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!
51 Comments
Tomi Engdahl says:
It operates at the resonance frequency of the coil. You can’t wind a coil without lots of capacitance between the turns, between the ends etc.
Small rubber antennas for VHF have quite a small a diametre and few turns. A 20 cm coil with diametre 25 mm wound with 0,5 mm will have a resonance frequency of a few MHz, less if the battery etc acts as a ballast.