Spark Gaps: Some food for thought

[Pilgrimman]

I have read that spark gaps that use points as opposed to flatter surfaces such as spheres tend to produce longer sparks. I am wondering if it'd be practical to use extremely pointy metal objects to increase the spark length. For all you drug addicts, you might use your spare syringes! What I'm unsure of, however, is whether a technique such as this would have a noticeable effect on the length of the spark, or is the improvement marginal?

[shud_b_rite]

I think this is only the case with static electricity. Because a sphere or pointy surface has much more space for charges to gather on it is more likely that sparks will be attracted/emitted from it. I dont think this increases the length of a spark (the length still depends on voltage) it is just a way of getting the spark to go where you want it, this is good for a lightening rod

[jimmy101]

The breakdown voltage between two eletrodes is a function of the radius of curvature of the electrodes. Pointy electrodes will spark at a lower voltage than will blunt electrodes.

So, Pilgrimman, you have it backwards. To get the longest spark possible you want dull electrodes. The optimal shape would be a big-ass sphere like those used in van der Waal generators.

But, the length of the spark probably doesn't affect the perfromance of the performance of a gun all that much. At, least with reasonable length sparks. 1/16", 1/8", 1/4", 1/2" probably all work about the same.

Of course, if you could get a 10" spark that might be useful. The tricky part with a very long spark is keeping it from sparking through the wire insulation, between connectors, though the PVC, to you ...

EDITED 17 Oct, 07, the para highlighted is backassward.
Pilgrimman was right, sharp and pointy to jump the longest possible gap at a given voltage.

[psycix]

I think a pointed electrode allows for a longer spark distance because of the electric field aroud the point.
The field will concentrate on that one point when using a needle and thus make it easier for electrons to jump over.
When using flatter electrodes like spheres for example there is only a weak electric field around the whole sphere.

[Pilgrimman]

@ jimmy

I know it won't affect performance normally, but I thought this might prove useful for hybrid ignition, since the maximum spark length shortens under pressure. The reason I posted it here is because I figured there might be more replies, as combustions could use the technique, and hybrid builders have usually dealt with this type of situation.

[jimmy101]

@ jimmy

I know it won't affect performance normally, but I thought this might prove useful for hybrid ignition, since the maximum spark length shortens under pressure. The reason I posted it here is because I figured there might be more replies, as combustions could use the technique, and hybrid builders have usually dealt with this type of situation.

Yep, it'll be much easier to get a spark in a hybrid with pointy electrodes than with blunt ones.

[jimmy101]

I think a pointed electrode allows for a longer spark distance because of the electric field aroud the point.
The field will concentrate on that one point when using a needle and thus make it easier for electrons to jump over.
When using flatter electrodes like spheres for example there is only a weak electric field around the whole sphere.

I reread my previous post and psycix is correct. When you want to get a spark you use pointy electrodes. When you don't want to get a spark you use spherical electrodes.

Pointy electrodes will spark across a larger gap at a given voltage then will spherical/dull electrodes.

[Pilgrimman]

I thought so, but I wasn't sure, and I wasn't going to question someone with 4x my post count! So, what's the consensus? Would using syringes or similar increase max spark lengths at a given voltage? I'm leaning towards "yes", but I'd like others perspectives based on the above posts.

[jimmy101]

Yes, using a syringe needle would increase the spark length, or decrease the voltage required for a given spark length.

Instead of syringe needles I would just use sewing pins. They are sharper and cheaper.