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Registered Member #1730
Joined: Thu Oct 02 2008, 08:12AM
Location: Poland
Posts: 35
I have one problem with working of my SSTC. When I turning it on its starting work, giving nice 5cm spark to air with laud soud. But after aroud 3sec fuse is exploding (4A). Some info: socondary high 55cm diamer 11cm, DNE 0,1mm, primary: 8 wdg. on diamer 15 cm. half-bridge on IGBT mg15q6es42 Feedback on Tc4422 and 4421 filtr cam 5x470uF/400V What could I do?
Registered Member #1739
Joined: Fri Oct 03 2008, 10:05AM
Location: Moscow, Russia
Posts: 261
Does the fuse explode alone? ;) If so - plant a more powerfull fuse, myself I have anythng below like 10A heating up and breaking apart in a few seconds as well, but that is for like 2kVA. If no, more direct info would be nice to see. Exactly, what schematic had been used and if you are sure the IGBT's are not cross-conducting or getting stuck on Miller plateu. From what I clearly see so far, the first issue is the lack of shielding. EVERYTHING should be in a box, as those things tend to have the same field nearly not depending on the power levels at all due to the spark's own "zener-effect". Also, your antenna geometry is not even remotely logical - the antenna should be long so that a very high voltage would be induced on an unclamped antenna which would ensure the best switching mode, but not very scaled so that the capacity in the distributed divider would not be excessive and not much current would be driven through the clamping circuit. In your design, you get a low voltage off the antenna (take the facts that it's too close to the primary that's under mains voltage, and the clamping network's capacity makes it even worse), but the impedance of the divider you get there is too low, that's why too much current is driven back. Make it taller, and it will add more voltage (regardless the fact the clamping diodes will bring more negative effect in this case), however the fact it's not that distributed will make it drive less currents back into the driver. Moving on. The primary is too low to get a good coupling, myself I used to cover up to 40% of secondary height - with that, you will achieve a better coupling, therefore an improved SWR and less magnetizing current for bigger power levels. 55x10 isn't much of a good geometry for an ISSTC, especially with such a thin wire. 50x20 sounds like a good idea, myself I use 38x14.5 @ 0.3 and it still gets pretty hot. Older versions used 0.18 wire with a smaller secondary running at like 300kHz, which caused it to heat up very fast, the new runs like 150-200kHz depending on spark load and still gets hot after like 30min runs. I took a look at IGBT sheet, looks like you are using a brick meant for 3f VFD applications. The 500nS delays feel too much for higher frequencies, also having the switches in parallel tortures your drivers ;) Why should you need a higher Fres however? Well, it should be clear by now that dropping the frequency that much by means of using a thinner wire is not a way to go, you'd probably prefer to make a thicker secondary with a topload and thicker wire so that the Fres would remain the same while the losses would be lower. Also, the coils that lack a topload fail to store enough energy, that's why lack of the ground and spark currents is achieved. The trick is - a topload makes the system store more energy while having the same voltage on the output, therefore it takes more spark current to drain it off the resonator and the system will be capable of transfering more power with the same magnetizing current flowing through the primary.
Registered Member #1730
Joined: Thu Oct 02 2008, 08:12AM
Location: Poland
Posts: 35
Wow :) THX The coil is working properly now. It really need much more fuse, like 20A. On 48V it's taking 3,3A, so proportionally, on 300V it could take around 18A. With 48V 3,3A my SSTC is giving 6cm spark to air. Rezonate feq of my sec is around 50kHz, so my (not to good) IGBT are working well not heating a bit. I know that 50x11 isn't best thing, but it wos maked by my home's things, with lowest price at best effect. Again, it not final look of sstc, it wos olny for try, and it work. I'm happy about it, and I will shurly make it better.
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Need help with SSTC
