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Spark generators

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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Spark generators

Unread postAuthor: broken_system » Mon Jan 11, 2010 11:28 am

Hey guys,
Just wondering about something. If you wanted a setup that did not require batteries or replaceable flints or piezo crystals, how else can you create a spark?

Does anyone know how those hand-wind flashlights charge by the cranking motion? My idea is that if you can add in manual labor, then allow that energy to be collected, you could probably create a spark sufficient enough for combustion withought having to replace anything other than fuel/air.

If the above is true then could it not be possible to store this energy in a spring, then by "pulling the trigger" so to speak, release the spring, which generates electricity then at the end releases it into a spark?

Any info would be great thanks guys.
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Unread postAuthor: jimmy101 » Mon Jan 11, 2010 11:53 am

Hand cranks generate fairly low voltage.

So you would need a capacitor that the generator charges up.
A suitable switch.
A high voltage coil to convert the low voltage high current from the cap to a high voltage low current spark.

Hardly seems worth the effort when you can often get a piezo for less than $5, or a stun gun for less then $20.
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Unread postAuthor: broken_system » Mon Jan 11, 2010 11:56 am

Its not a question of price really, its more a question of convinience. I found a couple articles on electromagnetic power generation and it seems like it can be done, if nothing else just to be different :)
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Unread postAuthor: psycix » Mon Jan 11, 2010 3:50 pm

I think a battery is more compact than your hand crank system, and a battery should last more shots than you usually fire.
On top of that, what's more convenient than "push button -> spark"?
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Unread postAuthor: jrrdw » Mon Jan 11, 2010 4:30 pm

I think you want something like you see in the movies when a soldier turns the handle boom the charge goes off. Something like that?
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Unread postAuthor: Skywalker » Mon Jan 11, 2010 4:33 pm

peizo is by far the most effective way of converting mechanical work into high-voltage electricity. Probably more efficient is frictional generation of static electricity, but that's cumbersome and unreliable.

The hand-crank flashlights all use a small, low-voltage (3-5V?) dynamo to charge a battery or capacitor. I suppose you could hack one of them together with a disposable camera's flash circuit, that'd get you up to 500 V or so.

you ought to check out those old dynamite plunger boxes: the thing that they use in cartoons to set off dynamite with. I think they had some kind of high-voltage dynamo inside. As you say, you might be able to replicate one of those by using a large spring to spin the shaft of a little flashlight dynamo. Hmm, tell me what happens with this!
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Unread postAuthor: Zeus » Mon Jan 11, 2010 9:45 pm

The turntable motors from microwave ovens output about 1kv which can
be fed into a CW multiplier to make upwards of 5kv which will cause ignition. Google cockcroft-walton voltage multiplier.
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Unread postAuthor: D_Hall » Mon Jan 11, 2010 10:01 pm

jrrdw wrote:I think you want something like you see in the movies when a soldier turns the handle boom the charge goes off. Something like that?


Which, of course, don't use high voltages and really, haven't even been made in probably 30 years.
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Unread postAuthor: broken_system » Mon Jan 11, 2010 10:54 pm

Thanks for all the input guys! Ive been doing some reading that was suggested and trying to come up with ideas.

For the time being though I meant to ask you guys about the sizes of piezo crystals and how many impacts they can withstand until needing replacement. For my use I could be firing up to 500 shots per use of the cannon.

As a side, with around 500 shots potentially being shot with my smaller, high rof cannon, I need an ignition source that won't require battery changes every 2 minutes.
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Unread postAuthor: Solar » Tue Jan 12, 2010 4:40 am

How about going old school and using a flint? No electricity needed!
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Unread postAuthor: jimmy101 » Tue Jan 12, 2010 3:31 pm

Skywalker wrote:The hand-crank flashlights all use a small, low-voltage (3-5V?) dynamo to charge a battery or capacitor. I suppose you could hack one of them together with a disposable camera's flash circuit, that'd get you up to 500 V or so.

That'll get ~300V DC and a 5~10KV spark. Just wire the hand generator across the two battery terminals. The flash board should handle up to about 3V DC input. More than that and you risk frying something. A 1.5 to 3V zenier diode would be a simple (and cheap) way to limit the input voltage. (Instead of a zenier you could use 2 to 4 standard diodes in series.)



A piezo should last for 500 shots. But you need to insure that it is being struck properly. Hit it too hard, or hit it when it isn't properly supported, and it will crack.

For a large number of shots I think your best bet would be a battery operated BBQ igniter. Swap the AA (?) battery(ies) for Cs or Ds. That'll give you a much longer battery life.

A stun gun is also a possibility but it would also need more battery capacity and it would be a good idea to add a heat sink to a couple of the internal components. Stun gun are not designed for continuous firing of more than a few seconds. Stun gun don't last forever, what do you expect from something that cost less than 5$ to make.
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Unread postAuthor: rcman50166 » Tue Jan 12, 2010 3:35 pm

Hank cranked HV? No problem

[youtube]http://www.youtube.com/watch?v=KidNSdGqaFE[/youtube]
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Unread postAuthor: Zeus » Tue Jan 12, 2010 7:39 pm

Remember those dynamos put out 100mA (and that's optimistic) and camera flash boards draw over an amp. So it could be done if you put
a rechargable AA cell in and used the camera flash board to charge a capacitor which is discharged into a pulse coil which in turn ignites your
fuel mix. It sounds complicated but it isn't. If you like I can PM you some details in the next day or two.
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Unread postAuthor: rcman50166 » Wed Jan 13, 2010 4:35 pm

I thought the idea of the thread was to think of ways to get HV sparks without using batteries or piezoelectric ignitors. If batteries are involved I'd reccomend a Marx generator.
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Unread postAuthor: ramses » Wed Jan 13, 2010 4:38 pm

I'll be honest, an igniton coil kind of sucks for ignition. It gives you a beastly hot spark, but it takes quite a while to recharge. If you replaced the cap with a 10uf one, that would improve cycling by a factor of around 10-20. The majority of the energy in the capacitor is wasted saturating the core.

I would suggest an electronic bbq ignitor, stun gun, or purpose built device from one of the sponsors.
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