Blumlein Generator & EMP / High Voltage / Forums

Forums

4hv.org :: Forums :: High Voltage

« Previous topic | Next topic »

Blumlein Generator & EMP

1 2 3 4 next

Move Thread

LAN_403

sparky99

Sat Dec 15 2007, 06:32AM

Registered Member #1159 Joined: Fri Dec 07 2007, 02:10AM
Location: Hudson Valley of NY State
Posts: 84

Hello all,
Picked up one of these off eBay. For those not familiar with this, it's a HV pulse generator similiar to a Marx generator, but capable of currents in the hundreds / thousands of amperes. Also WAY smaller than a marx generator. There are 5 pieces to this unit: the AC-DC board, inverter board, control board, charging transformer & HV generator. These came from a portable X-Ray device made by Golden Engineering, the Inspector 200. Originally used to x-ray unexploded ordanance in the field. When fed with the 9KVDC @ 100 ma from the charging xfmr, the Blumlein generator will output a 60 nanosecond pulse of 150 KV @ 100's of amps. This pulse is ued to fire a cold cathode (just how does a cold cathode x-ray tube work ?) x-ray tube.

I'm thinking I could use this thing to make some pretty impressive sparks. I'v got 2 concerns here: 1) EMP......I'm guessing this thing could fry close by electronics. If I put the electronics in a grounded metal enclosure to protect them from EMP, what's to stop the EMP from coming back down the line from the charge transformer to the inverter / control boards. And most important, what to use to prevent the pulse from getting into the AC line.

Your thoughts & ideas most welcome!

bob
Sparky99

Mates

Sat Dec 15 2007, 11:08PM

Registered Member #1025 Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566

sparky99 wrote ...

This pulse is ued to fire a cold cathode (just how does a cold cathode x-ray tube work ?) x-ray tube.

Cold cathodes uses special metaloxides on the surface which are very keen to emit electrones. (the same system is used in xenon flash lamps). It has an advantage, that you do not need a special low voltage circuit for heating the standart resistant wire based cathode which makes these HV tubes much more simple for construction...

plazmatron

Sun Dec 16 2007, 03:26PM

Registered Member #1134 Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351

The cathode of a Flash X-ray tube has a ring of very fine wire points. When a high enough voltage pulse is applied, electrons, are produced at these points by field-emission, as opposed to thermionic emission, which are then drawn towards the anode.

The principle of field emission is analogous to corona production around a conductor in air, if you had say a 1 inch sphere and applied 30 kV to it, the corona would be minimal, since the voltage per sq inch would be quite small, (about 9kV per square inch) however, if you apply the same voltage to a needle (say with a 0.001 inch tip) , corona will spray off the end, since the voltage per square inch is now a very respectable 30MV per square inch!

I have started a page at the following URL, with a brief explanation with diagrams of flash x-ray tubes, and power supplies:

Regarding EMP, I was using a 300kV marx generator to power my tube. The initial HV is provided by a royer driven flyback, with WC multiplier. Whils EMP doesnt seem to affect an uncased royer, or the multiplier, it will trip the breakers in the house, if I run it of a mains xfrmr! (I tried every filter combination I could think of!) So I ended up running it off of lead acid cells.

It will also trip the house breakers when running of batteries, if the marx gen arcs to mains earth, so the trick here is to isolate the -ve end of the marx from mains ground.

have fun!

Leslie

Marko

Sun Dec 16 2007, 03:39PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Can't resist not to ask now, would it be/was it possible to build a high-voltage diode or triode tube with cold cathodes, using needle arrays to promote emmision while keeping anode curvature smooth?

I never seen something like that so there must be reasons?

Marko

plazmatron

Sun Dec 16 2007, 03:49PM

Registered Member #1134 Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351

Military stole `em!

The military were very interested in shrinking valve technology since they are more EMP hardened than transistors, or IC`s

A quick google using the string field-emission tubes, reveals plenty of articles like:

There are other higher power tubes kicking about that use field emission, but they are few and far between, most manufacturers used radioisotopes on the cathodes, in cold cathode tubes, since they could be operated at much lower voltages.

Steve Conner

Sun Dec 16 2007, 06:32PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Marko, I think what you describe is called a corona rectifier or kenotron.

Nice to see another Scottish HV enthusiast on the board!

plazmatron

Sun Dec 16 2007, 08:38PM

Registered Member #1134 Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351

Not quite Scottish, I only moved here 6 years ago, not too far from you in fact, about 80 miles out in Argyll

I heard it was possible to rectify with corona right enough, I believe its possible to rectify the o/p of a tesla coil with it to some degree. I think the rectification works on the principle, that a sharp cathode, will more easily kick out electrons, than push away ions, so when you reverse bias the assy, some current will flow, but not much (since ions will move much more slowly).

The advantage is they are easily built, and will operate in air at STP, but they really are`nt that efficient.

Leslie

Tesladownunder

Tue Dec 18 2007, 12:45PM

Registered Member #10 Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424

plazmatron wrote ...

I heard it was possible to rectify with corona right enough, I believe its possible to rectify the o/p of a tesla coil with it to some degree. I think the rectification works on the principle, that a sharp cathode, will more easily kick out electrons, than push away ions, so when you reverse bias the assy, some current will flow, but not much (since ions will move much more slowly).
The advantage is they are easily built, and will operate in air at STP, but they really aren`t that efficient.

Here is a Coke can rectifier. Pepsi works too.
The presence of DC is indicated by the electrometer leaves which only separate under the influence of DC. They don't separate at the TC end or earth but do in the middle.
The sharp end is the cut surface of the ring pull. This faces into the smooth concave end.
They are poorly efficient due probably to capacitative effects with the small and relatively high frequency mini TC.
TDU

1197981855 10 FT35999 Tesladcelectometercenter

sparky99 wrote ...

Picked up one of these off eBay. For those not familiar with this, it's a HV pulse generator similiar to a Marx generator, but capable of currents in the hundreds / thousands of amperes. Also WAY smaller than a marx generator. There are 5 pieces to this unit: the AC-DC board, inverter board, control board, charging transformer & HV generator.

Any pics or schematics?

plazmatron wrote ...

I have started a page at the following URL, with a brief explanation with diagrams of flash x-ray tubes, and power supplies:

Excellent site. Will look forward to seeing more on it. The spinthariscope pics with the image intensifier make me particularly envious. Was that an x-ray II or a night vision II?

plazmatron

Tue Dec 18 2007, 05:47PM

Registered Member #1134 Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351

Aha! I knew I`d seen it somewhere! I wonder if your coke can rectifier, would work better if it was enclosed in a plastic tube? Air currents probably reduce efficiency a little. It would also be interesting to try it with a heavy noble gas like Argon perhaps (since some of the energy would be lost via the production of ozone, and nitrous oxides in air.)

Glad you like it, there is a load of stuff I still havent gotten around to writing up!

The spinthariscope was made from a generation 2 night vision image intensifier tube. They have fiber-optic input and output windows, so it can be built with no optics, which makes the job very easy.
I got the tube from e-bay for about Â£35 UKP (~$83 AUD)

Leslie

Tesladownunder

Thu Dec 20 2007, 05:04AM

Registered Member #10 Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424

I really must try the efficiency at high versus low freqencies (like 50Hz) or even DC to see how much inefficiency is due to capacitative losses. It might also give some clues as to how to make it more efficient at high frequencies so that it actually becomes useful in Tesla service.
Argon will increase the distance of sparking by 5 times and this will mean things have to be 5 times as big so I don't think that is the answer. Perhaps SF6 is with many small closely spaced needle vs concave gaps.

I don't seem to have written this up on my site like I thought I had. (with 200 projects even I am starting to lose track).

Anyone else have details on multi stage Blumlein HV generators. I have only seen a doubler which was still complicated.

TDU

1 2 3 4 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob