Terry's DRSSTC

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>

Hi All,

I wound a little 20 x 6 secondary so now I can run indoors again :-))  It 
has ~1360 turns of #28 wire on it.  With a small toroid Fo is 120kHz.  So I 
don't have to worry about weather or the big coil inside anymore.  Spent 
all day yesterday making the new secondary:

http://drsstc.com/~terrell/pictures/NewSecondary.JPG

I fiddled with some noise issues today.

It appears standard 1k logic pullups con be almost tripped by the noise 
running around.  Mostly radiated and some conducted coming back on the CT 
lines.  Standard TTL logic would fry, but the 74HCxx stuff seems rock 
solid.  I am sure everything in the main controller is find since it is in 
the metal box as well.

The noise is 17, 34, 60MHz stuff.  It is pretty independent of drive 
current!!  Since the primary LC dominates the current, not too much goofy 
stuff goes on current wise.  The noise seems all +-300V high speed voltage 
switching noise.  Right now it is getting into the unshielded protection 
logic board and keeps tripping the over current.  But a few caps sprinkled 
around seem to fix it fine.  They are 100 - 1000pF values so I need to 
order a bunch from Digikey since I don't have the "right" ones.  I should 
probably also reduce the dead time since that is when the noise rings freely.

I think I should increase the value of the gate drive resistors to slow the 
switching and reduce the noise too.  High power 60MHz is sort of 
intense.  Probably best to let the IGBTs heat up a little rather than have 
the thing be like a microwave oven inside.  But even as is, the noise seems 
perfectly controllable with the standard "add a cap" tricks.

So I am going to fix the weak noise spots in the circuits, and then go 
after the noise at the source.  Hopefully, I can get a good feel for the 
noise issues and how to take care of them.  I think we need to get things 
like noise pretty well figured out before everybody goes making DRSSTCs ;-)

So mostly just fiddling still ;-))

Cheers,

	Terry