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Re: Giant DC coil to run in Australia

Original poster: Greg Leyh <lod@xxxxxxxxxxx>

It appears that those 3.6mH limiters should be way more than sufficient to act as the charging reactor. Assuming a 12000Y to 240D xfmr setup, the ratio should be about 20784/240, or 86.6. The effective charging inductance seen at the secondary should be about 0.0036*2*86.6^2 or 54H. For a 12000D to 480D xfmr setup, the effective charging inductance would be about 4.5H. I'm wondering if the limiters are in fact saturating. A saturating reactor will also cause the gap to power-arc.

Original poster: syd <tesla@xxxxxxxxxxxxxxx>

Hi Greg,

First I'd like to say that your tesla coil work has been a huge inspiration to me.. so thanks!
The charging reactor that I was discussing as 'not finished' was for a DC resonant charging scheme like you have used. For current limiting I built three limiting reactors that I use in series with each of the transformers. The plan was to use those limiters to set a maximum current, and then adjust power with the conjunction of resonant charging and break rate. With the DC reactor not built, and the resultant smaller charging voltage, I needed to adjust the limiters to pass much more current than I had originally planned in order to keep the DC line from sagging.

But anyway.. that part of the web site with all the construction notes is a couple years out dated. Since then I designed and built two DC charging reactors that are 2H each, which I intend to run in series. They're built and hipot tested, but I haven't had the resources to integrate them i.e. space and power to take measurements outside of a show environment.
When I get back from Australia I hope to update everything. Here's some specs:

Cpri   .191 uF
Lpri   ~38 uH
Lsec   66.1 mH
Res Freq. ~59 kHz

The limiting reactors were nominally set to 3.6 mH for 240V delta use. I've wanted to use 480V, but the EI cores that I've been using couldn't quite handle the 4 fold increase in inductance needed without saturating (1.8T with these.. 3% silicon grain oriented). So I built three more limiters so that I can use two in series for each transformer. This also gives me more window space for heavier gauge wire, AND I'll be running with lower current of course with the 480.

Incidentally, I posted one other page of pictures on my web site which includes a couple photos of the new monster spark gap that I just finished and shipped. It has two 16 inch rotors and achieves 5000 rpm. All the pspice simulations that I ran showed a dramatic benefit to short dwell time, so this should bring me down to about 60 usec.

syd klinge