Try to make a full Bridge with IGBT and GDT

[JCF]

Thank for the message ...
About FDD8424H to driver output 2 capacitors voir schematic (I think no electrolitic) and 15 Ohms.

 

To day I make a new measure of resonance frequencies : Secondary  235khz, primary change capacitors to 20nF give  a new 212KHz.
Change cables Vbank with a big cable and 15cm lenght.

Measure with open cicuit and generator at 210khz then I close (FB) feedback input with current sense 1:300.

I measure current and output bridge with a differential probe and Vbank 120 DC







the maximum Vbank I want use is  400V. What is the primary current actual with current sense 1:300 ?

It remains to connect an other current sense to Over Circuit Protection, and what else ?



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Dave, thank's again for the precious help

[davekni]

The scope is showing about +-20V.  Is that measuring gate voltage rather than H-Bridge output?

With 300:1 CT, maximum OCD setting will be 127A on that driver board.

Yes, those are ceramic capacitors, not electrolytic.  So ESR isn't an issue.  I still can't explain the GDT waveforms you posted previously.  Perhaps FDD8424H gate voltage is low within that driver circuit?

Primary current at 400V will depend on what arcs you achieve.  Arc loading reduces Q which reduces current.

[JCF]

For this day, I measure the frequency résonance  at 213 KHz (generator open loop) and 200/205 KHz with curent sense. I am disappointed with the quality of the sparks that I get At 180/200V
My other small Tesla  coil with IRFP460 give betters sparks ( more noise at 200VDC and lenght more than 30 cm)
I must receive an other driver low cost but with variable self for adjust delay, it’s easy  to make  another test.
If is the same I try to use IRFP460 ...

[JCF]

The items are not yet in a box and the spool is on temporary support.
I am missing capacitors to correctly set the maximum current)
I attached below a photo with 190V DC spark about 25 cm  ? ? (F 223KHz). the maximum current varies very quickly from 210 to 230KHz, the primary coil has a calculated Q of 200 (javatc 3d)
Regarding the positioning and the space between winding I still have questions.
I am waiting for the capacitors and the next Ebay driver.
the interval between the turns of the primary is 10 mm. Is it good ? 13 turns, coil height 13cm
for the primary diameter 8cm, coil height 45cm 1000 turns Cu dia 0.40mm
this coil is noisier (finally) and the sparks thicker than my little one (tj 1000 turns, 0.25mm) go beyond 200 volts, I think I will do that outside

[davekni]

I think your coils are fine.  Looking back at your JavaTC results (in your reply #12), secondary reactance is ~24k.  That is lower than most designs, but should be fine.

Were you running open-loop (feedback from signal generator) for the 25cm spark picture?  If so, it should get better using CT feedback, especially if your new driver has phase-lead capability.

It looks like you have a foil guard ring at the top of the primary.  That is a good precaution in case sparks head down towards the primary.  I presume it is an open loop, not forming a shorted turn.

Glad to see performance improving!

[JCF]

With the Feed Back input connected to the sense current primary (10 ohms and 1: 300) the current frequency is Freq = 304KHZ Im 3.8V crete crete




Generator connected to the FeedBack driver sine signal 3 volt
primary transmission measurement with Capa 45nf
209-207 khz with maximum primary current Im 20V peak peak
other resonance at 277-279KHZ Im 10V peak peak[/size][/size]

[JCF]

New measurement of the resonance frequency of the primary in transmission = 220 KHZ
Idem for the secondary measured in reflection = 280KHZ

with Feed Back input connected to the sense current (10 ohms and 1: 300) the current frequency is 304KHZ Im 3.8V crete crete (current sense), in purple the signal at the bridge output (differential measure)

Why not 280KHZ



Generator connected to the FeedBack driver with sine signal 3 volts with

primary measurement with serial capa 45nf :

1 - 209-207 khz with maximum primary current Im 20V peak peak





2 - other resonance at 277-279KHZ with maximum primary current Im 10V peak peak  ? ?


I have troubles getting something good when looping with the SC ? ?

The sparks are only long with the generator connected to the FB ? ? ?

[davekni]

The driver appears to clamp the current sense input for the first few cycles.  The current waveform starts suddenly.  The current itself is not likely starting suddenly, so the driver must be shorting the sense input initially.  The driver also appears to be running the coil at a frequency not based on current feedback.  You will need to either find instructions for that driver or get a new driver that is documented.

Forgot to mention the standard advice:  Did you try reversing phase of current feedback (swapping CT leads)?

[JCF]

Tank you David.  I ordered 2 printed cicuit of UD2.7C to loneoceans