Removing GFI from a Franceformer.

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teslatron
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Removing GFI from a Franceformer.

Post by teslatron » Wed Mar 06, 2013 8:07 pm

I just acquired today a supposedly 'DEAD' 15KV 60MA Franceformer with GFI from a Neon Sign Builder. There was no ark generated from either side of the transformer when brought to ground. I found that unusual, because from my experience it is usually one side or the other that will go. So, I immediately suspected that the GFI circuit was faulty. At that point I was still suspecting that I would have to de-pot the transformer in order to remove the GFI. When I got home and set the Franceformer on the dining room table, I noticed a small access panel on the top surface directly above the red diagnostic switch. After removing the panel I could see that the GFI circuitry was accessible in its own compartment and contained no resin or tar. In order to access it however, I needed to remove the top cover. After doing that I removed the GFI by clipping the wires. There were two white wires, so I marked one of them prior to clipping. There was a black and white wire coming into the compartment together. I was assuming that these were line voltage piggybacks from the main power lugs on the opposite side of the Xfmer. Continuity testing confirmed my hypothesis. Using my understanding of wiring and what I thought was logical, I connected the two white wires together. The black wire I connected to the remaining two blue and orange wires. Then I powered up the transformer and crossed my fingers. I could hear a gentle hum coming from the box and to make a long story shorter, I was getting a nice arc to ground from both HV lugs.

Todd Massure
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Re: Removing GFI from a Franceformer.

Post by Todd Massure » Mon Mar 11, 2013 5:01 pm

Hi Steffan,

Thanks for sharing - since a lot (or all) of the newer NSTs are made this way, this could be really helpful to people wanting to do HV experiments.
I shelved the Franceformer NST after being frustrated with the GFI. If I find a new project for it I'll give your technique a try!

Todd Massure

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Chris Bradley
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Re: Removing GFI from a Franceformer.

Post by Chris Bradley » Mon Mar 11, 2013 5:54 pm

If you use the circuit I have suggested in viewtopic.php?f=11&t=4882#p27720 then I think it should work with most GFI transformers without tripping them. If it does tend to trip, still, then try adding serial resistance between C1/C2 and the diode junctions, which will soften the discharge time of C1/C2 through the diodes to the shorted potential of the load. Because it is HV/low current coming out of 'Y', then the resistance can be relatively high without it consuming/burning off too much power and losing too much voltage to the output. These resistors will then also serve to be, or to add to, your total ballast resistance.

Although the main function of GFI is to detect leakage from *its* load, it does also serve another 'useful' purpose still for HV circuit safety, and that is that it helps shuts things down if/when there are anomalous loads that cause the neutral to drift away from ground, because this is how it works to detect a leakage path. You really don't want the neutral of your domestic circuits to get too far away from ground, not least of which for general safety but also because of the potential electrical stresses within all the other electrical devices you have plugged into the house circuit that, internally, may have both neutral and ground potentials. Send a multi-kV spike through the neutral of your house wiring system and see what happens!! This is exactly what can happen if you have a sudden arc at the output of an HV transformer through a multiplier circuit with some capacitance in it, which will then have the effect of pulling up the potential of the transformer and causing this effect.

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