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Spark Gap

    The spark gap is the make or break part of a Tesla Coil, it is what times allows the tank circuit to resonate, and a poorly tuned SG will lead to a poorly working Tesla coil.  It is essentially a high frequency switch, allowing the amps to flow when it is on, and shutting off when they are to low to effectively transmit energy.  There are several types of spark gaps employed by Tesla coilers, single static, multiple static, synchronous and asynchronous rotary, and other stuff way to fancy to mention here.  Single static is by far the most simple, it consists of two electrodes, between which an arc is formed.  When the voltage potential gets high enough in the capacitors, the energy is discharged through the gap allowing tank oscillations.  In theory (and only in theory), it only discharges when the caps are fully charged.  It is tuned simply by adjusting the length of the gap, and often forced air, vacuum, or a magnetic field is used to promote proper quenching (which means it will stay unlit at the earliest notch possible).  Multiple gaps are better, as the heat is shared by several different surfaces, so cooling and quenching is easier.  I have never personally had good luck with multiple gaps, but virtually everybody else has, so try it.  Rotary gaps are next, there are two kinds, synchronous and asynchronous.  An asynchronous gap causes the firings to occur at a regular time period regardless of the voltage of the capacitor.  This means more consistent firings, and more even power put into the coil.  a synchronous gap does the same thing, but fires at a fixed interval with the current supply frequency.  The result is, assuming you phased the gap correctly, that you get maximum possible energy per bang, as the tank cap is always at max charge.  Phasing refers to the time in the cycle the gap fires, proper phasing is at the peak of the supply voltage, for a 120 BPS sync gap (or 100 in Europe).  You can also configure a sync gap to fire at other levels, like 240, or 480 BPS, whether this advantageous is dependent on a lot of variables, so you'll need to experiment.  Here are some gap pictures.
spark gap bolt style

this is my first spark gap, a simple two bolt arrangement, it sits atop the OBIT powering it, the capacitors are in the upper left, see the foil?
sucker gap sort ofsucker gap colse upsucker gap blower
sucker gap squirrel cage
This is called a Marx gap or "sucker gap" only mine doesn't suck, it blows (don't snicker, it's true).  The blower is a modified jobby built primarily by my cousin Jason (thanks a million).  Air is forced through the narrow opening between the two copper pipes, extinguishing the arc, I have used this gap with both my small and large TCs with good success.
experimental asynch gapmore of the same

This is my first experimental rotary gap, I never used it because it had serious construction issues, but it was still neat, so I decided to put it here.
SRSG backSRSG front
This is my best synchronous rotary spark gap, laboriously crafted by my cousin Jason and I, it is switchable between 120 and 240 BPS, and has an optional quenching gap, and a safety gap for over voltage protection.  It is the finest gap we have made to date.

Home, Hobbies, Tesla Coil.
Scott Bogard. 2007