Tiny Tesla coil tested

Tesla coils and other high voltage equipment that make sparks are always entertaining and potentially dangerous. There are  some portable tesla coils you can buy online that say, “safe, low current”, and yet they still produce lightning and have a high voltage output.700K Mini Coil Tube Neon Glow Coil With Transparent Plate Power Supply For Tesla is one such device I tested. Here is some story about it.

Let’s start with basics:The Tesla coil is an electrical resonant transformer circuit designed by inventor Nikola Tesla in 1891. It is used to produce high-voltage, low-current, high frequency alternating-current electricity.Ever since Tesla’s 1890s lectures, Tesla coils have been used as attractions in educational exhibits and science fairs. They have become a way to counter the stereotype that science is boring. They are old, but I this they are still cool!

700K Mini Coil Tube Neon Glow Coil With Transparent Plate Power Supply For Tesla page promised following technical specifications:

Color: As the picture shows
Power supply: 220V / 110V AC
About 700k frequency

arc can be touched by hand”
“Can light of incandescent lamp, energy-saving lamps, integrating scientific demonstration and entertainment, suitable as a magic props used in science and education, science and technology museum and school exhibits, etc.”

Package includes:
1 x Tesla’s Coil
1 x Adaptor
7 x Small accessories

The coil is around 100 mm long. So the device is quite small. The product I recieved looked somewhat different than on the product page picture showed, but the most important details were OK. Here is picture of the coil I received:

The electronics is pretty simple: One power transistor, few passives and the Tesla secondary coil:

The circuit is powered with mains power supply that gives out 9V 1A DC to the electronics:

The Tesla coil driver circuit is based on a version of quite popular Slayer Exciter Circuit. Electroboom article Slayer Exciter Circuit with a Tesla Coil has explanation (circuit diagram, text and video) how the circuit works. Here is circuti diagram from that page:

On my700K Mini Coil Tube Neon Glow Coil With Transparent Plate Power Supply For Tesla it seems that the diode is a LED – and some other slight modifications. The transistor circuit makes the secondary coil to oscillate as long as it gets proper feedback from the secondary coil (through capactance to ground). The circuit keeps oscillating on normal condtions, but in case the secondary gets shorted the or loaded too much., the oscillation stops – a good safety feature: coil turns off if you accidentally touch it (also protects electronics against overload).

Some maybe interesting measured data: The Tesla coil secondary on this unit I have has resistance fo aroun 55 ohms and inductance of around 370 microhenry. I would have wanted to measure the current consumption of he Tesla coil on use, but the cheap multimeter I tried to use for that failed to work properly near the Tesla coil (maybe it did not like the high electric field and/or high frequency pulsating current).

Here is the device prepared to make sparks. I added the yeallow wire to the device. It is connected to the output coil end that is connected to transistor base. I use that wire to make nice sparks.

The original documentation talks about 700 kHz operating frequency (if I undersand that 700k frequency right). The real frequency seems to be something quite different according to my oscilloscope: around 3.5 MHz. This was measured with normal oscilloscope probe aroudn 30 cm away from the coil on the table (I did not want to put it near the high voltage source that can damage my oscilloscope).

Many Tesla coils have some capacitive load on the top. Here is my attempt to add some capacitance on the top: piece of plastic wapped on aluminium foil. It chamges frequency.

The Tesla coil can in this configuration light up the supplied neon bulbs from some distance nicely. It can also make sparks (quite small compared to bigger Tesla coils). Neon indicator lamps are normally orange, but this package also had special green version also included.

Ggg

700K Mini Coil Tube Neon Glow Coil With Transparent Plate Power Supply For Tesla is cheap ($10) and quite funny high voltage device to play with. It might not be the most useful tool on electronics lab and does not make huge sparks (I woudl have wanted mych biggr sparks!), but it is still fun. Look at the following web pages for ideas what kind of experiments can be done with Tesla coils (some experiments ask for much bigger coil):

http://www.instructables.com/id/Tesla-coil-experiments/

http://www.techeblog.com/index.php/tech-gadget/7-cool-and-creative-tesla-coil-experiments

NOTE: Besides high voltage electrical field generation Tesla coil can be a big source of radio frequency interference. Keep the Tesla coil away from any sensitive electronics devices!

 

5 Comments

  1. Tomi Engdahl says:

    I was wondering on number of turns.
    With following tools
    http://www.daycounter.com/Calculators/Air-Core-Inductor-Calculator.phtml and
    https://m0ukd.com/calculators/air-cored-inductor-calculator/

    I got result that number of turns on Tesla coil secondary would have around 300 turns.
    Sounds reasonable number to me.

    Reply
  2. Tomi Engdahl says:

    Strange results on coil impedance:
    Another meter gave 1.3 mH and 53 ohms.

    I used this meter
    http://www.epanorama.net/newepa/2014/08/18/diy-electronics-tester-kit-m168/

    Reply
  3. Tomi Engdahl says:

    PCB Tesla Coil Is Perfect Desk Toy
    https://hackaday.com/2017/10/30/pcb-tesla-coil-is-perfect-desk-toy/

    A Tesla coil easily makes it to the top spot on our list of “Mad Scientist” equipment we want for the lab, second only to maybe a Jacob’s Ladder. Even then, it’s kind of unfair advantage because you know people only want a Jacob’s Ladder for that awesome sound it makes. Sound effects not withstanding, it’s Tesla coil all the way, no question.

    Unfortunately, winding your own Tesla coil is kind of a hassle. Even on relatively small builds, you’ll generally need to setup some kind of winding jig just to do the secondary coil, which can be a project in itself. So when [Daniel Eindhoven] sent his no-wind Tesla coil into the tip line, it immediately got our attention.

    The genius in his design is that the coils are actually etched into the PCB, completely taking the human effort out of the equation. Made up of 6 mil traces with 6 mil separation, the PCB coil manages to pack a 25 meter long, 160 turn coil into an incredibly compact package. As you might expect, such a tiny Tesla coil isn’t exactly going to be a powerhouse, and in fact [Daniel] has managed to get the entirely thing running on the 500 mA output of your standard USB 2.0 port.

    PCB TeslaCoil, USB powered
    http://www.megavolts.nl/en/projects/tesla-coils/201-pcb-spiral-teslacoil-en

    Reply
  4. Tomi Engdahl says:

    Low-End Parts Make Tesla Coil with a High-End Look
    https://hackaday.com/2017/11/25/low-end-parts-make-tesla-coil-with-a-high-end-look/

    We all know the saying: cheap, fast, or good — pick any two. That rule seems to apply across the spectrum of hackerdom, from software projects to hardware builds. But this DIY Tesla coil build might just manage to deliver on all three.

    DIY 3 volt tesla coil MUSEUM QUALITY
    https://www.youtube.com/watch?v=zbV1zyg_4qU

    Reply
  5. Tomi Engdahl says:

    How to Make a Tesla Coil. Experiments with High Voltage
    https://www.youtube.com/watch?v=33nv5sErrY4

    A Tesla Coil with a battery of 15 volts and also interesting effects with high voltage.

    http://anod7.ru/files/tesla-coil-scheme.png

    Reply

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