Re: Off Line - DRSSTC (OL-DRSSTC) - 3

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Terry Fritz <vardin@xxxxxxxxxxxxxxxxxxxxxxx>

Hi Steve and Mike,

At 09:14 PM 9/27/2005, Steve wrote:
> Terry,
>
> Are you using real IGBTs in your model?

"Sort of" simulated ones....

> If so, what do the gate rise/fall times look like?

I don't know...  I sort of set that up at my whim in the model so it 
obeys my "best guess"....  Maybe you have a better guess :-)  The 
models is not using voltage limiting since "I" don't care...

> and what is the gate voltage?

Depends on what size transorbs I have, but I am thinking around the 
25 volt range.  The 100:1 CTs take the primary current and feed it 
directly to the gates with a 25V transorb directly across it to limit 
the voltage.  So the gate signal is +-25V at 1/100th the primary 
current driving it.  If I have 500 primary amps, the gate drive 
signal is 5 amps.  Sort of "cool" in that the drive current follows 
the primary current in an analog way too!  Below 25V, the only load 
is the 5nF gate capacitance so the signal should "snap".  I also have 
a 5nF cap across the gates to act as a capacitive load.  The CT is 
14mH:1.4uH.  It seems to drive the gates like a rock.  I have about 
100 ohms shunting across then them too now to help get a little dead time...

> Maybe you could send me your simulation files (if they are pspice)?

I hope it works for you.  I messed with diode breakdowns and such but 
I set the model to use the included library file so it "might just 
work"...  They are MicroSim 9.1 freeV.

http://hot-streamer.com/temp/OL-DRSSTC-03.zip

It changes all the time and is now set to run at 120VAC at 15 
amps...  It is sort of a mess, but it is the model of the 
moment...  I decided to go to 120VAC since that is far easier for the masses...


> And keep in mind, dispite the 25J bangs, it likely wont create 
> sparks as long as a SGTC with 25J bangs at 60bps.  The energy 
> delivery time is just too long, so the peak power is much lower.

I fixed that some in the above model...  14J/bang mostly in 
500uS...  One can really play around with that stuff a lot....  But 
right now, I am just trying to get "any sparks at all" and I will be 
happy :-)))  The thing has no "brains"...  It only has two diodes 
:o)  All the timing is set by the component values...  It is sort of 
easy once you get used to it...   A way can probably be found to get 
back to 120BPS.  But for now, getting it "to work at all" is the goal...


> Steve

At 07:40 PM 9/27/2005, Mike wrote:
> Hi Terry,
>               Regarding your concern for the 185 UF Buss cap, and 
> the ~ 22 amp RMS, can you go to the standard 660 VAC 20 UF caps we 
> use in 480 volt input constant voltage filament transformers? Just 
> motor starter /run caps really, metal case for getting rid of heat, 
> etc. For your value that would be 9.25 caps so a bank of 10 would 
> do if they match this service.

Probably would have to go to motor run caps....  The problem is 
"cheap".  It has to be "really cheap"!!!!

The "present" spec is 450uF, 45 amps RMS, 200VDC...  But I can use 40 
DigiKey caps to do it!!!!  22uF, 200V in a 2 x 20 array 
(P5912-ND).  40 caps is a lot, but 40 of them only cost  $16.00 and 
they are only 0.5 x 0.8 inches each  ;-)))  It would be cool to keep 
this whole OL-DRSSTC mess less than $50 "total"!!  I am using $7 COTS 
CTs right now, but one could wind their own four tap CT for a 
fraction of that....

BTW - It appears that a "far smaller" than expected blocking inductor 
still resonates the cap charging voltage way up!!!  I suspect that 
the signal has big higher order harmonics...  But I seem to get very 
good voltage with only 5mH which is good since that inductor need to 
needs to be smaller and cheap too...  Keeping its resistance down is 
very important to preserve the "Q"...  The circuit seems to "need" 
this inductance or the system won't fire....  I don't know why...

Cheers,
        Terry


> Mike