25kV AC

I'd go with a 35kV full-bridge, with each leg using 35 1.2kV MOSFETs in series, with a 4x.26-type gate divider. I'm using IXTY02N120P, low-capacitance DPak parts, with a 70-piece minimum order, I just received 140 of them. Machine assembly.

Nah, just buy a big transformer!

--
 Thanks, 
    - Win

Please be careful with radii of wire ends and terminations, so that your kilovolts won't sizzle into thin air as corona.

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-TV

Yes, interesting, and much smaller. Probably too low a voltage. Also, we need hours of continuous operation.

--
 Thanks, 
    - Win

Formula for spark gap KV in air:

John :-#)#

To summarize the requirement,

Do you want a sine wave or a pulse?

What waveform/polarity/coupling?

Single ended or differential?

Load? Cable?

Rep rate/duty cycle?

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

Nice, thanks. Looks 40kV-ish.

drive it with a few hundred V AC? they usually have a ratio around 1:100

What exactly is your output waveform? It sounds like a 70kVpp of 5-10ms pulses at 60-400Hz rep rate.

Take a bunch of scrap AC power transformers that are identical size, tear them apart and stack them 4-6 inches, and wind your own primary first (near the core, so insulation is symple), and zig-zag (accordian) wind secondary. Winding start is ground end,naturally. Insulation needed is layer-to-layer voltage plus some safety (2X maybe).

AC power transformers are good to about 100KC depending on the drive.

Above is for continuous use; can be much smaller if used in pulse mode. Experiment with an AC transformer soaked in transformer oil for a few daze, input pulses of (say) 1KV..

these sets, with the two U-sections separated by the two I-sections - to m ake a toroid with enough space in the middle to make room for a useful numb er of turns of 25kV-capable cable.

needing a very long path through the ferrite to avoid saturation.

ransformers with enough room for cables that wouldn't arc through.

There's nothing like sleeping on a problem to drag out the other half of th e solution.

The high voltage windings would pancake wound, as stack of printed circuit boards.

Each board would be about 120mm long by about 60mm wide, and would have two square holes about 29mmx30mm to accommodate the (almost square) legs of th e extended core.

Each board would have - say - 500 turns (250 around each leg) which (at aro und 1turn per volt) would develop about 500V. There would be fifty of them to generate your 25kV.

You'd connect each board to the next with strip of berylium copper. For 1.6mm thick boards, the spacing between board would be about 5mm when y ou were soldering on the strip. You then flip the first board onto the seco nd, solder on another Be/Cu strip, and add the next, Z-stacking them until you have your fifty.

Then thread the ferrite cores through the stack - which is going to end up

80mm high (so two of the U-cores would give you enough winding space).

The energising/driver winding is left as an exercise for the reader.

The whole thing would go into a metal box with two 25kV coax sockets sticki ng out either side, and you'd fill it up with transformer oil or perhaps a high-voltage soft potting compound.

An obvious variant would be to use a pair of C-cores to make a toroid, feed ing a similar z-stack of boards (with only one central hole) to create the high voltage winding.

--
Bill Sloman, Sydney

I use spherical hadware-store fishing weights.

--
 Thanks, 
    - Win

Winfield Hill wrote in news: snipped-for-privacy@drn.newsguy.com:

Dag nabbit! Did my old eyes miss that itty bitty tid bit? :-)

Sorry 'bout that.

Yes, a neon sign xformer should do it. If you want, you can isolate it (read insulate: lucite box) and use a higher input voltage on it to get where you need to be. Or insulate both from ground and step up into it.

IOW I am saying it can handle the higher voltage, one just has to be mindful of any exposed nodes, which I am sure you already know about.

Another source might be looking into a couple popular Tesla coiler forums. They often have AC gear sources.

Winfield Hill wrote in news: snipped-for-privacy@drn.newsguy.com:

Not really. As long as they are all isolated from each other, the primary to secondary voltage differential will be the same.

Xfmr #10 simply cannot be allowed to be proximal to Xfmr #1

Actually, one wants full isolation of all of them from any of their bretheren. Then, there will be no arcs.

Take a 2:1 for starts.

# 1 120 in 240 out Pri to Sec separation: 120 Volts # 2 240 in 480 out Pri to Sec separation: 240 Volts # 3 480 in 960 out Pri to Sec separation: 480 Volts # 4 960 in 1920 out Pri to Sec separation: 960 Volts

This is where I would start to worry about winding to winding arcing (in air).

So, immerse remaining set in fluorinert dielectric fluid or xfmr oil.

# 5 1920 in 3840 out Pri to Sec separation: 1920 Volts # 6 3840 in 7680 out Pri to Sec separation: 3840 Volts

Possible arcing: # 7 7680 in 15360 out Pri to Sec separation: 7680 Volts # 8 15360 in 30720 out Pri to Sec separation: 15360 Volts

Definite arcing potential even in the oil or fluorinert # 9 30720 in 61440 out Pri to Sec separation: 30720 Volts #10 in out Pri to Sec separation: Volts

Transformers can be made with increased primary to secondary isolation capacity, but then efficiency will start to suffer at some point.

Yeah, this is not a good method...

The industry standard is 50Hz sine wave, often 24kV rms.

--
 Thanks, 
    - Win

Wond wrote in news:qmt6rt$j4j$ snipped-for-privacy@dont-email.me:

They are like 25kV @ 1mA. But any loading, even the 1mA drops (clamps) it way down.

Cause I hit myself with one way back in the '70s when I used one for a jacobs ladder. Then I touched it. Once. Good thing I am still here.

50Hz in a 60Hz country? Then they have to generate it. How do they do that? Learn how, then you can do the same.

The papers I've come across are all in the EU. But 60Hz is really an equivalent. I suppose the issue is how long the "zero-crossing" time is, when the voltage has dropped below an effective value. Somehow the electrospinning thread doesn't break, and when the voltage returns, a new thread starts. Soon there are many simultaneous threads.

--
 Thanks, 
    - Win

Used old portable 60hz X-Ray unit? Take the tube and rectifier out and you have a 100kv transformer with 120vac input.

Cheers

Martin Riddle wrote in news: snipped-for-privacy@4ax.com:

Old ECG airport X-ray unit has dual 40kV units if one follows your same instructions (remove multipliers).

The voltage multiplier units alone are worth some bucks.