Tesla Coil

In the early 20th and late 19th centuries, there was a man known as Nikola Tesla who was a brilliant and revolutionary electrical engineer. He is the true owner of the patent for radio transmission and this fact is often ignored in many history books. He invented a device that is named after him and is absolutely fascinating to behold. The tesla coil uses electrical induction to build up an strong electromagnetic field and discharge heavy bolts of electricity through the air. The main components are the high voltage transformer, very strong capacitor, and the primary and secondary coils. Tesla once built a tesla coil that used millions of volts and had discharges of amazing lengths. The sound produced by these discharges was absolutely deafening and could be heard for over 10 miles.

The following is a review of Information Unlimited's BC-3 Tesla Coil Kit:

Review of BTC-3 Tesla Coil Kit From Information Unlimited
April 23, 1992
Eric Bush
Falls Church, VA

Like many of you I am sure, I have read several autobiographies of Tesla over the years and have become fascinated with both the man and his inventions. I had for some time desired to actually BUILD a Tesla coil. Unfortunately, I suffer from a very poor education when it comes to basic electronics. The thought of building a device with such high voltage output was very intimidating to say the least! To my rescue came the Summer 1992 catalog from Information Unlimited. Add to this that I had quit my job (i.e. I had some time on my hands) and that $240 didn't seem to be an unreasonable amount of money to spend for a time killer (when not searching for a new job) and dream fulfillment.

It occurred to me that there may be other Tesla novices out there who might be interested in trying to "feel the power" of a real Tesla coil fashioned with their own hands. This brief write-up will let a novice Tesla coil builder, whom chooses to start their Tesla building career with a BTC-3 kit from Information Unlimited, to have a better idea of what to expect if using the BTC-3 kit.

The BTC-3 kit, when finally put together, delivered the 12" sparks as promised from the 250 KV output. However, a few screws necessary for the construction of the coil were missing from the kit and necessitated a trip to the local hardware store. The directions were cryptic and the drawings didn't match the eventual configuration as built. Some parts appear to have been substituted for those that were described in the directions requiring some improvisation in order to get things to work. The kit required very little in the way of tools, or knowledge of electronics, to put together and required a total of about 10 hours over two weekends to construct. In spite of some of the changes required during construction, I found the kit satisfactory and worth the price.

I also went on to buy the optional Toroid Terminal after completing the coil and I would highly recommend it to anyone considering building the BTC-3 kit. While the bare wire coming off the top of the coil produced considerable sparks, it was only when I attached the Toroid to the secondary coil that the coil seemed to "come alive" and produce an incredible discharge field and a constant output of 10" to 14" sparks. Well worth the extra $69.

Now, I am ready to move on to building a 1 million volt coil that I hope to build from scratch! (with plans yet to be determined....)

An initial quick inventory of the parts in the kit as compared to the parts list included with the kit showed that several screws were missing. These are the kinds of missing parts that are very frustrating. I figured the long distance phone call requesting Information Unlimited to send me the screws would be more expensive than just going out and buying the screws. Other than that, everything appeared to have been included. I feel that potential purchasers of the kit should also be aware of the following:

- The secondary coil included in the kit was wound sloppily and required about two hours of my time to get it wound tight and without any overlapping wires. I began wondering if I couldn't have wound a coil from scratch in the same amount of time and saved the money of having to buy a pre-wound coil.

- There were no screws included with the kit that could be used to attach the top (the part that the secondary and primary coils rest on) to the tank enclosure containing the transformer, capacitor, etc.

- There were no screws included that could be used to attach the transformer to the bottom of the tank enclosure.

- The ON/OFF toggle switch included with kit did not match the switch in the plans and because of a protruding tab could not be attached to the side of the tank enclosure. I was forced to cut off and file down the tab.

The plans include a nice brief introduction on Tesla coils - what they are and are supposed to do. The plans also include a nice conclusion that describe options that the builder can add to the coil (that will produce additional effects and features for the builder).

The drawings and diagrams in the plans appear to be taken from several different sources, or at least drawn at different times by different people. The formats of the drawings change frequently; in a couple of places two drawings of the same assembly on separate pages didn't even match. The drawings at times do not reflect the associated instructions. This led to occasional head scratching moments of pondering on how to resolve the problem, "Do I go by the instructions or do I go by the drawings?!" Generally speaking, the drawings were accurate and I used them frequently to make sure I was on the right track.

The instructions were actually pretty good. Descriptions were clear and followed a logical stepwise path through the construction of the kit. Thoughtful comments are sprinkled throughout the instructions indicating pitfalls to avoid and/or variations that are possible as the kit is put together. One gets the feeling that someone had written the instructions and then had actually gone through them and tested them for accuracy. The only exception to my praise of the instructions, though, is that the instructions had not been modified to reflect obvious last minute parts changes that were shipped with the kit. There were also a couple of instances where the instructions were verbally correct, but the drawing referenced by the instructions appeared inaccurate and did not reflect the associated instructions. I'm not sure that this is a fault of the instructions or of the drawings?!

- An interesting conclusion drawn after the construction of the coil was complete, was that the kit required no soldering at all. For peace of mind (and for habits sake) I still soldered all the obvious connections, but in fact didn't really need too.

- A finer treaded screw should be used for the spark gap adjuster. It takes quite a bit of fiddling to get the gap to the width that provides for continuous operation at maximum output.

- Generally speaking, the initial output of the coil was much less than advertised; perhaps 8" sparks at best. I added a second capacitor (identical to the one included with the kit) and wired it in parallel with the first and then got the spark output I desired. While it is possible that I didn't get the coil tuned properly initially, or that I hadn't assembled something properly, the addition of the second capacitor did the trick for output.

- The secondary coil comes with a plastic cap covering the top of the PVC tube used for the coil. This appears to be unnecessary and in the end I had to remove it so that I could patch some arcing that was occurring inside the tube.

- The plexiglass plate used in conjunction with the spark gap adjuster should have had an adhesive included in the kit for attaching to the side of the enclosure. I had to run out and buy some epoxy glue. It would have been a nice touch to have had this included.

- The power cord is supposed to be securely attached to the tank enclosure by using a plastic grommet. Unfortunately, the hole cut for power cord grommet was much too small for enclosed grommet.

- The neon bulb holder was too large to securely hold the bulb. This necessitated the elimination of the use of the bulb as part of the finished kit. This didn't effect the ability of the coil to run, but it probably would have added some "polish" to the look of the coil when completed and operational.

- It is an absolute necessity to corona dope all exposed wire attachments in the tank enclosure. Failing to do so leads to arcing inside the tank enclosure.

- I recommend that the secondary coil be insulated with a coating of paraffin wax as opposed to corona dope. The coil arcs through a single coating of dope as if it weren't even there. However, all arcing was eliminated with a single thin coat of paraffin wax. Its a heck of a lot cheaper than dope as well!

THANKS (credits):
A great deal of "thanks" goes to my good friend Dr. Rin Saunders whom without I never would have known about Tesla and whom acted as a patient guide and friend during the construction of the coil. It was he, back in 1986, that first enlightened me about Tesla. He had also once built a Tesla coil some 25 years ago as a young teenager and was therefore able to provide valuable guidance when the instructions and the diagrams (or parts) didn't quite match. I have included his commentary on the kit and its construction above.

Other Information on Tesla Coils on this Site:



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