The Beginnings of a Fusor Electrical System

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Duncan Wilkie
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The Beginnings of a Fusor Electrical System

Post by Duncan Wilkie »

Hello
A couple of days ago I received the preliminary components of the HV portion of my fusion system. I bought my X-ray transformer from a user of these forums. The electrical portion is the only area of the project on which I am a little iffy, and would appreciate guidance in these matters. I have perused the FAQ's and such, and the transformer I have appears to be smaller than Richard's faq post suggests. I will attach images of the transformer. It is quite greasy, suggesting earlier insertion in mineral oil. It was said to output 60kv at 10mA.
I couldn't get the img codes to work so I just linked the images. Sorry.
http://imgur.com/FgdW9cw

Here's the component bit; no idea what the little blue pot is. Some kind of relay, I guess.


http://imgur.com/fNEwU4i
http://imgur.com/DYrsMRC


I also will most likely get the diodes, capacitors, resistors, etc. within a few weeks. I would appreciate guidance as to where to proceed first.
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Bob Reite
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Re: The Beginnings of a Fusor Electrical System

Post by Bob Reite »

The blue item is not a "pot" but a thermal cutout to prevent damage to the transformer from overheating. The transfomer will need to be immersed in mineral oil again before full voltage is applied to it.
The more reactive the materials, the more spectacular the failures.
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Richard Hull
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Re: The Beginnings of a Fusor Electrical System

Post by Richard Hull »

In a 60 hz sysem, iron mass and copper mass determine whether the transformer can run continuously or for short periods only. Small iron mass, small physical size means short duty cycle.

Massive iron, (1 cubic foot), means the transformer is ready for hard action. Remember, X-ray transformers used to be made big, but then someone got the idea that most x-ray machines operate for a few seconds, at most, followed by a comparatively long down time and the iron mass got smaller. Finally, in the modern age, high frequency systems and fractional second exposure times meant that a well made oil immersed HF transformer could be the size of your fist and weigh a couple of pounds. These little guys are just totally unsuitable for fusor work.

Your item looks like a medium duty transformer and could be fusor capable. How much does it weigh out of oil?

Richard Hull
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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
Duncan Wilkie
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Re: The Beginnings of a Fusor Electrical System

Post by Duncan Wilkie »

The transformer weighs about 15-20 pounds. How long would the run time be on a mid-duty, fusor-capable supply?



Also, could you verify my opinions on wires? (Haven't tested with a voltmeter, only been few days) Here goes: The yellows are negative in/out, the red is positive in, and the white is ground.
How exactly would I test the device? I'm still trying to read up on transformer theory and learning how to build the rest.
Also: How would I go about immersing my connections in mineral oil? Would that include the wire up to the feedthrough? The transformer itself is tanked.

My transformer:
60kv @ 10mA, according to seller. (Is that 600 VA or 6 million?) It's C-type with a small resistor labeled "10K" and a thermal cutout.
Here is the image if the wires off the coils.
20161228_174741.jpg
I have found this guide on transformers helpful:http://sound.whsites.net/xfmr.htm and would recommend it to anyone that has a prior understanding of really basic circuit language. The transformer calculator is helpful.
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Re: The Beginnings of a Fusor Electrical System

Post by Richard Hull »

There are no plus and minus or negative wires on a transformer. I can't help you. I'm here and you are there. You need to ohm-meter the thing. Forget voltmetering it until you ohm-meter it. That will tell you what wires are what. Ohm-meter all wires against the core iron as well. One may be hooked to the core and that would be ground.

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: The Beginnings of a Fusor Electrical System

Post by Duncan Wilkie »

I measured 333 between the red and white wires on my multimeter's 2000K setting and a highly varying measurement between the yellows on the 20 setting.
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Re: The Beginnings of a Fusor Electrical System

Post by Rich Feldman »

Coils with large inductance can be problematic for auto-ranging digital ohmeters.

You can always descend to fundamentals for resistance measurement. Put the unknown element and a known resistor in series with a DC voltage source, so all three elements carry the same current. The passive elements will have voltages in the same ratio as their resistances. This exercise should be child's play if you have (or want to get) enough electrical knowledge to be playing with x-ray transformers. Many transformer windings can deliver small shocks even when energized with nothing more than a 1.5-volt battery or an ohmeter.

A milestone will be when you can draw a transformer schematic symbol that matches your XRT, based on visual inspection and electrical measurements. Should be able to see 1) all connection points, including the core; 2. which sets are electrically isolated from each other; 3) DC resistances between connection points within each not-isolated set. When you get to that point, we can show you a fun way to determine the winding polarities, so you can add phasing dots to your schematic symbol.
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Re: The Beginnings of a Fusor Electrical System

Post by prestonbarrows »

Rich Feldman wrote:Coils with large inductance can be problematic for auto-ranging digital ohmeters.
In case you didn't catch this Duncan, this is because modern DMMs usually measure resistance by outputting a fixed small current through the leads and measuring the resulting voltage. This assumes there is no (or negligible) reactance in the circuit. When applying the leads across a large inductance like a transformer coil (or large capacitance) the reactance will certainly not negligible. The current source from the DMM will store energy in the L or C and the voltage across the DMM will change over time. This can lead to ringing in modern autoranging DMMs if the time constant of the circuit being measured is on the order of the time constant of the autoranging feedback of the DMM.

For example, say the DMM starts with a high current at the 1k scale and sees no voltage so one second later assumes the resistance must be on a lower decade and switches to a lower current and a 100ohm scale. Now the inductor is charged up and when the current is reduced it responds with a spike in voltage which is compounded because the DMM is on the finer setting. So it thinks the resistance is higher than its range and switches back to the 1k scale etc. etc.


Rich's advice is good. You can also look into '4 probe measurement' to get some more background on the fundamentals of measuring resistances.
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Re: The Beginnings of a Fusor Electrical System

Post by Jim Stead »

I'm going to offer some thoughts on what I am seeing in your pictures, but that doesn't mean it's correct. You'll still need to test this out as discussed above.

Looking at the image, I see a small coil of wire between the two yellow wires. I suspect this is an isolated power tap, maybe for a measurement or control circuit in the original application. You won't need this for a Fusor. The red wire should be the HV output. You'll want to add a ballast resistor and a voltage measuring circuit to that before leading it out of your oil filled case with high voltage wire. See the HV FAQ's for more information about that.

In your first post you included links to pictures of the terminals. I believe these to be the inputs and ground connection. It appears each coil has a center tapped primary. Red and Black being the hot legs (maybe 220/240v), with the twisted copper pair in the middle of each as the CT. I agree that the white wire you identified is a ground.

What I don't understand, due to my limited knowledge of transformers, is why the HV output would exist on only one coil. The ground wire is wrapped directly onto the top of the non-HV coil, so I don't imagine there is secondary wiring on that coil at all. I'm guessing that coil exists just to add to the core flux.

The remaining question is the pair of cutoff black wires I see laying on each coil in one of the terminal photos. They may be from another power tap, or temp sensors, etc. I can only guess because we can't see the other end. If they are going to be unused, like the yellow wires, they should be properly terminated to avoid accidental contact/conduction.
Last edited by Jim Stead on Sat Dec 31, 2016 1:59 pm, edited 1 time in total.
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Re: The Beginnings of a Fusor Electrical System

Post by Rex Allers »

I guess I'll take a try at guessing some things about how this transformer might be designed. I've never actually had an xray transformer in front of me, but I know a little about transformers and I think I've picked up a little more about these from hanging around this forum for a few years. All of this is guess work, so hopefully Duncan can prove me right or wrong with an ohm meter and maybe some other tests later.

First, to aid the discussion, I copied the three pictures from the original links, reduced their size to not waste space here, and I'll include these here, now.
Xformer 1
Xformer 1
Xformer 2
Xformer 2
Xformer 3
Xformer 3
So it looks like we have two coil sections on opposite sides of a common circular(-ish) metal core.

Another member was recently working on a different xray transformer. For that one he had a pretty good schematic of the transformer in its circuit. The transformer basically had two high-voltage secondary sections. I forget the exact numbers but let me guess that the tube was driven by 70 KV across it. This was made by the two secondaries both producing 35 KV (out of phase with each other). So the bottom end of each secondary was tied to ground and also tied to the other. So the hot HV end of each secondary was making 35 KV relative to ground but because they were out of phase, the voltage between them was the sum or 70 KV. Just to be clear, by out of phase, I mean when one HV output was at the peak of its AC wave the other output was at its minimum. Looking at the connections on this transformer I think it might be built in the same dual secondary way. I think you said it should be a 60 KV transformer. That would mean 30 KV on each secondary If my guess is right.

Let's go with the assumption that the output has two secondaries in series with the common center point at ground potential. I think picture 1 makes sense as the high voltage output. Why are there 3 connections on the left-side coil? I think any xray tube would have a filament on the cathode end. On the left side, two wires are the same color (yellow), so I would guess between these two yellow wires are a very few turns to produce a low voltage for the filament across them. They are wound on the outside (HV) of this coil so they don't have a problem with insulation from ground -- the filament voltage is floating at 30 KV relative to ground. The red wire then would be the cathode (-) 30 KV. So that (in my view) makes the white wire from the other coil the anode (+) 30 KV output.

The transformers only make AC outputs. The implied (-) cathode and (+) anode potentials are derived from the AC, either by external diodes (as I will show in my later circuit sketch) or because an xray tube with a filament is essentially a vacuum tube diode that will automatically only pass the AC potential, that is across it, in one direction.

So in picture 1, I think the red wire is one HV output from the hot end of one secondary winding. If I'm right the white wire on the other coil would be the hot end of the other secondary winding. But where are the opposite ends of each secondary that I think should be grounded? In picture 3, there are two black wires on each coil that are cut off. These are toward the top of the picture and under the plastic housing of the transformer. The picture is cut off so we can't see where they are coming from but they must be out of the coil sections. Where did they go? Who knows? There is a circular pattern in the plastic. Maybe there is a hole in each circular pattern they could have passed through; maybe they just came out through the square holes where other wires are passing.

Why were they cut? Ask the guy who cut them. My guess is that they passed through the center of each circular pattern in the plastic (which we can't see in the picture) but that was the easy way to get the transformer out of the tank that used to hold it. Why are there two wires on each coil? Although we can't see in the picture my guess is the two black wires that are cut on each coil both come from the same connection. Why are there two? Possibly redundancy safety on the grounding of the HV source.

Now, let's think about the primary side coil(s). In pictures 2 and 3, there seem to be wires coming out of the coils, through the square holes in the plastic and connected to the terminal strip. I think these are the primary connections. It looks to me that each coil section has the same number of wires coming out, and with the same colors on each coil. So I would guess each coil section has its own primary windings and these are probably in identical configurations on each coil. From a manufacturing point of view, the coils would be made the same except in the last step where one coil would just get a single HV output wire, while the other coil would get a slightly different HV output wire, plus a few separate turns to make a coil for the filament voltage.

So I suspect that these primary wires coming out of each coil section will have the same configuration. For one thing, this could allow selecting 110 V or 220V input by either connecting coils of the two primaries in either series or parallel. So how are the primaries configured? There are a couple hints. Looking at picture 3, there is a terminal strip with 8 connection points. Counting from left to right, the coil wires coming to pin 2 and pin 6 seem to actually be two wires in parallel. This probably means it is the center tap of two serially connected coils. As Bob pointed out, the blue thing at the left of the terminals is probably a thermal switch for protection if the transformer gets hot. It looks to be in series with the black primary wire out of the left-side coil and terminal 1. I would think this means the black wire is AC input to one end of a coil.

There is an odd thing that I haven't quite figured out. Looking at picture 2, terminal 4 is the white wire from the left-side coil. This is wired to a strap around the middle of the core (possibly ground?) and it also goes to a 10K fairly high wattage resistor that then connects to terminal 7, that is the connection to the white wire from the right-side coil. So far I can't guess what this resistor might be doing.

Some smart ohm meter readings are needed on each of these primary side coil connections to figure out what's going on.

Here's a sketch I made of what I think the basic transformer looks like and the wires coming out of it. From the photos, I can't be sure if all the orientation is right -- maybe the way I drew the HV wires, the primary wire should be coming out the back side in my drawing. But that doesn't logically affect what is going on.
Xfrormer Diagram
Xfrormer Diagram
And then I made a crude schematic of how I think this may have been connected with an xray tube.
Possible original circuit
Possible original circuit
I think the general orientation might be right, but I clearly don't have the primary coils right because I have one too many terminals on each side vs. the wires out of the coils. I was just trying to get the general idea of how I think it might be configured.

Hopefully Duncan can figure out how to prove, with an ohm meter, if I am close or not. One part will be getting access to those black wires that are cut off inside the plastic case to see if they are the other end of the secondaries, as I have guessed.

Hope some of this makes sense and helps.
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Re: The Beginnings of a Fusor Electrical System

Post by Rich Feldman »

Looking good, Rex, but be sure to leave enough work for Duncan to figure out himself. :-)

If the resistor's location would permit it to be near cathode potential, then it might be a bias resistor.

In Coolidge tubes with three terminals at filament end, the isolated one doesn't go to a hot cathode (in my experience).
It goes to a metal part behind and around the filament, that goes by names like focusing cup, grid, or Wehnelt electrode.
That part can be optimized for zero bias (for simplicity), or for bias 100-200 volts more negative than filament-cathode.
In the second case, bias can be developed with a resistor, giving some HV current regulation as well as sharper focus.
wehnelt_bias.jpg
wehnelt_bias.jpg (15.53 KiB) Viewed 10066 times
My own mains-frequency XRT has that resistor and filament winding under the wrapping of one secondary winding. Took a while to figure it out from external resistance measurements.

Commonly, VF and VH are both 60 Hz AC, for "self-rectifying" Coolidge tube operation as Rex speculated. There's no HV current in half of each mains cycle. The average HV current is DC through the secondary windings, amounting to more than a few ampere-turns and shifting core flux toward saturation on one side. Sometimes (I don't know enough to say usually) compensated with a diode and power resistor in parallel, in series with the primary winding (and could be outside of HV tank).

Also, as a reminder, nominal voltage of X-ray transformer secondaries is generally peak, not RMS. The nameplate and meter on radiography systems say kVp.
Oh, and my old reverse-engineering post is still up, with image order reversed: viewtopic.php?f=11&t=4805&p=27643
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Re: The Beginnings of a Fusor Electrical System

Post by Rich Feldman »

On closer reading of Rex's post:
There is an odd thing that I haven't quite figured out. Looking at picture 2, terminal 4 is the white wire from the left-side coil. This is wired to a strap around the middle of the core (possibly ground?) and it also goes to a 10K fairly high wattage resistor that then connects to terminal 7, that is the connection to the white wire from the right-side coil. So far I can't guess what this resistor might be doing.
As you surmised, the two HV windings have their Start (inside) ends connected to the grounded core. Except one is connected through a resistor, for monitoring the actual current in the one and only HV circuit. In Duncan's transformer's original application, 10 mA would yield 100 volts.

Some designs bring that secondary wire out of the oil tank, as a terminal called Current Monitor, for use with an external milliammeter and/or resistor. If not connected externally, you would probably get a 10 mA arc from that terminal to ground.
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Richard Hull
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Re: The Beginnings of a Fusor Electrical System

Post by Richard Hull »

Rex has given one of the best thoughts on this yet. The multiplicity of wires can be daunting. You can go to the bank with the assumption that anything on that terminal bar is low voltage only. A good, non-autoranging ohmeter and about 10 minutes with it in the hands of a skilled electronics buff, who knows HV transformers, would have the basics of what this is down pat. I despise auto-ranging anything. I can turn a knob to select a fixed range. Inductance will not fool a fixed range, old, crude DC ohmeter and a smart user. Too many generalized assumptions are made in auto-ranging systems and can leave the average user often wondering what is going on.

I still have, and occasionally use, one of a pair of old d'arsonval metered VOMs. They never lie and warrant an easily read, averaging of a fluctuating voltage that would have a digital meter going nuts.

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: The Beginnings of a Fusor Electrical System

Post by Bob Reite »

Ah yes! A good old Simpson 260! I personally still have the Heatkit MM-1 VOM that I built when I was in Jr. High.
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Re: The Beginnings of a Fusor Electrical System

Post by Rich Feldman »

Happy new year, everyone.

Duncan, I know you haven't told us any ohms readings without also telling us the meter range settings. Autoranging issues are a red herring in this thread, and are probably my fault.

Back to your assignment, here's a first step that ought to be pretty educational. But before that, if you don't have a set of clip leads on hand after Christmas, get one. Maybe cashier will regard it as colorful Christmas lighting stuff, and give you the end-of-season discount. :-)
th.jpg
th.jpg (16.22 KiB) Viewed 10012 times
At the transformer, let's begin with white and yellow wires that emerge around middle of paper wrapping that covers each secondary winding. Connect a reasonably fresh 9 volt battery between the white wire and one of the yellows. Now with your meter on a DC voltage range, measure the voltage of each battery terminal with respect to the grounded core (accessible on terminal strip).
If you get values around +4 V and -4 V, then measure and report V on all other terminals. I expect interesting values at the 10K resistor and at the red wire next to the two yellow wires at mid-secondary.

Most other accessible wires will probably read zero volts, but that doesn't mean they are connected to ground. If you leave the battery connections undisturbed, but move your voltmeter's common probe to the negative battery terminal, the HV circuit should have voltages between 0 and about +9 V. If wires that read 0 before are reading 0 again, with different meter reference voltage, then you know they are isolated from the HV circuit. That's easy to double-check with no battery, and meter in ohms mode.

There may be a small, harmless spark when you disconnect the battery. Have fun!
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Re: The Beginnings of a Fusor Electrical System

Post by Duncan Wilkie »

I've measured 8.04 volts on the specified connections. Isn't that similar to what my multimeter does to measure resistance?
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Re: The Beginnings of a Fusor Electrical System

Post by Duncan Wilkie »

To help clarify, here's a picture of where the wires enter the transformer body from the connection board

20170101_172531.jpg
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Re: The Beginnings of a Fusor Electrical System

Post by Rich Feldman »

Duncan, I think you missed a key instruction, because of not knowing enough about electricity. There are online learning places much more appropriate than fusor.net. It's even better if you can engage a live teacher/mentor face to face. In fact it's essential, for safety among other things.

We get people here who should be sent away to learn basics. Here's one really good starter kit, with _no_ proprietary parts and no circuits to build without understanding. Power comes from a D cell (not included) with a rubber band around both ends to hold wires in contact. My wife found these kits at Marshalls before Christmas for $15.
Mr.Electricity.PNG
The next step is to introduce a multimeter, and series and parallel circuits more complicated than any in the kit. Circuit A might be child's play. What's the voltage on each lamp in circuit B? What's the voltage between points X and Y? It is sad to think of people seeking nuclear fusion before they can confidently answer those questions by inspection.
series.PNG
You could check the answers by measurement, using your voltmeter and a few incandescent holiday lamps. The kind that come wired in series. Time to sacrifice your parents' least favorite light string. Cut and strip the green wires midway between sockets. When you grow tired of measuring voltage, measure and report the current in the wire between the first and second lamps.

If you want to get right back to your transformer, here's more detail (no substantive change) on the original assignment. Let's number the connections:
xfrmr-1a.jpg
xfrmr-1a.jpg (34.76 KiB) Viewed 9997 times
xfrmr-2a.jpg
xfrmr-2a.jpg (23.68 KiB) Viewed 9997 times
Last time I asked you to connect points 1 and 4 to your 9 volt battery. Then tried to say: hold or clip the voltmeter's black probe onto point 8. Measure and write down the indicated voltage when the red probe is on points 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12. Then move the black probe to point 1 and repeat the sweep of red probe through all 12 points. For extra credit, put black probe on point 4 and walk the red probe around yet again. You can put the 36 measurements in a 3 by 12 table with a story to tell.
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Rich Feldman
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Re: The Beginnings of a Fusor Electrical System

Post by Rich Feldman »

Duncan Wilkie wrote:I've measured 8.04 volts on the specified connections. Isn't that similar to what my multimeter does to measure resistance?
Yup, but there's more. I bet the full exercise will confirm one probable topology for the complete high voltage circuit, and give you the DC resistance of three windings and two resistors, regardless of how your multimeter's ohm modes behave with multiple-henry loads. You would also be helping with a lesson for inexperienced readers, about the customary meaning of "voltage" at single points.

I was serious about using miniature incandescent holiday lights for elementary experiments in voltage and current measurement on series and parallel circuits. An additional learning experience comes when you try to reconcile the V and I results with measured resistance of the lamps. Please be sure the string is unplugged, and stays unplugged, when you start cutting the wires. :-)
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Re: The Beginnings of a Fusor Electrical System

Post by Duncan Wilkie »

Mr. Feldman
I do have some considerable experience with low voltage electrics (Arduino, Tesla coils, etc). I had that exact electricity kit as a kid. Good stuff.
I apologize for having led you to believe my lack of experience; I simply would like to exercise extreme caution in this process. Your original post said "If you get values..." and I wished to withhold from testing the other terminals because you do indeed know considerably more than I. I assumed the discrepancy in voltage confirms that there are two secondaries wired in series, however, I wished to confirm that my result didn't pose any risk to me.
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Re: The Beginnings of a Fusor Electrical System

Post by Rich Feldman »

OK, Duncan. It wasn't clear where you had measured the 8.04 volts, which looks like the full voltage of a nominal 9V battery that's seen some use or is rechargeable.

I am guessing that your transformer, as pictured, has a resistive path all the way from 1 to 4. It might or might not include the filament winding. Then a hidden bias resistor, then the left side secondary, then node 8 and the core, the visible 10K resistor before or after node 8, and finally the right side secondary winding. Total resistance on the order of 100 kΩ. You could see what happens if you measure 1 to 4 with an ohmeter.

Suppose that guess is right. In normal service, the white wire and the pair of yellow wires have high voltage AC of similar magnitude and opposite phase, with respect to the core and the equipment ground. In fusor service, you would have high voltage rectifiers on the white and one yellow, with their anodes connected together and to the HV ballast resistor. Point 8 and the core would be connected to _your_ equipment ground. With that full-wave rectification, each secondary winding would carry about half of the DC plasma current, in directions that cancel each other instead of adding (which could create a magnetic saturation issue).

If the only energy source is your 9 volt battery, I wouldn't worry about damage to battery or transformer or yourself. As explained above, I would expect point 8 voltage to be about in the middle of the battery voltage. Measured with respect to point 8, the battery terminals would be around +4 and -4 volts, and the other terminals at intermediate voltages according to the resistance ratios. Terminals in isolated circuits would read zero, no matter which point in the HV loop (battery circuit) is your reference.
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Re: The Beginnings of a Fusor Electrical System

Post by Duncan Wilkie »

So, I've measured 0 on everything but point 2 at the battery voltage in respect to point 4, and 0 on everything except for a 7.5V reading on point 2 in respect to 8. In respect to point 1, there are -6.6V on point 4 and -7.6V on either 8 and 10.
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Re: The Beginnings of a Fusor Electrical System

Post by Rich Feldman »

Maybe it's time for us to take this off line, Duncan. I will send you a PM.

Thanks for taking the time to try it my way. Even allowing for some ambiguities in your report, I see no way to reconcile the numbers with the model of voltage as potential, if the battery stayed connected between p1 and p4 for the whole experiment. How can p4 and p8 be 1.0 volt different when reference is p1, but not different when ref is p4 or p8? How can p8 be more negative than p4 (measured W.R.T. p1) when p4 is tied to negative battery terminal?

What's your voltmeter's input impedance?

On ohms range, is there any continuity between p3 and any other point? Is there very low resistance between p1 and p2?

The set of pins on which you found any nonzero voltage is 1, 2, 4, 8, 10. You could check that they are isolated from everything else, then we can nail down that 5-terminal network.
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Richard Hull
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Re: The Beginnings of a Fusor Electrical System

Post by Richard Hull »

It has been wisely suggested to make an x-y table of all the pins/wires/terminals and work your way through measuring resistances. This will speak volumes and identify all windings.

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Re: The Beginnings of a Fusor Electrical System

Post by Duncan Wilkie »

I've worked to identify the wires on the transformer. The x-y table of the resistances is listed below, and I've laid out the separate networks in a drawing labeled with the resistances.


image001.png


Resistor Diagram XRT.jpg
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