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Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
i have built myself a spark gap, as the crappy temp ones made out of what ever was available were getting to be too dangerous.
so i built this:
my question is this, how can a approximate the breakdown voltage...
do i use Paschen's law? Or just the 3MV per meter rule? my spheres are 0.625 inches dia. But when i look up the data tables i see them using 2 inch dia. spheres, does this matter?
EDIT: Jim Lux's HV handbook appears to not have his "sphere" table link working...
from HV wiki i see 30kV/cm. for spheres, DC... but it mentions nothing on radius.
Registered Member #834
Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644
30 kV/cm is when the spacing is much smaller than the radius. This formula works: Vbreakdown = E*4*d/(d/R+1+sqrt(sqr(d/R+1)+8)) E=30000 V/cm d=gap spacing in cm R=ball radius in cm
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Antonio wrote ...
30 kV/cm is when the spacing is much smaller than the radius. This formula works: Vbreakdown = E*4*d/(d/R+1+sqrt(sqr(d/R+1)+8)) E=30000 V/cm d=gap spacing in cm R=ball radius in cm
Excellent, once again antonio you save me! I was wondering if the HVwiki article meant flat plate distance ?
UPDATE: This should be easier on the eyes...
I hate ASCII math anyways... (Wrong dont use this!)
EIDT: i think i did it wrong im getting numbers which are way to big... i see it now, goofed it.
i think this is right now...
For a radius of 0.79 cm, a gap of 6cm, im getting 41 kV...
Registered Member #834
Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644
Paschen's law applies to very small gaps, where the breakdown voltage appears to rise when the gap is reduced. The essential effect is that if you find a breakdown voltage smaller than about 300 V the calculation is not valid. No sparks occur below ~300 V, no matter the distance.
For a radius of 0.79 cm, a gap of 6cm, im getting 41 kV... Correct. 40808.7 V by the formula. It's useful to add a scale to one side of the gap.
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a question about spark-gaps...
