Tuesday, October 23, 2012

Final Version of SGTC

I made some changes to the coil before tuning and running it again.
First, I replaced the corroded spark gap with fresh pieces.
Second, the size of the coil did not match the tiny size of the previously used topload. I needed more capacitance. Previously, I was unable to find a toroid large enough. That problem has since been rectified. By using a slightly larger tire, I made a stacked toroid.
Final results of my first SGTC are significantly better than the original run.
Now, the streamers created are significantly longer and more visible than the previous version's
Furthermore, ground strikes are now nearly a foot long.


Monday, October 1, 2012

Improvements

Because of the damage suffered by the secondary and the coupling issues due to the helical coil, I decided to  wind a new secondary and switch to a flat spiral primary, solving both problems.

Instead of painstakingly winding it by hand, I used a lathe with its autofeed. The spool of 28 gauge magnet wire unfortunately ran out before I was able to wind a full foot of secondary, so I ended up with a slightly shorter secondary coil. Difference in height is negligible though, tuning the coil should sort out any problems.


The toroid that I used is a scooter wheel wrapped in aluminum tape. This wheel is essentially the same wheel that was used for my previous toroid, only that unnecessarily bulky parts were taken off of this one. This particular toroid is a bit small for the size of the secondary, but considering that I searched for hours just to find something of the appropriate size, I think this one will do just fine.


Using a function generator and an oscilloscope, I was able to measure the resonant frequency to be 560kHz. This is higher than the previous coil, considering the fact that there are less loops in the secondary on this version. Resonant frequency is calculated by 1/2*pi*sqrt(LC), and if L goes up, resonant frequency goes up.


I made 4 small sections of PVC pipe to use as a holder for the primary coil. The primary wire has 8 turns maximum, and when finished, will be tappable each half turn.


The end product of all that winding looks like this. It's not circular, but Ampere's law should still hold.



Saturday, September 15, 2012

Tesla Coil!

This is my first blog post ever. But might as well jump right in.

The current project I am working on is, contrary to what the title of this blog may insinuate, a Spark Gap Tesla Coil. Tesla Coils are famous for their awesome ability to produce beautiful arcs of plasma that resemble bolts of lightning. Because of this effect, Tesla Coils are often described by laymen as "lightning machines."

The Tesla Coil is essentially an air core resonant high voltage transformer, wherein two loosely coupled LC circuits cause a massive voltage to build up on the secondary circuit's capacitor due to an effect known as resonance. The first LC circuit, the primary circuit, is connected to a high voltage transformer and has a spark gap running in parallel with the primary coil. The high voltage transformer charges the primary (tank)capacitor, whose voltage builds up high enough to ionize the air in the spark gap. This effectively forms a LC circuit. The energy stored in the LC circuit oscillates between the inductor and capacitor at its resonant frequency. Because of the loose coupling between the two circuits, some of the energy is transferred to the secondary each oscillation, and because the two have the same resonant frequency, this effect happens every single cycle, building up the secondary voltage until the electric field on the secondary's capacitor is too great, and an sparks start flying.

The coil that I am currently working on was initially completed before before this blog.
This coil ran on a Neon Sign Transformer with a output voltage rating of 7500 V and a current rating of 30mA. The tank capacitor is a MMC created with 10 Cornell Dubiliers each rated for .15 microfarads and 2000 volts. The resonant frequency of the LC Circuits are 265 KHz. The primary coil is 15 winds of 14 gauge wire of a helical coil.

Unfortunately, there were some serious design oversights in the first construction of this coil. The first, and most egregious of these was that I accidentally grounded my secondary coil through the windings of the primary. The second problem is that thee helical coil overcoupled the two LC circuts. The secondary coil was also badly insulated. These problems led to both primary-secondary arcing, and racing sparks.

Because of these problems, I am currently in the process of redesigning and recreating the coil.

Updates soon!