Re: chokes (fwd)

---------- Forwarded message ----------
Date: Sun, 18 Jan 98 15:39:36 -0500
From: Adam <absmith-at-tiac-dot-net>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: chokes (fwd)

>> I have two 3.5" OD ferrite chokes.  I got some RG 59 and stripped away the
>> outside and wound the choke with the center wire.  I have as many turns as
>> will fit and only come up with 1.078mH.

>Actually, if the chokes are used to protect the voltage source, the turn
>to turn voltage is relatively low. A thinner insulation is quite
>adequate. The problem comes in when you start to stack one layer on top
>of another. The voltage differential could very well break down standard

I wound my chokes with Radio Shack #20 stranded PVC-jacket hookup wire 
(dark brown 300V insulation)  I fit 150 turns on an amidon T400A-26 (iron 
powder, u=75) core to give me 5.55mH.

I needed to fit more than one layer, but I countered the layer-to-layer 
voltage problem by winding my layers intelligently.  I wound the first 
five turns, then went back to the beginning and wound four turns over 
these 5.  Then I wound 5 more turns on the core, then 4 turns over these. 
 I did this until I got 80% of the way around the toroid.  This is just 
like having a bunch of smaller 2-layer chokes in series, keeping the 
highest potential between opposite ends of the choke.

I left the ends about 1-1/4" apart to help prevent end-to-end arcing.   
My final chokes have a nice close-wound single layer around the outside 
diameter, and two layers on the inside, looking similar to a variac's 

As for wire-to-core arcing, I insulated my cores with 30mil poly + 
fiberglass electrical tape + 600V vinyl electrical tape.  This works 
fine, no arcs so far.