Win's next 10kV project, a 1us ramp

[Joerg]

Hello Win,

To make a nice 20us ramp the transformer needs a good low-
frequency response, which implies a fair-sized core. It
may not need transmission-line transformer HF bandwidth.

You can get very large cores up to almost three pounds of weight, just
have to make sure it's available in the right material:

http://www.fair-rite.com/newfair/pdf/LT.pdf#page=136

Regards, Joerg

 

[Joerg]

Hello Ken,

pivot 0================0===============0
! # !
Copper plate ================ ### ! ! ! ! ! Piston
Gap ### ! ======= ! assembly
Copper plate ================ ### ===== =====
Non conductive ! ! ### ! !
mounting ! ! ### X-X Steam valve
. ......### / \
. . ### ! ! Boiler
. . ### -------
. . Conductive
. . mounting
. .
. .
cam operated . . Lead wires
switch ! . GND
--- .
3KV -----O O-----+--------------- To load

The simplified midwestern edition would consist of just three parts:
Wires, a helluva big piezo, huge sledge hammer. And a six-pack of
Schlitz, of course.

Regards, Joerg

 

[Ken Smith]

John Larkin wrote...

Aren't those those things where the FBI comes and arrests you?

They will want to talk to you, but if satisfied, they'll go away again.
EGG now Perky-Elmer makes them, I think.

 

[Ken Smith]

Take a large enough core to make it easy for the techs. Up to 2" OD is
often in stock and should be fine, larger could be special order.

You can stack them up to make a bigger core.

 

[Ken Smith]

Gunpowder/supermagnet bullet/shaped coil.

I like designs that involve "solid copper boxcars" too.

 

[Winfield Hill]

Ken Smith wrote...

They will want to talk to you, but if satisfied, they'll go
away again. eGG now Perky-Elmer makes them, I think.

That's the other issue, will they even sell them to me? Do I
need to re-instate my security clearance to see a datasheet?

 

[Spehro Pefhany]

Spehro Pefhany wrote...

How fast can they switch, can they do 10kV/us or more?

PE say full off to full on in 100-200ns


Best regards,
Spehro Pefhany

 

[Winfield Hill]

Spehro Pefhany wrote...

PE say full off to full on in 100-200ns

I see a list of stuff at Perkin Elmer, but they make me
request the data rather than simply download it... OK.
http://optoelectronics.perkinelmer.com/catalog/Category.aspx?
CategoryName=High+Energy+Switches

Where do you see the 100-200ns detail?

 

[Spehro Pefhany]

Spehro Pefhany wrote...

I see a list of stuff at Perkin Elmer, but they make me
request the data rather than simply download it... OK.
http://optoelectronics.perkinelmer.com/catalog/Category.aspx?
CategoryName=High+Energy+Switches

Where do you see the 100-200ns detail?

Closed it.. let's see (click click) ah, here:

http://optoelectronics.perkinelmer.com/content/Datasheets/thyratron.pdf

Page 2. Note the nasty 100ns commutation spike wot comes out the grid.


Best regards,
Spehro Pefhany

 

[Joerg]

Hello Ken,

You can stack them up to make a bigger core.

Yes, but be careful in a HV project. You don't want to re-create the
northern lights in there.

Once I had a test setup where there was a somewhat regular clicking
noise. Since I was certain that it didn't contain relays I turned off
the lights and saw a blueish cloud. Upon a 'click' it disappeared and
slowly built itself up again.

Regards, Joerg

 

[Joerg]

Hello Win,

I like the constant-current into a capacitive load that a
flyback coil / transformer can deliver. If the transformer
has a 10:1 step-up ratio I could use 1kV MOSFETs to switch
5 to 10A on the primary... But I keep worrying about the
transformer's leakage inductance. If the secondary + load
was say 60pF total, then that'd have to be less than 17uH
for a say 5MHz bandwidth. Hmm, 17uH doesn't look so hard.

Get one that's not potted all the way. Take the long screws out or drill
away the rivets if it has those. Then you can remove the spacers for the
airgap between the core halves. AS long as you don't saturate it.

Regards, Joerg

 

[Fred Bloggs]

I think i suggested a flyback transformer.
Adjusting the supply voltage on the inductor (primary) can adjust the
slope / slew rate; maybe to 1% without too much trouble and the
amplitude can be controlled by the gated time - again (perhaps) within 1%.
One can easily have multiple KV insulation between primary and
secondary (ies).
And multiple drivers are not that big of a deal either.

That flyback isn't going to be doing much flybacking unless the load is
blocked off during charge up.

 

[Winfield Hill]

Joerg wrote...

Get one that's not potted all the way. Take the long screws
out or drill away the rivets if it has those. Then you can
remove the spacers for the airgap between the core halves.
AS long as you don't saturate it.

I was thinking a custom design. You're not suggesting a TV
flyback are you? Way too slow I'd think.

 

[Winfield Hill]

Spehro Pefhany wrote...

Winfield Hill asked:

Closed it.. let's see (click click) ah, here:
http://optoelectronics.perkinelmer.com/content/Datasheets/thyratron.pdf

OK, I had that (it's all you can get), but didn't read it
carefully enough.

Page 2. Note the nasty 100ns commutation spike wot comes out
the grid.

"During commutation, a high voltage spike appears at the grid of
the thyratron. This spike happens in the time it takes for the
plasma in the grid-anode space to "connect" to the plasma in the
gridcathode space. During this time, the anode is momentarily
"connected" to the grid thereby causing the grid to assume a
voltage nearly that of the anode’s."

Ouch!!

 

[Michael A. Terrell]

I want to know what class he's taking that gets this for a homework
assignment!

Didn't you get the memo? This is the driver stage for the newest high
power mind control equipment. It will penetrate a full quarter inch
thick aluminum hat. Just think about it. All of those suckers who just
wear tin foil hats won't stand a chance against this baby! A single,
full power pulse will vaporize the foil, along with the scalp and part
of the skull. That's why the thing has a 5% tolerance. If it was any
looser, it would cause the brain to explode! ;-)

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[John Larkin]

Ken Smith wrote...

That's the other issue, will they even sell them to me? Do I
need to re-instate my security clearance to see a datasheet?

I don't think it's that big a deal. P-E will ask you what the end use
is, and you can get in trouble if you export them. I have a couple,
surplused out of Los Alamos. I could post a pic.

You might wear them out if you pulse them a lot, though. They were
never intended to fire very many times.

John

 

[John Larkin]

John Larkin wrote...

AWESOME!! I'd have to use three or four in series?

Only if you honor abs max specs. I'd try it at 10KV. There's a lot of
vacuum inside one of those jugs.

John

 

[Robert Baer]

Sven Wilhelmsson wrote...



I've designed and made lots of fast high-voltage transformers
over the years, and this is a possibility. But one serious
problem is high-voltage transformers with good insulation tend
to have high leakage inductance, which could kill my ability to
create an accurate ramp waveform. So I'm not considering that
approach seriously right now. But thanks for the suggestion.

For very low leakage inductance and have good HV insulation, use coax
cable for the toroid winding, splitting the shield primary for parallel
input and 1:N ratio where N is the splits.

 

[Ancient_Hacker]

A better tube might be the good-ol 715-ABC! WWII radar modulator tube,
good for several amps at 20KV IIRC. At a very short duty-cycle of
course as the plate can only dissipate a cople dozen watts. Still
being made to this day!

 

[Joerg]

Hello Win,

I was thinking a custom design. You're not suggesting a TV
flyback are you? Way too slow I'd think.

Actually I was. They are (were?) quite good ferrites. Else it's probably
better to go for a huge pot core and a matching bobbin. That would be
easier to wind and to keep the HV winding firmly in place. Older PC
power supplies have one in there but I believe it's without bobbin.

Regards, Joerg