Original poster: "Gerry Reynolds" <gerryreynolds@xxxxxxxxxxxxx> Hi Curt,You and many others have wondered this so it is a good question. The short explaination is there are two components to the charging waveform. The steadystate response (60Hz waveform) and the transient response. This is the natural response created each time the spark gap fires. The transient response has frequencies related to the equivalent inductance of the NST and the Cp that is being charged (not the resonant frequency of the TC primary that occurs only during SG conduction). For LTR Cp's this is a lower frequency then 60 Hz. The total voltage presented to the sparkgap (when the SG is open) is the sum of these two responses. When this voltage get to the breakdown voltage of the spark gap, the spark gap fires. At any given moment in time, there may be many transients remanding from previous SG firings so it is somewhat unpredictable. The best way to see the behavior is with a computer simulation. The end result is there may be half cycles that have no firings and half cycles that have multiple firings (easy to see in a simulation). I have even seen both behaviors in the same setup at different points in time. The spark gap can and will fire even if the gap breakdown voltage is significantly higher than the open circuit voltage of the NST. All that is needed is for the transcients to add up with the steadystate voltage at a given point in time to reach the breakdown voltage of the gap.
Given the above, one can see how the BPS can be higher or lower than 120. Any value (within reason) of BPS can result and it is the average BPS that we mostly care about at a given Cp and spark gap setting. One can also see how important it is to properly set the safety or main gap to prevent overvolting the NST.
Gerry R.
Original poster: "C. Sibley" <a37chevy@xxxxxxxxx> In a discussion today I realized that I can't explain some assumptions I've accepted regarding static spark gaps. I've run a lot of designs through JAVATC and have accepted that the break rate increases as current increases (assuming all other things remain same). Depending on the current available the capacitor charges quicker and the break rate goes up. What I can't come to terms with is break rates in excess of 120Hz. Wouldn't the 60Hz input limit the break rate to 120Hz for a properly set gap? Based upon experience I realizes there must be more going on than just a simple RC circuit charging a capacitor. Am I missing the point? Thanks, Curt.