Re: Ferrite chokes & saturation - why toroids?
From: Gary Lau 25-Nov-1997 1031[SMTP:lau-at-hdecad.ENET.dec-dot-com]
Sent: Tuesday, November 25, 1997 8:55 AM
Subject: Re: Ferrite chokes & saturation - why toroids?
>From: Malcolm Watts[SMTP:MALCOLM-at-directorate.wnp.ac.nz]
>Sent: Monday, November 24, 1997 9:42 PM
>To: Tesla List
>Subject: Re: Ferrite chokes & saturation - why toroids?
>> Is there a good reason for using the toroid?
>Not for this application to my knowledge (other than to minimize
>radiation). But I've used ferrite rods in chokes with no real
>problems. Perhaps someone who chose that core shape could answer this.
I originally had been trying to use large air core chokes. I wound a
pair with roughly 8" by 2.5" dia of 30AWG, measuring 9mH. I used these
with 3K/50W series R's and bypass caps, but I couldn't lick the problem of
arcing between the base of my secondary and primary. The chokes were
mounted about a foot below my primary, and my theory was that the chokes
were coupling with the primary. Since compactness was a goal, moving
the chokes to a more distant location was not an option. Reasoning that
torroids are not subject to unintended coupling, I chose this form
factor, and have not had any pri-sec arcing troubles since. 51 turns
gave me 14 mH, and this was not difficult to wind, though I did take
great pains to insulate the cores well with a layer of LDPE.
It could also be that the fewer turns on the ferrite core vs. the many
more on the air core may be responsible for the improvement I saw, who
knows. A ferrite bar core would certainly have been easier to insulate.
Waltham, MA USA