OLTC Update - OLTC-2

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

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi All,

Today I have pondered many things...

The present OLTC works wildly well considering what a total disaster it
could have been :-))  There were only two issues that turned out as serious
problems.

1. Primary losses are higher than expected.  The primary loss should have
been 500uOhms instead of 3mOhms.  Miscalculations on my part and higher Vce
that expected in the IGBTs...  Probably be hard to get a primary Q of over
40 in an OLTC (normal TC is about Q=50).  However, the very high coupling
and perfect quenching of the OLTC can easily make up for this.

2. Secondary losses...  While not a big issue with conventional coil (or,
maybe it is??), it certainly made it's presence known here!  Never expected
this one ;-))  Not a basic OLTC problem but a general Tesla coiling issue
that was amplified in this case.  Redesign can fix this...  Comparing The
OLTC to a conventional TC of the same primary energy with a model:

http://hot-streamer-dot-com/temp/OLTC09-04-01.gif

We see the initial trapped secondary voltage is about the same:

http://hot-streamer-dot-com/temp/OLTC09-04-03.gif

But the high loss of the secondary eats a lot of power:

http://hot-streamer-dot-com/temp/OLTC09-04-02.gif

We need a much better secondary...


Things that worked!

1. Parallel IGBTs with anti-parallel diodes are a big winner!  They are
very stable and can takes LOTs of current.  Very good quenching and control.

2. Having a primary cap per IGBT to control current sharing is also a major
advantage!

3. Although it messes up our pretty computer models.  Multiple primary
loops in parallel to reduce primary inductance works very well.  It may
also be the key that allows much higher primary to secondary coupling.

4. Resonant charging works very well.  It adds a sort of heavy iron core
inductor to the system but it is totally reliable and well behaved.

5. The IGBT firing and control system work perfectly.  I just built it and
it worked right off. and gives zero problems.

6. High coupling.  This was an unexpected big bonus!  I never thought I
could run with 0.25 coupling.  Need to take total advantage of this now.
Never thought a one turn primary could do that! ;-))

7. All the theory and modeling proved to work just fine.  I didn't know
some of the "right" numbers but there was no great oversights or boo boos.
It all worked just as it should.

8. It didn't blow up!  It never broke.  The thing is rock solid and reliable.


So before, it was all new and in the dark, but now it is very well known
(probably better understood than any conventional TC!)  So we know it all
now ;-))
The present coil can't be modified to improve it much.  The secondary
losses require a pretty radical physical change.  Best just to leave it as
is.  There is not much to it so Making a whole new coil is not a big deal.


So it's time for a new coil.  The changes that need to be made are:

1. Go to a very large diameter secondary.  Maybe like 18 inches!  This
allows much higher Q using less and larger diameter wire.

2. Possibly go to a larger toroid.  But realizing that the voltage ratio
(Lsec/Lpri) needs to be maintained.

3. Possibly go to 15 IGBTs.  That helps the losses and does not stress them
with so much with super high current.  Probably worth the added cost. 

4. Put the primary inside the secondary.  If the secondary is larger, all
the electronics can go inside the primary with the secondary on the outside.

6. Don't use SonoTube.  It is known for low Q.  That is critical here.

7. Better balancing of everything for power transfer to the streamers.

8. Perhaps go to lower power but higher frequency with less primary
capacitance.


So I am think about the next coil to solve the Q problem.

Cheers,

	Terry