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mini hybrid win!

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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Unread postAuthor: saefroch » Mon Apr 04, 2011 9:22 pm

So to us, is the issue with using a piezo that it produces very little energy with a tiny current at very high voltage, and the inefficiencies in most transformers is so great there won't be much charge? My response to that is: "So what?" You only need a spark, just one discharge of any current, just at a high enough voltage that the low current doesn't suffer from the resistance of the mix too much.

Current research shows that closed-core and shell-core transformers actually have very high efficiency, though that seems wrong somehow.
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Unread postAuthor: JDP12 » Mon Apr 04, 2011 9:24 pm

define high efficiency though. A high number, or a high efficiency for what they do? For instance.. for a coilgun..8% efficiency would probably be considered high.
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Unread postAuthor: saefroch » Mon Apr 04, 2011 9:26 pm

I saw 98% on Wikipedia...
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Unread postAuthor: Zeus » Mon Apr 04, 2011 9:29 pm

You need current to produce heat in the air, an arc does have some resistance, the higher the current the more heat produced.

That's why you can't have very little current in an arc for ignition, piezos make some heat, but if you step up the voltage the current is reduced.

I've no doubt a transformer could be made for such a purpose, but it would have to be tiny. Look up saturation in transformers. You need some current to magnetise the core, once that happens then they are remarkably efficient.

98% is a little high, more around 90% for easily available transformers.
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Unread postAuthor: saefroch » Mon Apr 04, 2011 9:57 pm

But if you can generate enough voltage potential, you can create a spark off very little current, right? Honestly, how much current can there be in those millions of sparks I see flying off my flannel clothing at night...

I'm personally thinking of trying this if I can get my hands on a grill igniter, because it's not like a transformer is terribly hard to build... In any case, I have the transformer core from an old battery charger that I knew would come in handy, so I figure I may as well try it.

So you're saying that the biggest issue with transformer efficiency is reaching, but not exceeding the saturation point of the ferromagnetic material?

Would B=u<sub>o</sub>*u<sub>r</sub>*(u<sub>o</sub>*N*I/2r) work to calculate the strength of the B-field in the material?
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Unread postAuthor: Crna Legija » Mon Apr 04, 2011 10:02 pm

what about a car ignition coil, i have one but don't know how to get it to work. i can try zap it with a mini pezo..
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Unread postAuthor: JDP12 » Mon Apr 04, 2011 10:15 pm

yea people use those.. only problem is the whole assembly is extremely bulky.
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Unread postAuthor: Zeus » Mon Apr 04, 2011 10:17 pm

Thing is, voltage doesn't ignite stuff, current does. There will be so little current when you run a piezo through a transformer, it just won't have the heat to ignite anything.

I wouldn't expect anything from connecting a piezo to a ignition coil, the saturation current would be too high.

Try it by all means though, just because I say something won't work doesn't mean it won't.

Regarding that equation, I frankly don't know, I've never worked with such things, I only know what I do from electronics.

The core from a battery charger would need way more current to work, and it's got to be the right material too (iron for low frequencies, powdered iron for around 1kHz up, and ferrite for andthing else above that).
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Unread postAuthor: saefroch » Mon Apr 04, 2011 10:33 pm

I'm just looking for portability, partially because of the suggestion that JSR convert a hybrid into a hand-held, and because I'm looking for an alternative to the normally incredibly bulky hybrid ignition systems. I have a coil wrapped, 1 turn in the primary, 12 in the secondary. I replaced the bare copper wire that was originally around the transformer core in a battery charger with insulated black copper wire. As soon as I can get a piezo, I'm going to try it out.

EDIT: Friend's calipers say spark gap is .2" with transformer, and .208" without. Then again, that could just be my measurement error. Any ideas on how to verify if this is actually an improvement?

EDIT AGAIN: Even if the spark gap is the same, I did notice however that the normal thin blue line which you are probably all familiar with became a much thicker purple bolt with the transformer. I'll try to get pictures tomorrow, it's midnight right now.
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Unread postAuthor: jackssmirkingrevenge » Mon Apr 04, 2011 11:58 pm

saefroch wrote:I'm just looking for portability, partially because of the suggestion that JSR convert a hybrid into a hand-held, and because I'm looking for an alternative to the normally incredibly bulky hybrid ignition systems.


As stated before, a cigarette lighter piezo was enough to reliably ignite a 16x mix given a small enough spark gap. I imagine a BBQ piezo being slightly bigger is probably capable of more. One thing you would definitely need to include is the facility to change the piezo as they tend to break after a while.
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Unread postAuthor: Labtecpower » Tue Apr 05, 2011 6:58 am

I'm thinking about changing my 6 mm gun to a piston hybrid.
I guess I have to make an airtight piston?

Does anyone have experiences with power of stuff like this?
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Unread postAuthor: Crna Legija » Tue Apr 05, 2011 7:19 am

Labtecpower wrote:I'm thinking about changing my 6 mm gun to a piston hybrid.
I guess I have to make an airtight piston?



thats what im worryed about if i make one out of a 1/8''qev, the piston is only air tight one way so i can't add pressure behind the piston to increase opening pressure.
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Unread postAuthor: jackssmirkingrevenge » Tue Apr 05, 2011 7:25 am

Labtecpower wrote:I'm thinking about changing my 6 mm gun to a piston hybrid.
I guess I have to make an airtight piston?


Mymini-piston hybrid had an airtight piston but with an equalisation hole.

If i make one out of a 1/8''qev, the piston is only air tight one way so i can't add pressure behind the piston to increase opening pressure.


... but you can add a spring ;)
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Unread postAuthor: Crna Legija » Tue Apr 05, 2011 7:52 am

jackssmirkingrevenge wrote: If i make one out of a 1/8''qev, the piston is only air tight one way so i can't add pressure behind the piston to increase opening pressure.


... but you can add a spring ;)[/quote]

not really theres no room behinded the piston it move only about 2mm.
maybe if i made something like:

edit: if the there is 0.310 square inches of piston face exposed and say 130 psi in the chamber, how do i calculate the pressure on the piston?
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and thread it into the pilot of the qev, it would be a spring and pilot all in one.
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Last edited by Crna Legija on Tue Apr 05, 2011 8:19 am, edited 1 time in total.
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Unread postAuthor: jackssmirkingrevenge » Tue Apr 05, 2011 8:13 am

That might work but I would be concerned about the fact that there is a small contact point with the piston that would push the rod through it on firing.
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