~50KV from 1 CR123 3V Battery

Hotwired, Sun Aug 07 2011, 04:11AM

If this is not a new design do say.

Essentially it works on the same principle as a stun gun. Except its possible to construct from everyday objects and a couple of cheap mail order components.

1) A tiny oscillator circuit from a disposable flash camera is used to bump up 1.5-3V to 350V

2) A 0.22uf metal foil capacitor is charged to ~350V

3) A spark gap in the form of a gas discharge tube, in series with the capacitor and a HV coil is set to arc at 350V

4) Every time the capacitor hits ~350V the spark gap arcs and pulses the HV coil

How to:

First you need the capacitor charging circuit from a disposable camera. Any will do but the easiest way is to get a Kodak Fun Saver camera. The Wedding and Custom Kodak cameras are the same thing by the way.

Get the battery out of it, and short out the capacitor before removing the circuit:

Camerar

Chop off just that corner with the charging circuit on it :

Circuitsquare

Solder two pins and add four wires to make it usable :

Circuitwired

That's the difficult bit done.

The rest is plug and play. These are what you need :

Assemblym

The spark gap in this example is a 350V gas discharge tube (so it will arc at ~350V). You may also get by with an open air gap as commercial stun guns use which is two strips of metal crossing each other separated by a thin insulator.

To assemble follow the video:




It can be made smaller:

Tmpwu



I'm hoping to get it working with a solid state alternative to the gas discharge tubes such as a MOV or avalanche diode, anyone able to help out with advice in that respect?


Incidentally, although I use the tag of stungun, it has no relevance to its actual use. It was designed and made for flammable gas ignition. In potato guns.

Calling it a stun gun gets more hits than a high voltage spark generator though ^_^


Cheers.

EDIT: Images resized by moderator, read the rules about posting large images in post!
Re: ~50KV from 1 CR123 3V Battery
haxor5354, Sun Aug 07 2011, 04:17AM

how long will the discharge tube live?
Re: ~50KV from 1 CR123 3V Battery
Hotwired, Sun Aug 07 2011, 04:25AM

I've run this circuit flat out with two fresh AAA batteries for half an hour with no failure. Although as the batteries fade the spark rate does slow.

However the gas discharge tube does eventually fail, starts arcing at a much lower voltage and needs replacing. I can't really give a proper time period for that and doubtless neither can the manufacturer since normal use of these tubes is for surge protection not this lark.

Mind you while it does work it's an excellent and reliable switch for a set voltage.
Re: ~50KV from 1 CR123 3V Battery
klugesmith, Sun Aug 07 2011, 04:38AM

Nice demo.

Your pictures are much wider than the forum rules allow
(tho' we'be seen worse).
This is not a bandwidth thing, it's about readability on small
screens. If you use the "attach file" dialog, your post will
get a pretty large "thumbnail" image and clickable link to
the full size image.
Re: ~50KV from 1 CR123 3V Battery
Chip Fixes, Sun Aug 07 2011, 04:45AM

have you shocked yourself with it yet? And how did you cut the PCB? I was just wondering
Re: ~50KV from 1 CR123 3V Battery
Hotwired, Sun Aug 07 2011, 04:53AM

No and absolutely zero intention of finding out what a shock would be like, probably get quite a few jolts before a reflex could kick in.

The PCB was cut with a dremel using a thin cut off disk, much safer for the circuitry than waving a hacksaw at it.
Re: ~50KV from 1 CR123 3V Battery
kimbomba, Sun Aug 07 2011, 04:56AM

Can you give more info on the HV coil construction please?
Re: ~50KV from 1 CR123 3V Battery
Hotwired, Sun Aug 07 2011, 05:02AM

No I cannot.

Well I can, ish.

Ferrite core with the primary wrapped round that.

Secondary is wrapped on a plastic bobbin with 8 divisions over the ferrite core..

Whole thing is vacuum potted in epoxy.


The HV coil is not home made, it was hacked from a commercial spark generator which used a 9V and a solid state circuit to produce a spark for lighting a BBQ about twice a second.


The idea of the project was to make a driving circuit which could be added to any high voltage coil such as an ignition coil.
Re: ~50KV from 1 CR123 3V Battery
Conundrum, Sun Aug 07 2011, 08:00AM

Hmm, I have some similar coils here which I bought online from some shady guy who claimed that they were out of "some sort of igniter"... needless to say I haven't had much luck getting them to work.
I didnt pay that much for them but maybe the problem was lack of voltage- the primary measured less than 1 ohm so can't have been that many turns.

I once made a homemade transformer using one of those electronic gas lighters with the coil and 1.5V AA, by potting the secondary in Araldite.
Even though air bubbles were present it did work and the output voltage before arcover was significantly higher than before.

The commercial transformers are made using a stack of iron laminations covered in fibreglass cladding, with the primary wound around that.
Over the top of the primary goes a second fibreglass cladding, followed by a plastic insert where the secondary coil is pile wound in sections.
Connections come out on opposite sides to reduce stress on the encapsulant, then the whole thing is heated to about 70C and soaked in mixed encapsulant which can be styrene monomer+catalyst, epoxy, etc.
Then the unit is placed under vacuum and ultrasound agitated to release any trapped bubbles within.

My thought is that CCFL transformers aren't that heavy so maybe someone can hack these into HV generators by replacing the primary with a new one wound at right angles to the secondary i.e. across the windings and then vacuum potting the transformer ?

Wonder if when combined with a high voltage diode and 30KV rated 1500pF capacitor (cheap, saw these on ebay for under £2 each) you could make a Lifter power supply?

-A
Re: ~50KV from 1 CR123 3V Battery
Alex M, Fri Aug 12 2011, 03:15PM

Awesome!

BTW what camera did you use?
Re: ~50KV from 1 CR123 3V Battery
Ash Small, Fri Aug 12 2011, 05:30PM

Alex1M6 wrote ...

Awesome!

BTW what camera did you use?


Hotwired wrote ...

.
First you need the capacitor charging circuit from a disposable camera. Any will do but the easiest way is to get a Kodak Fun Saver camera. The Wedding and Custom Kodak cameras are the same thing by the way.

Get the battery out of it, and short out the capacitor before removing the circuit:

.
Re: ~50KV from 1 CR123 3V Battery
Nah, Fri Aug 12 2011, 10:37PM

I would use a neon discharge tube, used in relaxsation oscillators.
Re: ~50KV from 1 CR123 3V Battery
Fnord, Sat Aug 13 2011, 12:25AM

Ha! I see you here Hotwired.

Half an hour is a hell of a long time given your power source... impressive.

You should be pretty safe touching it, given camera flash circuits only run at about 1-2 watts output. A small crt FBT with a simple driver puts out way more and is generally not lethal(I just tested a big one sitting on my desk... it's using about 6-10 watts with a single trans driver).
The 350vt side of the circuit is rather unpleasant, though.

I'd throw a couple more caps on there in parallel and see if you can brighten up those sparks any.
Re: ~50KV from 1 CR123 3V Battery
Hotwired, Sat Aug 13 2011, 03:04AM

Hi Fnord,

I'm not testing it on myself anyway :P

No, this is for gas ignition which it does well, each spark is about 13mJ and you can see how fast it throws those out. The capacitor could be half the 0.22uF it is and still have enough energy for ignition.

I've got a 500mJ spark version in mind (1KV 1uF capacitor), It'll require a voltage doubling circuit and possibly a second power circuit. Heck, maybe two of each driving it. Still, it'll charge faster than the stock 100-150uF electrolytic which hold about 10J.

Now that is power hungry overkill for gas ignition but that hasn't stopped anyone using commercial stunguns for spudgun ignition yet.

I'll be doing that just to see how it could be done.

I'll be testing a GDT replacement later today. Got a bag of 330V SIDACs in. I have a suspicion they won't be able to run for half an hour....
Re: ~50KV from 1 CR123 3V Battery
Fnord, Sat Aug 13 2011, 02:10PM

You may not need a voltage doubler.
I think a common practice on here is to run two FBTs with the secondaries wired in series to get roughly double the output voltage. You'll probably have to glue the cores together for proper magnetic coupling.
Of course I'm not really the person to ask here since I've never done it and don't know how well multiple drivers would work together in such a circuit.
Re: ~50KV from 1 CR123 3V Battery
Tetris, Sat Aug 13 2011, 06:14PM

LOL Homemade tazer. Its like, I know how to make a tazer. Do not make me actually make one to make you stop teasing me. Otherwise teasing will qickly turn to tazing. "No teacher, this isn't a taser! Its my Kodak! *hides taser in kodak* I must have been charged with static! Anyways, that is a win. I didn't think you can get that much out of a camera flash board.
Re: ~50KV from 1 CR123 3V Battery
H8erade, Sun Aug 14 2011, 08:27PM

I was interested in your oscillator, so I looked up a few camera charging diagrams. Many of them seem to require a small capacitor, but I see your version doesn't. Do you have a schematic for that particular cut-out?
Re: ~50KV from 1 CR123 3V Battery
Hotwired, Sun Aug 14 2011, 09:32PM

smcerm wrote ...

I was interested in your oscillator, so I looked up a few camera charging diagrams. Many of them seem to require a small capacitor, but I see your version doesn't. Do you have a schematic for that particular cut-out?
Most camera circuits are full of redundant parts.

The small capacitor you talk of is the trigger capacitor which is dumped into a tiny transformer to create a few thousand volts on an ionising wire near the the flash tube and thus allow the large electrolytic to arc between the flash tube terminals.

There is no reason for that to be on this circuit.

The BARE MINIMUM to charge capacitors is this:

Tmpi

Took that several years ago by putting the component->component soldered circuit on a scanner. Battery input on the red wires, few hundred volts come out between the two free ends top and right.

One resistor
One transistor
One transformer
One diode

However the circuit square I show in the guide also contains +1 resistor and a LED. It glows when the output voltage is above XXX volts which is when the original electrolytic had enough charge to do a decent flash. Kinda redundant now since these capacitors charge in a fraction of a second but it also functions in a roundabout way as a power on indicator since these capacitors are such low capacitance the output voltage stays high enough for it to be on all the time.

You can chop off the LED and extra SMD resistor by taking off a corner of the circuit board but it barely matters power wise.

As for a proper circuit diagram, no I never did one but it's fairly simple stuff with just those handful of components.

However HowStuffWorks has... http://electronics.howstuffworks.com/camera-flash3.htm
Re: ~50KV from 1 CR123 3V Battery
H8erade, Sun Aug 14 2011, 09:41PM

Okay, thanks for the explanation. In that picture though, the transformer has five pins. If I come across one with six, will the setup still work if I just ignore the middle pin (on the secondary side)?
Re: ~50KV from 1 CR123 3V Battery
Hotwired, Sun Aug 14 2011, 10:22PM

smcerm wrote ...

Okay, thanks for the explanation. In that picture though, the transformer has five pins. If I come across one with six, will the setup still work if I just ignore the middle pin (on the secondary side)?
Definitely maybe.

Every transformer on a flash board I've seen and I've seen maybe a dozen models uses 5 pins even if it physically has 6 or even 8 pins.

The wiring is not guaranteed in any pattern if you use a transformer from a different circuit so you may need to play about and check which pins go where first if you're thinking of removing a transformer from a board to use it.
Re: ~50KV from 1 CR123 3V Battery
Legit_bacon, Mon Aug 15 2011, 05:08AM

Hello hotwired! you wouldn't happen to be the hotwired of spudfiles? love this little circuit you've got here very nice!
Re: ~50KV from 1 CR123 3V Battery
Hotwired, Mon Aug 15 2011, 02:57PM

Yes I hang about on Spudfiles too.

It's why I made this. Combustion potato guns need a high voltage ignition source. Sometimes stunguns are used. Stunguns are illegal where I am so I saw that as a challenge to make an equivalent.

It has far less power than an actual stungun but still loads for gas ignition. Your average commercial ignition for a BBQ or whatever puts out 10mJ sparks, this does 13mJ sparks and at a much higher rate too.
Re: ~50KV from 1 CR123 3V Battery
Forty, Mon Aug 15 2011, 03:25PM

lol stun guns are illegal but potato guns aren't?
this is a nice little use for all the camera transformers I've scavenged. Do you have any info on the transistor? I don't have any still assembled flash boards so i'll have to use a transistor from my collection. it's too bad those hv pulse transformers aren't more common. i'll have to try making one. I like that you've used one of those gas discharge tubes for your mini spark gap. I haven't read in to mov's or avalanche diodes yet, but when I do, i'll help you out. since the voltage is only ~400v, i'm sure you could get away with a hv transistor triggered by a 555 timer. then you could tune the frequency until you get the desired pulse energy/repetition rate.

Re: ~50KV from 1 CR123 3V Battery
Hotwired, Mon Aug 15 2011, 06:25PM

Yes potato guns are as well.

I don't fire much these days. Don't have the space or privacy and feel depressingly responsible.

I've been checking and a MOV or TVS is unsuitable.

They conduct very quickly when an overvoltage turns up but stop conducting when voltage drops to correct levels.

On the other hand a SIDAC or GDT will start conducting on an overvoltage but won't stop conducting until the current drops enough.

Basically the TVS/MOV acts as a pressure relief valve, only opening enough to let off excess pressure and the SIDAC/GDT act as dump valves. They'll let the entire capacitor discharge before they reset.

I've had some 330V SIDACs with me for the last few days but I've been feeling really lousy and haven't got round to trying them yet.


As for the transistor, I'll see if there's any markings and get back to you.
Re: ~50KV from 1 CR123 3V Battery
Arcstarter, Mon Aug 15 2011, 06:26PM

Cool project! I love pulse transformers.

I have recently been messing with the idea of large pulse transformers (and ignition coils being forced to spit out 100's of kv). It is much easier on HV transformers to output pulses than CW, so i think a homemade pulse transformer would be feasible if you want bigger sparks. A primary of a few turns, and then a secondary with hundreds or if possible thousands of turns over a ferrite rod. However i think a pulse transformer with a spark output around the size of itself would need to be vacuum potted with some paraffin wax or oil.

A more efficient way of switching the cap into the primary of the pulse transformer would use an IGBT and a diac/sidac (can be found in a light dimmer). I would use a circuit like this: Link2 It's reffered to as SISG (sidac IGBT spark gap) and it is typically used to replace the spark gap on Tesla coils. The sidacs could be replaced with anything that will reliably break down at the voltage you want the circuit to fire at, which charges the gate of the IGBT and it acts like a closed spark gap. The difference is that it will only drop a few volts when it is on, while a spark gap has high resistance when it is on.
Re: ~50KV from 1 CR123 3V Battery
Hotwired, Mon Aug 15 2011, 06:58PM

Spent all of 2 mins setting up the circuit and the 330V SIDACs work fine in place of the 350V GDT.

Mind you the 20V difference seems to be an issue on the HV coil, the terminals are ok for the 350V GDT but when using the SIDACs they are too far apart to arc.

Nevermind, can always put a few in series for higher voltage pulses.

The SIDAC didn't seem to heat up during prolonged use as I was worrying.

Arcstarter wrote ...

A more efficient way of switching the cap into the primary of the pulse transformer would use an IGBT and a diac/sidac (can be found in a light dimmer). I would use a circuit like this: Link2 It's reffered to as SISG (sidac IGBT spark gap) and it is typically used to replace the spark gap on Tesla coils. The sidacs could be replaced with anything that will reliably break down at the voltage you want the circuit to fire at, which charges the gate of the IGBT and it acts like a closed spark gap. The difference is that it will only drop a few volts when it is on, while a spark gap has high resistance when it is on.

Looks like that would double the component count of the circuit by itself :P

As far as the original intention of the circuit, that doesn't add anything over a SIDAC or GDT switch aside from size and added complexity. There's a fixed spark gap and the goal is for it to arc that using the smallest possible device with enough energy for gas ignition.

Not sure what you mean by high resistance in a spark gap when its on, plasma is high resistance?
Re: ~50KV from 1 CR123 3V Battery
Hotwired, Thu Aug 25 2011, 10:53AM

Thought you might like an update, I boxed the circuit into a usable form and it's now powered by a rechargeable lithium CR123 which charges to 3.8V.

Shell is made of 2.5mm PVC and the circuit is essentially in a brick of hot melt glue.



Again, I'm using the word stungun simply because that's what people are more likely to understand. It has 3-7 times lower energy output than a proper stungun and is for ignition purposes.

I've revised my estimate of the voltage after rummaging about for the breakdown of air using sharp electrodes.

Source here claims 42.6KV to 51.0KV at 3cm for a 50% chance of a breakdown of air using pointed electrodes: http://www.eurojournals.com/ejtaer_1_06.pdfTmpl

What do you reckon? Is 50KV realistic?
Re: ~50KV from 1 CR123 3V Battery
radhoo, Fri Aug 26 2011, 09:38AM

very nice, compact design.

LE: you can actually use this for a highly portable x-ray generator, see: Link2
Re: ~50KV from 1 CR123 3V Battery
radhoo, Sat Aug 27 2011, 06:51PM

I need to build something similar for auto-ignite my flame thrower: