Hi all,
Yes, neon sign transformers (NSTs) are designed as cheaply as possible for supplying a current limited source of high voltage for excitement of gas discharge tubes. Although they are pretty much "the transformer of choice" for powering small to medium sized spark gap fired Tesla coils, this type of service is most certainly outside of their design envelope. Coilers have been able to work around the fragility of NSTs through permanently set Richard Quick (RQ) style stationary spark gaps (SGs), triggered SGs, or synchronous rotary spark gaps (SRSGs) with a larger than resonant (LTR) primary capacitor. Opening a stationary SG too wide or running the coil with an asynchronous rotary gap is pretty much a sure fire way to kill an NST PDQ, though!
Variable speed asynchronous spark gaps (ARSG) work great for larger Tesla coils that are powered by a more robust high voltage transformer, i.e. pole pig or PT, but the disadvantage to running with these types of transformers is that they are quite heavy, they are often expensive and/or hard to get and they require external ballasting, which adds additional cost and weight. And let's not forget the lethality of these types of transformers if you get careless and let it "bite" you! Also, the rotary gap assembly itself necessarily becomes more robust and co$tly for larger, higher powered systems. So you can end up with a real money pit of a system with a control panel/cabinet that weighs multiple hundreds of pounds, if you try to incorporate all of the power and control components into a single control panel unit. As an example, the control panel that I built for my big pig powered coil (Green Monster) is an old-style 24"x 32" deep x 72" tall server rack that houses a 10 kVA pole pig (~ 250#), a 4-stack 1256D variac (~280#), and a homemade ballast that weighs about 100# by itself, plus all of the control circuitry components and items for mechanical reinforcement. As a result, this behemoth cabinet/control panel weighs an estimated 1000 to 1100 lbs and the Tesla coil tank circuit itself probably weighs another >250 lbs! I have the control panel and the Tesla coil tank circuit assembly each mounted on heavy duty casters, but it is still quite a task for me (~210#) to roll around the half-ton control panel cabinet on a hard flat surface! Its definitely fun to watch the beast spew out those white-hot 12+ footers, though ;-)
Bottom line, if you want really big sparks, you're gonna have to have some really big hardware. ;-) Dual resonant solid state Tesla coil systems (DRSSTCs) are becoming ever more popular amongst the coiling community due to their elimination of the need of bulky high voltage transformers, ballasting, SGs and large high voltage pulse capacitors, as well as more fine control of the output spark characteristics, but they are also much more complex (and more fragile) and require more sophisticated test equipment and knowledge to build than the classic SG driven system, and larger versions of this type of coil system are also very co$tly and become quite cumbersome as well if you're wanting those monster >10 ft. sparks!
David
robert massa <massahbob@xxxxxxxxxxxxx> wrote:
>asrg doesn't work for nst's. srsg is the only way for nst's. IMHO, BOB
>
>
>On Tuesday, September 16, 2014 8:26 AM, Brian Gray <armagetto@xxxxxxxxx> wrote:
>
>
>
>Noob coiler here, putting together components for a 15kv NST SGTC and was
>wondering if a $4 Radio Shack resin perfboard would be okay for my terry
>filter? I've noticed a few people using higher quality (or at least I
>assume higher quality) fiberglass perfboards and I wondered if it was maybe
>because of potential heat issues with the bleed resistors or something like
>that.
>
>Brian Gray
>Armagetto@xxxxxxxxx
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