Re: OLTC Questions

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

Original poster: "Stephen Conner by way of Terry Fritz <teslalist-at-qwest-dot-net>" <steve-at-scopeboy-dot-com>

At 21:57 19/01/03 -0700, you wrote:
>Original poster: "Terry Fritz" <teslalist-at-qwest-dot-net>
>
>Details on this are at:

(snip)

OK, thanks for the information. I put together a basic schematic of my 
proposed OLTC. Note: I left out EMI line filters etc and I may need to 
change the value of the charging reactor.

http://homepages.strath.ac.uk/~cnbp111/oltcschem.gif

It's basically a small DC Resonant charging tesla coil with the spark gap 
replaced by an IGBT. Rather than triggering the 'gap' as soon as the 
charging current hits zero, I used a de-Qing diode like in normal DC coils, 
so I can run at any break rate I want. Does anyone have any thoughts on the 
validity of this approach?

The main issue is that the primary current is going to hit 400A peak but 
the biggest IGBT I can find just now (Infineon part# BUP314) has a pulse 
rating of 160A. So I have to either parallel three IGBTs (using a separate 
primary coil/tank cap/gate drive for each one to ensure sharing) or use a 
tank cap one-third the size and then go up to 1200bps to get the same power 
as before. Can anyone comment on whether increasing the BPS would impact 
the spark length even if the power level stays the same? I.e. do a few 
large bangs give a bigger spark than many little ones?

Your thoughts much appreciated

Steve C.