Re: Ferrite materials (was Re: A CW TC without a tube + Re:

To: tesla-at-pupman-dot-com
Subject: Re: Ferrite materials (was Re: A CW TC without a tube + Re:
From: "Malcolm Watts" <MALCOLM-at-directorate.wnp.ac.nz> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
Date: Thu, 13 May 1999 22:54:21 -0600
Approved: twftesla-at-uswest-dot-net
Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

Hi Marco,

> Original Poster: "Marco Denicolai" <Marco.Denicolai-at-tellabs.fi> 

<snip>

> >From the same series "I can't way no more", yesterday night I quickly
> wound a 50
> turn primary and a 200 turn secondary on the N27 U-cores. As I had no bobbin
> formers, I used two round pieces of PVC pipe 5 cm diameter. Then I
> short-circuited the secondary and checked the primary current: almost no
> change!
> It must have been so that the coupling was too loose. (This is my first
> transformer, after all :) )
> 
> So I left my primary and wound a primary ON the same bobbin of the
secondary. I
> shorted again the secondary and now the current did increase: I measured
14 uH
> of leakage inductance. Then I started increasing the air-gap up to
removing one
> of the U-cores and then both U-cores: there was a minimal variation in
leakage
> inductance, about 0.05 uH.
> 
> I guess this is due to the fact that the most of the magnetic field is
coupled
> through air and only a little part through the core: remember, I have a huge
> clearance between core and bobbin. It seems to me I really need a kind of
> bobbin
> former, so that the copper is very near to the core surface, like in
commercial
> transformers. Next step will be to build a kind of bobbin former, tonight.
> 
> What do you think about the above experiments? Suggestions?

Agree with what you say. Coupling to the core is way below what it 
should be. It will be interesting to see just how good a degree of 
coupling you can get with the correct bobbins and the coils wound on 
opposite legs of the core. If my past experience is anything to go by 
you will probably get more leakage inductance than you desire with 
this configuration. I still think best is to wind the primary under 
the secondary and leave the opposite core leg free. Coupling is still 
not going to be stunningly tight because of the overall height of the 
secondary above the core. Thanks for the update.

Regards,
Malcolm

P.S. - have you published the TC design you will be using for your 
expts? Are you going to use just the one or several?