Effect of humidity on spark gap

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Postby SpudBlaster15 » Sun Feb 25, 2007 7:28 pm

Well, it is cold and dry up here in Canada, and I have been noticing an issue with my combustion launcher lately. I use a piezoelectric grill igniter as an ignition source, and it hasnt been working properly in the dry air. The current produced by the igniter will not jump my spark gaps, unless I blow into the chamber, effectively increasing the humidity a fair amount. When I do this, an arc occurs on every attempt, and this condition will maintain for upwards of 20 seconds, until the moist air is displaced by dry air. Has anyone else had a similar experience, and does my theory involving humidity sound like a plausible expanation as to what is occuring?

Thanks.
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Postby BillyBobJoe » Sun Feb 25, 2007 7:38 pm

Seems plausible to me - higher humidity lowers the dielectric strength of air. Its interesting to note that Van der Graff generators and other static producing devices don't yield as much of a spark length in humid weather, as humidity and slight water deposits on insulators essentially shorts out such low current (static dependent) devices.

This is obviously not the case here, and can (as you would assume) be fixed by moving the eletrodes closer together.
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Postby spuzi14 » Sun Feb 25, 2007 8:44 pm

What's your chamber made of?
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Postby SpudBlaster15 » Sun Feb 25, 2007 9:30 pm

Thanks for the reply, BillyBobJoe.

The chamber is made of ABS pipe, though I dont see how that would effect anything.
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Postby TurboSuper » Sun Feb 25, 2007 10:16 pm

I would think that the addition of particles in the air increases electrical conductivity.

I've always figured that you get so much static in the dry air since it can't discharge as easily as in humid air.


I could be horribly wrong though[:p]
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Postby spuzi14 » Sun Feb 25, 2007 10:21 pm

<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote">The chamber...anything.<hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">

I was making sure your chamber wasn't something like metal.

Where are the screws located? Toward the cap or toward the barrel?
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Postby An Apple Pie » Sun Feb 25, 2007 10:22 pm

Yes that is true. I just remember that static electricity slowly goes away due to the water droplets in th air. So the more humidity, the faster the charge goes away.
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Postby randomvictim » Tue Feb 27, 2007 9:06 am

That wouldn't apply to a piezoelectric sparker. For the microsecond that the charges would actually be traveling in the wires leaking charge is insignificant. What is important is the dielectric constant of the air.
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Postby Sardaukar » Tue Feb 27, 2007 9:49 am

Can you shorten your spark gap? That would solve the problem.
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Postby aturner » Tue Feb 27, 2007 10:16 am

I agree, it sounds like this problem is related to the humidity.

When setting up spark gaps, I recommend finding the maximum possible gap, and then reducing this gap in order to improve consistency. The most annoying thing is when you've got to keep clicking the button on a piezo.
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