Tesla Coil
c. 2002?
If you look closely, you can see a spark between the toroid and the iron rod.
I can’t remember what year it was (sophomore?) but in high school a friend and I found a 50 kV transformer in the cabinets of the physics class room. I’m not sure how we managed to basically play with it unsupervised but we did. At first we used coat hangers to make a Jacob's ladders in various shapes. Eventually we got the idea to make a tesla coil (not sure where) and began researching.
We found great guides online and hit up the hardware store. The primary coil was pretty straightforward and was made of 1/4 “ copper pipe. I don’t remember having to do any tuning. The secondary coil was magnet wire carefully wound around a PVC pipe then coated with several coats of urethane varnish to help fix the wires in place and act as an insulator. The toroid was dryer duct.
The spark gap was just two metal rods spaced apart but we eventually added a fan to blow the energized air away to keep the resistance between the electrodes more consistent. This allowed the circuit to charge to higher voltages in the capacitor bank before jumping the gap.
The capacitor bank took a good amount of trial and error to get working right. The outer electrode was a coffee can filled with brine, the dielectric is a glass jar and the inner electrode is a copper pipe also in brine. Glass is a great dielectric but on our first run the energy just simply jumped arched over the lip of the jar which significantly reduced the capacitance.
We then added vegetable oil to float on top of the brine to act as an insulator but the energy just shot through the oil and arched over the jar again (splashing oil everywhere). Luckily it it didn’t start any fires! Finally we carefully cut styrofoam into disks to cork the top of the jar above the oil and reused the coffee can lids to block the outside of the jar.
That worked great except the energy was so strong that it cracked the glass killing the capacitor. So we made more and put them in parallel to share the load and increase the capacitance.
We brought it to school to demo for our physics class and never had to do homework for the rest of the semester.
The toroid.
The cone shaped primary coil and the tightly packed secondary coil in the center.
The capacitor bank. The outer electrode is coffee can filled with brine, the dielectric is a glass jar, and the inner electrode is a copper pipe also in brine. Those took a lot of trial and error to get right.
The spark gap. We used a fan to blow the energized air away to keep the resistance between the electrodes more consistent.