My Triple MOTs Tesla Coil

[Mathieu thm]

Hello, I will present to you a tesla coil that I made a few years ago, I think it may interest you.

I started making a spark gap tesla coil about 4-5 years ago when I was 14, I started building the primary circuit, without the capacitors , and the secondary circuit. It was only after 2-3 years that I bought the capacitors.
The primary power supply is composed of four MOTs (by testing the power supply, it draws 60a on 230v by making electric arcs! In normal operation the tesla coil draws about 10-12a), the capacitors are 940c 150nf 2000v well known of the coilers.

The secondary coil was an adventure, it's the first time I've wound such a big coil, when winding, everything went well but when putting on the varnish, the coil completely expanded, which failed.
After a few months, I decided to try again to make another secondary coil and it was a success, the coil is pretty well done !
The rotary spark gap was also an adventure, I had to do 5 or 6 different versions before the final version.

summary of specifications :

• Triple MOTs
• 75nf 16kv MMC with 940c 150nf 2000v cap
• Rotary spark gap
• Secondary coil on a 125mm by 58cm PVC tube with 0.4mm copper wire
• consumption: 10-12a on 150Vac (not measured and not really tested at full power)
• around 180cm of streamers
• Primary supply: 6.6kv for about 600-800ma
• 120 cm total height

Here are some pics of the coil :

overview:


Power Supply :



Spark Gap :



MMC : (4 groups in parallel of 8 capacitors in series, with 10Mohm 1w balancing resistors)



Control Box :



Some pictures :



bad photo when a lightning strikes the power cord of a neon lamp :



Some videos :

Test at "low" power, Approximately 180Vac on larger arcs and approximately 100Vac on smaller ones

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And in this video the input voltage is about 150Vac
https://www.youtube.com/shorts/feoHkGc6uiU

[davekni]

Nice coil with good output!  Interesting idea for shielding base from arcs.

Looks like a variable-speed non-synchronous spark gap, presuming the knob labeled "motor" is for speed control and not just on/off.  What range of spark rates (BPS) do you run?

[Mads Barnkob]

It is some very good spark length, especially achieving that early in life can be addicting

Was the RSG 5-6 versions due to imbalance?, looks like its very hand-made and that naturally gives stabilization problems with something going at those speeds and mass/weight.

I first saw that kind of base shielding in 2012, used by Daniel Uhrenholt and Finn Hammer. Very space efficient for transportation. I think its just a handful of welding rod material?

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and pictures from it: https://kaizerpowerelectronics.dk/teslacoils/finn-hammer-and-daniel-uhrelholt-show-in-fredericia-denmark/

[Mathieu thm]

Looks like a variable-speed non-synchronous spark gap, presuming the knob labeled "motor" is for speed control and not just on/off.  What range of spark rates (BPS) do you run?

Yes the spark gap is a non-synchronous spark gap with variable speed, and yes the knob labeled "motor" is for speed control for the spark gap.
I didn't really try to calculate the BPS of the spark gap, I think it is between 100BPS and 200BPS, I noticed that the tesla coil had good performance with not very high BPS, and I likes the sound and the "slow" streamers it produces with not very high BPS.

It is some very good spark length, especially achieving that early in life can be addicting

Was the RSG 5-6 versions due to imbalance?, looks like its very hand-made and that naturally gives stabilization problems with something going at those speeds and mass/weight.

I first saw that kind of base shielding in 2012, used by Daniel Uhrenholt and Finn Hammer. Very space efficient for transportation. I think its just a handful of welding rod material?

Thanks !

for my base shielding i use 2.5mm^2 wires

For the spark gap :

Here is the fifth version with a 3D printed disc (it was to try) the problem was that the disc turned yellow and became brittle because of the UV produced by the sparks (in this photo the spark gap was not finished) :



Here is the sixth version of the spark gap with this time back to a wooden disc but the electrodes were a bit too small, so in operation the electrodes became smaller and smaller quite quickly :



Here is the final version, the only change is the change of the electrodes, switch to 6mm instead of 4mm :

[thedoc298]

Thanks for the post, really nice streamers and nice looking coil. Did you spark gap ever crash..?

[Mathieu thm]

Thanks for the post, really nice streamers and nice looking coil. Did you spark gap ever crash..?

Thanks  I no longer have a spark gap problem with the final version.