Demo Fusor Progress Update

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John Futter
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Re: Demo Fusor Progress Update

Post by John Futter »

Jim
I gave that diffusion pump to Steven you can buy a 110 volt heating element for it
your glass 100 meg ohm resistors are not suitable for the voltages you are using they are range resistors out of an electrometer or similar
look on this site there are very cheap 7kV resistors available from Element14 RS components Mouser ETC I have put the part type up on this site several times i use the 68meg ohm variant for my dividers 10 in series to give some margin for 50kV
Jim Enright
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Re: Demo Fusor Progress Update

Post by Jim Enright »

John, thanks for the insight! For the diffusion pump, the outside noted that it is a 240V system. Can I just replace out the heating element for the 110V without issue? Any thoughts on where I could find that heating element? It looks like a great pump and we were excited to have Steve give it to us! We drained the oil, cleaned it up inside and out, and purchased new oil for it. We are anxious to get it up and running!

Thanks for the info about the resistors. I had waited to buy the ones I had shown in the image, thinking that they weren't quite right. I will search for the correct ones. Richard noted that I could hook up 10 of the 100 Meg ohm to reach the required ohm. We are still figuring out some of the resistor technology - how will the 10 count of 68 Meg ohm resistors equate to 50kV on the gauge?
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Re: Demo Fusor Progress Update

Post by John Futter »

Jim
A bit of a pity you replaced the oil
I had cleaned it and put a new charge of santovac 5 in it ( a light straw coloured oil)
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Richard Hull
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Re: Demo Fusor Progress Update

Post by Richard Hull »

No matter what, in the end, you must think not only of the resistance, but how you achieve it. This means the resistors must not "bridge-arc" at your voltage impressed over the string. You are not in Kansas anymore toto. You are in a world of electrostatics. A world of intense electrostatic fields where no power need exist to create electric arc bridges, where Tritchel pulses in the fields can form ionized regions, where real surface currents can travel freely over smooth insulating surfaces. 50 kv is not a really high voltage at all at the extreme end of electrostatic field work, but at the amateur level where soldered leads and disjoint non-continuous surfaces abound, the choice of resistors and their assembly is critical.

I will show a 50kv resistor divider in air that works which I built and tested. You will notice the 100meg resistors are long in length. The solder joints and discontinuities are are encased in RTV. No 50kv arc on earth will jump this string. You will also note that it is in air and potentially, (no pun intended), deadly if approached in an operating system. I stressed this to the buyer. It is up to the user to isolate this from idiots who like to fondle things. I call this species Tactillian-Electrocuriotis an ancient form of life with weak brainstems they will never suffer complete extinction, but die one by one.

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Re: Demo Fusor Progress Update

Post by Jim Enright »

John, unfortunately by the time I got it, there wasn't much oil left and what was in there was pretty thick. I'm not sure if it had been used much before Steve sent it to me, but it definitely needed a cleaning. It was shipped to New Hampshire so I'm assuming that the oil was drained before being shipped.

Richard, thank you for the information! I had previously bookmarked the metering thread that you referenced, which included the images that you have shown. We are trying to digest the information, and hope to start working on the build in the upcoming weeks.
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Re: Demo Fusor Progress Update

Post by John Futter »

VR68 series resistors about US$40 per hundred
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Re: Demo Fusor Progress Update

Post by Jim Enright »

John, thank you so much for the resistor information! We have a 50uA gauge that we are intending to use for a 50kV meter. In looking at Richard's diagram of a voltage meter, he had 10 of the 100Meg ohm resistors in series and spaced out between a threaded rod and a piece of plexiglass, which results in resistance of 1,000,000,000. Using the 68 Meg ohm resistors would require 14 or 15 and the math doesn't work quite as evenly. I'm probably missing something or not understanding what you are trying to tell me. Would it be easier to use 10 of the 100 Meg ohm resistors? Thank you John, we truly appreciate your help!
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Richard Hull
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Re: Demo Fusor Progress Update

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My stack was 5 200 megohm resistors count them.... five resistors.

There are other ways to skin the cat.... Resistor shunt the meter to turn the 50ua meter into a 100 ua meter and use only 5 100 meg resistors. It would still read as a 50kv meter, just draw twice the current from your supply (100ua at full scale = 50kv). Critical thinking and a good bit of electronic metering experience and simple algebra need to be brought to the problem.

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: Demo Fusor Progress Update

Post by Jim Enright »

Thanks Richard, I see the error of my ways about the number of resistors! In the text boxes, 100 Meg ohm resistors had been mentioned, and I just quickly looked at the image of your design and continued referring to 10 resistors. But I do understand that it needs to get to the 1,000 million resistance so either 10 @ 100, 5 @ 200, etc. We will start tackling this metering problem as soon as we can get the resistors. Thank you!
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Dennis P Brown
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Re: Demo Fusor Progress Update

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My HV probe is a standard looking HV probe rated for 45 kV (where it has a 'safe' range to 45 kV so that I treat as its upper limit. It scale reaches 50 kV.) It had a single 1.0 G-Ohm resister inside (now 1.1 G-ohm) that connects to the 50 um-A meter. The resister is about 6.5 inches long and inside an enclosed plastic case that has a handle with an upper 'shield' on its opposite end and a metal tip on the 'business' end. The meter is housed between the two just below the plastic 'shield'. There are no long strings of 100 M-Ohm resisters. I had no issue buying the long 1.05 G-ohm resister new from a Chinese supplier - as to checking it, I had a known voltage supply and it tracked it like my original resister so it was certainly accurate in its ohms value.

That all said, if I decided to use that for continuous service, yes, I'd submerge the resister under oil both to prevent arcing and to dissipate possible heat build up.

Still, why use a string of resisters that require careful soldering (ball is best) and big oil containing system if one could get a single, very long 1 G-ohm resister or are none now available?

Also, why not a simple voltage divider under oil? Use a single long 100 m-ohm and wire to a 1 M-ohm. Read between ground and the other end of the 1 M-ohm resister (so you have a 100:1 reduction in voltage) It will be a lot smaller then a chain of 100 M-ohm resisters and any cheap voltmeter will work (here I'd definitely place that assembly under oil or encased in silicon (cleaner)). Not very difficult to build that system either and far more compact.

Now if you are going above 50 kV, that is another matter and very tricky. There I'd certainly consider a long chain under oil.
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Re: Demo Fusor Progress Update

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The simple 100 meg system sounds nice for 50kv but that resistor would need to be a 25 watt resistor! 50,000/100e6= 500ua.... 500e-6 X 50 e3 = 25 watts demanded and wasted from your 50kv supply just to measure the voltage with a single simple resistor! Not many 25 watt 100meg resistors on the market. To limit heating and drift you might look for a 75 watt 100 million ohm resistor! Good luck!

Gotchas all over the place here. What sounds so simple, the math and the availability crush to dust.

5X10E4/10E9 ohms = 50ua.....50X10E-6 X 5X10E4 = 2.5 watts. With 5 200meg resistors in series 0.5 watt resistors demanded. With 10 100meg resistors in series only 0.25 watt resistors demanded. The thermal drift in high ohm resistors being heated by dissipation is terrible and thus the measurement accuracy suffers. In this paragraph, 2 watt resistors would be ideal.

Smart money does the math and matches it against the resistors you can actually buy and the amount of power you are willing to lose from you 50kv supply just to measure the voltage output.
High voltage measurement demands a bit of consideration.

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: Demo Fusor Progress Update

Post by Dennis P Brown »

The difference between an engineer's solution and a physicist's; so, the cow being assumed spherical does not work in reality! ;)
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Richard Hull
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Re: Demo Fusor Progress Update

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I'll never forget my fellow engineer, Tom Ligon, Doc' Bussard's lab rat, telling me he was Bussard's set of "gravity boots".
physicists feel if it can be imagined, surely, there is kit to make it happen. An engineer needs to be there to say, "they haven't invented that yet or they don't make something that is that big or that capable." Material science has stopped many a project or idea from getting out of the starting gate.

In this case it just crushed the idea of a single resistor 50kv metering effort. But there are always clever methods and workarounds that can make it happen. You just gotta' make some extra space and use what is readily at hand.

I have 2 electrostatic volt meters... Rather giant contrivances with infinite resistive loading that go to 40kv in the largest reading. It has U.S. Atomic Energy Commission marked on its case. (Hamfest buy)
They work on the needle moving across the scale as two chorme-plated plates are being electrostatically moved into various physical alignment based on coulombic action. Most all GM service manuals prior to 1980 stipulate the use of an electrostatic voltmeter to set the high voltage. (effective zero loading)

I attach an image of such a meter. They contain zero electronic parts being 100% capacitively based electro-mechanical action in nature. These leviathans weigh about 20 - 30 pounds. One of mine has three ranges changed by pulling a knob out of the case at three detents which vary the static plate to three precisely determined positions. I own both of these style meters

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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: Demo Fusor Progress Update

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Impressive instruments. Yes, being practical is both a necessity and part of training for engineer's. But spherical cows could have some advantages ... wonder if biologist have considered that issue?

Understand the effect of a high voltage electric field all too well; my 100+ kV voltage multiplier created a field (while under oil) that really impressed me (in a bad way.) Even my high voltage probe responded without contact. I gained a powerful respect for voltages in those ranges.
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Re: Demo Fusor Progress Update

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Electrostatic fields of intense magnitude within a high dielectric constant fluid insulator can actually mechanically stir and move that media. Intense Amperian currents within a highly conductive molten metallic media can likewise stir and move it as is seen in molten aluminum reduction operations where tens of thousands of ampere currents are common. Such studies and rarely seen events are far outside the gaze of virtually all living beings. It is enough to know that they occur in singular high field events. Electrostatic fields where the currents are in the picoamp range with potential differences of many thousands of volts with almost no magnetic field present create motion within a medium. We also observe motion within intense surrounding magnetic fields in suitable conductive media where the potential difference is almost non-existent within the medium.

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: Demo Fusor Progress Update

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Dennis,

Got to hook that bad boy up to an ion engine :-)

-Matt
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Dennis P Brown
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Re: Demo Fusor Progress Update

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Uh, the spherical cow?
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Re: Demo Fusor Progress Update

Post by Jim Enright »

Thanks Richard and Dennis for the additional information! I have been trying to figure out the best solution to this dilemma, and am considering using two 500 Meg ohm resistors in oil. My preference is to have the resistors in oil rather than in the air. If it turns out that the math works better with five 200 Meg ohm resistors, and that the availability of products is better suited to the 200 Meg ohm resistors, then I will go that route. I am only using a 30kV power supply but have the 50uA gauge that I'm using to keep the math and variance easier. Now, I'm just combing eBay looking for the right resistors...unless of course someone has the right ones available for sale?
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Re: Demo Fusor Progress Update

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Richard, you had inquired about the vacuum pump I was using for my set up as to whether it was a Yellow Jacket 5 CFM pump. It was actually a Yellow Jacket 8 CFM but it has been giving me problems to the point where it will not pump down even below 10k microns when I have my digital gauge attached. I suspect that that is causing many of our problems. You mentioned that you have a Yellow Jacket 5 CFM pump that works fantastic, pumps down to 10 microns, and you highly recommended it. Can you share with me the model as I am looking to purchase a new pump. I do have a Welch 1405 that we are going to rebuild in a few months, but I would like something that will be well-suited for our demo fusor for right now. Thank you!
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Richard Hull
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Re: Demo Fusor Progress Update

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10k microns ???? Ten thousand microns!!! that is ~10 torr. Did you buy the pump new or used? Real used refrigeration pumps can be worn to death. Have you changed the oil? Used pumps can store gunk and even after an oil change, the new oil can foul, especially if it is run long and hard to get good and hot. Have you measured the vacuum at the head of the pump with a well sealed joint?

I hope you did not assemble your entire system without checking the pump's pressure directly at the pump inlet!! ( a gross newbie mistake and demanded in all the FAQs.) Those long hoses have to go! A very long vacuum system hose is one foot long!

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: Demo Fusor Progress Update

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Don't know if that yellow jacket pump is dead, just seriously dirty, or if the system you've constructed is the issue (massive leaking or a questionable gauge?) Yet you have that belt driven Welch vacuum pump - those are easy to open and inspect (if needed.) Rather easy to clean, too. Those are excellent vacuum pumps so I'd think putting efforts into getting that Welch vacuum pump up and running might pay better dividends. Focusing on vacuum is priority #1 since all else doesn't matter until one has a decent pump.
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Re: Demo Fusor Progress Update

Post by Jim Enright »

Hi Richard and Dennis, thanks for the replies! Richard, I am not sure what is happening with the Yellow Jacket pump, and it may just be a matter of a faulty gasket or other leak in the system. We of course drained the oil and added new oil (the oil specifically noted for Yellow Jacket pumps), and tested it with a digital vacuum gauge connected to the pump. We started off with the ballast open, and then closed it. We very well may be making a silly mistake, and will try it again. This is the same pump that my son and I used in July 2020 when we reached plasma in our borosilicate chamber, so it would seem like it should be fine. We changed the oil at that time, but will change it again to see if that makes a difference.

Dennis, I agree that the Welch should be a viable pump. We purchased a rebuild kit from Duniway and are waiting for it to be delivered. The kit includes all gaskets, seals, valves, o-rings, springs, vanes and mechanical shaft seal. We had not intended to rebuild the pump, but it got to about 1000 microns and wouldn't get any lower. We bought the Welch for $100 last Winter and knew that it might possibly need some work. Unfortunately, we have no experience rebuilding vacuum pumps or motors, but we are going to give it a shot.

In the meantime, we are gathering parts for the voltage and mA metering. We are hoping to do some more work on our system this weekend.
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Dennis P Brown
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Re: Demo Fusor Progress Update

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I've open a similar Welch pump and they are much simpler and easier to rebuild than most current two stage vacuum pumps. I think you will have no major issues.
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Re: Demo Fusor Progress Update

Post by Jim Enright »

Thanks Dennis! We are eager to receive the rebuild kit and get started. It seems to be taking a bit for Duniway to ship their products (I ordered viton gaskets on 12/22 and they still haven't shipped from Duniway yet). But once we get started, I will post pictures.
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