John Beutz Fusor... The Story so Far

Current images of fusor efforts, components, etc. Try to continuously update from your name, a current photo using edit function. Title post with your name once only. Change image and text as needed. See first posting for details.
Post Reply
John Futter
Posts: 1848
Joined: Wed Apr 21, 2004 10:29 pm
Real name: John Futter
Contact:

Re: John Beutz Fusor... The Story so Far

Post by John Futter »

A very good ballast resister is needed that will not flash over under short circuit conditions

this for safety yours and your electronics (diodes metering etc)
User avatar
Dennis P Brown
Posts: 3160
Joined: Sun May 20, 2012 10:46 am
Real name: Dennis Brown

Re: John Beutz Fusor... The Story so Far

Post by Dennis P Brown »

I have stressed electrical safety but one needs to be aware that over 35 kV fusor operation x-rays start to be significant; this radiation is an extremely dangerous component of a fusor; that is, fusor walls start to become transparent at these energy levels so be aware of this and have a detector that can handle x-ray detection (a BF3 or He-3 tubes do not.) A very cheap ionization chamber detector or a somewhat more expensive GM detector are good. Since you have a Ludlum unit adding a GM tube would be an ideal and very low cost approach - just remember to lower the voltage on the Ludlum unit for GM tube operation.

So besides electrical safety, radiation safety becomes critical - also, if one does go to 50 kV you will be producing x-rays that can be very penetrating so provide proper shielding if you do go above 30 kV. My system reaches 32 kV max and I have never detected any x-rays but I have a fairly thick steel chamber and a one inch thick view port. Despite that, I have some lead shielding and a mirror so I never get in front of my view port just to play it on the safe side .

Aside: Speaking of ballast resistors (required to help protect the x-former by better stabilizing conduction in the plasma for the fusor), I placed my ballast resistor under oil; besides relaxing the electric field so flash over is less likely, this method provides a safe, and low cost method to attach my HV cable. That is, the hardware was obtained from a hardware store and since it is all under oil, no issues to worry about. Also, my resistor does not have to have be as long allowing me to get a proper ceramic resistor of the required ohmic level that has a center hole (to further improve heat dissipation.) Being a good bit smaller compared to an air tolerant unit, this resistor was very inexpensive - furthermore, the oil also provides cooling!

You can see images of the setup here: viewtopic.php?f=11&t=10837&start=30#p72610

In the upper image you can see the diode array in the "blue tank" (no oil added yet) and my 'return' ballast resistor (I have a main ballast resistor in a separate "oil tank" which can be partly seen in the lower image - these also include the oil.) The x-former is, of course, on the right. By the way, I use 100% synthetic motor oil; I read a research paper on this subject and that class of oil has outstanding high voltage electrical properties. The additives, it turns out, helps!

I also used oil submersion for my diode array - I used two 20 kV diodes in series to provide a safe buffer (that is, while my max voltage is 32 kV, my didode array can handle this with some margin of error. To enable my full circuit I use eight diodes total for the two paths and two polarity reversals that my x-former undergoes.) These diodes were under $4 each! The diodes are mounted on a plexiglass sheet using glue that affixed them to the base; since I have oil, I used standard wire and electrical connectors between the diodes to save $$$ on much of that setup. All leads that leave the tank, are of course, HV insulated wiring - good to only 35 kV so not something I would use very far from the oil tank, however! That is why I have an upper plexiglass sheet over the entire system.

My main cable that leaves the tank/cabinet is supposed to be good to 50 kV but I did have a single flash over event once. Probably due to damage I did at some point installing but the point is, always assume that will happen to your HV cable and design the route of the HV cable to the fusor so you will be safe if this occurs (the only recourse after that, is to cut away that end of the cable - repair isn't really an option.) While my HV output cable is shielded (and that is grounded, as well), the shear power of 30 kV rapidly burns through all remaining insulation when that ground shield is being hit. Connecting a HV cable to the fusor and the main power supply is also an issue one needs to master - errors there can destroy a x-former and could also be a dangerous source of exposure to HV. Again, caution and understanding these types of issues for HV operation are paramount.

Well, I reached my my thousandth post!
John Beutz
Posts: 52
Joined: Fri Sep 02, 2016 2:35 pm
Real name: John Beutz
Location: Minnesota

Re: John Beutz Fusor... The Story so Far

Post by John Beutz »

Resistor I may use as a ballast. It has a hole through the center and is about 15cm long
IMG_1031.jpg
John Futter
Posts: 1848
Joined: Wed Apr 21, 2004 10:29 pm
Real name: John Futter
Contact:

Re: John Beutz Fusor... The Story so Far

Post by John Futter »

That resistor will have to be under oil to work
it is far too small for use in air
John Beutz
Posts: 52
Joined: Fri Sep 02, 2016 2:35 pm
Real name: John Beutz
Location: Minnesota

Re: John Beutz Fusor... The Story so Far

Post by John Beutz »

Alright. I'm going to replace the bucket it's in now with a larger container since the resistor won't fit. Plus that gives me more space for diodes and a resistor chain for voltage measurement
JoeBallantyne
Posts: 327
Joined: Tue Jul 20, 2010 4:08 pm
Real name: Joe Ballantyne
Location: Redmond, WA

Re: John Beutz Fusor... The Story so Far

Post by JoeBallantyne »

You don't. Many Geiger counters and Ion Chambers are not setup to make it easy to adjust the voltage they supply to the detector. They typically come with a detector that works well for the voltage they supply, and the user is not expected to make any adjustments.

Some scalers and counters have a knob on the front that allows the voltage to be adjusted. Typically they will have a switch that allows you to set the meter/display to Voltage mode, and the meter will have a voltage scale on it as well. Usually these units are a little more pricey than the units that do not have adjustable voltage output.

The Ludlum Model 2200 Scaler ratemeter is an example.
User avatar
Dennis P Brown
Posts: 3160
Joined: Sun May 20, 2012 10:46 am
Real name: Dennis Brown

Re: John Beutz Fusor... The Story so Far

Post by Dennis P Brown »

I see that your question was answered in another post AND that this question was a multiple post. That is very poor Etiquette because it is confusing for readers who respond to a post that is answered elsewhere (like I just did!) More to the point, I wrote then had to removed my rather extensive answer to your question and you completely wasted my time! That is not something I desire to do here and I most definitely do not appreciate.

Also, this isn't the forum to post questions. Pick the correct forum to post in.
John Beutz
Posts: 52
Joined: Fri Sep 02, 2016 2:35 pm
Real name: John Beutz
Location: Minnesota

Re: John Beutz Fusor... The Story so Far

Post by John Beutz »

Sorry about that. Removed. I'll remember that in the future
John Beutz
Posts: 52
Joined: Fri Sep 02, 2016 2:35 pm
Real name: John Beutz
Location: Minnesota

Re: John Beutz Fusor... The Story so Far

Post by John Beutz »

Tubing. May cut to smaller length and use two kf25 elbows in the line if I get a new pump, which seems likely.
1048-1.png
Rex Allers
Posts: 570
Joined: Sun Dec 30, 2012 3:39 am
Real name:
Location: San Jose CA

Re: John Beutz Fusor... The Story so Far

Post by Rex Allers »

Question for John Futter
John Futter wrote:That resistor will have to be under oil to work
it is far too small for use in air
Seems to me that the space between resistor terminals will be more than 14 cm. Assuming the max voltage might get to 50 KV, is that not enough to avoid an air arc? Is there an internal failure mode that is more likely?

Just wondering what you think is the minimum size for a buffering resistor on a 50 kV supply fusor?
Rex Allers
User avatar
Dennis P Brown
Posts: 3160
Joined: Sun May 20, 2012 10:46 am
Real name: Dennis Brown

Re: John Beutz Fusor... The Story so Far

Post by Dennis P Brown »

That is an excellent connection arrangement for the fore-pump/DP system. I use a short piece of identical tubing to connect my DP to a KF mount and steel bellows line (already had those components.) If it works well, don't upgrade just to upgrade; spend your time and money on other issues that further your goal of achieving neutrons. After that, upgrades/improvements can be done but when something works well, move on to your goal.

As for their ballast resistor - notice its wattage - 100 (extremely low value for that system); the x-former can provide 10 -15 milliamps @ 100 kV; math don't lie nor does reality (despite what some people's best efforts to deny that of late in the news media ...lol.) That resistor had better be under oil. And best to have a small component of vertical angle mounting so convection is faster/easier.

My fusor can achieve 40 milliamps continuous and 100 milliamps surge at 32 kV; my resistor is a big 1500 watt ebay deal and without being under oil, would have failed in no time (in air tests, it got very hot in under a minute.) Why spend $$$ for a monster, air cooled resistor when the solution is so simple and allows for a far cheaper (and more available) type of resistor to be exploited?
John Futter
Posts: 1848
Joined: Wed Apr 21, 2004 10:29 pm
Real name: John Futter
Contact:

Re: John Beutz Fusor... The Story so Far

Post by John Futter »

Rex
In a perfect world the 14 cm would be more than enough.
However it has terminals at right angles to the body - this causes disruptions in the electric field launching corona which causes ozone which when you get enough will easily jump a distance much further than what is there.
It is also a safety item and should be indestructilbe and if it overheats and goes open cicuit must not arc over the damaged section.
User avatar
Richard Hull
Moderator
Posts: 14992
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: John Beutz Fusor... The Story so Far

Post by Richard Hull »

It must be remembered that all such wire wound resistors are well insulated. 30ma in a normal 60k ballast resistor like mine will drop a bit over 1900 volts and at 50 ma 3000 volts.
A 1inch long resistor would never arc in air. Most 60k wire wounds are over 5 inches long and will be fine in air. At 1 million n/s I typically draw 12-15ma and drop less than 1,000 volts in the resistor (15 watts). If you need over 100K of ballast there is an issue with your supply. Admittedly the average professional Spellman with full electronic limitiing might need a huge and wastefully large value of ballasting resistor.

Recently at VCU (Virginia Commonwealth University), I had to insert a 500k ballast just to have their lovely $5,000 electronic switching supply light and stay lit in glow mode!!! At 17kv on the meter and 12ma on the current meter the resistor gobbles up 6000 of those 17,000 volts! The fusor was left with only 11,000 volts to try and do fusion. Their supply is capable of 30kv @ 20 ma but it demands this kind of ballast to light off and stay lit. We did not go any higher as their resistor was not of a wattage that could support that voltage and was not wire wound and arced carbon turn to carbon turn. I will have to go back after they purchase a wirewound string. I suggested (10), 50k, 20-30 watt wire wounds. In this manner we might string them to together to determine a minimum working ballast, hopefully, below 500K. The beat there, goes on. There is such a thing as too much money and too little understanding.

My old junk linear variac controlled x-ray system only needs a 63k, 100 watt resistor. There was so much room in the giant, oil-filled, x-ray tank that I ripped out the kenotrons and fil x-former and put in silly-con diodes and the ballast resistor. The resistor did not need to be in oil.......

Any air mounted wire wound of appropriate value will never arc. A good feature would be to blob on some silly-cone HV putty to the resistor lugs after soldering on the HV leads. (field suppression) Air will cool those old ceramic wire wound resistors just fine.

In my vacuum tube days, I have seen these suckers turn black after smoking off the grease and body oils and ultimately shed their ceramic outer coating and show dull orange turns, while under power. You can't do that with anything but wirewounds. This was a good visual indicator that something was wrong somewhere, usually a cherry red plate in a tube indicated a coupling cap was leaky. You replaced the capacitor only. The tube was still good and the resistor was still good.... just sweep out the ceramic flakes and discard them.

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
John Beutz
Posts: 52
Joined: Fri Sep 02, 2016 2:35 pm
Real name: John Beutz
Location: Minnesota

Re: John Beutz Fusor... The Story so Far

Post by John Beutz »

Tested the XRT with my grandpa and an engineer from Xcel energy who works on the power lines and transfer stations today. One secondary is grounded to my metal fusor frame, and the other is attached to house ground through to variac, We confirmed AC input from the variac, and no shorts on the transformer with an ohmmeter. Attached rectifier on secondary and 6kV probe attached to voltmeter measured nothing with small amount of AC input, not even the negative sign you'd expect from the rectified negative dc output. We may not have the wires all attached in the right place or there might be an interior problem in the transformer. The seller on eBay said it came from a working unit.
IMG_0616.jpg
We also made a wood frame to hold the ballast resistor, but it was not installed during this testing. The wood should absorb the oil and keep the resistor vertical, and keep it separate from the transformer. The engineer from Xcel may have a transformer that I can use, as well as a vacuum pump with a larger inlet so I don't have to deal with the flare adapter that's choking the vacuum. I reattached the full chamber to the vacuum pump with the new rubber hose. There is an audible leak on the ball valve on my jury-rigged gas inlet copper tube, and by my estimation we're not any better than 2 torr. Swagelok and ss tubing is on the way to replace this. A cord on my thermocouple cable snapped as well. Once I've repaired that, I'll send precise pressure data.

I'll upload photos as updates come.
Rex Allers
Posts: 570
Joined: Sun Dec 30, 2012 3:39 am
Real name:
Location: San Jose CA

Re: John Beutz Fusor... The Story so Far

Post by Rex Allers »

Maybe it's just me, but the transformer testing you have done does not inspire confidence.

First it sounds like you were trying to use the full HV output between the two HV wires. I don't think that is safe or even desirable. If your x-ray transformer is rated at 100 KV, you should be able to use the two secondaries in parallel (but through rectifiers to isolate them from each other) and still get up to a 50 KV max which should be more than enough to run a fusor.

Borrowing from an image you posted in a different thread, and editied a little to remove any complication of a current monitor, this is basically what the configuration in the original x-ray application probably looked like.
Basic x-ray configuration
Basic x-ray configuration
The bottom end of the two HV secondary coils are tied together and tied to ground. So HV1 is 50 KV relative to ground. HV2 is also 50 KV relative to ground but reversed AC phase to HV1. So if the x-ray tube is connected between HV1 and HV2 it sees 100 KV across its terminals, but neither end of the tube is grounded. Both are at 50 KV with respect to ground.

You said this... "One secondary is grounded to my metal fusor frame, and the other is attached to house ground through to variac, ..."

So you were trying to use the two secondaies in series with one of the HV secondary wires grounded and the other HV secondary wire as the full voltage sum of the two secondaries. To do this, the center of the two secondaries would have to be tied together but floated, not tied to ground as shown in the diagram above. I don't know if the coils could stand this high voltage (50 KV if driven to full voltage) that would be at this center connection. The transformer was designed expecting this point to be at ground and could arc over if configured this way.

If the secondaries were wired as shown in the picture above and you tie one HV wire to ground, you have shorted out that coil. That could be one possible explaination of no output.

Not as your first test configuration, but as an eventual goal after you have figured things out, I think you should head toward a configuration like this.
Simple Fusor circuit
Simple Fusor circuit
That is the simplest circuit. It leaves out any load-limiting resistor or any current sensing resistor but shows the simple full-wave rectification to use the two secondaries feeding in a parallel push-pull mode to produce DC through the rectifiers. The diodes shown would probably actually each be several HV diodes in series. They have to be able to withstand the full voltage of one secondary without blowing up. But before trying to get anywhere close to this configuration you need to understand your transformer better.

As covered extensively in the "The Beginnings of a Fusor Electrical System" thread, you should first try to figure transformer configuration using resistance measurements. The primary side of the transformer very well could have more than one coil or may have tapped coils. If we look at the simplest probable configuration as shown here.
Transformer terminals
Transformer terminals
Use resistance measurements to figure things out. Is B already connected to C? Is B and/or C already connected to the core (G)? Is the primary side as simple as one coil (1, 2) or are there multiple coils or possible tapped coils?

Once you think you know what is going on with the coil configurations, don't connect the secondaries to anything external until you really understand what is happening. For initial testing, don't put anymore than a few volts AC on the primary side and carefully measure voltages on the secondary. Someone suggested a good thing to do is get a step down transformer designed to make 6 or 12 VAC output from 120 VAC input. Connect the variac to the primary of this transformer and use the dropped secondary output to drive the XRT primary. This way you can finely control the voltage and it can never get above about 6 or 12 V into the XRT.

If we assume the x-ray transformer is designed to make 50 KV on each of the secondary coils with 120 V on the primary, then 12 V on the primary would still make 5 KV on each of the secondary coils. Much better for testing but still a lot of voltage to be playing with. Best to start with very low voltages on the primary (1 or 2 VAC) for initial measurements. If you keep the voltages low while doing this initial testing, you don't need to have the transformer in oil because hundreds of V, or low KV won't have arc-over issues that the oil is there to prevent.

What you described doing doesn't sound anything like this kind of small steps procedure. It doesn't sound like you have followed or understood all the information in FAQs and in several recent threads.
Rex Allers
Post Reply

Return to “Images du Jour”