My Fusor Progress

For posts specifically relating to fusor design, construction, and operation.
Rex Allers
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Re: My Fusor Progress

Post by Rex Allers »

On Spice, I agree with all Joe said. But LTSpice is a great program and free.
On the AD LTSpice page that Joe gave a link for, in addition to pgm download there are some links to docs and a video or two.

If you do a web search for LTSpice, one of the returns should be a pdf from MIT of a Power Point presentation intro that might also be a starting place.

I found this website link, too, that looks pretty good to me...
http://www.simonbramble.co.uk/lt_spice/ ... _spice.htm

There is also a user group on 'groups.io'
https://groups.io/g/LTspice

You first need to create an account at groups.io and then request to join that group.

Oh, one small thing I'd suggest, after you install LTSpice.
Under your Windows, Documents folder, find the folder that was created for LTSpice and creat a new folder under that. Then when using LTSpice you can save any circuits you create into that folder. See this small screen cap...
add-Dir.png
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Rex Allers
Rex Allers
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Re: My Fusor Progress

Post by Rex Allers »

Richard,
I can relate to all you say about Bob Pease and EDN magazine.
Bob at Nat Semi and Jim Williams at LT were both analog gods and gurus.

2011 was a very sad and ironic year. First Jim Williams died suddenly and then Bob Pease, returning from the funeral gathering had a car crash and also died.

I didn't know them but I saw, and said hello, to both on separate occasions at the Foothill ham flea market.

I have the book that you mentioned and two others that are similar. I just searched by the titles and they all seem to still be available, used and new.
The first two are compilations of articles by many experts, edited by Jim Williams. Not a textbook or guide but interesting.

"The Art and Science of Analog Circuit Design"

"Analog Circuit Design: Art, Science and Personalities"

Then my favorite, with lots of practical information and methods.

"Troubleshooting Analog Circuits" by Bob Pease

Also, unrelated to Bob or Jim but a great overview and reference:
"The Art of Electronics", by Paul Horowitz and Winfield Hill

Back to Bob Pease.
I felt good when I saw pictures of Bob's office, as is discussed with pictures here:
"What’s All This Messy Office Stuff, Anyhow?"
https://www.electronicdesign.com/techno ... uff-anyhow

My office was headed in that direction but far from the magnitude of Bob's.
However (quick story)...

On day I was sitting in my cubicle, talking with a customer, and trying to provide him some technical guidance on some aspect of a product. I reached for some document that I knew where it should be, but oops, I started a small avalanche of documents and other stacked stuff that fell onto my phone and hung up on the guy.

After calling back with apologies, I finished the call. But I did decide that it was probably time to do a bit of clean-up.
Rex Allers
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Rich Feldman
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Re: My Fusor Progress

Post by Rich Feldman »

Like Rex, I exchanged a few words with Bob Pease at the flea market -- in my case during the De Anza College years before the overhead solar panels. Bob's son Ben introduced me to trail mapping with wheel and compass, before handheld GPS receivers became common. AFAIK, that method still works better when thick forest foliage blocks GPS signal.

Like Rex, I have a notoriously messy cubicle but it never suffered a major collapse of stuff.
https://dilbert.com/strip/1997-11-10
https://dilbert.com/strip/1997-11-11
All models are wrong; some models are useful. -- George Box
Nicolas_Malo
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Re: My Fusor Progress

Post by Nicolas_Malo »

Today I tested my finished power supply. I managed to get around roughly 2.5-3cm of distance between the wires before it failed (probably some arcing inside ferrite transformer). I haven't precisely measured the voltage but according to air dielectric strength I'm guessing It got to around 60-70kV. Here's a video before it failed (2cm distance). https://www.youtube.com/watch?v=S8tq4W4 ... sicsAddict
Nicolas_Malo
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Re: My Fusor Progress

Post by Nicolas_Malo »

Transformers are fine! A capacitor leads of a CW voltage multiplier were out of the oil and shorted once voltage got too high. Stupid mistake
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Matt_Gibson
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Re: My Fusor Progress

Post by Matt_Gibson »

Don’t let the CW multiplier arc, it’ll wreck your diodes from overcurrent.

Edit: I see you’re using a resistor so you’re diodes may be okay, but your gap contains sharp points. The arc will jump a further distance which means your voltage isn’t as high as it would seem. If you can get some spheres, you could better estimate your voltage. Better would be to go ahead and build a high voltage divider to measure voltage accurately. You’ll eventually need this as well as a way to measure current so you know what you’re able to supply under load.

-Matt
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Richard Hull
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Re: My Fusor Progress

Post by Richard Hull »

A rank amateur mistake to let an already stressed and kludged HV supply working on the raw edge, arc in air. A truly destructive path to disaster for all the hard work. Only line operated HV transformers can directly air arc as they are more of less designed to "take it on the chin" like that. The arc I saw was thready and thin, indicative of no really energy in or behind it. I felt sorry for your HV supply system while watching that arc. It tried to perform but the weak link prevailed as it always will in any voltage multiplier system in the 40kv and above system will.

Any voltage multiplier system can be strengthen by careful design and employment of the highest quality, (read expensive) components. Arcing such systems will indeed prove them capable as it is the most horrid and needless test of same.

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.
Nicolas_Malo
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Re: My Fusor Progress

Post by Nicolas_Malo »

Thank you Matt and Richard, I did not know that arcing the supply for such a short period was going to be that bad for the components. I will check the diodes. I will also build a voltage divider system upon future testing. I did notice Richard that the arcing was really weak. We'll see after my repairs if it can deliver at least 30ma at 30kv.
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Dennis P Brown
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Re: My Fusor Progress

Post by Dennis P Brown »

I assume you have a very high frequency (15 kilo-Hertz or higher) and fairly beefy transformer. Otherwise, getting that much power is not going to occur
Nicolas_Malo
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Re: My Fusor Progress

Post by Nicolas_Malo »

Yes Dennis, I'm using a ZVS driver with a frequency of around 100kHz. I will double check the frequency. Here's a picture of my ferrite transformer.
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Mark Rowley
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Re: My Fusor Progress

Post by Mark Rowley »

Nicolas,
You may be interested in my earlier efforts regarding a ZVS driven PSU. The end result was a decent and reliable supply which provided enough power to activate a respectable array of different metals.

Keep in mind this supply was designed to operate for my specific fusor. It is not suitable for a large cavernous system.

viewtopic.php?t=13907

I'd also recommend your read the FAQ's on Precipitatior PSU operation. The do's and dont's tend to parallel ZVS driven systems. Learning the pitfalls will save you a ton of time and money.

Mark Rowley
Matt_Gibson
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Re: My Fusor Progress

Post by Matt_Gibson »

Nicolas,

The capacitors are capable of supplying peak current during shorting that can kill your diodes. Seeing that you’re using a ballast resistor, you’re probably okay for now. Just don’t keep doing it as it’s still stressing them.

Another potential issue will be your 100khz operating frequency. From what I understand, ceramic capacitors, like the ones you’re using, don’t like high frequency. Your diodes are probably also getting pretty stressed at 100khz. Finn Hammer did some testing and found his diodes weren’t happy beyond 50kHz and I think he settled around 30khz. His power supply is pushing 3kW I believe.

-Matt
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Finn Hammer
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Re: My Fusor Progress

Post by Finn Hammer »

The issue of drive frequency is the result of design decisions, which arise from the "can of worms situation" which a power supply design process inevitably ends up as.
It is worth noting, that as an amateur designer, one does not always make the wise decisions that the more seasoned industrial designers would chose, based on decades of company experiences.
In my case, I started out wanting to use 100kHz drive frequency, simply because I had had a Spellman supply that used 100kHz drive frequency.
At that time, I had little experience with rectifying diodes, but I soon found out, that even fast 20nS reverse recovery types buckeled under at that frequency. During a long iteration of experiments, I found out that 50kHz was the upper limit of the 2CL2FP diodes I had on hand.
But that was not the end of it, because even at that frequency, the ferrite core would heat to uncomfortable levels, no matter how low a flux level I chose. (Remember that ferrites are saturation limited below 20kHz, above that, the limiting factor becomes the core loss, and the core loss goes up with frequency and flux density.
The final compromise landed my design at 35kHz, where all components were happy, and funny enough, that is around the values where most commercial high voltage switchers operate.
Once the magnetics are sorted, the power throughput is only limited by heating of the copper due to resistance, instead the limit occours in the driver electronics. In my case, 96A SIC mosfets warranted resilience at up to at least 2.5kW, but I think it could well go as far as 5kW.

Cheers, Finn Hammer
Matt_Gibson
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Re: My Fusor Progress

Post by Matt_Gibson »

Hi Finn,

How’s that transformer FAQ coming? Magnetics wasn’t my strong suit in college…Ferrite material, volts/turn, and frequency all get me turned backwards. Seeing as this seems to be the future for fusor power supply, I bet many would find themselves just as turned around :-)

-Matt
Nicolas_Malo
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Re: My Fusor Progress

Post by Nicolas_Malo »

Hi everyone, I can’t stress enough how much I appreciate all your replies. I did some little testing over the last couple of days and got some interesting results. Firstly, 1 of the diodes did die after arcing. I had gotten 8 for less than 10$CAD so it isn’t much of a trouble. I was using some microwave diode because I wasn’t aware of the concept of recovery time. I figured 100kHz wasn’t going to impact their functionality. I recently saw an old Richard’s post on HV diode where he did mention that they had a slow recovery. I examined them and found that their cutoff was as low as 1kHz. I do have 1 diode from a microwave switcher supply. It’s a UX-F5B rated for 8kV, 150mA, and 150ns recovery time. I tested it and it was fine at 100kHz. They’re inexpensive and would be a perfect fit if it wasn’t for their 8kV limit. In my CW multiplier, each diode would have to be able to withstand a maximum of 25kV. I’m pretty sure I already know the answer, but would I be able to push that 8kV limit to 25 if I were to put their connections in epoxy and under oil?

Secondly, I did some testing of the primary inductance of my ferrite transformers and found it to be around 75uH. With 2 in parallel connected to my ZVS driver, the total inductance will be 37.5uH and the capacitance of the ZVS is 2uF giving a theoretical resonant frequency of around 18kHz which matched my recent experimental result. This meant that I was way off with my initial 100kHz estimation.

Thirdly, in further testing, I noticed that my secondary coil was arcing to my core and thus my primary even under oil (See first video link). In the next couple of days, I will look at buying a new high voltage/high-frequency diode, rewinding a new secondary coil in epoxy, providing more isolation between secondary/core/primary and might look at buying a more resilient capacitor as they are known to lose considerable value over time.

Finally, while ramping up my voltage, I noticed that my variac was humming a considerable amount until the ZVS input voltage reached its 12V minimum voltage requirement. Does anyone know why exactly? I was thinking of adding a 12V/25-30A relay to the input of the ZVS If it were the source of the problem. I added an exact schematic of my circuit for reference.

Here’s a link to the arc to the core:
https://www.youtube.com/shorts/nTbfXjm2Grs

Here’s a link to some fooling around I did with some extra transformer I had made:
https://www.youtube.com/watch?v=9rOxToG ... e=youtu.be

Sorry for the bad quality of the videos
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