This is a modified version of the first SSTC I built, the Kaizer SSTC I. It uses the same secondary, topload and driver board. New things is a full bridge of IRFP460 MOSFETs, audio modulation, shielded drivers and a new casing.
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In the quest for longer sparks I decided to use a full bridge to take advantage of the full voltage on the bridge.
The MOSFETs will be mounted on top of a heat sink so its easy to change them by only removing the secondary platform and solder them off.
The drivers will be shielded in order to avoid the EM field generated by the Tesla coil itself to inject noise into the drivers.
|Bridge||4x IRFP460 MOSFETs in a full bridge configuration.|
|Bridge supply||0 – 260 VAC from a variac, 8 A rectifier bridge and 1500 uF smoothing capacitor.0 – 365 VDC on the bridge.|
|Primary coil||115 mm diameter, 1.78 mm diameter isolated copper wire, 8 windings.|
|Secondary coil||110 mm diameter, 275 mm long, 1000 windings, 0.25 mm enamelled copper wire.|
|Resonant frequency||Self tuning at around 250 kHz.|
|Topload||100 mm small diameter, 240 mm large diameter, toroid.|
|Input power||Continues Wave mode: 2000 – 4000 Watt at 200 VAC input voltage.
Interrupted mode: 100 – 2000 Watt at 260 VAC input voltage.
Audio modulated mode: 300 – 400 Watt at 150 VAC input voltage.
|Spark length||up to 475 mm long sparks.|
The UCC3732X are MOSFET driver ICs, one non-inverted output and the other inverted, in order to get a push-pull drive of the gate drive transformer. A gate driver IC can deliver the high peak currents needed to drive MOSFETs efficiently.
The 74HC14 is a inverting hex schmitt trigger, it is used to get a proper solid 0-5V square wave signal from signals that are not perfectly square, the antenna feedback can vary a lot in waveform and amplitude, the 74HC14 converts this to a clean drive signal for the MOSFET drivers.
All unused input pins of a 74HC14 has to be tied to ground, floating inputs and a noisy environment is a recipe for trouble. The noise can couple between the gates internally and make the whole IC not work properly.
The music modulator works by amplifying the audio signal in the LM741 and at the BC547 transistors. The 555 timer ensures that the signal length of the generated square wave is much shorter than the audio signal, in order to not have too long on-time and thus damage the MOSFETs / IGBTs from over-current.
15th March 2009
I took apart a 19″ LCD monitor and a 24″ CRT monitor, from these respective computer parts I salvaged a good piece of acrylic from the LCD monitor and a fairly sized heat sink from the CRT. I cut the acrylic in half for a 2 level platform and the heat sink was cut in 4, its necessary to isolate the MOSFETs from each other as their housing is also a conductor.
19th March 2009
Driver electronics and audio modulator are installed under a metal casing from the CRT monitor to shield it from the heavy EM field surrounding the Tesla coil, this is to avoid problems with the driver being interrupted by its own EM field.
The bridge is made out of four IRFP460 MOSFETs, four MUR1560 diodes, four 5R resistors. The power supply is a 8 A rectifier bridge with a BHC 1500 uF/450 V smoothing capacitor, a 27K 7W bleeder resistor is added in the final build.
The audio in jack was later removed due to it making a short through its metal housing to the ground rail, I had overlooked that the audio in negative was not common with the ground rail, but there is a capacitor inbetween.
The secondary is held in place by a crate for ventilation on houses, its an easy and quick way of taking the coil apart for transport or storage, and it holds the secondary firm and tight.
A acrylic tube is added to support the antenna, in this way it is possible to adjust the coupling of the antenna to the secondary simply by pulling the wire.
The new shielding of the audio in signal is made from a piece of shielding from a industrial cable pulled over it and grounded.
The secondary with terminations. 110 mm diameter, 275 mm long, 1000 windings, 0.25 mm enamelled copper wire.
The complete coil looks, except maybe the electrical tape used to hold the topload together.
At 250 VAC input voltage, 350 VDC on the bridge, it was possible to reach 475 mm long sparks, in interrupted mode, to a grounded object.
More pictures of sparks in interrupted mode, it is running at about 4 – 5 BPS.
3rd May 2009
Continues Wave mode
At 200 VAC input voltage, 280 VDC on the bridge and a power consumption around 10 A, peaking at 20 A, the coil was drawing somewhere in between 2000 to 4000 Watt. This resulted in very hot, thick white arcs punishing the dead iPod shuffle which remarkably left the player relatively unharmed considered what had just taken place.
These flame like sparks are 250 mm in length.
18th August 2009
I constructed a new topload from two cheap aluminium frying pans from Ikea. With handles cut off and screw from it grinded away it had a smooth surface and was fixed with a long screw through both of them.
6th September 2009
During a run of CW at full input voltage, the full bridge blew apart completely, with a loud bang.
I use a audio modulator made by the user Reaching (Martin Ebbefeld) from 4hv.org.
For sound input I use a cheap children’s keyboard from a toy store, its far from perfect for the job, especially because its waveform is highly distorted and its not clean tones but seems to involve a lot of modulation inside it to simulate different instruments. But its cheap and expendable.
Watch the film and look at the schematics for more about the audio modulation.
Upgrading the SSTC I with a full bridge was a absolute must. It is small changes compared to the better performance and the driver have no problems at all driving four MOSFETs instead of just two.
Getting sparks at 475 mm length in interrupted mode and white power arcs at 250 mm length is truly satisfying for this little coil, the secondary winding itself is only 275 mm in height in comparison.
Enjoy the demonstration.
Demonstration of different modes.
New topload, running in interrupted mode.
New topload, running in CW mode.
New topload, running in interrupted mode and closeup of sparks.