25kV AC

[Winfield Hill]

Bert Hickman wrote...

I'd recommend using a small oil-immersed 60 Hz dental X-ray
transformer powered from an autotransformer. The frequency
should be in the right ballpark, you can easily tweak the
output voltage, and the power level should be in the ballpark.
Larger X-ray transformers are also available on the surplus
market if you need higher power.

Ah, dental X-ray transformer, awesome, thanks Bert!
Do you think I'll be stuck with using transformer oil?
Maybe with degreasing and vacuum degassing thrown in?


--
Thanks,
- Win

 

Michael Terrell <terrell.michael.a@gmail.com> wrote in
news:96d91df4-3bd0-44b7-8a20-3fa7bf26edb0@googlegroups.com:

On Monday, September 30, 2019 at 11:33:36 AM UTC-4, Tauno Voipio
wrote:
On 30.9.19 18:17, Winfield Hill wrote:
Tauno Voipio wrote...

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.

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


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


Smooth, rounder solder joints are the rule for HV, instead of
the typical method of just enough solder for a good connection.
Some HV second anode wire was made to handle up to 40KV

I had to teach our assemblers how to make a solder joint insuring
good wetting, and then make a round blob on it without sending it
through the hole to the other side. All the while making sure the
multiplier diode or cap remained suspended above the PCB a bit, also
an EIC QA fail. But not for HV!

Because it is hard to definitively QA the solder joint, one has to
trust the assembler to have made good wetting and not just a dry blob
joint. (after all they are so hard to light and get a good toke from)
Hehehe..

 

[Bill Sloman]

On Tuesday, October 1, 2019 at 7:10:50 PM UTC+10, DecadentLinux...@decadence.org wrote:

Bill Sloman <bill.sloman@ieee.org> wrote in
news:744aac08-c0ed-405b-8c79-f46f52ecee58@googlegroups.com:

It doesn't make kV potentials across the primary - the points
would have arced over if it had.


Sure does. Points DO arc. That is why they have the condenser,
because if they did not metal transfer would occur and ruin the
points in short order. That ONLY happens when an arc is present.

So the points are closed and the coil fully energized for the
entire "dwell time", and when they open the bettery is OUT of the
circuit and the field collapses and the slew rate it slams down at
induces a high voltage in the secondary. 16 thousand times every
minute for a good average (v8).

The field doesn't "collapse". It decreases fast enough to induce a rapidly increasing voltage across the secondary, and the changing voltage charges the interwinding capacitance of the secondary, which induces a current that largely compensates for the rapid decline of the current through the primary.

You can write out the equations for the process - which is a bit more helpful than saying that the field "collapses" though it does - initially - go down pretty fast.

> Take your 100:1 ratio. 14 V in makes 140 V out. NOT enough.

That's not what's going on.

So the collapsing flux field is the mechanism by which the
secondary snaps up to a high voltage

It doesn't "snap" up to a high voltage. It rises rapidly - at a rate set by the self-resonant frequency of the ignition coil. Calling it a "snap up" is unrealistic, and rather unhelpful.

and the plug gap fires on the
secondary side and the point gap fires on the primary. The primary
side gets the condenser because it keeps the points from eating each
other up.

That is what the coil gets. Regular system voltage. So I said 14V
as a good number.

The 14v sets the current through the primary of the ignition coil, and it sets the starting point for the voltage rise after the points have opened.

You would see about 140V across the secondary of the ignition coil when the current first started ramping up, but it drops as the current rises and the resistance of the primary starts limiting the current.

It's irrelevant after the points have opened.

--
Bill Sloman, Sydney

 

[Bill Sloman]

On Wednesday, October 2, 2019 at 12:00:40 AM UTC+10, DecadentLinux...@decadence.org wrote:

Bill Sloman <bill.sloman@ieee.org> wrote in
news:5f0807db-74fa-4aba-ba5d-2b34cc21f86c@googlegroups.com:

The field doesn't "collapse". It decreases fast enough to induce a
rapidly increasing voltage across the secondary,

Oh it full on collapses. That is how the event gets generated.

A sine wave is too soft to induce more than the standard step up
ratio offers. A high slew rate event, however, steps into the realm of
infinity because the event is of near zero length. Other physical
factors clamp that down, but that is the mechanism. That high slew
rate (collapse) is the driving engine.

Do the math.

--
Bill Sloman, Sydney

 

Bill Sloman <bill.sloman@ieee.org> wrote in
news:5f0807db-74fa-4aba-ba5d-2b34cc21f86c@googlegroups.com:

The field doesn't "collapse". It decreases fast enough to induce a
rapidly increasing voltage across the secondary,

Oh it full on collapses. That is how the even gets generated.

A sine wave is too soft to induce more than the standard step up
ratio offers. A high slew rate event, however, steps into the realm of
infinity because the event is of near zero length. Other physical
factors clamp that down, but that is the mechanism. That high slew
rate (collapse) is the driving engine.

 

DecadentLinuxUserNumeroUno@decadence.org wrote in news:qmvjk3$507$1
@gioia.aioe.org:

> EIC

errr... IPC

 

One thing I forgot to mention. Shunt regulators can give off low energy X-rays.
Low Energy X-rays are not fun, as their tissue adsorption is very high. A 1/8th inch thickness aluminum box was sufficient for our purposes.

Steve

 

[Lasse Langwadt Christense]

tirsdag den 1. oktober 2019 kl. 10.58.03 UTC+2 skrev DecadentLinux...@decadence.org:

Robert Baer <robertbaer@localnet.com> wrote in
news:KZAkF.9594$O_.6196@fx39.iad:

DecadentLinuxUserNumeroUno@decadence.org wrote:
whit3rd <whit3rd@gmail.com> wrote in
news:22395bd0-b492-48aa-8713- e26daf08651d@googlegroups.com:


Well, 20-year-old auto coils did 40kV peak, so there's
at least SOME commercial units that can do the deed.


They did no such thing s they are NOT "transformers" in the
sense
we know of them.

They rely 100% on the field collpase of a DC energization of
the
COIL that is curtailed by (the opening of) a switch. That sudden
field collapse is why the voltage is so high. Running AC into
the primary of a car coil does NOT provide the same 25kV that the
coil makes when a set of points open on a big DC Standing field
and it slams back in at a high slew rate.

That is the entire principal on which a points operated DC
fired
car coil ignition works. It even makes kV potentials on the
primary when it happens. That's why it needs a damping
'condenser'.

Well, son, ya gots it ron / konfutzzled.

You have already fucked up with this stupid shit.

The configuration is as follows: it is a transformer, with
low-Z /
relatively low number of turns primary and a high-z / large number
of turns secondary; common ground.

Yeah... I know what an ignition coil is, chump. (or is it pops?)

When the points close, the battery is connected to the primary
and
current increases until the points open

Yeah... That is exactly what I said. Current reaches max very
fast though, so your "increases until opened" crap is well.... crap.

THEN the points open.

and the (NOT "damping")
condenser across the points

Never said it did. It does not even get in the circuit until and
only WHILE the points are OPEN. Otherwise it is shorted across the
closed points. D'oh! You are getting senile, pops.

/or, usually/ from ground to primary
high end then resonates,as in a standard flyback system.

A flyback is a TV anode transformer. An old points based
automobile ignition coil and circuit is a different animal than a TV
flyback. Still a transformer, still a primary and secondary. No
diode string in a car coil though.

some ignition coils have diodes in series with the secondary

some claim it is to remove the risk of a spark when energizing the primary
other as a clever way to use a single coil for a four cylinder

https://www.hella.com/techworld/assets/images/10032328a.jpg

 

Also we used to use arrays of jets, either pressurized needle, or gravity cone, driven with 1 Gig ballast resistors off the same PSU.

How you get into tens of grams per minute is what I can't discuss.

Steve

 

Win,

Um, AC is the hard way to increase production, unless your in a certain Russian non-wovens factory where they run the whole plant off a big transformer.

Start a Espin jet with the usual DC. Note the voltage where the Taylor cone ruptures and the jet starts. Note that you can decrease the HV until the jet starves for current, however they tend to make smaller fibers if you decrease the voltage a little Say 5-10% after starting.

Note if you really increase the voltage over the static start voltage, the Taylor cone nearly implodes with the impulse and starts the jet fast, but it is unstable.

This is where I mention the words "Grounded Grid Shunt Regulator" such as 6EN4, but I imagine some of the Russian Surplus ceramic RF triodes would work just as well, if you cant find a 6EN4.

Basically shunt the jet assembly to not quite ground. Makes a pulsed DC, that acts like AC.

This idea should be credited to Dominick Galluzzo at Gamma High Voltage who used to sell the fast shunt switch box as a made on demand product. We bought our HV PSUs from Dom, usually the dual PSU with +30Kv adjustable and -30KV adjustable, in the same box. As his PSUs have a good protection stage built in, they tended to withstand student and professor abuse such as shorting and arcing and low impedance loads for years.

Basically we used mechanical means to get around this. I used to have a Basic Stamp drive a simple servo swinging a fiberglass rod from one PSU pole to the other on the dual PSU as a means of testing reversing of the field. This would let us shoot high speed video of the process your thinking about.. When your around 60KV, you like simple, robust, and cheap. You also isolate your measurement and control PCs with long plastic fiber optics, but that is another story.

I also tried various Kilovac HV relays and spinning disk DPDT switches.

But it is easier to do things mechanically.

As for increasing production:

You can do things like a spinning cup of polymer with a serrated edge. Centripetal force pushes the liquid to the edge, and the edge is fine toothed bandsaw blade. The fluid "climbs up" and launches from the sharp field at the tooth. You can get a lot of polymer into the air this way, but your collector drum needs to be above the cup and grossly overcharged.

The other technique I like for multiple jets involves naturally rough, thin, tungsten wires dipping into the polymer pool. Say six wires 30-60 cm long mounted between two 6 cm spinning disks on the same shaft.

Yet another technique involves one wire wound into a tight helix that dips into and out of a polymer solution pool along its long axis.

Steve

 

See Also:


Review of Scientific Instruments 79, 093904 (2008); https://doi.org/10.1063/1.2981699

Review of Scientific Instruments 80, 026106 (2009); https://doi.org/10.1063/1.3079688

While not related to your problem, it gives a good overview of what happens with closed loop control.

Steve

 

[Jan Panteltje]

On a sunny day (Tue, 1 Oct 2019 09:30:28 -0700 (PDT)) it happened
sroberts6328@gmail.com wrote in
<443d29d7-c518-49e9-940a-1a2b99ec0503@googlegroups.com>:

One thing I forgot to mention. Shunt regulators can give off low energy X-rays.
Low Energy X-rays are not fun, as their tissue adsorption is very high. A 1/8th inch thickness aluminum box was sufficient for
our purposes.

Steve

Yes, this was also a thing with KTV parallel stabilizers (PD500) at 25 kV
https://www.radiomuseum.org/tubes/tube_pd500.html
a colleague of mine ran a set without the metal screening and get his face all burned red.

After a while the glass would turn a bluish color from the Xray radiation.
https://www.youtube.com/watch?v=MooYX2RqJTs

Once had a bunch of these tubes...

 

[Bert Hickman]

Winfield Hill wrote:

Bert Hickman wrote...

I'd recommend using a small oil-immersed 60 Hz dental X-ray
transformer powered from an autotransformer. The frequency
should be in the right ballpark, you can easily tweak the
output voltage, and the power level should be in the ballpark.
Larger X-ray transformers are also available on the surplus
market if you need higher power.

Ah, dental X-ray transformer, awesome, thanks Bert!
Do you think I'll be stuck with using transformer oil?
Maybe with degreasing and vacuum degassing thrown in?

Win, it does indeed need to be operated under mineral/transformer oil to
prevent corona and tracking damage. If the transformer has been pulled
out of the X-ray head and oil for any length of time, it should be fully
re-submerged and vacuum degassed to remove entrapped air. Since you only
need ~25 kVRMS, a variable autotransformer will allow you to easily
reduce primary voltage for the desired output.