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| etlprts |
 Posted: 07/28/2010 11:47 AM Post subject: Ignition Problem |
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Private
Joined: 28 Jul 2010
Posts: 6
23.80 Spud Bux
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Hi,
I've got an issue with my combustion cannon where the ignition will spark for the first couple of goes, but then nothing....
If I then short the ignition pins with my finger, it'll spark again. As I'm still trying to figure the best fuel mixture (it's a hot dog cannon built with a grease trap, so the combustion chamber is fairly small) it's not too easy as I've got to remove the cap on the grease trap everytime to make sure it's sparking.
Does anyone else have this issue, and how do I get around it? Do I need to earth one of the pins?
Thanks
Paul |
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| SpudFarm |
| Posted: 07/28/2010 11:49 AM Post subject: |
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Captain Slow
Joined: 04 Nov 2006
Posts: 2579
1492.77 Spud Bux
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What kind of ignition system are you using?
I am using a camera capacitor and a ignition coil and that have worked great for every gun I have ever built. |
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| etlprts |
| Posted: 07/28/2010 11:52 AM Post subject: |
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Private
Joined: 28 Jul 2010
Posts: 6
23.80 Spud Bux
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I'm using a BBQ ignitor, that's arcing via 2 wood screws (I live in the middle of nowhere so I'm being all low-tech!)
When it fires it's great, but it seems a bit too hit and miss to me! |
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| jor2daje |
| Posted: 07/28/2010 11:56 AM Post subject: |
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Lieutenant Colonel
Joined: 05 Oct 2008
Posts: 416
787.14 Spud Bux
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| What fuel are you using, you could be gumming up your wood screws so they wont spark, and then cleaning them slightly when you put your finger on them. |
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| etlprts |
| Posted: 07/28/2010 12:02 PM Post subject: |
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Private
Joined: 28 Jul 2010
Posts: 6
23.80 Spud Bux
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Hi,
I'm using Lynx (Axe in the rest of the world) deodorant, I'm pretty sure it's not down to dirty contacts, as even with no propelant I'll get 2 or 3 arcs and then nothing.
Cheers
P |
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| ramses |
| Posted: 07/28/2010 12:56 PM Post subject: |
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Major General
Joined: 29 May 2008
Posts: 1517
3974.45 Spud Bux
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it sounds like it's building up a field between the contacts that interferes with the operation of the piezo. When you short them, the voltage becomes effectively zero, and the piezo can function again.
Do you feel any kind of shock when you short it with your finger? |
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| jimmy101 |
| Posted: 07/28/2010 15:59 PM Post subject: |
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Lieutenant General
Joined: 28 Mar 2007
Posts: 2866
11974.95 Spud Bux
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Spark gap distance?
You should be using sharp screws (fine thread drywall screws are excellent) and the gap should be 1/8" or less for a typical piezo BBQ sparker. |
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| etlprts |
| Posted: 07/28/2010 16:18 PM Post subject: |
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Private
Joined: 28 Jul 2010
Posts: 6
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Thanks for all the pointers, there's no shock when I short the points, and I'm using wood screws with around a 60mm gap, it was sparking happily yesterday (and flinging hotdogs happily too, when it wasn't blowing apart!)
I'm wondering if it's something as annoying as humidity, it's felt a bit too clammy for my liking in these parts today! |
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| jimmy101 |
| Posted: 07/28/2010 17:57 PM Post subject: |
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Lieutenant General
Joined: 28 Mar 2007
Posts: 2866
11974.95 Spud Bux
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| etlprts wrote: | Thanks for all the pointers, there's no shock when I short the points, and I'm using wood screws with around a 60mm gap, it was sparking happily yesterday (and flinging hotdogs happily too, when it wasn't blowing apart!)
I'm wondering if it's something as annoying as humidity, it's felt a bit too clammy for my liking in these parts today! |
60mm (2.4 inches)? Doesn't sound likely, do you mean 6mm (0.25")? I would cut it down to about 3mm (1/8") or a bit less. |
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| etlprts |
| Posted: 07/29/2010 0:25 AM Post subject: |
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Private
Joined: 28 Jul 2010
Posts: 6
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Sorry, you're right, I' meant 6 mm! I'll give it another go with 3mm and see where I get to.
Cheers
P |
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| etlprts |
| Posted: 08/02/2010 16:49 PM Post subject: |
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Private
Joined: 28 Jul 2010
Posts: 6
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Thought I'd let you now, it's now working a treat!
I've shortened the gap slightly, it's now around 4mm, but I still need to short the contacts after it's fired.
The biggest difference came from airing the combustion chamber each time. I'm using a sink grease trap as part of the combustion chamber, and removing the bulb from this and airing the chamber whilst loading another hotdog made the thing fire pretty much first time everytime - 15/16 so far.
Thanks for all the pointers, need to find something else to fling now  |
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