Jacobs Ladders & Stacking Transformers?

In theory you could wire them in series aiding and get the sum of the voltages out. In practice, realize that you are dealing with very high voltages. Your wired connections need to be clean and the insulating material needs to be rated for the voltages. Be careful. Tom

Since both primaries would be referenced to the same point, I think the stress on the transformer insulation would be doubled, and one or the other might short out. I.E., suppose you ground one end of one of the secondaries; then the most remote point from that ground reaches sqrt(2)*28kV = 40kV peak, across insulation designed for half that, within the second transformer.

-- John

In a word NO! Most likely the 14,000 volt secondary is center taped with the center connected to the case. This makes it 7,000 volts to the case from either terminal. There is no practical way to series windings from two transformers without breaking the center connections. Secondly, if they could be series'd there is insufficient insulation in the windings, terminals, etc. for the resutant 28kV. The best solution is to get a 30kV sign transformer. Keep in mind that these sign transformers are magnetically current limited so they can withstand the heavy load of an arcing jacobs later. High voltage transformers that are not so protected are very dangerous and are not suitable for an arcing application. They can blow breakers, burn your house down or worse. Be careful.

Just off the top of my head, I'd say it'd be incredibly stupid. With 14 KV at 30 mA, you could make a Jacob's Ladder that could go two stories high - it depends on the physical design of the Jacob's Ladder. Once you start the arc, as long as it's arcing, it's a negative resistance - the only thing that will limit the size of the arc is your ballast. (which, AIUI, neon sign transformers have built-in, which might be a snag.)

But stacking those kind of transformers can be lethal, if you don't know _exactly_ what you're doing.

(I suppose you could put them in a big box and pot them, but from that point you're on your own. =:-O )

Good Luck! Rich

I think that if the two transformers are the same model, you can wire both primaries and secondaries in parallel, and the transformers will work okay. You don't get a bit more open circuit voltage, but you get twice the arc current that will produce a hotter arc that will climb a wider gap. Each transformer should protect itself from the effective short of the arc.

There are some transformers out there that don't stack in series well because the secondaries have points somewhere or somewhere else either not too well insulated from, or outright connected to, the primary.

An example is neon sign transformers. Most have secondaries with their center taps connected to the case. I doubt the insulation between the primary and the case withstands reliably, maybe usually not at all, half the secondary voltage. If you put two neon sign transformers in series, their cases will have one full secondary voltage between them. Even powering the primaries with isolation transformers can be a problem if interwinding capacitance is not greatly smaller in the neon sign transformers than in the isolation transformers - insulation breakdown even with the low current flowing through interwinding capacitance will cause a problem sooner or later, so in an isolation transformer scheme you need to connect one end of each neon sign transformer to its case. You will need two isolation transformers that withstand reliably half the secondary voltage, or one that reliably withstands the full secondary voltage.

I think this gets Rube-Goldbergish and is asking for big trouble.

Two neon sign transformers in parallel will give you an arc of same starting length, but that will stretch longer before it breaks. However, if you get zapped you are more likely to die.

- Don Klipstein ( snipped-for-privacy@misty.com)