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Re: The Beginnings of a Fusor Electrical System

Posted: Thu Aug 03, 2017 12:39 am
by Rex Allers

Reread my post of Mar 7 in the middle of this thread. See the one picture where I redrew your node diagram with some extra labels? I highlighted where I think the coils are by coloring the lines red.

So yeah, two primaries, each with a center-tap.

I suggest, put your low voltage AC input across pins 5 and 7. Put your meter common wire on pin 8 and the other meter wire on pin 3 (top of coil).

Slowly ramp up the voltage. I would expect with about 1 Vrms in, you may see about 250 V on pin 3.

If I am right, turn it off and try moving the meter lead from 3 to 4. About the same result with 1 V in?

Now try input across 9 and 12. I would expect again about the same.

What if you jumper (directly connect) 5 with 9, and 7 with 12 and put input 5 to 7?

Extra points for feeding less of the primaries (say 5 to 6) or hooking the two primaries in series (jumper 7 to 9, and input 5 to 12).

Now how do you figure out the turns ratios of primary to secondary?

Re: The Beginnings of a Fusor Electrical System

Posted: Sun Aug 27, 2017 8:40 pm
by Duncan Wilkie
The output voltage measured between pins 3 and 8 and between pins 4 and 8 was a very stable 400V at 1V input. Similar results were observed with the other primary. However, when jumpering them in parallel, there was only a 100V increase in voltage from the original 400. Jumpering in series yielded a decrease in voltage to ~100V and feeding half of the primary lead to an increase to about 500V. The turns ratio (primary/secondary) is 1:400.

Re: The Beginnings of a Fusor Electrical System

Posted: Mon Jan 08, 2018 2:49 am
by Duncan Wilkie
I have a question regarding current metering. The schematic on the FAQ for a center-tapped transformer (here) shows grounding to a metal case. I don't have a metal case on my device. I assume I simply place it in the ground loop of my device, but can I do this with an ac transformer?

Re: The Beginnings of a Fusor Electrical System

Posted: Mon Jan 08, 2018 3:34 am
by John Myers
The center tap of that transformer is grounded to its own metal case.

The meter and sense resistor is connected in between system ground and the metal case of the transformer.

Re: The Beginnings of a Fusor Electrical System

Posted: Wed Jan 24, 2018 2:02 am
by Duncan Wilkie
I want to pull together here all I can gather from postings here and ask some final questions to close this discussion. Clearly from resistance measuring the 3 and 4 pins of my transformer are HV outputs and pin 8 was clearly a center tap. The inputs are where the contention lies. Richard Hull had speculated that 120 and 220 volt inputs were differentiated within a single primary, while Rex Allers conjectured the series/parallel configuration of the primaries together was the difference. I would like to know if the voltage measurements I took back in August provided insight into what the true nature of the primaries is.

I have little background in AC circuits. I am, however, familiar with DC and really simply need direction as to where to plug my 0-150v variac for a working fusor. As much as I would love to learn the intricacies of electromagnetism studied by Faraday, Maxwell, and Lawrence, it has been correctly stated that those intricacies require 2+ years of collegiate study well beyond my reach. For the time being, simply have a bit of patience with my ignorance and give me things to measure and report so your minds, more familiar with the field, can help me finish this HV system.

To progress,


Re: The Beginnings of a Fusor Electrical System

Posted: Wed Jan 24, 2018 5:37 am
by John Myers
It looks to me that the two primary's are meant to always be in parallel. Putting primary's in parallel is done to increase the current that can be transferred to the secondary not to increase the voltage at the secondary.
I agree with Richard about the 120/220V based of the resistance difference between 5<--->6<->7 and 9<--->10<->12.

Re: The Beginnings of a Fusor Electrical System

Posted: Mon Feb 05, 2018 4:49 am
by Duncan Wilkie
I do still have questions about measuring current on my system. The FAQs are written for someone with a DC transformer, and I'm not really sure how to apply them for an AC rectified one. Also, how do I insulate the resistors and such for a current measuring system? I would assume that since one is directly measuring from a 40kv lead that considerable precaution is required, however, it didn't appear that way on the FAQs. Also, I would appreciate advice on the next step for my system.



Re: The Beginnings of a Fusor Electrical System

Posted: Mon Feb 05, 2018 11:51 am
by Richard Hull
Read the FAQ's It is all there.

There is no DC transformer in any FAQ! There is no DC transformer on earth. All transformers are AC transformers. All transformers used for all nuclear work are rectified and out of the rectifiers come only DC current. (no AC polarity reversal) Only postive or negative DC voltage, be it filtered or unfiltered DC. Sounds like you need a course in basic electricity.

Current is always measured in the ground leg of a high voltage system as shown and noted in the FAQs. Not need for insulation at all.

Voltage is typically measured in the high voltage line and insulation is needed. Air insulates just fine if the high ohm series resistor in mounted in a suitable plastic container well away from where a human can get too near to it. Much depends on how high a voltage you are handling. Read , Read, Read.... Read the FAQs.

Richard Hull

Re: The Beginnings of a Fusor Electrical System

Posted: Mon Feb 05, 2018 12:53 pm
by Dan Knapp
Just for the record, there is a DC transformer on earth. Google Richard Nebel, plasma based dc transformer. It has not yet been fully developed and obviously is not something a fusor enthusiast would employ, but it does exist.

Re: The Beginnings of a Fusor Electrical System

Posted: Tue Feb 06, 2018 2:42 pm
by Dennis P Brown
Looked it up and it is based on a plasma and called an AC-DC transformer for his first and only successful (i.e. built) design that is listed. Now he has speculated on magnetic re-connection relative to a DC-DC (but still uses induction and hence has to have a time varying component) but that requires a complex magnetic field/plasma interaction relationship (related to MHD generation - a concept that even Faraday talked about.) Don't see any working examples of that device (not going to search further.) I will stick with and go with Richards statement for accuracy.