25kV AC

~100 small 230V/12V transformers with primaries connected in series should do the job. This is 10x10 grid of them, doable and reasonably compact.

Best regards, Piotr

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

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

snip

Try the ignition coil from a 4 cylinder wasted spark engine. There are two transformers inside with the ends isolated that go to the spark plugs. The coils are driven separately and use the flyback energy to develop the high voltage. You can probably put the coils in series to double the output volt age. The transformers are cheap, readily available, and small and light.

So if you can use pulses instead of a sine wave, this may be your ticket.

Thanks, but they'd need to be able to make 5ms pulses, that's ms, not us.

Yep, nice stuff, lots of stuff, but all DC not AC.

Whoa!! Huge arcs from secondary to primary destroys the transformers, sorry.

The driver circuitry would be a real trip, with the transformers having no chance of withstanding 25kV. Maybe repalce each of those 100 transformers with a series of 25 of them, with high Rs to equalise V drop :)

I don't know of anything ready made, it's custom time. Early TV EHT transformers produced a few kilovolts at piddlyamps from mains. Such supplies were a real hazard.

If you didn't give a whatsit about the waveform & only wanted it briefly for testing I daresay you could produce dc & use motorised contacts to make ac. Crude would be the word. Enjoy the ozone.

NT

Hmm... What would happen if you put a 1 nf cap across the secondary? Probably ring, but at what voltage?

Win, I don't see how you can expect to get by with 10uA. Parasitic capacitances alone will take more than that!

What's this for?

Jeroen Belleman

Two CRT flybacks + pair 6BK4C + HV optos to drive them (since Vgk ~ 100V). :^)

One flyback needs to be heavily isolated, suggest LEDs + PV for expedient isolation; otherwise, a custom resonant transformer will do.

Tim

-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Design Website:

My thought would be an extended ferrite core - made up of perhaps two of t hese sets, with the two U-sections separated by the two I-sections - to mak e a toroid with enough space in the middle to make room for a useful number of turns of 25kV-capable cable.

You could extend it further with more I-sections

None of them are cheap.

It might give you a way of setting up Piotr Wyderski's array of lots of tra nsformers with enough room for cables that wouldn't arc through.

Flyback plus HV diode, one each for pos and neg pulsing, into a 35kV cap, make a 25kV square wave? But we also do need some time at zero volts.

This is for AC-driven electrospinning. OK, at 60Hz, with 100pF wiring, the AC load is j26 M-ohms, making an AC current of about 1mA. At 400Hz it'd be 6.3mA, consuming 157 watts if in phase. OK, that's a point. Maybe a 400VA transformer isn't overkill after all.

B&W TVs used ~15KV flybacks running around 15,756KC and were AC output until the HV diode which was external in many cases.

Is the frequency a problem? If not then as suggested use a colour TV flyback and cut open the shell to remove the HV diodes and that will probably work. Flybacks are in the uA range, and I assume you aren't looking for any current here.

A single flyback would then suffice. Still available from sources such as:

Possibly

I have a small pile of colour TV flybacks from both projectors and TVs - any one of which will likely work.

John :-#)#

When I was a kid, we'd bum old neon sign transformers from the sign companies. I had a nice 18KV unit with an insulator on each end. I guess neons are all high frequency now, or fake-neon LED things. Maybe there are some old trannies around.

I think neon looks better with 60 Hz drive. The high-freq stuff looks fuzzy or something.

I recently tested a Hammond toroidal 50/60 Hz power transformer. It worked fine to over 50 KHz. Most power transformers work fine in the audio range.

You might make some HV DC, and drive an h-bridge to make a sine. It wouldn't be unreasonable at your power levels.

Or some C-W multipliers where you modulate the input. Discharge could be slow at your frequency. There are maybe possibilities for push-pull C-W.

How about car ignition coils and rectifiers, or commercial HVDC modules, back-to-back? Needs a little management.

The tens of kilovolts need careful attention to electric field strength. The wires and terminals need to pretty bulky to keep the field strength under control.

Tubes are not a bad idea at all here. A fiberoptic fed cascode would be fun.

Win, can you use differential drive into your gadget? Maybe a full-bridge with the uppers just constant-current, so the lower grids are near ground.

Watch out for x-rays.

Yes indeed. We use a nice 4.8mm dia wire, AWM 3239, with a 40kV rating, CSA TV-40. Judd Flexrad HV.