Flashlamp Video

[Draco]

I would think that would work, these type of NST are mid point grounded so it's basically a center taped transformer with the center tap at ground and due to there construction they self current limit, at least the transformer types, i dont have any experience with the switcher units that are now mandatory in new installations for neon.
I have 5 of these types of transformers and i can do a test with a variac if need, mine are made by fransformer are are a different mounting style from the one in the video that he made.

That said i would still not be comfortable with a that type of transformer and would want the floating pole to be covered over with a insulating cap. NST transformers generally are higher voltage but a 5kvac unit using the case min point ground and one side should be 2.5kvac. I have one NST that is 15kvac terminal to terminal and seems to be half the voltage from terminal to case.
i would not use an ignition transformer from a fuel oil furnace, NST where usually more reliable

but for what it's worth thats my 2 pennies worth

[mixedgas]

I don't condone this, but if you mount the mid-tap grounded NST 100% surrounded by a double later plastic box, Ie Plastic, Air gap, Plastic,
It becomes a floating transformer.. With the caveat that IF you do not properly insulate it, touching the case of the floating transformer is an instant, perhaps LETHAL, nasty shock...

I would not normally suggest this.. Hence the call for double insulation and other precautions..

Steve

[planters]

I would avoid the complexity of the NST conversion. If it were me, I would get a MOT (and two MOT's in series if you are using 230V), pick a suitable ballet resistor in series with the input and then send the output to a voltage multiplier circuit. Microwave rectifiers and capacitors are just the right capacity for this set up. With a 20:1 step ratio for the 120 V MOTs, a 230 V source will give you 5,000V DC with a simple doubler, at as many A as your heart desires (and much more than it will withstand). Use a cheap variac as the limiting resistor and you have a very powerful capacitor charging circuit for very low cost and work load.

[Draco]

What is an MOT? Microwave oven transformer?

I think i would prefer a microwave transformer but they are not current limited and can deliver a lethal shock with out the capacitors but i think are more predictable then an NST
The NST on it's own is a hell of a painful shock but 30ma generally wont kill you until rectified and sent to the cap's they just put out too much voltage, say with my system, my caps are 2.5kvdc one side of the nst is 2.5kvac or 6kvac and rectified. one pole of my smallest NST comes out to 3,535 volts, so a slip of the variac and i would have a catastrophic accident. but i digress the breakdown tester i have can do the same thing, it can do just over 2,000ac and i am using a doubler so i can stay in a safe range on the supply

I guess this means i am mixed on this, treat the transformer as lethal, put it behind plexiglass, I have not had a fault of the internal ground on the NST and have always used them with my Tesla coils, the transformer was always out of reach when i displayed the coil

another option i guess would be a cheap switcher that you can get from ebay, there are a lot of options for less then 100 bucks,, they just take a long time to charge the caps. I even used a Dynamotor at one point in this experiment.

[absolom7691]

I would avoid the complexity of the NST conversion. If it were me, I would get a MOT (and two MOT's in series if you are using 230V), pick a suitable ballet resistor in series with the input and then send the output to a voltage multiplier circuit. Microwave rectifiers and capacitors are just the right capacity for this set up. With a 20:1 step ratio for the 120 V MOTs, a 230 V source will give you 5,000V DC with a simple doubler, at as many A as your heart desires (and much more than it will withstand). Use a cheap variac as the limiting resistor and you have a very powerful capacitor charging circuit for very low cost and work load.

This would probably be the route I would go if I were to set something like this up. I use MOTs for my tesla coil. They are very beefy. I have yet to burn one out.

What is an MOT?

Microwave Oven Transformer

[Draco]

I used to use MOT's to literally blow stuff up and melt things, oddly up to now that's what i used my breakdown voltage tester for.

I had always been too nervous to use them for a Tesla coil, a NST has an inductive current limit built into them, a microwave transformer does not, drawing an arc from one can draw over 20 amps on the primary side, so some experiments ate fuses like candy and dimmed the lights in the room...fun times

[planters]

You can use a very restrictive current limiting resistor on the MOT. You could limit the current to whatever value you want. The variac can be placed upstreem of this in order to limit the ultimate charge the caps can reach.

[Draco]

I had forgot about using a variac for current control and a bit embarrassing because i was building a system for a distribution transformer, one was to limit the current and the second variac to control the voltage, i dont know what they are called over seas but we call them Pole Pigs, the 300 pound transformer that takes 14,400 volts from the grid to a 240 volt center taped for the house, the one i have can have the secondaries put in parallel and use it backwards, 120 or 240 in and 14,400 volts of fun out at huge amounts of current, i need to find oil for mine and repair the case, same morons that destroyed 3 of my 160mfd caps badly damaged my pig as well, i have new bushings i got from a salvage yard, now it's just fear that slows my progress and besides it looks cool sitting in my laundry room, i had to make it's own cart with wheels, at the time i got it i wanted to build a coin crusher, pole pigs rarely come up for sale to the public, at-lest at a cheap cost.
back on topic I am using a 100k 50 watt resistor to bleed down my caps, i was wondering what values you use Planters for your cap ? am ok or under or over? I am thinking of using a high voltage relay to switch in more if needed as well

[Draco]

here is the latest version of my doubler , the two caps are 2mfd, 4kvdc the diodes are a fast recovery at 12,000 volts at 800ma if my data sheet was right and it can sustain around 200-300ma when fast charging the bank, ramp up with the dial, I doubt it would tolerate a full input with a discharged bank, and it's all made from stuff i had laying around the lair. front is inlet and upper side is the outlet, old meter is inlet current

[planters]

Most rectifier diodes have a peak current rating that is 20-30 x the average rating and the rating you indicate is almost certainly an average rating. Don't worry about charging the cap bank with those.

Another name for a pole pig (there are probably others) is a line transformer. I will be using one of those. Like the MOTs they are very robust. The concept is to set up a working system with all the bits and components working together and then when the only limitation is say average power then move to a more powerful component to remedy that.

Your resistor seems a little off. If you intend to bring the caps to 4,000V then the bleed rate with that resistor will be 40mA. The peak dissipation will be 160W and depending on your duty cycle this resistor would get pretty hot. If the resistor was a switched dump resistor (I use both) then the resistor should be able to absorb an occasional load.

What are you going to do for a lamp?
Are you going to use a vacuum pump or a sealed commercial lamp?