Feedthrough Questions

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Luca Aldridge
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Feedthrough Questions

Post by Luca Aldridge »

Try as I Might, I could not find an FAQ or previous question about feedthrough construction. I want to build myself one that will last all the way up to neutrons. From what information I have gleaned, I need a copper stalk insulated by alumina on the vacuum side and ceramic metal on the atmosphere side.
How are these parts sourced, fabricated and connected to the flange?
Thanks in advance!
Luca Aldridge
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Richard Hull
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Re: Feedthrough Questions

Post by Richard Hull »

What few discussions revolving around feed through construction were never in a FAQ, but were loosely lost in numerous regular postings where much discussion and useful images came forth.

A good Boolean search of the HV and construction forums, specifically, should prove worthwhile.

Hand made, scratch built feed throughs to handle 40kv and above would make a great FAQ if the person writing it has built one and used it to such levels with great success and gave full details on components needed to achieve the desired goal. Most such discussions I mention had several failures and break downs, but seem to have served well enough in the end, certainly to 30kv or a bit more. Most successful attempts right out of the chute have involved buying a professional 30kv feed through and doing great efforts in extending its air insulated voltage range against the nearby grounded chamber. These include field control, oil filled enclosures, extended tube attachments with silicone HV putty, etc.

In short the best results tend to stem around a professional insulated feed through that is reworked to handle far more than its original design allows for.

Manufacture at the rank amateur level of such a successful feed through from scratch would, at all events, be difficult.

Here is but one discussion that I found in 2 seconds of Boolean search here. Frank, you did a great job!

viewtopic.php?p=94572&hilit=hull+insulator#p94572

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Luca Aldridge
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Re: Feedthrough Questions

Post by Luca Aldridge »

Hi Richard,
Thanks for your reply.
For now I’ll be borrowing a friend’s 30kv feedthrough until I gain adequate knowledge to either buy one myself or make one.
Luca Aldridge
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Cade Neely
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Re: Feedthrough Questions

Post by Cade Neely »

Luca

I recently purchased a 30kv 2.75" conflat feedthrough from MPF for $220. You might want to look into that. Best of luck.

https://mpfpi.com/shop/power-feedthroug ... 0234-7-cf/
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Liam David
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Re: Feedthrough Questions

Post by Liam David »

That isn't a terrible price for a new feedthrough, but there's one on Ebay for $175 and the seller has offered me $125, so you could try submitting a best offer.
Luca Aldridge
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Re: Feedthrough Questions

Post by Luca Aldridge »

Thanks Liam & Cade, I’ll use my friend’s for now and when I need a beefier one I’ll look into buying one.
Luca Aldridge
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Dennis P Brown
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Re: Feedthrough Questions

Post by Dennis P Brown »

I have made a few HV feed-thru's that worked well below 35 kV.

All were based on using a telescope mirror blank as a base to build from which is superior to metal plates since one has less insulation issues between the HV rod/wire to the metal base plate; obviously, the glass plate must seat against an o-ring surface - clamping is optional.

Getting a ceramic rod large enough is not inexpensive and one needs to have access to a lathe (and skill to use it) unless one gets lucky to find a hollow ceramic rod that meets all their size constraints. Further, a drill press is essential for boring out the glass plate (in some ways, far easier than steel!) Finally, ceramic adhesive and a good epoxy are need to seal the conductive rod/wire that runs thru the ceramic tube.

Bottom-line, this is neither a project that is extremely low cost nor one that requires little skill.

Do note that my last HV feed-thru system (as Richard showed) used an extremely inexpensive commercial HV feed-thru assembly (under $40 w/shipping) because it would break down around 15-18 kV due to a possible defect (as noted clearly by the seller.) Mounting it on a glass plate solved that issue so I now have a HV feed-thru that is likely good to 80 kV (I've only tested to the mid 30 kV range to date.)

Again, this required a (smaller) telescope glass blank and boring with an inexpensive (China, $18) glass drill*. One MUST use a drill press at lowest possible speed and water (Use plumbers putty to make a ring to hold the water.)


* See Amazon: BLENDX Diamond Drill Bits - Glass and Tile Hollow Core Drill Bits Extractor Remover Tools Hole Saws for glass, ceramics, porcelain, ceramic tile, Pack of 10 ( include a series of sizes in the pack from 1/8 inch to 1 inch in diameter!)
Luca Aldridge
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Re: Feedthrough Questions

Post by Luca Aldridge »

Dennis,
Thank you for this excellent outline. Once I get round to making my own I’ll follow this with additional questions if needed.
That’s a long way away as I have a temporary solution currently.
Luca
Luca Aldridge
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