Re: Terry's DRSSTC

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>

Hi Sue,

At 01:24 PM 11/24/2004, you wrote:
> Me Too!
>
> I am glad to see that there is someone else is still working on these things.

I guess there are "two" of us now :o)))

> Someone commented that there has been a lul in the solid state work, but I 
> have been  quietly working here in my lab too. I finally put the finishing 
> touches on my Plamasonic I PCB that I started two years ago, and also 
> finished stuffing the two resonant driver boards that I got from Dan.

I takes time for the rest of us that work like snails to catch up...

> I found two nice beefy 24 volt center tapped transformers on Monday that 
> will work well to power both the driver circuit and two muffin fans!

I just got a 2 amp one off DigiKey for $20!  They don't give them away 
anymore unless you try hard.  They have to make room for lots of safety 
labels these days...  Since a few have flamed up in the past, I guess I 
can't complain for a little more safety ;-))

> I drilled out some holes in the chassis for the Plasmasonic, but the drill 
> walked a little in spite of my making divots first. The problem is that I 
> have a hand drill with no press, so I will have to move a few holes today :-p.

Making small holes first and then working up by steps works pretty good.  A 
variable speed one (even cheap from Harbor Freight) helps a ton too...

> I built the high voltage rectifier PCB, but I changed my mind and want two 
> fuses instead of just one. I want one ahead of the bridge rectifier and 
> bulk caps in case something shorts there, but I also imagined another 
> scenario. What if a MOSFET shorts? - All the energy that is stored in the 
> big bulk caps will discharge across that short and KABOOOOOOOOM!!! (Dave 
> Sharpe says it so much better than me!). So now I want another fuse 
> between the bulk caps and the MOSFETs.

Problem is that circuit also carries the full primary current unless you 
can bypass most if it out with big poly caps local to the IGBTs.  Fuses may 
not do well in the primary path but maybe they could do OK if they were 
just the right kind.  Low RMS current with high peak current.  But they may 
not help incase of an IGBT failure still...   Just got a ton of parts 
sitting here, so I will ponder it now...  At work, MH circuit breakers do 
well here, but they are not cheap (except on the used market ;-))...

> Your line filter sounds like it's really top notch, lots of good 
> protection and all too! I don't have anything between my line cord and HV 
> supply except a fuse :-o. Maybe I need to re-think things a little better. 
> At least I have a commercial line filter on my built from scratch SSTC. 
> That's a great idea you have there - using the same psu/filter assembly to 
> power each coil. That would save on parts and space consumption.

I would at least drop in some MOVs.  They could sink a cap over voltage 
event and keep it off the line.  My variac box also has MOVs and line 
filters ;-))  But I like over kill, especially with a house full of 
computers...

> I have also been playing with the driver a bit and swapping out different 
> MOSFETs and IGBTs. I had these discontinued 47 amp devices from ST that I 
> thought would be perfect for my coil, but the gate capacitance is 
> tremendously high, and the waveform was awful, and the driver supply 
> current was above an amp!
> I swapped to the IXYS 48 amp ones and they were much better. I dropped the 
> gate resistors to 4 ohm and added schottkys, and the results were better 
> still. Beautiful waveforms, and the supply current was only 0.6A. People 
> who complain about their driver chips getting hot should experiment like 
> this. Even different brands of devices with close to the same ratings can 
> be considerably different.

Lots has changed in the last few years and "new" devices are far far 
better!  Unfortunately they demand higher prices too...

> I think you are right on the Poly filter caps at the IGBT bridge. I think 
> Dan himself had one on his DRSSTC that he demo'ed at the Teslathon, but it 
> isn't in the schematic.

;-)))))

> I should have the Plasmasonic one up and running by tonight.
> My DRSSTC progect is going to start out as a SSTC for now until I can find 
> those capacitors at a reasonable price, or in someones garbage :-).

Mine are left over from the OLTC, but no extras here...  Might have to call 
Rell.com anyway...

> I still have a ways to go yet on that project. I still have to wind the 
> 1:2 GDTs, and wind the much lower Fres secondary. No more cheating and 
> using my medium sized SGTC secondary for all my solid state excursions any 
> more!

I think it would be cool if the DRSSTC drive could be sort of a "drop in" 
replacement and work on existing coils...  More to think on there...

Cheers,

        Terry


> Good luck on yours Terry!
> Sue