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Registered Member #1104
Joined: Tue Nov 06 2007, 07:38PM
Location: Wisconsin, United States
Posts: 34
How important are gate resistors exactly?
I doubt they are my main problem but I powered up my coil (no gate resistors) to about 70 volts with a variac. However I get only about 1 inch of sparks off the coil. My problem sounds similar to coillah's in that my feedback is extremely weak. I don’t get any sparks unless I wind the bottom of the secondary around the antenna. Even with that I get horrible sparks.
My coil is 8†of winding (30awg) around a 2.5†form with 7 primary turns. I know the diameter is a little small but I doubted that would make a huge impact on performance.
Registered Member #1403
Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968
FireBird wrote ...
How important are gate resistors exactly?
I doubt they are my main problem but I powered up my coil (no gate resistors) to about 70 volts with a variac. However I get only about 1 inch of sparks off the coil. My problem sounds similar to coillah's in that my feedback is extremely weak. I don’t get any sparks unless I wind the bottom of the secondary around the antenna. Even with that I get horrible sparks.
My coil is 8†of winding (30awg) around a 2.5†form with 7 primary turns. I know the diameter is a little small but I doubted that would make a huge impact on performance.
Gate resistors limit parasitic oscillations but they also slow the switching times, I use around 4R7 to 10R.
Are primary and secondary coils wound in the same direction? It could be a phasing problem.
Registered Member #1517
Joined: Wed Jun 04 2008, 06:55AM
Location: Chico CA
Posts: 304
Got a new batch of FETs in yesterday, and I spent all morning putting my bridge back together.
Powered it up and had some arcing between the primary and secondary. Which means I'll have to insulate that some more.
For the first couple of power ups no sparks at the break out occurred, but the computer sitting nearby did exhibit some fritzy behavior, so I know some kind of field was being generated. After a couple of runs, the primary and secondary broke down and arced.
Now my bridge has returned to a lifeless state. Should I assume blown fets? They did not pop.
I plan on replacing the FETs later this evening if they are indeed what is currently broken on the coil, but I would like some second opinions...
Also I tested my bridge resistors and they are different by about 0.3R considering they have to do with timing I will replace them as well.
Another thing of note is my cooling fan behavior. When the coil is powered on with the bridge functioning, the fan seems to loose power. It is running off of the same 12VDC supply as the driver chips... I mean the same regulator. Is this an issue?
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First Light, Full Power? Mini SSTC (Steve Ward)
