RPI E-Club Tesla Coil History
(A detailed history of this particular Tesla coil)
A Tesla Coil Story: In 2005, Alex Patsos and I were senior Electrical Engineering students at RPI. Being the EE geeks we are, we didn't just study our subject... we lived it, as part of the Electronics Club, a rag-tag group of scroungers/hackers/builders -- in retrospect, it was a community of Makers, though that name hadn't become popular yet. (MAKE magazine had just published their first issue in January of that year.) So, it was finals week, and instead of studying, we were doing some high voltage tinkering and realized the club had [nearly] all the parts to construct that most mythical and famous of high voltage devices, the Tesla Coil.
Long story short, Alex and I spent the week before graduation (including a couple of sleepless nights and long days in the shop) building (and then tuning) a pretty respectable coil -- I recall being especially satisfied with its performance considering it was built largely from scrounged parts. I've attached a picture of the first night we really got it tuned properly (captured by the incomparable Andrew Armenia) --the evidence of our all-night Tesla coil tuning binge becomes apparent when you realize the cardboard sheets insulating the capacitor strings (white cylinders, bottom left) from the metal slats in the floor were the remnants of the pizza boxes that had fed us earlier that night. The only major changes made from that picture to the present was the mounting of all the components on our own wheeled cart, and the shielding of the spark gap inside a black plastic box (it's light is otherwise fairly blinding -- that's what illuminates the left half of the room in the picture).
The "E-Club coil" was known for its regular appearances at Bill Mielke's "Electronics Fun Day" the famous last-day culmination of the wonderful Intro to Engineering Electronics (IEE) course, complete with heavy metal music, a coil gun, a 100,000 amp electromagnetic pinch (used to crush aluminum cans and shrink coins), and a dynamically balanced rotary inverted pendulum (at least until the year the tesla coil accidentally destroyed it --oops!). The RPI Physics club even made the coil part of an outreach event to a local high school.
But dark times followed, as first the IEE class was removed from the curriculum, and then the the E-Club was shut down. Things looked bleak for the E-Club Tesla Coil, but since I was still at RPI as a grad student, I managed to extricate the coil from the E-Club shop, and Bill helped relocate the coil safely into deep storage. A few years passed, and with the establishment of the Tech Valley Center Of Gravity, (a makerspace right down the hill from RPI in Troy), there was renewed interest. So, during the planning for the inaugural Emma Willard Mini Maker Faire (co-sponsored by Tech Valley Center of Gravity), the search for presentations and demos led to a request for the good ole' E-club coil to make an appearance.
Bill helped me get the coil out of storage, and I dusted it off, re-coated the secondary where it had been scratched, and brought it back to the stage. It had been a few years, and the coil looked a little rough, but it still worked great! In the hopes of attracting new members to our fledgling makerspace, I subsequently brought the coil to the Tech Valley Center of Gravity for the [Halloween-themed] Troy Night Out event. Running it briefly every few minutes was great fun, and what with its loud, dancing sparks the Tesla Coil attracted a steady stream of onlookers -- many of whom had never seen one up close before. J.t. Higgins captured some great footage of the coil running that night, and posted a great compilation video. This is probably the best video that's ever been captured of this particular coil.
I have three comments about the video:
Despite the title, there was actually only one Tesla coil that night at Troy Night Out... to avoid any confusion: the stick I'm holding in the video actually had a grounded metal sphere on it (you can see the ground wire dangling from it, if you look closely) -- hence the affinity for the coil to arc to it.
As good as this video is, the camera didn't seem to capture how much hotter (brighter, louder, more blueish) the hard arcs (sparks to the handheld, grounded sphere) are than the long forked streamers. Also, the microphone was pretty swamped by how loud the whole thing was, and seems to have reduced its volume significantly during the run of the coil. Make no mistake, this thing is pretty loud -- people who stopped by that night said they'd heard the coil from over a block away.
My claim of 750kV at the beginning of the video may be a little charitable, and could be complete baloney, because the standardized distance relationship for air breakdown voltage assumes numerous ideal conditions, and a Tesla coil spark is in no way ideal -- that "guesstimate" included a lot of hand waving. I CAN tell you that it will blow a 120v branch circuit with a 20 amp breaker in about 2 minutes of operation, so looking at a standard breaker trip curve, in terms of POWER, probably about 4kW was being drawn from the wallplug. How much of that energy ended up as lightning is difficult to say (spark length suggests ~1.5kW), but with numerous other factors to consider, the /voltage/ is much more difficult to estimate based on spark length alone. (Google for more info if this topic interests you). In my defense, I've been quoting the 750kV figure since Alex and I built the coil in 2005 (when I knew and cared less) and such big numbers always seem to excite the crowd... I'm actually surprised no fellow coilers ever came up to me afterward to call me out on that little bit of engineering-impropriety-in-the-name-of-showmanship.
I don't know what the future holds for this coil, but there have been requests for a build-your-own-Tesla-coil workshop at the Troy makerspace (Tech Valley Center of Gravity), and although I haven't had a chance to address those requests yet, until such time, the coil is safely in storage.
--Charles "Casey" Goodwin, January 2014