Subject Impulse Generator
Posted by Carl Willis on 2005-28-09 22:01
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Below is a photo of the core component in a Golden Engineering Model 200 Inspector handheld x-ray machine--an impulse generator that accepts 9 kVDC input and produces 150 kVDC pulsed output. How it works I don't know! If anyone has suggestions, please share. My idea is that it is either a capacitor and spark-gap-switched pulse transformer, or a multi-stage Blumlein generator.
I added a heavy 1" dia. phenolic feedthrough, through which passes a 3/8" copper tube that was soldered to the stainless ball on top. The lower end of the tube mates with the HV output terminal deep within the impulse generator's central cavity. Everything was filled with mineral oil. Even so, there is still sparking between the ball and the top of the impulse unit--about six inches. The worse problem is that sparks have destroyed now two pieces of phenolic tube by passing right through the walls! The sparks sound like a small bullwhip, at a rep rate of once per second. The destroyed phenolic tubes have visible "exit wounds" from the sparks that killed them. This should be a nice tool but I need to get it under control.
-Carl |
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Subject Re: Impulse Generator
Posted by Dave Cooper on 2005-29-09 02:34
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Carl -
There is a device known as the Spiral Line Generator that resembles a combination of a Blumlein and an induction coil.
Built like a rolled capacitor, with about 10 turns or so. It is charged and then discharged by a spark gap at the far end, which creates a discharge current that is magnetically coupled so as to add the voltages per turn.Typically get one multiple of charging voltage per turn.
They are usually small capacity, and only a few applications. Some folks at Maxwell labs were keen on them at one time. And there are a few papers, one in the British IEE. A bit of a brain spinner understanding exactly how it works.
You are sure that the input actually is DC?
It could be a mini-Marxx generator.. but doesn't seem too likely.
As to the puncture breakdown of the phenolic...you should try something extruded... rather than a composite.... like PE or even a cast Epoxy...But you will need some wall thickness probably up to an inch or a bit more.
Dave Cooper |
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Subject Re: Impulse Generator
Posted by Richard Hull on 2005-29-09 13:11
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I sold these units to Carl at the HEAS meeting. I had two of these units. I gutted one of them
The the big light blue item is the entire assembly from one that I left in, AS IS, condition. The dark blue doughnuit is half the unit from the gutted unit. (the same as half of the light blue unit.)
The big, complete, light blue item section that is oil filled is a blumlien spiral wound capacitor like device, as Dave noted.
I gutted the first unit (dark blue item) unwound and saved the superb copper foil. The dark blue unit is the HV multiplier/unit and is potted. I figured the unit used a blumlien type booster, but had little idea it would do a 5-6 inch leap!! inside the metal pyramidal side piece is a long sealed spark gap. I got the potted piece to throw out about 10-15kv or more. Never took it to the limit.
Oh....Carl...... you got oil on your carpet there buddy.
Richard Hull |
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Subject Re: Impulse Generator
Posted by Carl Willis on 2005-29-09 21:01
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Thanks Dave and Richard.
It's interesting that the side protrusion is indeed a spark gap, since it only makes a faint clicking during discharge (provided the sparking from the output terminal is suppressed).
I also found out the hard way that the closed outer loop of copper foil actually has a vital function. Removing it and firing the impulse generator caused EMP which destroyed a $15 multimeter nearby, and damaged the display circuit on my regulated DC power supply (supply still works, but does not display the correct voltage). My computer, 16 ft. away, rebooted itself and failed to show anything on screen after Windows loaded. I determined after much nervous sweating that only the AGP graphics card was damaged and replaced it today with a new one. The old card provided an output only in "safe mode", and I think that may actually be VGA from the motherboard itself. Anyway, moral of the story is that I need to restore that copper strap!
When Richard gets back I'd be interested to hear anything you can remember about the internals in the generator you sacked such as the type of dielectric, the type of liquid inside, etc. The electrical circuit for the spiral line generator is pretty simple and it should be possible to homebrew these things.
Dave, the phenolic was from the scrap pile at a local plastics shop and I have a lot of it. I do have 1" solid acrylic rod but no way to drill a clean 3/8" hole down axis through an 10" long piece. I think I'll just have to mount the generator in a custom acrylic tank and fill with oil asI have done various other transformers.
The supply should be very useful for intense pulsed x-ray work or even neutron tubes.
-Carl |
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Subject Re: Impulse Generator
Posted by Richard Hester on 2005-29-09 23:33
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| When I get some time, I'll take some pictures of my 100kV radar pulse transformer. It accepts 20kV input, and I have some caps that would make a decent PFN so that I can get a reasonably rectangular pulse out of the output. I think it would be fun to drive a fusor with 100kV pulses at a couple of amps from an impedance limited source... One could use a bubble detector as a cumulative dosimeter.The price was right, and it sure beats winding my own. |
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Subject Re: Impulse Generator
Posted by Dave Cooper on 2005-30-09 00:34
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Carl -
The Maxwell folks had some high hopes for the Spiral Line generator HV sources, and I have some doodles made over the years with applications of them...But I think they are great, small devices. Not sure how large you could make one..Also, if my memory serves me correctly, there were words in one of the papers I've read, that there's a practical limit to the multiplying effect... something like 10 -15 times is maximum.
The things are not hard to make... two strips of foil, and two strips of dielectric adequate for the charging voltage. Wind it up into a roll making the desired number of turns for multiplication, and either pot it or better, put in an oil bath, connect up the spark gap at one end, charge it and stand back.
Oil types are either Silicone Dielectric Fluid, Transformer Oil or even Castor Oil... latter was about $18-$20 per gallon at Mc Master -Carr... listed under lubricating fluids!! As a dielectric fluid, castor oil was the preferred liquid in the aerospace applications for very high voltage/power devices. It is thick, sticky, messy and slightly smelly, but it does work well.
Also is not a hazardous waste product. That counts for a lot these days.
The other dielectric fluids would be Transformer oils like Shell Dialla AX, think there is also an Exxon brand too, and possibly still Mobilect ..?? . Stay away from the Pyranols, Askarels, and like stuff (they are all PCB types) The Silicone Fluids are made by GE, Dow Corning... Union Carbide.. but not cheap. All of these are reusable... with filtering and a desiccant treatment.
Hope that's some help
Dave Cooper |
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Subject Re: Impulse Generator
Posted by Mike Veldman on 2005-30-09 11:19
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I posted a picture a while back of a couple of 100+kv pulse transformers I picked up with similar intentions. Reading Larry's posts on his pulse ideas and reading the articles on pulsed plasma experiments I'd sent him started me thinking in that direction. I also have a bunch of varied PFNs and hard tube modulators as well as radar power supplies of all sizes I'd be happy to share if someone gets serious about trying this. It's difficult for me to stay focused on any one interest for long periods so someone may get to this before I do.
The reason I have all this radar stuff is because I do a fair amount of hydrocarbon tracking instrumentation research with another old (older than me) engineer who does manage to keep me mostly focused on our reasearch by entertaining my ideas about all the other neet things I can think of to do with our accumulated radar sets. Don't mean to hijack the thread.
mike |
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Subject Re: Impulse Generator
Posted by Richard Hester on 2005-30-09 17:00
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| Tobe-Deutschman made a small spiral impulse generator for use in triggering spark gaps. You fed it with around 7.5kVDC and got about 30-50kV out. They used a krytron to switch the thing. |
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Subject Re: Impulse Generator
Posted by Dave Cooper on 2005-30-09 18:20
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I have not built one, but they are not hard to make for a non- critical application.
The major item requiring a little attention is removing the sharp edges on the foils strips. Copper is clearly the best of standard conductor materials, but a demo unit could be made with aluminum foil. I would fold it lengthwise from both sides to the centet to make smooth edges. For a few kV charging voltage, some clear 7 mil Poly sheet will work nicely. Kapton is even better, but pricey.
Key thing is not to expect a huge energy output, since the total energy storage is in a capacitor the size of the foil area and the dielectric layer thickness. With polyethylene dielectric you will get about1.8 mJ/sq inch at 1000v/mil, that's 7kv on a 0.007" dielectric
Cute gadget in any case; and understanding how it works will test your comprehension of electromagnetics.
Dave Cooper. |
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Subject Re: Impulse Generator
Posted by Brian Willard on 2006-14-02 18:31
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| I could find verry little on the net about spiral line impulse generators . So I did a search on the US Patent Office website and found this patent. Seems this device found use in high energy discharge lamps. I also found other patents with the spiral impulse generator including one by Fitch. The USPTO is a research tool I use often , especially for hard to find stuff. |
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(Carl Willis)
(Brian Willard)
