Re: Coupling vs secondary voltage chart

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Steve Ward <steve.ward@xxxxxxxxx>

Hey Terry,


>
> Hmmmmmmmm,  seems to be working "better" than expected.  Might be due to
> the better AC line.  But lowing the K does not seem to have hurt it ;-)))

Not only that, but secondary to primary flash-overs are non-existant now.


>
> The program gave "ICprimary RMS/sqrt(BPS) = 3.976"....  multiply that
> number buy the square root of BPS:
>
> 3.976 x SQRT(120) = 43.55 primary RMS amps.

Ah, ok, thanks for clearing that up.  My pspice sim seems to disagree
on a few points, one of them is that the primary RMS current is up
near 80A or so... but im not exactly sure how pspice is doing its
math.

>
> The "sqrt(BPS)" factor seems strange....  But that is what it
> is....   Trust me ;-)))
>
> Over six strings, that is 7.26 amps per cap.  They are rated at 13...  Are
> you caps "old or new"?  The newer caps have a higher current rating.

They are very old caps (the old caps have a noticably larger diameter
than the newer ones!).  They have been used and abused for some time
now, i wont be too sad to see them go up in flames ;-).

>
> My tests at:
>
> http://hot-streamer.com/TeslaCoils/MMCInfo/GeekCaps/GeekCaps.htm
>
> put them at 8 amps each (old caps)....  There might be things that need to
> be looked at here...  The caps "should" be fine.  They might get to body
> temperature, but if they get hotter, something is wrong in our assumptions
> or the caps.

I think we are assuming that the RMS current is lower than it is.  I
personally dont know how to calculate the RMS current, so i can only
look to pspice to do its magic.

>
> We may have to do an "autopsy" on your caps someday in the future.

Sure thing!

  The
> problems you are having do not have an obvious explanation...  I will have
> to review your website to see if any physical mounting things may be the
> cause...  DRSSTCs seems to push caps ever harder than "every other"
> application on Earth :D

My website doesnt reflect the current configuration.  Here it is:

http://www.stevehv.4hv.org/DRSSTC1/450nFMMC.JPG

Its mounted upside down so the caps reside below the sheet of PE.


>
> The very high K was killing the fast streamer "power" time.  It had a high
> "first peak" time, but the "real energy" was delivered far later.  Better
> off with a lower K that provides more power over a longer time even if it
> does initially get off to a slow start.  Jimmy (an others ;-)) seem to have
> been right about that, but blindly raising the K is not the completely
> right solution...

Yep, further understanding sure does help things.

>
> John's formula (120 BPS) is 18.6 x sqrt(bang power) = 49 inch sparks.
> :-)))  But you don't have a spark gap eating up all the power.  We probably
> need a new number to replace the "18.6"....  If you were getting 80 inch
> arcs at 7 joules, the new number is "30.2 x sqrt(bang power)"
> ;-)))))))))    That actually IS "about right" for DRSSTCs...  I have never
> had a thermal problem with my IGBTs and I don't think anyone else has
> either...  We have all that old spark gap's waisted power going into "our"
> sparks now ;-))  We still need to watch primary losses....

Without any forced air cooling my IGBTs get to about body temp.

>
> Has anyone ever had their IGBTs run warm or hot on a DRSSTC?????  We can
> certainly blow them to bits due to cross conduction, but from just "getting
> too hot" over time???

Nope.  On my smaller coil where switching losses are greater, the
IGBTs got hot to the touch, but could run like that indefinately.


> Only 1700Vcap...  But heat is all due to current, not voltage.  One can
> barely hold a 50C object.

Ah, then it was likely less than 50C.  Im a wuss when it comes to
holding hot objects too, so i always overestimate how hot things
really are ;-).

  Body temperature is 37C.  The temperature
> "might" be "ok"...  A lot depends on how fast they heat up.  If it takes an
> hour to get to 50C, or 10 seconds to get to 50C ;-))  But in general,
> obvious dramatic heating is a "bad thing"...  Keep the runs short...

The runs were maybe 1 minute in length.  I went and felt the caps say
10 seconds after powering down to check the temp.  Uncomfortable to
touch.  I should note that the heating built up over several 1 minute
runs, with maybe 2-5 minutes between runs for tuning etc.


> > > This is using the programs new "streamer power vs. time" function.  It
> > > shows the energy delivered to the streamer as a function of time.

Ok, in pspice i told it to do "integral(W(Rstreamer))"  and i get 14J
(after the bang is over).  If i do "integral(W(Rprimary))" i get
15.5J.  Is this not the correct way to figure out the energy from a
single shot?  I also looked at the voltage on my buss caps (in the
sim) before and after the bang and figured the energy difference was
about 15.3J, so the 2 numbers above make sense, and also go along with
the coil drawing over 15A at 120V.  So why does ScanTesla give
energies of ~half this?  Am i missing something?


>
> We have been playing the "model game" for many years with great
> success.  There my be problems in the little details, but the big picture
> is very solid and well understood.  Lowering K for better performance in
> your case is based on very solid evidence beyond this program....  The
> program just make is look "obvious" now ;-)))



>
> Very happy to here your coils is working better from all this!!!!!

Yep, it sure is impressive to see, i will have to capture some
pictures next time.  I put a larger toroid on top for the next run,
hopefully that will direct the streamers outward further.  I got a few
strikes to the primary wiring that made me quite nervous, but the coil
kept going along as if nothing had happened ;-).

>
> Those of us that like to run coils on a computer screens, can kick "real"
> a** now and then ;-)))

It seems we compliment eachother nicely ;-).

Steve

>
> Cheers,
>
>          Terry