Re: OLTC Questions

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

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

Hi Steve,

Since you are charging a big DC cap, things a far simpler than my OLTC that 
had a lot of timing and triggering thought.  A great way to go here since 
it will solve many problems I had.

I just used "1.5KE150CADICT-ND"  Bi-directional TVSs from DigiKey right 
across the primary.  I just strung them together with short leads to keep 
the inductance down.  Shown circled in black here:

http://hot-streamer-dot-com/temp/OLTC10-08-01a.jpg

R1 and C3 seem sort of strange to me.  In my schematic at:

http://hot-streamer-dot-com/temp/OLTC8-14-02.gif

Rsec is the resistance of the secondary wire, Csec is the capacitance of 
the toroid and secondary combined.  Rarc and Carc are the streamer 
impedance.  Carc would would be about 2pF for a 100 watt coil.

Your voltage amplification is about 1/2 SQRT(Lsec/Lpri) = ~50 so with 350 
volts in, the secondary voltage should be about 17500Vpeak.  That seems 
sort of low to me.  Maybe think about a smaller primary or larger 
secondary.  I have about a 500x factor.  Of course, a lower factor "may" be 
better.  I don't know...

Your project looks really cool!!  I am looking forward to seeing what you find!

Cheers,

         Terry


At 03:58 PM 1/20/2003 +0000, you wrote:
>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.
>