A 50kV supply with 33mA drive ability

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Richard Hull
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Re: A 50kV supply with 33mA drive ability

Post by Richard Hull »

I doubt if a pressure versus voltage will be of any value based on fusor type and size and special circumstances due to this. We have observed this forever, here. Every odd fusor from big to small demands the operator to learn how his pressure voltage and current respond to actually do fusion.

As to kickback in a struck plasma, this never happens in a stable, fully functional power supply that is not some sort of current controller mess of a supply that is being operated on the ragged edge of its capability.
A huge strong supply of 4kw of continuous capacity will never burp once the plasma is lit. It has never happened to me with my heavy x-ray transformer. There is no multiplier and no storage capacitor in the entire system! It is 120hz full bore ripple! I will let others chime in who have had it happen to them and I recommend when they chime it, they give full data about their fusor, shape, size, etc., and what supply they are using.

I am unaware of any living being here doing significant fusion who is using non-multiplied 40-50kv full wave rectified, non-filtered HV at 120hz full ripple. Most with issues are using HF switchers professional or of the precipitator type that are ostensibly pure smoothed DC. while at the same time, they are working close to the ragged edge of its capability. Some seem to have mastered this cliff-hanger supply situation like Mark Rowley, which means he is a plus-ultra operator and has the skill set for his specific device under his full and able control. Mark has had a few smoke plumes in his early work, but not lately. He has learned the "rope limit" while circumnavigating his switcher supply, with a suitable supply of spare components in case he dare challenge the supply and lose that bout in the ring.

The big hassle for many is that monster startup current drain. All gas glow systems have a large start up hysteresis. In the case of my fusor, once conditioned, this can be 15kv work of differential. wants to smoothly run at startup at 15kv but strikes at 26kv. the 63k ohm 125 watt resistor takes it on the chin until I dial the voltage back. Due to my skilled operation, I usually have it functioning at 30kv glow a minute or two after striking. From there I do my spider monkey routine adjusting the pressure smoothly to meet a "feel" for the current as I creep the voltage and fusion ever upward. It is an art. It makes it easy when you need not even let your power supply capability enter your stream of consciousness.

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
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Finn Hammer
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Re: A 50kV supply with 33mA drive ability

Post by Finn Hammer »

Victor,

You are right, basket coil winding is a lost art, and a complete separate project.

I bought a MoReCo winder on EBay, and it is a piece of junk, really, but if you nurse it a bit, it can be brought to work. There is a lot of unwanted slack in it though.

It looks like this:

IMG_20210119_145318.jpg

The brass handle on the *drive shaft* is the center of action, and turning it creates the two required motions, the rotation of the bobbin and the reciprocating motion of the wire guide.
The drive shaft also has a cam which produces a reciprocating motion on the (shall we call it *cam shaft* ;-) ) which transmits it to the wire guide.
The bobbin is fitted between 2 wooden cones at the far left on the *winding shaft*. the drive shaft and winding shaft are meshed together with a set of gears, where the driving gear is the smallest, and this is important, because to get a proper lay of the wires, the winding shaft has to lag the drive shaft.
You can see it on the sketch here: each successive layer must not cross the preceding layer at the edge where the wire changes direction. A very important point.

IMG_20210119_161838.jpg


The bobbin has a layer of double stick tape to insure the first layer stays snug on the bobbin.

firstlayer.jpg



The wire must be cotton or silk covered to create enough friction between windings, otherwise the wire slips off and creates a mess.
I wish you good luck with your coil winding endevour, and do not be discouraged when your junk basket starts to look like this:

pitstop.jpg

It is the norm, rather than the exception.

Cheers, Finn Hammer
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Richard Hull
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Re: A 50kV supply with 33mA drive ability

Post by Richard Hull »

Really cool old basket winder mechanism. Even with the machine, slack in the mechanism forgiven, it is just another art that must be mastered, just like running a fusor. The box full of fails shows you have the stuff needed to get the job done. Adversity abounds in any thing worth doing.

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
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Re: A 50kV supply with 33mA drive ability

Post by Frank Sanns »

Winding fine wire on coils is challenging. Too loose and they slide off. Too tight and they pull to the side as the layers increase and they slide off.

A solution that I have used with nearly 100% success is to spray the windings with some clear fast drying urethane or lacquer. Just enough to make it tacky and hold. I do this each time I get enough work into the coil that I don't want to loose the last portion of work. A light spray of the entire coil when you finish will make it look uniform.
Achiever's madness; when enough is still not enough. ---FS
We have to stop looking at the world through our physical eyes. The universe is NOT what we see. It is the quantum world that is real. The rest is just an electron illusion. ---FS
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Re: A 50kV supply with 33mA drive ability

Post by Finn Hammer »

Frank,
Thanks for the tip. So you have a basketwinder too? Which brand is it?

I have used CA glue for the same purpose and I gather there is even prefabricated wire with a coating which can be made sticky, by passing it through a bath with solvent, but up to now, have not managed to procure any of it.
I am just at the end of restoring an old lathe,

IMG_20210119_145508[1].jpg

and when it gets operationable, I may try to make multi section bobbins, although I am not sure they will help me in any way, but just take up more space in the winding window. The ability to accomodate 2 separate windings on a single core really appeals to me, and this may not be possible with multi section bobbins, which tend to be wider and not so tall.

Cheers, Finn Hammer
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Re: A 50kV supply with 33mA drive ability

Post by Frank Sanns »

Finn,

My wire winder was the two handed one. Early on I did use my father's small lathe but it was too powerful and I did not want to have the wire grab and pull my hand in or slice through it. The lathe was only

The biggest project I every did by hand was around 4 miles of 22 gauge magnet wire on an 18" phenolic tube. It was a pseudo Tesla coil but it really was a pulsed air core transformer. Easily 5 foot sparks with each pulse. Plenty of fine tendrils.

Well worth the effort.

My technique was to make wooden plugs for each end of the tube with a hole in the center. A brass rod ran the length. At one end was a V block for the rod to sit in. At the other end, it was bent to form a handle. Using gloves, I would guide the wire in single layer as my wife turned the crank. I think we finished in in around 4 non-consecutive nights. It was tedious and I learned very quickly the trick to pull the windings tight and tape after every several turns. Then before the tape was removed, I sprayed it down untaped areas with insulating varnish, Once it dried, I removed the tape and sprayed the entire coil. I figured a little more dielectric between the windings was a good thing.

Yours look mighty pretty. Wish I had one of those machines when I was making smaller coils. Unfortunately I did not have the finances or space for such things when I was working on them.
Achiever's madness; when enough is still not enough. ---FS
We have to stop looking at the world through our physical eyes. The universe is NOT what we see. It is the quantum world that is real. The rest is just an electron illusion. ---FS
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Re: A 50kV supply with 33mA drive ability

Post by John Futter »

Nice Lathe Finn
I had one of those until about 16 years ago sold it because I bought a Colchester Chip master lathe and an Bridgeport mill to replace it. I sold the milling attachment seperately
The Timken head bearing is very expensive in those Boxfords.
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Re: A 50kV supply with 33mA drive ability

Post by Joe Gayo »

Finn,

Is your supply current/voltage mode controlled, or is it an open loop? If you are using feedback, how did you design the resistor divider for the voltage feedback? I find that this is the most critical part when designing a closed-loop high voltage supply. It has to be the right balance of DC and AC feedback. Have you performed any stability analysis?

Joe
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Re: A 50kV supply with 33mA drive ability

Post by Finn Hammer »

Joe,

Open loop, I'm afraid.
For one, I fear that the plasma would react faster than any feedback system, and could lead to oscillations.
Another reason is that I am not so good with bode plots and phase shift.

Cheers, Finn Hammer
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Re: A 50kV supply with 33mA drive ability

Post by Richard Hull »

System hysteresis at such energies is a big issue. Closed loop systems that oscillate are bad. Nothing beats the "bungy cord" of a nice high watt, suitable resistor in the HV line in starting a fusor plasma. The terror is momentary and experienced only at startup in a good system with a suitable supply under the control of a human being who can reduce the supply voltage quickly once started and adjust the pressure and voltage to a current the supply is happy to supply continuously.

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
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Re: A 50kV supply with 33mA drive ability

Post by Finn Hammer »

All,

After a lot of beginners rant in the appropriate beginners forums, I am happy to be back here where I feel I am a bit more in controll of things, and then perhaps not. This delay in posting is the result of unforseeable trouble in obtaining a proper supply of high thermal conductive potting material.
But now I am in posession of 10Kg og Robnor PX700k-1/BK, and that ought to last my remaining lifetime.

I had previously potted one multiplier, a 30kV model and it functioned as desired, putting 50mA out without problems:

First prototype to look alright
First prototype to look alright

I also had a 60kV prototype on the floor, waiting to be potted:

Guts of the 60kV variant
Guts of the 60kV variant

This is the connector I use: a 4mm banana plug, some heatshrink and some pneumatic fitting. It works fine but I should probably put my lathe to some good use and produce something that looks more serious.

Plug detail.
Plug detail.

After the potting had cured It was time to hook it up to the trusty 1.6MOhm load:

60kV potted and ready to go
60kV potted and ready to go

And brace myself before starting to wind the variac towards the endstop. I admit to being scared this time, the ion wind from the hissing resistive tower load was noticable, but perhaps it was just the fear of a failiure that got me.


Scope readout
Scope readout

But then not so shabby! 63.8kV @ 37.5 mA. That ought to doo even for the most power hungry fusor. (for a while, at least ;-) )
Cyan and Magenta traces carry the real magnitude labels, although Magenta is in Ampere, not volts, for gate signal and primary current respectively, the yellow voltage trace magnitude labels are a result of a 20000:1 voltage probe and a probe setting of 20X so it reads 20kV/division.

So far so good, what now?. Obviously, a 100kV unit is within reach, just a matter of field controll here and there. I am willing to share, the question is how much more is needed before I have told enough for others to replicate, should they want to.




Cheers, Finn Hammer
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Re: A 50kV supply with 33mA drive ability

Post by Mark Rowley »

Looking great Finn!
Potting is definitely the way to go for optimal performance. Tbh though, I’m not brave enough to do it. Just too worried about one component failing and not being able to replace it. It looks like you spared no expense by utilizing top quality caps and diodes so failure maybe be very unlikely.

It’s great to see more neutron capable power supplies using multiplier circuits. Undoubtedly the future PSU of the fusor hobby.

Mark Rowley
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Re: A 50kV supply with 33mA drive ability

Post by Finn Hammer »

Thanks, Mark.

Spellman and all the other big ones have done it for decades, time to catch up.
One thing I'm pondering is the benefits and tradeoffs by having either a small or large stage capacitance.
A small capacitance will have a larger ripple, and I imagine this will lead to a neutron output determined not by the peak voltage, but rather peak minus half ripple. A problem in this scenario is, that the breakdown of the feedthrough is determined by the peak voltage, so this component will have to be overengineered related to neutron output.
A large stage capacitance otoh, has small ripple, so the neutron output will relate directly to the quality of the feedthrough. But the energy released in a short from grid to shell may shatter or even evaporate the grid.
The latter would be preferable with respect to the chances of schrapnell ending up in the turbo, already coasting down since the controller got fried by the EMF wave from the shorted supply.
Perhaps I worry too much.
These multipliers of mine have 22nF stage capacitance. I solemny promise to build a version with 3.3 nF stage capacitance, so some time in the not so far future, I will be able to answer that question myself.

Cheers, Finn Hammer
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Re: A 50kV supply with 33mA drive ability

Post by Richard Hull »

All of your work is appreciated my those who seek to make everything in the power circuit more bullet proof. Ripple vs. pure, or close to it, DC with its attendant stored energy capacity is always going to be a tradeoff. The critical breakover ionization potential is always an issue. That is why the ballast resistor comes into play to save the day and the supply and grid.

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
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Re: A 50kV supply with 33mA drive ability

Post by Finn Hammer »

All,

It is a big day, when a selfmade PSU goes into the cabinet of it's own, and as always, this cabinet shows up to be just a tad bit to small, but for now it is ok.


IMG_20210526_110900.jpg

Sitting nicely in the fusor's frame it has readout for Mosfet temperature, transformer core temperature and output current. The switch to the right is a combined Kill/reset switch.

IMG_20210528_091038.jpg

It powers the fusor with great authority, so great that I have plans for an upgrade consisting of a PFC frontend booster, and an intermediate buck voltage control.


The PCB below is from a TI reference design, for a 3kW PFC, and I will populate this board, but that is going to be a project for the next winter.

IMG_20210529_190137.jpg


Cheers, Finn Hammer
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Re: A 50kV supply with 33mA drive ability

Post by Dennis P Brown »

As always, your home made equipment is extremely professional and rather state-of-the-art. Great pic's and progress. Do be careful of x-rays - 60 kV at over 35 ma will produce a very dangerous flux.

I built a 120 - 150 kV voltage multiplier and while it was all under oil, its nearby static effects convinced me to shut it down and place it in mothballs the first, and only time I charged it up.
Voltages in the 100 kV+ range can get rather flaky and difficult to safely shield. I also realized the accelerator it was to be tied to would produce just too dangerous of an x-ray flux; I went with my nearly done fusor instead.
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Re: A 50kV supply with 33mA drive ability

Post by Mark Rowley »

Very nice setup Finn. I especially like your temperature monitoring arrangement for the typical problem areas. I’ll probably follow your lead here when begin my next phase of psu upgrades this summer.

Mark Rowley
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Re: A 50kV supply with 33mA drive ability

Post by Finn Hammer »

Dennis,
Thanks for your kind words, and yes, radiation is a subject I will have to pay very serious attention to from now on. At present I am relying on below 30kV and the lead glas in the Lesker viewport.

Mark,

If you want to try the LLC topology, and need a PCB, then you know who to contact.

Cheers, Finn Hammer
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