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Registered Member #3114
Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608
So my coil was working great, i was getting ~7-8 inch sparks off of it. I put everything on a piece of plexi glass (not changing anything) The only thing different is the distance to the coil and antenna.
My usual cap i use is 2.2uf which gives long thick sparks and when i change one of the 10k pots i can make it shorter and hotter but not CW...(it will still pulse)
Well now the sparks are always short and hot (flame like) and if i change the 10k pot it will run in a CW mode with no pulse O.o
Also i have a lot more Mosfet heating
Here is the layout vs old layout
In the older set up the picture shows 10 turns, that was reduced to 4 and it was working perfect with little heating
Registered Member #1403
Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968
There is no tuning to made for a SSTC like this, it uses the feedback from the antenna. The resonant frequency of the secondary is picked up and used to drive the primary with.
It could be that your driver electronics are now closer to the secondary without any shielding, interference is a cruel mistress.
Have you tried to reverse the phasing of the primary coil, its been a long while since I last experimented with a SSTC so I am not too sure on this will help.
The MOSFETs properly just heat more from running CW, they will spend more time in the liniar region and thus dissipate more heat.
Registered Member #3114
Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608
Thanks :)
I found the answer, it has to do with the type of ground i use.. I get smaller sparks with an earth ground then I do with like a giant metal latter outside near my shop, or a big metal shelf... why is that?
New problem... (sigh) I was running the coil with a really small cap and it was making a straight thing arc like a SGTC, when i drew the arc with a ground rod for a sec i tripped the breaker... When i flipped it back on and powered up the coil again the same thing happened it tripped again, i repeated this many times over trying different things same outcome. I replaced the FETs and chose a different (reliable) cap, same thing happened... Whats up?
Could it be the fast diodes (shorted) that go across the Gate and Source? I am using 20v zeners back to back for protection. what could cause this ? Schematic
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Hi, I think your problem is coupling of magnetic field of the coils to the driver electronics. The primary field is usually very strong near the coil, so you should keep some distance (around 2/3 diameter of the primary coil) and then put the electronics into a fully enclosed metallic case. You must keep the distance otherwise even the metallic case will get heated by eddy currents. I did an experiment with my 1.8 kW VTTC, placing a steel sheet 5 centimeters under the primary (the primary was 12.5 cm diameter), made the sheet really hot within 10 seconds of operation.
PS. I just noticed your electronics are not under, but next to the coil. The magnetic field there is weaker, but anyway I would shield the circuit. The electric field from the topload can also mess things up good.
Registered Member #3114
Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608
Thanks Dr. Dark Current
The problem was the Bridge had failed and was shorting out the AC
Its seems i couldn't leave well enough alone and i broke it completely (sigh). I was playing with a CW mode and blew my 1/2" long AC in traces which probably from my testing fried the UCC chips and maybe the 74hc14 chip as well, I only ordered 1 of each chip (haha i hate my self sometimes) so im going to order more chips, diodes, ect.. and replace them and it should work.
After all this is my first SSTC, i expect some mistakes like these
OK, i have another question, When i put my hand between the coil and the antenna it will stop producing arcs, then when i move it out of the way it works just fine. This is how i blew the traces in CW mode
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SSTC 5 min tuning?
