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Re: Archived - European Fusor

Posted: Fri Sep 15, 2017 11:03 am
by Dennis P Brown
Why are you reluctant to place that transformer under oil? It would certainly be safer - both for you and the x-former! Especially if you intend to get up to 40 kV; above 25 kV electrical items get flaky (they can short to places/distances that normally one would not guess) and oil can provide a lot of safety margin in any system. The oil also allows less chance to have the high voltage jump to something that you are near or touching that would normally be safe ... .

Those diodes look extremely under rated for any significant current (I use 1 amp, 20 kV diodes (two in series, of course) and these costed me $2 each.)

Your chamber and high voltage feed-thru are impressive.

I see in the image those diodes are shorting to the mounting plate (wood?) You need to make a proper mount and seriously consider placing the diodes under oil (besides electrical isolation, provides improved cooling.) I mount my diodes on a plexiglass plate. I use ceramic stand offs to hold the plate up (to increase insulation) in a plastic tub that I fill with oil. The diode assembles lift out easily. Besides cooling the oil makes corona issues go away. I also save money because the wiring between diodes is just normal low voltage wire (110 v stuff); I only use the expensive 40 kV stuff outside the oil.

I use inexpensive synthetic motor oil (a research paper on dielectric properties showed that this oil was equal/superior for these applications so I decided to try it) and it works extremely well up to 60 kV (so far, max voltage I have tested to date.)

Re: Archived - European Fusor

Posted: Mon Sep 25, 2017 8:54 pm
by Werner Engel
@ Dennis:
Using oil was an idea – but I try to stay dry as long as possible. The transformer has about 40 kg – so moving it and building a hull around it seems not to be that easy. I once thought about using SF6 instead of oil – but it was not possible to get it anymore.

Regarding the diodes: I already put them in epoxy – works perfect.
More currents seems a good idea to me. Which diodes did you use and where did you get them from?

Re: Archived - European Fusor

Posted: Tue Sep 26, 2017 11:15 am
by Dennis P Brown
I got them on ebay and there from china. They really do a good job and are a steal considering. They are rated to 20 kV and an amp but I hardly trust that so I use two for 32 kV and my system has a max surge of 100 - 200 ma.) They will handle 100 millamps without an issue and could do a good bit higher I bet - as for 2 amp, well, please but they are really big.

I like oil because it is fool proof (mostly) and just letting the item drain over night cleans most off. Then a bit of alcohol and a cloth does the trick. Using cheap synthetic motor oil (same or superior performance to x-former oil) makes even large systems easy and cheap to immerse.

OK, found them: ... 37BR1E7QgA

These are a bargain at under $2 each! They really do work nicely (have never lost even one for any reason) - of course, just never use them near their highest rated voltage! If you exceed 16 kV, do use two in series. At these prices, can't go wrong so get extra in case you decide to do more systems (shipping and waiting for them is a hassle) - I have a lot of extras for those reasons. Their direction is as marked on their sides.