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Tippman C Ignition - possible for spudguns?

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Unread postAuthor: Technician1002 » Tue Apr 14, 2009 10:09 am

Hotwired wrote:The trigger cap through the small coil I'm using does not produce a spark capable of igniting a gas stream, it's barely visible.

Enough of them together will work.


Many flash units tie the ready Neon into the trigger circuit to keep it at about 60 volts on the contacts. The neon doesn't draw a high enough current when it triggers to fire the flash. Doubling the voltage in a cap increases the stored energy 4X. Have you removed the neon and re-testd at 200-300 V. Supply current is low in this portion of the circuit, so don't use a VOM to measure it.
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Unread postAuthor: jimmy101 » Tue Apr 14, 2009 11:57 am

Some of the descriptions are correct, some are not. The spudwiki page has some info on how the disposable flash circuits work.
(http://www.spudfiles.com/spud_wiki/inde ... mera_flash)

An excellent page describing several cheapo camera flash circuits is http://www.talkingelectronics.com/proje ... asher.html

The trigger cap is generally 0.022uF or 0.033uF (22~33 nF) low ESR. The energy in the cap is (1/2)CV<sup>2</sup>. If charged to 300V there is (ignoring losses in the trigger tansformer) ~1mJ of energy in the trigger cap. The minimum igntion energy for propane in air is roughly 0.5 mJ so the flash trigger setup is pretty marginal as an ignition system. Sometimes you can get it to work but you really need a bit more energy in the cap.

In some circuits the ready light is across the trigger cap but the cap is still charged to 300V, not 60V. The neon light does indeed limit the circuit a bit. Often though the ready light is wired across the main cap instead of the trigger cap. Even when it is wired across the trigger cap it is done via a pretty large resistor which drops the voltage before it gets to the neon bulb. So the neon bulb is seeing (dropping) 60 or so volts but the 300V source voltage is also being dropped across a resistor as well as the neon bulb.

Often, if you measure the voltage across the trigger cap with a DVM you'll get a voltage in the vicinity of 60V. That is not the actual voltage on the cap. The cap is up at 300V but it is being supplied via a very high resistance resistor, typically a couple hundred Kohm to a couple Megaohms. When you try to measure the trigger cap's voltage your DVM's internal resistance is similar to the limiting resistor so you get a voltage divider. The DVM reads much lower than it should because the DVM draws significant current compared to what the limiting resistor can supply. A typical DVM has input resistance of from 1 to 10 Mohm.

Anyway, back to the problem at hand. The typical trigger cap is a bit small to be used as a spudgun trigger, there is just barely enough energy in it, any losses and there isn't enough. Increasing the capacitance will help. If you could boost the cap by a factor of two that might be enough. A factor of ten would be better. You do have to worry about overpowering the trigger transformer though. If the core of the trigger transformer is operating near saturation with the standard cap then boosting the capacitance won't help. (I have no idea how close that transformer is to saturation.)

The other approach is to use the stock cap and set the spark gap width correctly. Since the energy in the flash trigger is marginal to begin with you need the gap set just right. The output voltage of the trigger transformer is limited by the gap width. If the gap is too small it breaks down before the voltage gets up to the 2KV to ~5KV the circuit is designed to produce. When the gap breaks down prematurely you get a longer duration lower voltage disharge. You never get quite enough energy in the gap to ignite the fuel, the energy dissipates too fast and you don't get ignition. If you can get the gap just right so that it doesn't break down until the trigger reaches it's full output voltage (and power) then you get a short duration high energy spark that can ignite the fuel. The tricky part is that if you make the gap a tiny bit bigger it won't spark at all (and may well fry something on the flash circuit board).

You can see the same behavior sometime with BBQ piezo igniters. A very small gap between very pointy electrodes often won't ignite a fuel mixture. Increase the gap a bit and it ignites consistently. My long handled butane lighter "poppers" are very sensitive to the gap width. Too big gives no spark and no ignition. Too small gives a spark but no ignition. It has to be just right to work consistently.
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Unread postAuthor: Technician1002 » Tue Apr 14, 2009 12:12 pm

Hats off to you for homework fully completed. I hadn't calculated the energies. Wow, nice. :D . My pleasure to meet another electronics guru.

As far as saturation, many transformers are limited in iron content in a powdered rod for fast rise times, which unfortunately limits the spark energy and duration, but helps reduce or eliminate core saturation. Some flash units use air core transformers. I'm not sure on the disposable camera ones. I'll have to stick a magnet on one to test for ferris content.

***Edit*** I just looked at the schematic on your second link. The resistor to charge the trigger cap is 4.7 Meg. The Neon is in parallel with the trigger cap with a 10K ohm in series. The trigger with that divider is pretty much at the mercy of the ionization voltage of the neon. Remove the shunt neon and permit the trigger cap to charge to the main flash cap voltage.

From your math, it looks like a larger energy storage is still needed for a spark of proper energy. o.o22 uF isn't big enough. Would an automotive cap work? I think they are near .47 uF and work fine with the peak primary voltages in an automotive ignition.

***Edit*** looked up the value in Google. Found this;
http://answers.yahoo.com/question/index?qid=20090320120149AAwN5ST
but they were about 0.2-0.3uF 200V
That should put us in the ballpark energy wise.
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Unread postAuthor: Hotwired » Tue Apr 14, 2009 1:27 pm

What this really needs is for someone to dig into their pocket and get some cash out ^^

Went out a couple of hours ago and bought myself three capacitors. Polypropelene with metal foil and Metallised Polypropelene.

No idea about the difference between the two, probably the same thing, don't care much either.

Point is I bought two 0.22uf capacitors.

There was a particular reason for that number and it wasn't anything to do with automobiles. It's a value used in stunguns. (I do my homework too ^^).

Both .22s cost £2.something each which is comparable with buying online if shipping is considered unless you're buying over 500 each.

The difference between them is that the poly with metal foil is rated to 1250VDC or 600VAC and comes as a red epoxy filled box: 19x32x41.5mm or otherwise visualised as 6xAAA batteries in a 2x3 stack.

The other which is metallised poly is somewhat smaller as a yellow cylinder 28mm long 18mm fat (need to keep up the technical terms) rated to 1000VDC or 500VAC.

Both work. Spark is somewhat skinny but healthy enough, more specifically it can ignite a gas stream. Arcs across 15mm with my setup.

I'll be returning the red brick later. Can't be bothered with something three times the volume for the same output.

By the way Tech, I'm not using a flash camera board. I'm using my desk, individual components and test leads. So when I was testing the trigger cap that was literally the trigger cap removed from a board, charged and shorted through the coil.
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Unread postAuthor: jimmy101 » Tue Apr 14, 2009 4:15 pm

Hotwired: Sounds like it's working pretty darn well. I wonder why the cap is so damn big. The 0.022uF cap in the photoflash is pretty small. High capacitance means a bigger cap but the ones you describe are down right huge. I searched at Mouser and Digikey and couldn't find any suitable low ESR caps. The tricky part is finding something with a 300V (or more) voltage rating.

Technician: Sounds like an automotive ignition cap might work. 200V is probably too low but it is close. The cap needs to withstand at least 300V continuously. An ignition cap just needs to withstand a hundred or so volt spike created when the points open and the ignition coil creates a back EMF (which is actually a forward EMF but it always seems to be called "back").

google time ... "condensor" or "condenser" is the old name for capacitors.

Looks like 0.2 to 0.5uF was common, perhaps 200V rating. Amazingly little actual spec information though. Lots of places sell'm but they don't say what the ratings are. I looked at Mouser again for any caps with voltage ratings greater than 300V and didn't find anything practical.

The ignition cap certainly sounds like it is worth a try. Darn, I used to have a couple of them laying about but it's been so long since I had an engine with a points based ignition that I suspect I chucked them. I think you can still get igntion caps at a decent automotive parts store for a couple bucks. Or, visit the local car junk yard.

If they are rated to 200V you could use two in series to get the needed >300V capability. The total capacitance would be half the capacitance of the individual caps.

For best results the cap really should be tuned to the coil. This is true for both automotive igntion systems and coil guns. Small changes in the value of the cap may give pretty big changes in the behavior of the coil.
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Unread postAuthor: jimmy101 » Wed Apr 15, 2009 12:14 pm

Technician1002 wrote:I just looked at the schematic on your second link. The resistor to charge the trigger cap is 4.7 Meg. The Neon is in parallel with the trigger cap with a 10K ohm in series. The trigger with that divider is pretty much at the mercy of the ionization voltage of the neon. Remove the shunt neon and permit the trigger cap to charge to the main flash cap voltage.

In the first circuit the Neon is across the trigger cap. If you scroll down to the other circuits with an indicator it is across the main photocap.

In a quick spice simulation of the fuji circuit (the first one on the page) it does indeed look like the Neon bulb limits the trigger cap to about 100V (or whatever the breakdown voltage of the neon bulb is modelled as). I wonder why they did that. It drops the available energy in the trigger cap by a factor of 10 or so.

In the Kodak circuit the neon is across the photocap via a 390K resistor. I can't imagine the Kodak circuit is limiting the photocap to 100V (or whatever the Neon bulb's breakdown voltage is). I must be doing something wrong in the spice model, or Ne2 bulb doesn't behave as the typical spice model for them says they do in this application.
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Unread postAuthor: Hotwired » Wed Apr 15, 2009 3:43 pm

Look what I found :shock:
[youtube]http://www.youtube.com/watch?v=K5zPoKGDRfk&fmt=18[/youtube]
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Unread postAuthor: Technician1002 » Wed Apr 15, 2009 5:31 pm

Hotwired wrote:Look what I found :shock:


It looks like a reed relay (the yellow on the right) feeding a something?? feeding a monitor flyback transformer. In computer monitors due t the many sweep speeds the sweep is often not combined with the high voltage transformer for the CRT. These run and higher frequencies than NTSC or PAL TVs and are therefore smaller.

Did they post a circuit?
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Unread postAuthor: Hotwired » Wed Apr 15, 2009 8:51 pm

I sent you part of it a few days back ^^

That's a miniature stungun letting rip on my desk :wink:

The yellow is the .22 I bought the other day. It's cycling reasonably fast in that clip, perhaps ~20hz, it's discharging at about 3-400V so the recharge rate is substantial.

Discharge rate is a bit hairy at the moment, it's operating on a spark gap which welds and corrodes itself. Needless to say, with a spark gap only about 1/3 of a mm in open air it doesn't stay stable for long.

I have two variants on the same theme of component on order to replace the spark gap switching method and with any luck that'll be the last I spend getting this working perfectly.

Battery usage is not too bad I might add. Doesn't beat the heck out of them as repeatedly charging a 120uf cap does.
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Unread postAuthor: THUNDERLORD » Wed Apr 22, 2009 12:40 pm

It was mentioned the joke shockers (pens, flashlights, lighters etc.) are probably only a few hundred(or) thousand volts.
But still, I'm wondering how long/if they can handle a 9 volt or two (@18v) so the output would be multiplied???

Another possible compact spark source I forgot to mention, but was wondering about (no idea) was the mercury gas flourescent household light bulbs that fit standard light sockets (energy saving ones that last for --years).
The normal large tube flourescents have large ballasts.
I noticed the small bulb replacements mention not to "use outdoors" and "caution shock hazard"
Wonder if there's anything useful for making compact sparkers inside?
Course the mercury vapor in the tube is nothing to tinker with.

Looks like Some new stuff to research here! :)
I have about 60 disposable flash cameras, but was thinking about a compact disc-launcher design (For something else) for a while.
Or a flashy blinding light thing! (to mount on a muzzle or... skateboard):P
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Unread postAuthor: Hotwired » Wed Apr 22, 2009 1:40 pm

No, it's not a good thing to put several times the voltage into those toy shockers.

It's not because they'll put out dangerous voltage.

It's because their transistors will overheat like hell and burn out.



On another note, I think the current stungun style circuit I have is a bit overpowered just for ignition, also it costs about £20-30 to make.

I'm going to try and make one half the size now for about £10-15.
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Unread postAuthor: jimmy101 » Wed Apr 22, 2009 1:59 pm

THUNDERLORD wrote:I noticed the small bulb replacements mention not to "use outdoors" and "caution shock hazard"

That is probably because the bulb assembly isn't water tight. Get it wet and create a short to the 120VAC mains and that is more than enough to zap someone. No need for any type of high voltage circuit.

As to the possibility of using the circuitry for an igniter, probably not possible without some modifications. IIRC the "starter" part of the circuit generates 600V-1000V DC from the 120VAC mains. Probably not high enough for a decent spark. And, since it's DC you can't use a doubler, tripler, etc.

Since the source is 120VAC you would have to plug it into the wall.

There are some interesting things in the electronics. Might be a good source of moderate capacitance high voltage caps, high voltage transistors etc. for things like home-brew sparkers.

I'm sure somebody will hack the guts of a compact fluorescent into something interesting. The guts contain a 120VAC to ~160VDC converter, an oscillator (converts the DC back to AC) and a step-up transformer.

Wonder what would happen if you took the high frequency output from one of these circuits and ran it into a flyback transformer? Or automotive ignition coil? Or custom made coil?

There is a pretty good instructible on how to safely open up a typicall compact flourescent:
http://www.instructables.com/id/Take-ap ... cent-Bulb/
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Unread postAuthor: Technician1002 » Wed Apr 22, 2009 2:10 pm

jimmy101 wrote:Since the source is 120VAC you would have to plug it into the wall.


A little more expensive unless you shop Goodwill.. Consider a bug zapper. It has the potted transformer and is current limited to prevent burnout. As a bonus, you could do custom blacklight glow paint.
:D
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Unread postAuthor: Hotwired » Wed Apr 22, 2009 2:22 pm

Well the transformer in a CFB is very easy to disassemble and rewind, it's also reasonably small. If I was making a higher power HV device I'd probably molest that for my first stage transformer (the oscillator which takes the battery voltage up to X volts)

As for the bug zapper, maybe you have a different one but what I have doesn't have a potted transformer and the transistor burns out if you overvolt it without a substantial heat sink.
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Unread postAuthor: Technician1002 » Wed Apr 22, 2009 2:27 pm

Hotwired wrote:Well the transformer in a CFB is very easy to disassemble and rewind, it's also reasonably small. If I was making a higher power HV device I'd probably molest that for my first stage transformer (the oscillator which takes the battery voltage up to X volts)

As for the bug zapper, maybe you have a different one but what I have doesn't have a potted transformer and the transistor burns out if you overvolt it without a substantial heat sink.


In mine it is simply the bulb balast with no electronics. It has an added secondary to feed the zapper grid. The secondary is off to the side with a magnetic shunt like a microwave transformer to limit the shorted current. It is mains powered. There is no transistor, just an old school flicker start starter.
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