct 28 2009, 02:00AM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
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Posts: 843

Harry what I was planning to do was to fill the bobbin assemblies with epoxy or RTV (I haven't selected one yet, but I'm leaning toward MG Chemicals' encapsulating epoxy), and then put the assemblies into the chamber and pump it down.

I don't know yet exactly what the volume of the assemblies will be, but I can't imagine it being more than 150 ml or so.

BTW, here's a nice setup someone is putting together and selling on ebay:

I already have a pump and all the necessary hardware (i.e., gauge, valve, tubing)...all I need is the chamber. An aluminum stock pot like he's got there seems like a good idea. And as for the lid, it looks like it's 12" x 12" x 1" thick plastic, probably plexiglass rather than polycarbonate, considering the price he's asking.

MinorityCarrier

Wed Oct 28 2009, 03:32AM

Registered Member #2123 Joined: Sat May 16 2009, 03:10AM
Location: Bend, Oregon
Posts: 312

If you can find a nice thick panel of acrylic and a sheet of good gasket material you can make something like what that guy is selling, at a reasonable cost. The dessicator chamber would be kind of flimsy, may work, but would certainly cost more than the cooking pot/acrylic plate approach. You can also heat the metal cooking pot to help with the evacuation process.

I would recommend you de-gas epoxy first before potting an assembly. Trying to degas after potting may trap gas bubbles inside your assemblies. With an acrylic plate, you could add another port through which you could flow epoxy to your assemblies while they are in a vacuum.

jpsmith123

Wed Oct 28 2009, 03:52AM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
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As far as the acrylic plate, I found a nice 12" x 12" x 1" piece for $24.59 here:

I'm still debating what to do for a gasket.

I think I'll go down to the local restaurant supply house tomorrow and see if they have any 12 quart aluminum stock pots with welded-on handles. Once I see what the edges look like, maybe that'll generate some ideas for gasketing.

And yes, I agree that flowing the epoxy in while the assemblies are under vacuum would be better, but in this case it may not be worth the extra hassle. I'll have to think about it some more.

Proud Mary

Wed Oct 28 2009, 04:54AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

The argument against using epoxy is that if you make a mistake, or if arcing should start inside, you have no means of repair.

Oil dielectric has the advantage of being self-healing, so if a minor flash-over should occur between windings, it will be automatically repaired by the ingress of fresh oil.

jpsmith123

Wed Oct 28 2009, 11:25AM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
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Posts: 843

What about this thing?

That would seem to be ideal...if it's heavy enough to withstand vacuum. At $14.99 the price is certainly right.

Bored Chemist

Wed Oct 28 2009, 06:40PM

Registered Member #193 Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022

Just a quick "heads up".
The polycarbonate vessels in the first post are perfect for many things.
Unfortunately they will craze then implode if used with any organic solvents (such as might be present in the potting resins).
You would probaly get away with it once- maybe twice but I'd not try it.

mikeselectricstuff

Wed Oct 28 2009, 11:24PM

Registered Member #311 Joined: Sun Mar 12 2006, 08:28PM
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Posts: 253

Something I used a while ago, purely because it was available, was a paint pot designed for use with compressed air - no window, but nice and strong, with ful-diameter removable lid ane air fittings already there.

teravolt

Thu Oct 29 2009, 03:22AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

I don't know how intent on epoxy you are but I use parifin wax. its cheap and a grate insulator and repairable. its great for insulating old style flybacks for more output

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