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RE: [TCML] The Dreadful Task of Ballasting (longish)

I can't speak with any experience in these matters, but in researching
transformer principle in general before I started, one web source (see
footnote) stated that the traditional text book illustration showing the
primary on one side with the secondary on the other linked by a square core,
was in fact a poor design that is usually avoided, as there can be a high
leakage flux. 
One coil wrapped around the other is the best way to avoid this. This was
also pointed out to me in reply to a post on the 4HV.org forum. Because of
this I thought it was going to have some effect, but not as much as it has
Arc welders, or at least the ones I've seen inside, also use a separate
secondary and primary. I know that is so the movable core can move in
between them, but I suppose this layout also aids them as well.  I certainly
did not adopt this layout on the off chance it would, it's just a bonus that
I " stumbled" on. In fact I've stumbled on a quiet a few things these last
couple of weeks but it has been interesting.
As for running without a ballast, I have a 20 amp Variac 'in the post' as I
type, so I may give it a try.

Thanks for off list info on your DVM Bart. Worth looking out for.

Footnote: All the web sources I found usefull can be found on my webpage of
the tranny




-----Original Message-----
From: bartb [mailto:bartb@xxxxxxxxxxxxxxxx] 
Sent: 12 May 2009 01:36
To: Tesla Coil Mailing List
Subject: Re: [TCML] The Dreadful Task of Ballasting (longish)

Hi Phil,

I'm with Jay, the cores you have are amazing! Regarding the 60V when the 
sec is shorted. I would not have expected your transformer to have this 
much leakage. This must be due to the hv coils placement on the core 
since you don't have shunts installed nor an air gap. You may have 
stumbled upon an interesting approach to self limiting. I wonder if a 
ballast is necessary?

BTW, nice ballast!

Take care,

Phil Tuck wrote:
> Bert, Scott, Harvey, Bart  et al
> The situation has taken a slight turn for the better now. I am basically
> waiting on the company who sold me my DVM to get back about a replacement,
> so in the meantime I wound a permanent ballast
> http://homepage.ntlworld.com/follies/tesla/inductor.jpg  by the 'suck it
> see ' method. Eventually after gradually chopping bits off the winding I
> to my desired 16 amps (this gives the secondary a reasonable current). Out
> of curiosity more than anything I tried it on the coil and the safety gap
> firing is significantly reduced. There are a few too many safety gap
> to be happy with, but it is on the way to success. I am now wondering that
> maybe my previous temporary ballast's, that also gave 16amp, were in fact
> saturating. Could this have been the culprit ?
> The small MOT got hot pretty quickly and the welder is only a cheap 150
> which also has a rather inadequate core that got hot. Whereas the ballast
> wound only gets slightly warm to touch after 5 mins on a Jacobs ladder.
> With the new ballast I am still getting around 60 volts across the tranny
> when the secondary is short circuit, so the tranny is still partially
> behaving like an NST
> As my caps are woefully STR anyway I'm ordering some more CD 942's to take
> me up to 75nF (currently I have 42nF). This increase, though still STR,
> definitely move the resonance point and is something that the coil needs
> anyway. If I still get safety firings with the new cap size I know then
> my stubbiness to stick with my heavy duty single static gap is the problem
> and I can then complete my RSG (I milled the motor's rotor  months ago).
> When I get a DVM I will use Bart's spreadsheet and post the actual
> Regards
> Phil
> www.follytowers.co.uk/tesla

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