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Re: Ferrite chokes & saturation - why toroids?


From: 	Malcolm Watts[SMTP:MALCOLM-at-directorate.wnp.ac.nz]
Sent: 	Wednesday, November 26, 1997 1:24 AM
To: 	Tesla List
Subject: 	Re: Ferrite chokes & saturation - why toroids?

Hi Adam,

> From:   Adam[SMTP:absmith-at-tiac-dot-net]
> Sent:   Tuesday, November 25, 1997 10:02 AM
> To:     Tesla List
> Subject:    Re: Ferrite chokes & saturation - why toroids?

<snip> 
> I guess the toroid is so popular then because it is a common type of 
> closed-core form (flux contained) that is readily available.   Rods and 
> slugs are great for making chokes for many applications, but I suspect 
> that if these open ended core forms get too close to the Tesla primary, 
> you could be in for some seriously unwanted induction- esp. if the cores 
> are lined up axially with the tesla coil!  For those of use whose power 
> supplies are housed just below the coil itself, closed core chokes are a 
> must.  This is what led me to the double "U" cores from my flyback 
> xfrmrs, though I suspect mine saturate at my current power levels.

I run chokes on ferrite rods right next to my primary. The primary on 
that particular coil is a helix. I obviously don't stand the chokes 
on end. 

> That leads me to another question- If I cannot find larger "U" core forms 
> than the flyback material (which I have in abundance) to build higher 
> current chokes, can I simply wind four (or more) identical chokes and put 
> them in series-parallel to increase power handling while maintaining the 
> value (10 mH)? This seems like a valid approach, and should also better 
> distribute the voltage across the chokes in series.

That sounds like an awful lot of trouble. You can heavily gap a core 
but then you are approaching air permeability. My next chokes are 
going to be air cored. I am going to wind them on old solder bobbins. 
I will put de-Q'ing resistors externally and make sure the heating in 
the chokes themselves is kept to a minimum. But then again, I am just 
about moving away from chokes altogether, at least for neons.

Malcolm