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martialaw

Wed Sept 02 2009, 02:05PM

Registered Member #2330 Joined: Wed Sept 02 2009, 01:47PM
Location: germany
Posts: 9

Hi there!
4HV is something everyone reads severals times while
doing intense internet search. So I decided to register here.
Because I have done very intense internet search!

My project is to build a device, which can ignite and burn
an arc. While single sparks would be defined as arc for me
as long as it fires them faster than 10Hz frequency.
The spark gap should not be shorter than 3 or 4 mm.

That would be no problem if there would not be the second
limit I have... _Size_
The whole device including batteries should fit in the pocket!
(I don't want to put it in the pocket but as size comparison)
So to say it has to be as small as possible!
As this limits the battery's capacity I only need about 30min
continous operation.

Summary:

Continous arc or >10Hz sparks, 3-4mm
Battery-driven, 30mins continous operation
Fits in a pocket

After I did internet recherche and forum searching without
success for about 2 weeks now, I am curious of anyone here
can help me.

So feel free to reply with anything that could help me,
as I don't know HV professionals if there aren't any in here.

Martialaw

PS:
I am familiar with both electronics and basic HV
Goal of the project is a modeling flamethrower

Voltwad

Wed Sept 02 2009, 02:47PM

Registered Member #1829 Joined: Sun Nov 30 2008, 01:06AM
Location: Raleigh N.C.
Posts: 74

Well, I've got a 1.3" cube flyback I made from an SMPS transformer. It's currently being driven by a 1.5" square 555 driver board and an IRFP250 on a 2"x3" sink. Although if you run it from 3 AA batteries it probably won't need the sink. At 5 or 6 volts, it'll start an arc at about 1/2 a mm and can draw out to 5 or 6. The whole mess'll fit in your pocket but not very comfortably. A smaller transformer, a professional smt driver board and an expensive, custom battery pack would probably do it.

martialaw

Wed Sept 02 2009, 03:04PM

Registered Member #2330 Joined: Wed Sept 02 2009, 01:47PM
Location: germany
Posts: 9

Voltwad wrote ...

Well, I've got a 1.3" cube flyback I made from an SMPS transformer. It's currently being driven by a 1.5" square 555 driver board and an IRFP250 on a 2"x3" sink. Although if you run it from 3 AA batteries it probably won't need the sink. At 5 or 6 volts, it'll start an arc at about 1/2 a mm and can draw out to 5 or 6. The whole mess'll fit in your pocket but not very comfortably. A smaller transformer, a professional smt driver board and an expensive, custom battery pack would probably do it.

Thanks for your reply.
So you take a mini transformer like the ones in disposable
camera flashs and drive it with a 555, right?
Or is the SMPS something special?
I do DIY and have to access to SMT or
transformer winding machines :[

Unfortunately starting with a small arc and drawing it larger is
bad, it should burn the desired distance right away, as it
is being designed to be remotely-controlled.
You think it would be possible to archive what I want with
a 9V block battery? Although I guess a camera flash transformer
will die right away if I pump a 9V square signal through...

Dr. Dark Current

Wed Sept 02 2009, 03:06PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Make a circuit similar to the stun gun or taser: a little transformer with a self-oscillating single transistor driver steps the battery voltage to few hundred volts (to be fired with a SCR) or to ~1-2kV (to be fired with a spark gap), which charges a small foil cap, which is then periodically discharged into a small pulse transformer.
If you do the pulse transformer right, you can easily get over 1/2" loud buzzing spark.

Electroholic

Thu Sept 03 2009, 04:03AM

Registered Member #191 Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720

Try the little HV transformers form laser printers. The ones that look like a mini flyback transformer have internal rectification and can be pushed to produce a few KV.

...

Thu Sept 03 2009, 07:29AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

You are not including one of the most important factors in the design, which is the characteristics of the arc, or what you plan to do with it.

If you only need a small arc, a camera flash transformer pcb, with the primary cap and flashlamp, and use the trigger transformer. If you are up for it you can make the board much smaller (see

for my attempts and shrinking a camera flash), mine fit into a cube less than a cm on a side. You would need to modify it to be self triggering, but a neon bulb in series with the trigger coil would probably do the trick (if not you would need to add a scr)

That will run off a single AA battery, the run time would be determined by the pulse rate and size of the trigger capacitor, but you can always parallel more batteries to improve the run time. The spark output would be fairly week, but should at least make noise and be visible in dim light.

On the more powerful side of things, you could use a transformer from a cold cathode lamp, which will put out a few watts of power, and is fairly small, but will require quite a battery to run for 1/2hr. If you want 5w of power for 30 minutes that is 9kj of energy, which would be a few D cell sized batteries, or a 3000mah 7.2v lithium battery (with a lithium battery the whole assembly could probably be made to fit in a deck of cards)

martialaw

Thu Sept 03 2009, 07:32AM

Registered Member #2330 Joined: Wed Sept 02 2009, 01:47PM
Location: germany
Posts: 9

Thanks again for your ideas.

Rebuilding a stungun as it's done by several
guys around the world (most impressive: steelrats)
requires winding at least my own pulse transformer.
Unfortunately I have no experience in doing this, and
no lathe for winding either.
Or are small pulse transformers that survive this
procedure available from junk parts?
A stun gun is maybe even too much power :D

laser printer flyback... nice idea, if I can one of these!
Don't know if I can...

Of course I have some ideas too, maybe one of them
was done by someone here with success:

What about the idea of a stepup driver combined with
a Cockcroft-Walton-Multiplier?

Small drivers could be:
- disposable camera flashs, or 2
of them, gives 300 or 600V (secondary in series)
- CCFL inverter from car accessories or flatscreen monitors
gives 900-2000V depending on the model
- portable bugzapper (the tennis racket type)
gives about 1000V (estimated)

Problem is I don't know if this can do sufficient
voltage AND frequency at the same time... the larger
the multiplier (caps and stages) the lower is the frequency.
Could one of the mentioned drivers be hooked up to a
CW-multiplier for enough power to arc?

* mod edit: Combined double posts *

sorry for double posting but I wrote my last reply without
having read ...'s post.

The characteristics of the arc are stated in my first post.
A 3-4mm continous arc (continous means >10Hz) capable
of igniting flammable gases or liquids.

As I know well that those CCFL inverters need a lot of power,
I tend to camera flashs, because with AA cells it's easy to work with.

I already tried using the original trigger transformer, unfortunately it's
to weak, it cannot pass 1mm through air!

But I read your desktoy and the original candybox documentation,
If you already have a flyback, where is the advantage of driving it
with a camera flash over just driving it with a 555?

Thanks so far

martialaw

Thu Sept 03 2009, 09:26AM

Registered Member #2330 Joined: Wed Sept 02 2009, 01:47PM
Location: germany
Posts: 9

Mod edit: Don't double post! Go back and edit your old post in cases like this.

Voltwad

Thu Sept 03 2009, 01:37PM

Registered Member #1829 Joined: Sun Nov 30 2008, 01:06AM
Location: Raleigh N.C.
Posts: 74

If you want a good circuit using two camera transformers and a cockroft walton setup you can look on the third page of this thread. That's the circuit I used for the supply of a mini Tesla coil. The spark gap fired at about 2 mm max. but upping the battery from 1.5v to 3v might work. As for winding your own, I've done it several times quite successfully. Find something with a switchmode power supply, (PC power supply or computer monitor), pull a suitably sized transformer off it, (Whatever size you think will work), drop it in a jar of paint stripper for a few hours or a day until you can wiggle the core out. Then desolder the wires and unwind the bobbin. If there's a gap in the core, you're good to go and if not you can add a small piece of cardboard between the two halves. Winding it is a relatively simple affair. A lathe or homemade winder is useful but for a small bobbin, (say 1.5" cube) you can do it by hand in a few hours. Here's a thread about one I wound. These SMPS cores are a great middle ground between TV flybacks and camera transformers and I love seeing how much voltage I can get in a small package.

martialaw

Thu Sept 03 2009, 02:52PM

Registered Member #2330 Joined: Wed Sept 02 2009, 01:47PM
Location: germany
Posts: 9

Interesting way to combine the 2 flash transformers.
I've also read the rest of the thread but could not
figure out how the others were doing it...
with multiple flash transformers, outputs parallel for
300V with more current or in series for more voltage?
I cannot imagine that they all are in resonance...
don't the AC waves disturb the other circuit?

You think with your setup and a fullwave CW multiplier
I could draw >10Hz 3-4mm sparks out of 2 camera flashs?

EDIT: just found http://4hv.org/e107_plugins/forum/forum_viewtopic.php?30389
This comes pretty near to what I want. Could I use 2 flash circuits
combined anyhow to get a stable arc?

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