My Fusor Progress

For posts specifically relating to fusor design, construction, and operation.
Post Reply
Nicolas_Malo
Posts: 14
Joined: Wed Jun 16, 2021 11:38 pm
Real name: Nicolas Malo

My Fusor Progress

Post by Nicolas_Malo »

Hi everyone, this is my progress. I’ve started to construct my own fusor at the end of summer 2021 after doing a lot of research, mainly on this website. I’ve spent around 2k$CAD for this project. Money well spent I might add. I’ve learned so much more about high vacuum, high voltage, programming, radiation… and still have a lot to learn. So, here’s what I’ve come up with so far.

High vacuum system.


For my high vacuum system, I have an old Edward E2M1 mechanical pump which is rated for an ultimate vacuum of around 0.3 microns. The pump is connected to a nice Pfeiffer TMH-261 turbo molecular pump that can supposedly go downwards of 7.5*10^{-5} microns. It did not come with a power supply or an operating panel. I manage to make its own power supply and get it running. I am still working on implementing a remote-control function on my fusor interface (later discussed). They are yet to be fully tested on the chamber.

Image

The connection between these pumps is regulated by an ordinary high vacuum pneumatic valve that I’ve modified to become mechanical for money reasons. The fore line pressure is monitored by a TPR265 Pfeiffer pirani compact gauge that can measure down to 0.3 microns.
The adapter (ISO100 to CF40) for the turbo pump is yet to be made. I bought a separated ISO100 and CF40 nipple for less than 100$CAD. I will later this month make a hole in the ISO100 flange with a CNC machine and TIG weld the parts together for free.

The fusor chamber is simply a 4-way CF40. I have attached a viewport, a ¼ VCR flange for the gas line and a 30kv feedthrough. This is then connected to a T flange that has a KR251 Pfeiffer Cold Cathode that can measure down to 3.8*10^{-6} microns. Finally at the other extremity is a regular CF40 high vacuum valve to separate the chamber from the pumps.

High voltage system.

The high voltage system is based on the ZVS circuit that Mark Rowley constructed. Just like him, I made my own ferrite transformers. I still haven’t finished the circuit because I’m lacking free time and waiting on receiving my bleeding resistor. Here’s a picture of the schematic for the system and what I have constructed/have so far.

Image
Image

It’s not very aesthetically pleasing but who cares?

Gas system.

The gas system is made from a brass low flow Metering Valve, 1/4 in. Swagelok Tube Fitting that leads to a SS-DLV51 Swagelok diaphragm-sealed VCR valve, 1/4in (As seen in the high vacuum system picture) with a 3D printed handle. The extremity of the diaphragm valve is then connected to a syringe that will contain the deuterium gas.

The deuterium gas is synthesized with a PEM cell. The gas is then dried in a homemade dryer tube (Drierite) and stored into a syringe.

Image

Fusor Interface (Vacuum gauge pressure, High voltage, Radiation, Spectrometer, Remote control, Camera feed, Neutron count, etc)

The fusor interface that I created is made to show the value of each of my sensors in real time. I have an Arduino that reads the pressure of each of my vacuum gauge, the high voltage of my system (on the low voltage side) and the radiation from my digital dosimeter. I also made my own basic spectrometer that will analyze the plasma composition. I then added a camera to safely view the reaction.

I also bought a Russian SMN-12 tube for neutron count. I will design the circuit eventually and make some moderator. I am aware that they aren’t very good because of their size. I might buy a bigger tube in the future.

The data of each of those components will then be fed to the Raspberry pi that will act as the computer for the interface. Here’s the first iteration of the interface. I made it quite a while ago and need to update the interface to integrate the spectrometer that I made recently.

Image

I might be forgetting things, but this is what I have accomplish so far. As of now, I still haven’t encountered real difficulties. The hardest part was to find affordable parts and repairing/adapting most of them. It was also the most time-consuming.

Feel free to critique my fusor, ask question or find flaws in my design. I’m sure there will be upon testing each system, but it would be nice to find some in advance. Thank you
Attachments
Interface.jpg
Highvac.jpg
Gas.jpg
Circuitelec.jpg
Circuit.png
Nicolas_Malo
Posts: 14
Joined: Wed Jun 16, 2021 11:38 pm
Real name: Nicolas Malo

Re: My Fusor Progress

Post by Nicolas_Malo »

Forgot to mention that the High voltage circuit will be under Mineral Oil.
User avatar
Richard Hull
Moderator
Posts: 13897
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: My Fusor Progress

Post by Richard Hull »

Great base for the effort with good materials. All the best in your build.

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.
User avatar
Dennis P Brown
Posts: 2598
Joined: Sun May 20, 2012 10:46 am
Real name: Dennis P Brown
Location: Glen Arm, MD

Re: My Fusor Progress

Post by Dennis P Brown »

Really impressive build and progress. You certainly are proving that someone with effort can do amazing work. Hope to see your power supply tested soon.
Nicolas_Malo
Posts: 14
Joined: Wed Jun 16, 2021 11:38 pm
Real name: Nicolas Malo

Re: My Fusor Progress

Post by Nicolas_Malo »

Thank you very much M.Hull and M.Brown. Theses comments means a lot. I will continue to add my future progress of my build on this post.
User avatar
Mark Rowley
Posts: 900
Joined: Sun Dec 29, 2002 12:20 am
Real name: Mark Rowley
Location: Sacramento California
Contact:

Re: My Fusor Progress

Post by Mark Rowley »

Excellent work!
Just a couple of suggestions:

1) Delete the drierite tube. There's too much air embedded into the drierite rocks and all it will do is contaminate your gas and lower your neutron count. Drierite is good on a permanently closed system with a tank of gas where you can thoroughly and permanently purge the system. My testing and experience indicates that drierite is a detractor for syringe / PEM cell based systems. Fwiw, I did get a slightly notable improvement after repeated purges with D2 gas but it's nothing to write home about and it's an unnecessary waste of deuterium. If you want to experiment with drierite do so after you make your first batch of confirmed and peer accepted neutrons.

2) This one is simple.... dont push that PSU design too hard. It works great, but the secondary windings will get fussy when pushing it too hard. When (not if) the secondary's begin to short or arc, wind the next batch in epoxy resin. It's a night and day difference.

Have fun and looking forward to your progress.

Mark Rowley
Nicolas_Malo
Posts: 14
Joined: Wed Jun 16, 2021 11:38 pm
Real name: Nicolas Malo

Re: My Fusor Progress

Post by Nicolas_Malo »

Thank you M.Rowley. Good idea, I will get rid of the drierite tube for my first couple of run but I would like to experiment with it after. As for the PSU design, I did put some red insulating varnish on the coil (MG chemical 4228) while winding but it might not be enough. Therefore the next iteration will certainly be under epoxy.
Rex Allers
Posts: 520
Joined: Sun Dec 30, 2012 3:39 am
Real name:
Location: San Jose CA

Re: My Fusor Progress

Post by Rex Allers »

Nicolas,

Sorry to be critical but your HV supply schematic looks wrong in several ways.

1) I assume the circuit on each of the output transformers is supposed to be a rectifier/doubler and you intend to connect 4 of them in series for the HV output.

Those circuits are mangled. Here's what a doubler normally would look like.
doubler.png
Note where the ground and output are, and the orientation of the diodes for Neg output. To then string them in series, the bottom one's ground is the ground for the whole HV supply output. The (-) output of the doubler then connects to the "ground" of the next doubler and etc. That seems to be your intention but the doubler circuits got scrambled.

2) Why the MOT? You're using it as a voltage stepdown of /3 , right? Does the mysterious ZVS driver need an input <100 V?

As to the ZVS, switching at zero volts or maybe zero current is a good idea but not necessarily easy to pull off. I assume you have something in mind?

3) I did some rough numbers looking at what you showed.
The symbol is odd but I assume the transformer at the 120 input is an auto transformer and you show one in one of your pics. Normally one of them can go up to 140 V out. So lets assume that. Rough rounded numbers follow...
120 * 1.414 = 198 V peak
then the MOT
198 / 3 = 66
rectified and filtered, that's the DC voltage you will be switching into the output transformer primaries. You say the turns ratio is 280 so
66 * 280 = 18.48 kV
then a doubler
* 2 = 37 kV
and four in series
* 4 = 147 kV

Seems very unlikely to work and, if it did, way too high a voltage for any level of safety in a first fusor attempt.

Another consideration, if you string those doubler stages together the "low side" of the secondary on the top section gets the sum of the other three into it. It can be hard to keep that voltage from arcing through to the primary side or some other ground path.

More typical HV supplies use 220 V input or 120 doubled, then rectified and filtered to make about 310 V which is switched into the ferrite HV transformer.
A typical turns ratio for that transformer might be 16 giving about 5 kV out. Then this is run through multiple multiplier stages. For 5 kV from the transformer, 10 stages would give 50 kV out.

Then there is power to consider. A completely open issue with your design. I would think a minimal supply to do fusion would be 300 W out, with 600 or 1200 W being a lot easier. If the supply was 300 W and 40 kV that would be 7.7 mA. More would be better.

4) One last thing. The DC filter into the ZVS. I would expect the cap to be much bigger than 60 uF and the 100 ohms you show in parallel will be drawing about 44 W even at the low 66 V calculated above. I assume the resistor would be to bleed the cap voltage down when switched off. For 66 V I would have 50 kohm or more, or maybe no resistor.

It's good to try to do your own design but I think what you show isn't looking quite right so far.
Rex Allers
User avatar
Joe Gayo
Posts: 398
Joined: Sun Jan 06, 2019 9:34 pm
Real name: Joe Gayo
Location: USA

Re: My Fusor Progress

Post by Joe Gayo »

Nicolas,

Rex is correct that you have a schematic issue. If you go back and look at the pictures of Mark's power supply, the output schematic is as follows:
CascadeTransMult.PNG
Joe
Nicolas_Malo
Posts: 14
Joined: Wed Jun 16, 2021 11:38 pm
Real name: Nicolas Malo

Re: My Fusor Progress

Post by Nicolas_Malo »

Thank you very much M.Allers and M.Gayo. First, I have to say I made several errors on the circuit schematic as I made it in a hurry before posting. The first transformer symbol is a variable core transformer intended to show a variac (the program that I used did not have its symbol). The second error is the number of turn N2/N1 of the MOT, it’s supposed to be 20/120=0.17. Therefore, the highest voltage out of the dc filter will be around 120*0.17*1.414=27VDC-> 27*280=7560->5660*2=15120->15120*4=60kv. The third mistake was the doubler circuit that I drew. I’m pretty sure they are correctly connected in the circuit just not in the drawing. I will double check tomorrow morning. As for the capacitor it’s a 60k uF. I remember calculating C=I/(2*f*V) =30/(2*60*(2*27))=4629uF and bough a 60000uf for good measure. Finally for the bleeding resistor I chose 100Ohm for the circuit to discharge within seconds. For 100Ohm at 27V the resistor emits 7.29W and can completely discharge the circuit in less than 10 seconds if I remember clearly. Hope this clarify some things and let me know if I forget some details.
Rex Allers
Posts: 520
Joined: Sun Dec 30, 2012 3:39 am
Real name:
Location: San Jose CA

Re: My Fusor Progress

Post by Rex Allers »

Ok Nicolas, those numbers make better sense to me.

I guess this design is a version of Mark's supply from this thread:
Custom Fusor Power Supply
Post by Mark Rowley » Mon Mar 08, 2021 12:57 am
viewtopic.php?p=90707#p90707

I saw that thread but didn't follow it in detail. I see that the Chinese ZVS driver he used does take a low voltage input. Mark definitely proved that this design works.

Joe, if you are still reading, I guess you created the Spice simulation schematic yourself. Is that right?

Nicolas, I'm curious, where did you get the cores for the HV transformers and have you wound the coils yourself?

Keeps at it, all looks good.
Rex Allers
User avatar
Joe Gayo
Posts: 398
Joined: Sun Jan 06, 2019 9:34 pm
Real name: Joe Gayo
Location: USA

Re: My Fusor Progress

Post by Joe Gayo »

@Rex

Yes. I thought the easiest way to communicate what needed to be done was to spend a couple of minutes drawing it in Spice. I assumed my schematic is what Mark did because it's what would work for a cascaded transformer arrangement. Many years ago Chris B did something similar viewtopic.php?t=4887

The downside of both approaches is that one component (either the transformer or coupling cap) has to support the full (cap) or Nstage-1 (transformer) output potential to ground. I do think transformers are weaker on isolation than a good-quality ceramic or film cap.

Joe
Nicolas_Malo
Posts: 14
Joined: Wed Jun 16, 2021 11:38 pm
Real name: Nicolas Malo

Re: My Fusor Progress

Post by Nicolas_Malo »

Rex the cores where from amazon for quite cheap (25$ for 5 pairs) if you're interested. Here's the link : https://www.amazon.ca/gp/product/B07MT3 ... UTF8&psc=1. I indeed wounded the coil myself. I 3d printed the bobbin for the core dimensions and then wounded the 28awg coil in some MG chemical varnish for transformers. Rex and Joe, you guys seems quite experience in electrical engineering. Would Spice be an easy program for me to try and simulate my circuit response ?
User avatar
Joe Gayo
Posts: 398
Joined: Sun Jan 06, 2019 9:34 pm
Real name: Joe Gayo
Location: USA

Re: My Fusor Progress

Post by Joe Gayo »

In the immortal words of Bob Pease (look him up) - "Spice lies". What he meant is that if you don't fundamentally understand the function and behavior of components and circuits, it's quite easy to get a non-sense answer with Spice and be fooled. This principle is true with any simulation or modeling tool. Design should always start with a "1-D" (simplified) analysis of the problem, then progress to more sophisticated methods that can be compared with the "rough" calculation.

Having said all that, I encourage you to learn more about electrical engineering basics (youtube channels I think are great - https://www.youtube.com/c/FesZElectronics and https://www.youtube.com/user/sambenyaakov) and also download LTSpice (https://www.analog.com/en/design-center ... lator.html) from Analog Devices. Analog Devices bought Linear Technology (LT) and has a wealth of tutorials on their website.

Good luck, Joe

P.S. I encourage you to apply for a grant if you need additional equipment - viewtopic.php?t=14425
User avatar
Richard Hull
Moderator
Posts: 13897
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: My Fusor Progress

Post by Richard Hull »

I use to love "Pease Porridge" in EDN. The man was a true engineer and his analog world of adventure stories were to die for. Every EE worth his salt grew to appreciate him and his wisdom gained through experience. The company copy of EDN was tattered and worn by the time all we engineers had Xeroxed the article. In the lunch room lots of ketchup, mayo and grease spots got on the corporate copy. I have the 1994 soft cover book on analog circuit design produced by EDN. The cover image speaks volumes for all who design circuitry..... While Bob has only a section in the book which extolls the contribution of many EEs to the analog world, Bob still is with me in that book.

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.
Rex Allers
Posts: 520
Joined: Sun Dec 30, 2012 3:39 am
Real name:
Location: San Jose CA

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
add-Dir.png (41.02 KiB) Viewed 1135 times
Rex Allers
Rex Allers
Posts: 520
Joined: Sun Dec 30, 2012 3:39 am
Real name:
Location: San Jose CA

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
User avatar
Rich Feldman
Posts: 1421
Joined: Mon Dec 21, 2009 6:59 pm
Real name: Rich Feldman
Location: Santa Clara County, CA, USA

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
Posts: 14
Joined: Wed Jun 16, 2021 11:38 pm
Real name: Nicolas Malo

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
Posts: 14
Joined: Wed Jun 16, 2021 11:38 pm
Real name: Nicolas Malo

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
Attachments
279290650_370415918361962_6975520265256676880_n.jpg
Matt_Gibson
Posts: 320
Joined: Thu Sep 23, 2021 10:36 am
Real name: Matt Gibson

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
User avatar
Richard Hull
Moderator
Posts: 13897
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

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
Posts: 14
Joined: Wed Jun 16, 2021 11:38 pm
Real name: Nicolas Malo

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.
User avatar
Dennis P Brown
Posts: 2598
Joined: Sun May 20, 2012 10:46 am
Real name: Dennis P Brown
Location: Glen Arm, MD

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
Posts: 14
Joined: Wed Jun 16, 2021 11:38 pm
Real name: Nicolas Malo

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.
Attachments
279257418_923005272428904_471671663124603830_n.jpg
User avatar
Mark Rowley
Posts: 900
Joined: Sun Dec 29, 2002 12:20 am
Real name: Mark Rowley
Location: Sacramento California
Contact:

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
Posts: 320
Joined: Thu Sep 23, 2021 10:36 am
Real name: Matt Gibson

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
User avatar
Finn Hammer
Posts: 276
Joined: Sat Mar 05, 2016 7:21 am
Real name: Finn Hammer
Contact:

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
Posts: 320
Joined: Thu Sep 23, 2021 10:36 am
Real name: Matt Gibson

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
Posts: 14
Joined: Wed Jun 16, 2021 11:38 pm
Real name: Nicolas Malo

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
Attachments
Screenshot 2022-05-15 192114.png
User avatar
Mark Rowley
Posts: 900
Joined: Sun Dec 29, 2002 12:20 am
Real name: Mark Rowley
Location: Sacramento California
Contact:

Re: My Fusor Progress

Post by Mark Rowley »

ZVS drivers MUST be initiated at the starting voltage. Slowly ramping them up to the starting voltage causes overload issues with the fets and will surely cause them to fail (catastrophically sometimes) in short order. In other words, never start a ZVS driver at zero volts and ramp it up. That humming you hear is a ton of amperage being absorbed by the two mosfets fighting each other.

To properly start a ZVS driver, identify the startring voltage and build a psu that can give it the full voltage/amperage rating at an instant. Meaning, if starting voltage is 12 volts, turn it on with a 12 volt starting voltage. From that point you can slowly ramp up the voltage to the drivers maximum rating. Just make sure your PSU can supply the needed amperage at the higher voltages, if not, then your going to detonate your mosfets.

Best advice I can give you is dont overcomplicate this. It's really basic if you follow some essential guidelines. I know some folks here disagree, but minutia can bog you down for months, in some cases years.

Mark Rowley
User avatar
Dennis P Brown
Posts: 2598
Joined: Sun May 20, 2012 10:46 am
Real name: Dennis P Brown
Location: Glen Arm, MD

Re: My Fusor Progress

Post by Dennis P Brown »

No, you can't raise a diodes operating voltage by placing them under oil or in epoxy! The maximum operating voltage of any diode is an innate electronic property of the diode material/design and cannot be changed. Never exceed its max. voltage - a huge failure will occur. One has to chain the diodes in series in order to achieve higher operating voltages (i.e. two 8 kV diodes in series can handle 16 kV; but do note that does NOT increase their current capabilities) - of course, placing in epoxy or oil reduces corona issues for a final design and covers up any bad soldering issues.

Aside: do be careful of RMS voltage issues for AC systems
User avatar
Finn Hammer
Posts: 276
Joined: Sat Mar 05, 2016 7:21 am
Real name: Finn Hammer
Contact:

Re: My Fusor Progress

Post by Finn Hammer »

Matt, all

The transformer FAQ is up for preview in the high voltage FAQ's:

viewforum.php?f=29

Cheers, Finn Hammer
Matt_Gibson
Posts: 320
Joined: Thu Sep 23, 2021 10:36 am
Real name: Matt Gibson

Re: My Fusor Progress

Post by Matt_Gibson »

Thanks, Finn. Looks like I found a problem with my design already: I built a 6 stage full wave multiplier but I’m only driving it with a single coil. I see that I need a second coil, so that may explain why I’m not getting what I expected! Looks like I have a new rabbit hole to go down…

-Matt
Post Reply

Return to “Fusor Construction & Operation (& FAQs)”