RE: Pushing the IGBT Envelop

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

Original poster: "Steve Conner" <steve.conner-at-optosci-dot-com> 

 >It's rather impressive just on general principles to produce an 11ft arc
 >using 600V mains!

It sure is. I think Steve's setup just plugs into a standard 240V outlet and
uses a voltage doubler rectifier to give around 600V dc.


 >I'm not exactly certain what an 'OLTC' entails, but essentially the ALF
 >would employ a rather
 >straightforward capacitor -> series-switch -> primary arrangement

Well, that's exactly what an OLTC is- a DC resonant charging Tesla coil with
the spark gap replaced by an IGBT switch. Terry Fritz did the first
"amateur" one, he called it the "OLTC" and the name stuck. There have been
about nine or ten built since.


 >For the 1:12 ALF prototype I've settled on
 >~2400V -at- 2800A peak,
 >representing a compromise between I2R losses and device ratings.

Yay! That means my OLTC II is a 1:2 scale model of your 1:12 scale model. I
used 1kV -at- 5000A peak, so if your system performs similarly to mine you'll
get

73" x (2400/1000) x sqrt (2800/5000)= 131"

See the tech spec of the OLTC II coil here
http://www.scopeboy-dot-com/tesla/t4spec.html
There is also a pic (by James Pawson) of it producing a 6'1" arc at Derby
2004
http://www.scopeboy-dot-com/tesla/oltc2_6foot1.jpg

 >The trickier issues lie in charging the capacitors from the mains, and
 >managing the energy properly
 >as it bounces back and forth between primary and secondary.

Again, I just used DC resonant charging from a 600V DC supply, which I got
from 240V AC with a voltage doubler. As for managing the energy, I opened
the IGBT switch at the first "Notch" to trap it all in the secondary. I
reckoned it would do less harm there, than sloshing around the primary
heating up the IGBTs. In practice though, my giant IGBT blocks seem to run
cool no matter what I do.


Steve C.