Custom Fusor Power Supply

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Mark Rowley
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Custom Fusor Power Supply

Post by Mark Rowley »

After having good results with the 60kV Precipitator power supply, I’ve decided to build a better version based on the same 4 flyback series arrangement.

The major downside of the Chinese PSU is its lack of serviceability. Each of the four flybacks are 15kV DC output. Unfortunately, the secondary coil and rectifier diodes are encased in resin which basically means the transformer is junk if any component within fails. Luckily, most of the failure occurs within the driver circuit which is considerably over engineered for basic fusor use. However, the flybacks do occasionally go bad resulting from diode failure or to a much lesser degree, coil damage. The coil appears to be wound with 36awg which is about as thin as you can get for this type of application. It’s just not designed for the rigors of fusor use. Again, this does not imply the 60kV precip isn’t a great starter or mid-grade psu. It just requires very careful application and operation as explained in the FAQ.

The Upgrade Design
The new design incorporates 4 custom flybacks driven in parallel with the outputs in series. Rather than utilize the damage prone 36awg, each flyback is wound with 1400 turns of #28 AWG. This results with an output of approx 8kV AC. A 2nF single stage CW multiplier on each flyback will bump up the voltage to 16kV. The 2nF’s will theoretically allow for 25mA however 7mA is about all that’s needed for the size of a cube or cylinder fusor (Fusor2020). All four outputs will be in series resulting with an expected potential of ~64kV.

The flybacks are driven with a common $40 1000 watt / 50a Chinese ZVS module.

Except for the driver, the entire assembly is operated under oil.

Unlike the precipitator, this assembly has easily replaceable components as well as serviceable flyback secondaries. The multiplier circuits are modular making for easy removal and servicing.

Shown are the segmented flyback bobbins and soon to be machined blanks. The cores are from the old 60kV precipitator supply.
7EBAB9AA-DC32-4BB2-9C41-AFE7929582B6.jpeg

Machining the bobbin. It’s highly recommended to use HDPE as it’s easier to work with. Unfortunately these four are made from UHMW which, as someone correctly put it, is like machining Silly Putty. It was not a enjoyable process. Shown below is HDPE from an earlier project.
30631983-D406-4C90-8172-22D53E8378CC.jpeg

Completed bobbins fitted to the ferrite cores
04716F54-36AF-4C3A-804E-4EBBB6327367.jpeg

Winding the bobbins was a snap with this inexpensive $40 coil winder.
A5BBF54B-6B86-4A57-B606-B405F21CF771.jpeg

Skipping ahead, this is the completed supply with the four separate single stage multipliers.
9A11846F-1D24-46A0-B57E-6F329A180FFB.jpeg

This is the cheap $40 ZVS driver. As a side note, the production quality is lacking. No heat sink compound as well as a few cold solder joints. Best to give these the once over before using them.
31263EB6-7354-48BC-BBA8-ADD13B98C0C5.jpeg

Similar to the precipitator, no load voltage testing results in an output approaching 100kV. Under load / fusor conditions it idles along nicely at 65kV with less than half the input rating for the driver. I’ve yet to go past this point but will continue with rigorous testing over the next few weeks. A sustained 30-45 minute run is the end goal.

Today’s fusion run was far from anything I had previously done due to no active cooling (I’ve yet to hook it up) and a total absence of wall loading. Once I started the BoT2021 project the Fusor had been sitting on a table collecting dust. Today’s test was literally plug-n-play with no prep or chamber servicing. However, the numbers were good enough to activate silver with no issues.

Not the best pic but it’s a neutron producing Star Mode from earlier today.
E8FF1294-BEB5-499A-88DD-598967BEE932.jpeg

I’ll update as I continue through the testing process.

Mark Rowley
Last edited by Mark Rowley on Mon Mar 08, 2021 1:13 pm, edited 1 time in total.
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Richard Hull
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Re: Custom Fusor Power Supply

Post by Richard Hull »

That is a lot of great effort. I wish you well with it and hope it pans out to be all you expect from it after all the effort that has gone into the idea.

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: Custom Fusor Power Supply

Post by Bob Reite »

Nice job on those transformers!
The more reactive the materials, the more spectacular the failures.
The testing isn't over until the prototype is destroyed.
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Mark Rowley
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Re: Custom Fusor Power Supply

Post by Mark Rowley »

Thanks Bob and Richard. It’s met it’s goal of 60kV and can power my fusor all day at that voltage. Nothing gets hot and throttling from the variac is very stable. Quite honestly, I could leave it as is and be perfectly happy.

Testing requires intentionally pushing the design to failure. So as I was hovering near the 1E+06 n/s mark (*60kV/3mA/37mTorr D2), I dropped the pressure to around 30mTorr so I could ramp up the voltage without incurring a big increase in current draw... a common practice with the precip supplies. As expected, the neutron count jumped way up as I got close to 80kV. It was at this point flyback #4 began to arc (under oil) between the primary and secondary windings.

Whats really nice about this design is the ease of serviceability. Removing the supply from the fusor cart took one minute and pulling off the bad flyback took about 5 minutes.

At first I thought the arc-over was caused by an air bubble trapped behind some Kapton tape. So I removed the tape, rewound the bobbin and reinstalled. Same problem at 80kV. So it’s fairly evident the dielectric properties of mineral oil aren’t strong enough to ward off the potential in such a narrow space. Before the windings became too damaged I slid a small piece of acrylic sheet between the primary and secondary. This helped immensely until eddies in the oil caused it to slip out and the arcing resumed.

Over the next day or so the plan is to fortify the dielectric strength in the arc-over region with acrylic or pvc shielding as well as some silicone rubber (or similar) over the windings on that side of the bobbin. I’ll reserve epoxy encasement as an absolute last resort.

During the fix, I added an extra nF of capacitance to each multiplier. The flyback and driver are more than capable of handling the extra load and as expected it provided more reserve current during operation.

Even though it’s a stable supply at 60kV, I’m going to raise the bar to 80kV so it can have a 20kV safety margin.

*When loading is optimal, those parameters typically result in more than double the neutron count.

Mark Rowley
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Richard Hull
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Re: Custom Fusor Power Supply

Post by Richard Hull »

Really did not want to say anything at the time, but I thought that even under oil the primary spacing to the secondary looked kind of tight. I used a lot of oil in the tesla coil days and never trusted just oil. Spacing is still critical even under oil. (oil stirring is a sure sign of too much field between items.) High frequency operation really serves to heat and stir oil under tension. Same goes for air, of course. High frequency in any dielectric tends to heat it and lead to failures. I think Bob will concur. I have seen mica G-5s heat to where you can't touch them in RF service. They can take the heat unless they get so hot they lose their water of crystallization. ~900deg F

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: Custom Fusor Power Supply

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Excellent results today. 30 minutes of testing without any issues. Operationally speaking, it’s similar up the precipitator unit with some subtle differences. I’m still learning how to drive it and find the operational sweet spot. As of now it’s clear I have to get the chamber cooling back in order as my neutron rate is getting poisoned after about 3-4 minutes of operation.

This video is of today’s cold start. The raw count rate was about 4500cpm on the Ludlum 2221. Voltage was slowly ramped up from 27kV to just under 40kV before I switched it off. Deuterium pressure was 37mTorr. I’m still not at the numbers I was at last year but am slowly getting there.

https://youtu.be/Qdrmq-Er8AM‬


Star Mode pic from the video:
22DFFEC8-E9AB-4E5B-904D-D546CEA437CF.jpeg
The last few mods to the power supply were as follows:

PVC insulators around the flyback primaries
Acrylic shields between flybacks and multipliers
Silicone Rubber on secondary of Flyback #4
Replacement of 3 faulty multiplier caps
Installation of 1gig ohm resistor for voltage meter

It’s not as aesthetically pleasing as before but it’s much more functional with minimal signs of oil churning and no arcing.
054E6B0A-5A88-4A95-B4D0-931CCDA02F32.jpeg
Next few mods will be to shorten the leads from the ZVS driver to the flyback by 75%. If workable, the 12awg leads will be replaced with two pieces of 3/8 copper tubing.

So far I’m not overly impressed with the 1nF/20kV caps. I’ve had 3 fail including another in an unrelated 7 stage voltage multiplier. Other HV enthusiasts have noted similar issues with these caps so it may be worthwhile to upgrade. I’ve got some Soviet doorknob caps I may try at a later date. But FWIW, none of them failed during today’s run. Perhaps the arcing from last week damaged them... time will tell.

Once the water cooling is in place I’ll conduct a sustained 30 minute operational test.

Mark Rowley
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Richard Hull
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Re: Custom Fusor Power Supply

Post by Richard Hull »

Mark, as a 10 year veteran of tesla coiling with a great deal of experience with ceramic HV capacitors. I have found that 100% of this type of capacitor working at high frequencies and high powers (high peak pulse energy) will lose value by shedding the silver vapor deposit (plates) on the ultra high dielectric constant Barium Titanate slugs. Too much voltage will naturally have internal arcing in spite of the epoxy encasement.
Ceramic Capacitors in parallel lead to uneven stresses as one seems to always lose more value than its mate in parallel. Disruptive spark gap coils often placed 50 amp peaks through the caps in even smaller coils. Ceramics in bigger coils rarely performed more than an hour's worth of runs before needing retuning to keep the spark length up due to loss of plate area. The solution was polypropylene foil energy storage caps

If you caps heat after a run, then they are shedding plate area and dropping in value. The weakest cap in the serial discharge multiplier will control the output. I assume when you say they failed, it was due to internal arcing?

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: Custom Fusor Power Supply

Post by Mark Rowley »

I can’t say for sure why they failed. No physical damage. Just a total loss of value which appeared sudden as opposed to gradually. Almost exactly how others have stated.

Only arcing I was specifically referring to was the earlier breakdown of the mineral oil between the primary and secondary. Very small arcing took place in that region which coincided with the cap failure.

This is the tiny arc (now remedied) that resulted with the cap failure:

https://youtu.be/q8KR4qslSYU

Maybe a spike somehow found its way from that arcing to the three bad caps.

Btw, I got my fusion star videos accidentally mixed up. This one is of the higher neutron count rate, 4500-5000cpm on the Ludlum 2221.

https://youtu.be/yRAZMjBiNaY

Once I get cooling set up and run this for it’s make-or-break 30 minute test, I’ll check the capacitance on each ceramic and report back. It’s not big deal if the whole idea fails. Other than the $40 ZVS and some fasteners it hasn’t really cost anything other than my junk pile raids.

I suppose I could add two more flybacks and forgo the multipliers... ;)

Mark Rowley
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Re: Custom Fusor Power Supply

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Hooked up the cooling and let it run for 30 minutes at about 35% input power to the ZVS driver. Neutron output to the Ludlum 2221 / CHM11 at ~17cm distance averaged 7500cpm for the duration. Removing the moderator dropped the neutron count to background. No hiccups in power supply performance....yet.

This evening I’ll conduct a higher powered 30 minute run. If this pans out ok I’ll get the gamma spec operational and try to activate some Manganese.

MR
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Re: Custom Fusor Power Supply

Post by Richard Hull »

I'm glad someone has got a fusor doing great. Good work Mark! Mine sits in the cold, awaiting my continued efforts.

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: Custom Fusor Power Supply

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Over the past three days I’ve literally thrown the kitchen sink at the supply and have had no reportable performance issues. Collectively, it’s now got about two hours of run time and has incurred two 30 minute non-stop operational runs.

Tonight I decided to “destroy” the supply by running it full tilt (saturation point of the rewound MOT which supplies the driver). Well, it wouldn’t fail, just kept going and the neutron numbers just kept climbing. The maximum raw CPM/N on the Ludlum 2221 was over 23,000. Based on this fusors ability to load, I’d suspect tomorrow’s run will be in the mid 30k range.

So far the value of the multiplier caps are remaining true to their specs. But tbh, I really don’t care if one blows out at this point. Each capacitor is about 50 cents, so if I have to replace one every now and then it’s no big deal. Additionally, it’s modular design makes for a 10 minute process to replace. The performance to capacitor replacement ratio is well worth it...providing its ultimately required.

Now the real difficult stuff begins, getting the gamma spec system up and running. We built a new computer a month ago and the sound card isn’t working well with the MCA software. The ultimate goal is to activate Molybdenum and detect Technetium via the MCA, so that’s now priority.

Here’s the latest run with the flyback supply. Please excuse the clutter, I know it’s a mess:

https://youtu.be/arbNemCBjho

Mark Rowley
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Re: Custom Fusor Power Supply

Post by Richard Hull »

Great work and a great supply. Nice video. You continued removal of the 3He tube from the moderator is great. All newbies need to take special notice of this wonderful proof of fusion with a thermal neutron detector as "running proof" that you are fusing. It looks like you have a super supply that is fully capable. Again, great work.

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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Dennis P Brown
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Re: Custom Fusor Power Supply

Post by Dennis P Brown »

A really impressive feat on the PS. Good pics. Also, could you supply a schematic of your power supply?

A pic of the fusor and overall system would be nice, too.
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Re: Custom Fusor Power Supply

Post by Mark Rowley »

Thanks Dennis
The fusor hasn’t changed at all. It’s the same as listed in the original threads.

viewtopic.php?t=13503

viewtopic.php?t=13536

Regarding the schematic, I really dont have one as it’s assembly is extremely basic. On page one, you can see the basic outline of the components which almost by itself is a perfect schematic.

In a nutshell, it’s just 4 custom AC flybacks being run in parallel. The outputs are individually fed into separate single stage multipliers. The outputs of the multipliers are placed in series providing the 60kV.

As Richard correctly pointed out, the ceramic capacitors do tend to loose some value after lengthy run times. However, nothing to the point where performance was compromised, at least to a noticeable level.

Twice now, I’ve intentionally pushed this design to the point of destruction. The last failure occurred at ~89kV / 5mA. A arcover condition occurred in the #4 multiplier causing a surge that took out half the diodes. Zero damage to the flybacks, ZVS driver, or caps. The diodes were rated at 20kV (which is ok for the multiplier circuit) but the almost 90kV arcing over made the diodes easy pickins. Being that I designed this to be a 60kV supply, the failure is actually a success. A success that under harsh conditions the flybacks survived as well as the driver. Replacing the diodes only took about 30 minutes and it was good as new. I’m fairly pleased as it’s proven to be a very stable design for 60kV.

I’m currently in the process of making a couple design changes that may or may not make a difference. First, each multiplier will be changed from half wave to full wave. And secondly, I’m replacing the ceramic caps with 2nF 30kV poly/foil types. As with the ceramics, I’ll be periodically checking the values for any signs of degradation.

Once reassembled I’ll update.

Mark Rowley
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Bob Reite
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Re: Custom Fusor Power Supply

Post by Bob Reite »

You might be able to get away with smaller capacitors if you switch to full wave, as the ripple frequency will now be doubled.
The more reactive the materials, the more spectacular the failures.
The testing isn't over until the prototype is destroyed.
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Re: Custom Fusor Power Supply

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Finally got around to building the multiplier module with the new axial poly caps. As before it’s a very basic arrangement except that this version is full wave and a bit bigger due to the larger caps.

597B8658-D664-40EA-A0F4-F77427C1606B.jpeg

FC29DAE2-4F84-49C6-B279-EFF6774829BE.jpeg


Had just enough time to conduct a brief 10 minute test run with the fusor. Operationally I didn’t notice much difference but it does seem to have a slightly higher voltage ceiling. Over the next few weeks I’ll focus more on long term sustained runs as opposed to pushing it to the point of failure.

Mark Rowley
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Dennis P Brown
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Re: Custom Fusor Power Supply

Post by Dennis P Brown »

Very impressive build and I really like the clear box for the VM system and x-formers.

One suggestion for the future (well, two.) Use balled solder joints for joining wires and do away with sharp corner metal nuts where ever possible (I use plastic hardware.) Even under oil these issues can lead to problems for long term high voltage operation.
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Re: Custom Fusor Power Supply

Post by Mark Rowley »

Thanks Dennis
Those clear containers are actually medical radioisotope lock boxes. Very thick plastic and 100% leakproof (as mandated by hospital regs). By sheer luck the size was perfect and the need for modifications was minimal.

Another mod on this go-around was the addition of fused quartz insulator sleeves between the primary windings and the cores. I also elected to rewind flyback #4 while saturating the wire in Alumalite epoxy resin. Very little air (if any) is within the windings. Expectedly, this mod alone almost doubled the output of the flyback. As stated earlier I wanted to avoid that type of arrangement as it makes coil repair almost impossible. I used a different method of winding this time which may allow for repair... hopefully such a repair won’t be necessary. The flybacks have actually held up nicely unless I push them way beyond what I designed them for.

If I end up doing major surgery again I’ll try the blob method on the solder joints. There are only two areas where this could be mostly beneficial.

Mark Rowley
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Re: Custom Fusor Power Supply

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Conducted a sustained 30 minute run this afternoon at roughly 1.5E+6 n/s TIER. No signs of problems so this just may be the final iteration for awhile.

This is a video of it powering the fusor during the aforementioned run. The noise in the background is the Ludlum 2221 counting the moderated neutrons.

https://youtu.be/gGG1GeDi3nw

I have some larger ferrite cores I may try this upcoming summer but for now I’m fairly pleased with its performance.

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Re: Custom Fusor Power Supply

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It’s been about 6 weeks and roughly 20 runs since the last update. No problems with performance and the poly caps are holding up perfect with no change in value.

In the meantime I’ve been experimenting with some different flyback cores as well as epoxy encasement. Initially, epoxy was off the table as it eliminated the possibility of any repair to the windings. However, since the supply has been tested under adverse conditions which would normally obliterate a commercial precipitator unit, it’s concluded the larger gauge windings and stronger diodes removed most of that concern. For comparison, I wound an identical flyback but this time encased the windings in Alumalite brand clear epoxy. By doing so it almost tripled the voltage and current capacity over a non-resin flyback which only used mineral oil as an insulator.

This opens the possibility of completely removing the multiplier circuits and running four rectified ~20kV custom flybacks with the outputs directly in series. In theory, this should greatly increase the current capabilities of the supply.

Mark Rowley
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Re: Custom Fusor Power Supply

Post by Dennis P Brown »

Impressive work; you are really setting the bar for a home made power supply for a fusor that most could build. Keep experimenting and posting - you've created a great thread.
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Re: Custom Fusor Power Supply

Post by Mark Rowley »

Ordered a set of beefier cores and made new secondaries with 2000 turns of #30. Each secondary was wound while submerged in epoxy resin. The single stage multiplier circuits will employ 40kV rated 100mA diodes. Preliminary testing will begin in a few days.

The unmultiplied output in series (under load) could be high enough to operate a fusor with little to no issue. Testing on that aspect will happen later but first will be a reduction in multiplier capacitor value to 510pF. Those items are still on order so the original multiplier module will be employed until then.

E31433B5-9A3C-4167-9037-AB8168CDE43C.jpeg
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Re: Custom Fusor Power Supply

Post by Richard Hull »

Those are beefy cores! Wound under epoxy resin? Slow setup time I image? Arc proof if under oil for sure.\
Great effort!

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: Custom Fusor Power Supply

Post by Dennis P Brown »

Where did you get the cores?
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Re: Custom Fusor Power Supply

Post by Mark Rowley »

Hi Dennis,
Picked them up on Amazon a few months back. The seller recently more than doubled the price for a pair as they’re now almost $26 a set. Id look elsewhere for a better deal.

Mark Rowley
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