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piezo ignition depletes ?

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piezo ignition depletes ?

Unread postAuthor: ozoncqp » Tue Mar 31, 2009 1:22 pm

I apologize if this has been up before. But i just spend 45mins browsing wikipidia, and this forum to find anything about my problem.

I got this lovely piezo ignitor, its been working for the around 500shots in my beta cannon. Just by having 2 electrodes it does spark from anything in between .1-15mm.
However as im making a new cannon I want to make a sparkstrip, just to get 2 sparks.
Im making both the chambershort and the sparkstrip. (depends what works the best.)
The electrodes on the strip is 2mm stainless TIG welding rods, the gap is 4mm between all 3 electrodes. And the spark is powerful and yummy.
But fast clicking makes it fail. If I only click every say 15-20secs theres no problem.
So my question goes, can the crystal inside the piezo deplete ? if I just hold it in my hand clicking it I get shocks all the time. So its not broken, and the 2 wires are seperated aswel
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Unread postAuthor: jimmy101 » Tue Mar 31, 2009 1:48 pm

Nope, a piezo element never "depletes". What does "deplete" is the spring and escapement mechanism. Over time the mechanism will wear and sometimes it'll quit working.
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Unread postAuthor: ozoncqp » Tue Mar 31, 2009 1:58 pm

Hmm strange then, its as if it has to recharge before working again.
However i changed the electrodes on the strip with 4 very thin copper plates. Making 3 sparks with 4mm gaps. sparks during quick clicking. Time to glue em on and see how it works tomorow.
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Unread postAuthor: psycix » Tue Mar 31, 2009 2:18 pm

No the crystal cannot deplete. Besides wearing down the mechanism, it is possible to break the crystal, making it unfunctional.
But fast clicking makes it fail. If I only click every say 15-20secs theres no problem.

I have the idea that the crystal has to get back into its shape in order to be stroke again, and that takes some time.
I once had a "squeeze" sparker and when fully squeezed it came back slower, making sparks. If you really need to stop this problem I'd short the wires. When the current is allowed to flow, the crystal can go back to his original shape.

BTW:
Your spark gaps should be shorter then 4mm, especially with three gaps.
Make them as short as possible.
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Unread postAuthor: Biopyro » Tue Mar 31, 2009 2:24 pm

I think the TOTAL gap is 4mm.

I have heard before that the crystal needs to return to it's original shape, so you're probably right on that one.
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Unread postAuthor: ozoncqp » Tue Mar 31, 2009 2:26 pm

Oh i had the undestanding that as many big sparks as posible. oh well ill reduce em by 2 mm each then
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Unread postAuthor: psycix » Tue Mar 31, 2009 3:11 pm

Nope, as small as possible. A spark is a spark, and thats an ignition point, if you can see the spark, it is (way) powerful enough to ignite the mix.
Longer sparks have no benefit, they just make it harder for your spark system.

Changing the piezo's shape creates an voltage between some sides of the crystal. When current is allowed to flow, the crystal deforms easier.
Now when the piezo goes back to its original shape, it is going to deform again, which produces a voltage, but now in reverse.
If you short it out, it can let current flow and it can go back to its normal shape. If you do not do that, the crystal will simply leak the current through himself, which takes longer.
On some occaisions this can also produce a spark. I had a lighter which produced 5 sparks on press in, and 5 on release. However, when I enlarged the spark gap, the amount of sparks reduced, and when shorting it (infinite amount of sparks) the thing was far more easy to squeeze.
Though most piezo igniters work with a hammer system, and not with a squeeze system.
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Unread postAuthor: ozoncqp » Tue Mar 31, 2009 3:40 pm

Yeah mine is the hammer/stencil? system. It sparks when I press/click it down, and the spring makes it popup again.
Think I sorted it now. Lucky for me I read the shorter gap before I applied the glue. Running 3 gaps of 1.5mm.
Dunno I just had the idea that longer sparks was better. But then again the piezo from ligthers can ignite so I am just not thinking straight today.
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