OLTC update

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

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

Hi All,

Tonight we had our Tesla meet and I ran the OLTC coil in the 240 PBS mode
with the new 33mH resonant inductor.  A few minor adjustments and it ran
perfectly throughout.  I was worried that the new mode my be unstable, but
it proved to work perfectly fine.

This new inductor has the current capacity to go to 240VAC and it only
weighs 4 pounds.  The whole coil is at 40 pounds now.  25 of that is in the
controller, secondary, and top terminal.

My top priority now is to gear it up for full 240VAC operation.  It has
only run in the 1/4 power mode (120VAC) so far and Bill's lab only has 120
VAC right now due to an "odd" wiring system.  The things I need to change are:

1.  Fuses need to be 7 amp fast blow type RS# 270-1013.

2.  Change kickback transorbes to two arrays of 600V types.

3.  Increase gate drive to 27 Volts from 18.

4.  Decrease gate drive resistance to 10 ohms.

The first two are trivial changes to accommodate the higher power.  I need
higher gate drive voltage since the peak primary current may get to about
5000 amps now!  If I don't have enough gate drive voltage, the IGBTs may
start to back off and dissipate high power.  A "bad" thing...  I am not too
sure about decreasing the gate drive resistance.  It help for a fast turn
on of the high currents but it also endangers the IGBTs form high speed
switching problems with Ccg.  I'll probably use my peak current setup to
study that one more.

Here is a neat picture I took with the coil lighting a mercury vapor bulb.
I think they sell these at the hardware store for less the $10.

http://hot-streamer-dot-com/temp/P9290027.jpg

Cool that the streamers were coming off the glass and were so straight at
first.  I think I'll get on of these neat bulbs myself!

We also cooked all kinds of things like these three CDs taped to the toroid:

http://hot-streamer-dot-com/temp/P9290030.jpg

So it is still holding together rock solid and the new inductor clears the
way for full power 240VAC operation.  At 120VAC the coil does not like to
breakout well since it seems to have high secondary current but not a lot
of voltage.  Hopefully, it will hold together at 240VAC which is about 1500
watts of input power!

Cheers,

	Terry