RE: SSTC Question from a newbie.

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Mccauley, Daniel H by way of Terry Fritz <twftesla-at-qwest-dot-net>" <daniel.h.mccauley-at-lmco-dot-com>



> 2. On the SSTC schematics I have seen so far, everyone uses a xfmer gate
> drive.  Is there any reason noone has used a gate driver chip to direct
> drive the gates? 
> 
Yes there is a reason.  You want to isolate your output circuit from your
control circuitry.  Remember, some of your FET gates are swinging at high
voltages.  


>  If the output current is not enough for the frequency
> (the IR parts I was thinking about only go up to half an amp I think),
> there are schematics that show how to multiply the output current up to
> 6A.  If isolation is a problem (I cant believe that the wire people are
> using on these xfmers can withstand any voltage, maybe 600V at max...)
> 
I use 1000V Teflon coated wire.  You do really need too much withstand
voltage.  For most 240VAC circuits, you only would need about 600V.

> then maybe using one of these gate drive chips with some form of optical
> isolation would be in order.  Maybe fiberoptic cable?
> 
> 3.  Do any of these circuits work at voltages as low as 12V up to say a
> max of 48V?  I would like to run the thing off a lower input voltage
> while I am first learning. 
> 
Absolutely.  Either input DC or use a step-down transformer to get your
12-48VAC or use a variac.

However, you may have a problem if you are half-rectifiying your ac if you
are using a AC step-down transformer.  Half-rectification creates a DC
Current component which may saturated the core of your step-down
transformer.

>  Would running at a lower voltage (even if it
> means higher current, say up to 100A) be possible for an SSTC?  Remember
> I would be happy with arcs as short as 6" for my first coil, and 12"
> would be awsome!  (I am easy to please arent I? ;)
> 
6-12" arcs should be extremely easy to obtain if you build a standard
H-Bridge circuit.  The biggest problem will be dissipating the heat of of
the FETs.  My earlier SSTC's using IRF460 FETs got extremely hot even at
120VAC input.  I later changed over to 1000V IXFN24N100 FETs which worked
incredibly great except that they cost about $70.00 apiece.


> 4. (This question may show just how little I know about tesla coils ;) I
> was wondering if it may be advantagious to place the SSTC primary inside
> the secondary instead of outside.  Does this make sense?
> 
> Would it be possible to use a
> conventional flat primary (external of course) with an SSTC driver? 
> What would the pros/cons of this configuration be?
> 
      Wouldn't really work that well.  With a SSTC you want very close
coupling.  Pancake coils can be used with conventional tesla coils since
they are run at very high voltages (12kV +) Thus the fields created are very
large even at the distances from the pancake coil to the secondary.  SSTC
coils are run at very low voltages (<1000V) therefore need to be tightly
coupled to the secondary.  The reason tightly coupled coils aren't used with
conventional coils is because of flash-over reasons among others.


If you are interested in building a SSTC, i have two kits available:

1.  Bareboard SSTC1 - This is my spare board from my first coil.  This is
$50.00 and only includes the bareboard and i'll throw in (6) IRFP460 FETs as
well.  

2. Bareboard SSTC2 - This is my spare board from my second coil.  This is
currently listed on ebay and ends today i think.  This is also a bareboard
(no parts) except for (4) IXFN24N100 FETs i'll throw in ($280.00 value
itself), and the (2) large heatsinks.

Both these boards have full documentation (SSTC2 is still in test right now)
and can be seen at my website:
www.spacecatlighting-dot-com

dan








> I think thats enough questions for now.  I am sure I can come up with
> more ;)  
> 
> Thanks,
> Mike
> 
> 
> 
>