## The Beginnings of a Fusor Electrical System

This forum is for specialized infomation important to the construction and safe operation of the high voltage electrical supplies and related circuitry needed for fusor operation.
Rich Feldman
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### Re: The Beginnings of a Fusor Electrical System

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.
All models are wrong; some models are useful. -- George Box

Duncan Wilkie
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### Re: The Beginnings of a Fusor Electrical System

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.
Some say the glass is half full. Others see it as half empty. I say it is twice as big as it needs to be.

Rich Feldman
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### Re: The Beginnings of a Fusor Electrical System

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?

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.
All models are wrong; some models are useful. -- George Box

Richard Hull
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### Re: The Beginnings of a Fusor Electrical System

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.

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

Duncan Wilkie
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### Re: The Beginnings of a Fusor Electrical System

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.

Some say the glass is half full. Others see it as half empty. I say it is twice as big as it needs to be.

Richard Hull
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### Re: The Beginnings of a Fusor Electrical System

3 and 4 are your HV outputs with 8 being the center tap of the HV winding. Wire number 11 may be a high voltage metering tap relative to the center tap, (wire 8). NOTE: does wire 8 measure 0 ohms to the metal core?..It should. If not, it must be grounded by you.

1 and 2 might be the filament winding

5, 6 and 7 might be the primary with 5 and 6 being 220 volts and 6 and 7 120 volts. I would try the `120volts across 5 and 7 first. USE A VARIAC!! see what the output voltage is.
10, 12 and 9 are an identical winding to 5,6,7 and may be a companion or related primary.

All the above assumes this is a 60 hz transformer.

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

Rex Allers
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### Re: The Beginnings of a Fusor Electrical System

Duncan,

Your table of resistances is good, but I don't think what you have presented is sufficient.

You have assigned the terminals or connections the numbers 1 through 12. I think first you need a simple table that describes what each of these numbers (1-12) means. I couldn't easily figure that association out and in your table you have a color on each of these numbers that didn't make sense to me on a quick look.

Your transformer is made up of two coil sections. For working things out and labeling your terminal definitions, I'd call one coil Left and the other Right. With the transformer in front of you you can decide which one makes most sense to call Left. For the sake of this discussion, let's say the Left coil is the one that has the 3 HV output wires with colors Red, Yel and Yel. So then the Right coil would be the the one with one corresponding white wire.

Then let's call the side of the L coil with the Red, Yel, Yel wires the coil "Top". Each coil also has wires going to 4 consecutive terminals on the plastic terminal strip. Let's say each of these wires comes from the coil "End". The 4 wires from the coil "Ends" to the terminal strips each have color codes that (I think) are the same for each of the coils (L and R). I would also put these wire codes in the definition table.

So the first definition table entry might be for over-all terminal 1, and this might also be terminal strip connector 1 and be the black wire from the L coil End. Some other over-all terminal definition (Lets say #9) might say it is not on the plastic terminal strip, but is the red wire on the Top of the L coil.

In your resistance table, you have assigned terminals 1 through 12. I assume this is terminal strip terminals 1 through 8, plus the 4 wires on the Top of the two coils (3 on L and one on R). I don't think this is enough.

Using the coil Top definition for where the (probably) HV wires are, the the opposite "Bottom" side of each coil has two Black wires that appear to have been cut. I think you need to get access to these wires, strip their ends and add them to your definition and resistance tables. My guess is the two black Bottom wires from one of the coils are probably connected together and can be treated as one connection. If you get two these wires and find the two black wires from one coil have zero resistance between them, you can treat the two wires as one terminal, so you would only need two more terminals in your tables rather than four more. 14 terminals total vs. 16.

I hope this makes sense to you. You might want to go back to the early post I made in this thread, trying to guess what the connections might be. Until proven wrong, I'll stand by the big picture of what I think the connections were.

Oh, I almost forgot. You also have the blue thermal switch and the power resistor to contend with. Their connections and resistance need to be factored into the analysis. I think the thermal switch should be like a closed switch, so if that measures true, can be though of as an extension of the wire that connects to it (Black End wire, I think).
Rex Allers

Rich Feldman
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### Re: The Beginnings of a Fusor Electrical System

To all: Duncan's pin numbers were pictorially assigned by me in a preceding post: viewtopic.php?f=11&t=11223&start=10#p74002 We decided to save the black wires for later.

Duncan, it's good to see you back. You didn't give me credit for off-forum help with your DC resistance table, long ago. I filled in the upper triangle (by symmetry) and color coded the isolated groups (by inspection). Richard Hull was first to call for the plain resistance-table attack, etc.

For the network consisting of pins 3, 4, 8, and 11, your diagram has six paths. If you connect six resistors as drawn, the node-to-node measurements will all be lower than what you observed.
We want a simple circuit model that matches all six of your measurements and would work in an x-ray generator.
Three elements are sufficient, in a series string (as opposed to a wye configuration). Looks like what you have is:

Pin 3: HV end of secondary winding for cathode (close to filament winding pins 1 and 2).
*R1* 160 K ohm coil resistance
Pin 8: LV end of cathode winding, core connection in picture, and (implicit) external ground.
*R2* 10 K ohm current sense resistor
Pin 11: LV end of anode winding, and (implicit) external current indicating meter
*R3* 160 K ohm coil resistance
Pin 4: HV end of secondary winding for anode.

Verstehen Sie?

Now go figure the voltage drop and power dissipation in one HV winding, from a DC current of 20 mA.
One shudders to think of fusor kids who don't learn enough about electricity to answer those questions.
In full-wave-rectified operation (two diodes), each winding sees all the voltage and half the power.
All models are wrong; some models are useful. -- George Box

Rex Allers
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### Re: The Beginnings of a Fusor Electrical System

OK, I follow the numbering now, and agree with most of what Richard and Rich have said.

To make it clearer to me about the physical meanings, I interpreted things as I mentioned in my last post. Here are two pictures showing that.
Top view
Terminal End view
So in my labels TL=Top Left, TR=Top Right, EL=End Left, and ER=End Right. I also added the transformer wire colors to my labels. The resistance node map provided was very helpful in visualizing the connections. To help my understanding, I edited the image to add my physical labels. After looking at it, I also added red lines on the map to show the actual transformer windings and one orange line to show the power resistor. Here's the result.
Node map of connections
On the primary side there are two matching sets of two series coils on the Left and Right. I would expect that the left and right sides would be connected in parallel for 110V or in series for 220V (ish). Not sure about using all or part of each side series coils. I'd start with the maximum coils or across 5-7 (left) and 9-12 (right). So for (eventual) 110VAC input I have one AC wire to 5 & 9 and the other AC wire to 7 & 12. Other opinions welcomed. As others suggest, I'd start feeding it with a very low voltage and measure outputs for sanity check.

Maybe others have a good approach for figuring out how much of each side's primary to use. I've suggested starting with AC across 5 & 7 (both coils in series). It could also be 5 & 6 for just one coil. The second would make higher output voltage but too little primary would saturate and do bad things. I'm not sure how to work out the proper connections for an input voltage.

There's also that thermal switch to eventually get correct. I think it is between terminal 5 and the black wire of the left transformer coil. If my parallel connection suggestion is correct, the Thermal opening would only cut out one coil. Something needs to be changed to have this thermal switch opening, switch off all primary.

Assuming the 10K resistor is to measure current in the original operation with load between HV outputs of 3 and 4, this wont be right for fusor operation with the two HV outputs feeding push/pull into two diodes for a full wave rectifier. Shouldn't 8 & 11 be connected together with some sense resistor between this node and ground?

If It was me, I'd also fish out at least one (for starters) of the cut black wires on the bottom of the coils and see how it relates to the other nodes. They must be there for something.
Rex Allers

Richard Hull
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### Re: The Beginnings of a Fusor Electrical System

Sad,sad,sad. I am fortunate to own metering and systems up the wazzoo. AC or DC metering high and low voltage for each....Variacs that are fully metered in currnt and volts, etc. I would have had this puppy noodled out and turned on in minutes. Bottom line....If you don't have the gear needed, you are looking somewhere between time tortured guess work and and a possible early death in the family as you play "guess the windings". Some are obvious using an ohmeter. Many good and perhaps correct answers abound here, but when the rubber has to meet the road, only good instrumentation, in hand, will figure out what you really do have.

Fire it up and tune for minimum smoke......

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
Retired now...Doing only what I want and not what I should...every day is a saturday.