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Registered Member #989
Joined: Sat Sept 08 2007, 02:15AM
Location: São Paulo, Brazil
Posts: 476
That is my latest work of tesla coil, I am "finishing" today (Its need a few more work)
I was able to get 15cm sparks to air.
-> Half-wave Retification -> Secondary with AWG25 and fres of 500kHz. -> Sphere topload that puts down the Fres to 380kHz -> Self-ressoant without interrupter. -> 127VAC, 2A -> Half-bridge of IRFP250
I was base mine schematics on the Half-bridge SSTC of Steve Ward.
Pics:
Video: or
I was thinking here, what can I do to make greater sparks, my Topload has 6pF, and I try to put more toploads, but I didnt get a big difference (only on the current). Is there anything I can do to increase the sparks (I will try someday to put a Full Bridge, but I think 2 TC4429 wont get GDT for 4 Mosfets)
Other thing, I get too many noise one my Sound Amplifiers and other things, how can I remove the noise?
Registered Member #1025
Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566
Mestre Racerxdl wrote ...
I was thinking here, what can I do to make greater sparks, my Topload has 6pF, and I try to put more toploads, but I didnt get a big difference (only on the current).
You did not specify your transistors, but you could try voltage doubler to increase the input voltage, alternatively quadrupler in case your transistors are rated for that voltages...The doubler works also as a current limitter so you can play with caps sizes to increase/decrease the power and the spark lenght. Best caps for that are foil caps (I'm using big foil caps for electric motors)
Registered Member #989
Joined: Sat Sept 08 2007, 02:15AM
Location: São Paulo, Brazil
Posts: 476
Thanks :D Sorry, I really forgot. I am using two IRFP250 with 2x 680nF Siemens caps (like classical ones), the two capacitors I see that is a voltage divider. I was thinking if I can put more voltage at it because the IRFP250 are rated for 200V, I dont know if voltage divider is really dividing voltage across two mosfets.
Hi Mestre Racerxdl About the FETs and the voltage - you are running them on 120VAC, so this is about 170-180 VDC, so it is close to the breakdown voltage so i wouldn't suggest using higher voltage. No matter you are using voltage divider for the other half of the bridge, the FETs are seeing the whole supply voltage (when the upper FET is conducting, the lower FET must sustain the full supply voltage and vice versa). On the other hand the IRFP250 can handle a lot of current - 2A for them is quite low (if they are heatsinked well). I would suggest that you decrease the number of primary turns (if the FETs are not heating in the moment that is). Cheers Huben
Registered Member #989
Joined: Sat Sept 08 2007, 02:15AM
Location: São Paulo, Brazil
Posts: 476
I think the turns of my primary are to low now. I have only 3 turns arround the 3.5 inches secondary (At the base). The current Is a bit low, but my fets are heating a little. The heatsink is of a old P4 (the 478 ones), Today I bought Mica for put in the middle of the IRFP and heatsink, I was using a rubber that I removed from a Computer PSU (Of big SBLXXXX diodes). And I put some thermal paste in there. Other thing I bought is that MUR860 Diodes. That I have put in parallel of the Drain Source.
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[WIP] Medium SSTC
