Paper Clip Safety Spark Gap?
Chris Maness, Mon Jul 13 2015, 05:45PMI am getting my commercial HV caps today. My JavaTC spec says the caps will see 15kV, and to use caps rated for 35kV. I am thinking a 20 or 30kV gap made from paper clips would be good to protect them. What is the proper spacing for the fairly sharp edges of a paper clip for a gap? I know 50kV/in is a good rule of thumb, but not sure about sharper objects.
Thanks,
Chris
Re: Paper Clip Safety Spark Gap?
Ash Small, Mon Jul 13 2015, 07:12PM
Generally, because you can't predict exact breakdown voltage, it's 'experimental method'. Start with a small gap, and open it up until it's right.
You can use a capacitive voltage divider to get an idea of actual voltage, depending on what you have available.
Maybe others can add to this?
Ash Small, Mon Jul 13 2015, 07:12PM
Generally, because you can't predict exact breakdown voltage, it's 'experimental method'. Start with a small gap, and open it up until it's right.
You can use a capacitive voltage divider to get an idea of actual voltage, depending on what you have available.
Maybe others can add to this?
Re: Paper Clip Safety Spark Gap?
loneoceans, Fri Jul 17 2015, 08:44PM
This this a conventional spark gap coil? If you're using a 15kV NST the peak voltage is sqrt2*15kV. In any case, I think it's probably a better idea to use something more robust than paper clips which after a few firings will probably melt. A cheap solution is to simply use brass bolts as the electrodes and round end-caps as the spark electrode.
This will also allow easy fine adjustment of the gap distance. For the actual spark gap you'd want something that quenches better, such as one made from an array of parallel copper pipes. To adjust the safety gap, I usually slowly open up the gap until it no longer sparks across when connected to the NST, and then go back just a little bit. The actual spark gap can be set to have a total breakdown voltage slightly less than the safety gap.
loneoceans, Fri Jul 17 2015, 08:44PM
This this a conventional spark gap coil? If you're using a 15kV NST the peak voltage is sqrt2*15kV. In any case, I think it's probably a better idea to use something more robust than paper clips which after a few firings will probably melt. A cheap solution is to simply use brass bolts as the electrodes and round end-caps as the spark electrode.
This will also allow easy fine adjustment of the gap distance. For the actual spark gap you'd want something that quenches better, such as one made from an array of parallel copper pipes. To adjust the safety gap, I usually slowly open up the gap until it no longer sparks across when connected to the NST, and then go back just a little bit. The actual spark gap can be set to have a total breakdown voltage slightly less than the safety gap.
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