Matt Gibson Fusor

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Richard Hull
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Re: Matt Gibson Fusor

Post by Richard Hull »

Wrangling voltages above 60KV or 70KV put one in a new dynamic for sure, especially at high frequencies where all switching is at impulse levels.
Dielectrics become critical and flat planes of great insulation break down. Capacitors are stressed to their limits.

There is no smooth sailing here.

All the best in conquering these heights.

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
Retired now...Doing only what I want and not what I should...every day is a saturday.
Matt_Gibson
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Re: Matt Gibson Fusor

Post by Matt_Gibson »

Smoked my new xfmr. One of the coils arced over and it looks to be deep enough to be a death blow. I was getting 160mR/Hr on my Ludlum running close to 70kV, 10mA, and 9 microns.

I’ll start looking at some other options rather than rewinding. That’s was a real pain in the ass. Bloody hell.
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Richard Hull
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Re: Matt Gibson Fusor

Post by Richard Hull »

So Sorry to hear of the failure of the insulation. High voltages at high frequencies have a way of wasting insulating qualities via dielectric characteristics of materials that are great insulators at DC and very low frequency equivalent potentials. Rest a while and plan some form of new attack on the issue.

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
Retired now...Doing only what I want and not what I should...every day is a saturday.
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Finn Hammer
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Re: Matt Gibson Fusor

Post by Finn Hammer »

Matt,
Richard is right, as usual.
There are a couple of other things.
You have wound a very wide coil, this results in a large layer to layer potential. This might not lead to failure, unless you had made error number 2: winding all the way to the end of the insulating interleave. By doing so, the full potential of the coil is presented from bottom layer to top layer, with only the wire insulation to prevent breakdown. ( Which it cannot due to its dielectric lossy nature).
Therefore you have 2 options: Do as Mark R. already has showed: make narrow sections, and submerge them in oil afterwards (or cast them in epoxy, vacuum to expell air inbetween turns)
Or you can wind it in layers with interleaving tape, and start by winding only 3mm to the edge of the tape. Then as you progress, wind one turn less, each end of every turn, so that the coil ends up with a rhombic cross section. This will make it hard for the high potential end of the coil to start tracking on the surfaces, and finally arc the full distance.
High voltage coils in RF switch mode supplies are narrow and high, for a reason.
You can forget repairing that coil, it is toast.

I hope this helps

Cheers, Finn Hammer
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Re: Matt Gibson Fusor

Post by Matt_Gibson »

Yup, the multi section bobbin seems to be the best way forward, I just have zero access to any machinery nor any friends :-(

I’ll have to backup and punt. I still have my old transformer configuration to play with until I think up something.

Edit: https://www.thingiverse.com/thing:5241175
This looks like a potential solution. I could choose nylon for the material which should be a lot better than the other choices. Also, this one looks big enough to create two coils in for a center tap, no?

-Matt
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Finn Hammer
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Re: Matt Gibson Fusor

Post by Finn Hammer »

Matt,

If you have a 3d printer, then this looks like a viable solution.

Cheers, Finn Hammer
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Re: Matt Gibson Fusor

Post by Matt_Gibson »

Hi Finn,

I don’t have one, but I can upload the file to a number of different services for a price ($$$). This is how I got the bobbins for my existing transformer.

I was thinking that I would use 5 slots for each coil and save the middle slot for the center tap. Should give me more than enough turns.

-Matt
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Re: Matt Gibson Fusor

Post by Matt_Gibson »

Decided to go for it and order the 3D print using polished nylon (whatever that means). I scaled it up by 13% to accommodate my monster ferrite.

Should I plan on putting this in oil, or should this multi section design perform in air just fine at the voltages that I’m running (12kVp-p)?

As a plan B (or C), anything stopping me from using two of those super beefy flyback transformers from amazing1?

https://www.amazing1.com/transformers-h ... uency.html

They have one wound with 1000 turns of 28awg, capable of 230mA.

-Matt
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Mark Rowley
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Re: Matt Gibson Fusor

Post by Mark Rowley »

***OIL***

Mark Rowley
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Richard Hull
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Re: Matt Gibson Fusor

Post by Richard Hull »

Ditto..Always under oil over 30kv attempted, especially with high frequency switcher and multipliers, if possible.

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
Retired now...Doing only what I want and not what I should...every day is a saturday.
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Re: Matt Gibson Fusor

Post by Matt_Gibson »

Okay, no open air then. How about epoxy? Which is going to be the hardest to deal with? I’m thinking that oil will bitter penetrate the wound layers than epoxy or polyester resin, but oil is oil :-)

Edit: Decided on a custom acrylic container to fill with oil. Don’t like the idea of how permanent epoxy is.

-Matt
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Mark Rowley
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Re: Matt Gibson Fusor

Post by Mark Rowley »

Matt, neither did I as repairability was a priority. However, epoxy won out by providing more stability and a higher end potential.

Winding was surprisingly simple. I mixed the epoxy and slowly poured it on the windings as it was being wound. Messy yes, but provided a very solid end product which performed to expectations. So yes, a combination of oil AND epoxy resin.

Fwiw, I used Alumilite resin from Hobby Lobby but undoubtedly there are better epoxy's out there with a better dielectric strength and resilience to the involved frequencies. I was more than pleased with the outcome but important to note, I wasn't running the amperage you were. My system went the route of higher voltage so there are distinct differences regarding component stressors. Experimentation will ultimately decide what's needed for your arrangement. The requirement for oil however will remain a constant.

Side note, don't forget about the feedthru. I cannot see any possibility of running a 60-100kV system without the feedthrough being totally submerged.

Mark Rowley
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Re: Matt Gibson Fusor

Post by Matt_Gibson »

Hi Mark,

Hopefully oil, alone, will suffice. I use a multiplier so voltage isn’t as high…My multiplier capacitor stages can’t go over 12kV anyways…

The high end of the multiplier is connected under oil and then a continuous run of high voltage wire is run to the top of the resistor string before going over to the ballast resistor and fusor. So far, so good. I’ve run up to 70kV without and arcs along the way.

-Matt
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Re: Matt Gibson Fusor

Post by Matt_Gibson »

I saw this on another forum being mentioned:

https://raytechgels.com/products/raytec ... -power-gel

Anyone have any thoughts about potting the coil in this? Calling it “magic power gel” raises my suspicions…It claims 23kV/mm

-Matt
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Richard Hull
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Re: Matt Gibson Fusor

Post by Richard Hull »

I firmly believe and am positive that this product is worth someone else spending their money on this product and reporting back to us.

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
Retired now...Doing only what I want and not what I should...every day is a saturday.
Matt_Gibson
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Re: Matt Gibson Fusor

Post by Matt_Gibson »

I may be down for some experimenting (probable waste of $$$) down the road :-)

On a side note, picked up a mini x ray transformer (ferrite) that was too cute to pass up. There’s one more on eBay in case anyone is interested in it.

https://www.ebay.com/itm/175365993798?m ... media=COPY

I dressed mine up and connected the two coils for a center tap. I also paralleled the primary coils (located underneath the secondary coils). Going to dunk this in oil and see what it can do! This is all while I await my 3D printed bobbin.
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Richard Hull
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Re: Matt Gibson Fusor

Post by Richard Hull »

Looks nice. Drive it right and it might surprise you. Nothing beats ready-made as long as it isn't pushed.

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
Retired now...Doing only what I want and not what I should...every day is a saturday.
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