Re: ferrite toriod chokes (fwd)

---------- Forwarded message ----------
Date: Mon, 12 Jan 1998 19:35:28 -0500
From: Thomas McGahee <tom_mcgahee-at-sigmais-dot-com>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: ferrite toriod chokes (fwd)

> From: Tesla List <tesla-at-pupman-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: ferrite toriod chokes (fwd)
> Date: Monday, January 12, 1998 7:11 PM
> ---------- Forwarded message ----------
> Date: Mon, 12 Jan 1998 17:12:05 -0500
> From: Kevin Wahila <wawa-at-spectra-dot-net>
> To: tesla-at-pupman-dot-com
> Subject: ferrite toriod chokes
> I just got some ferrite toroid cores today.  I have four with an O.D. of
> 1".  I wound one with a dozen or so turns of sinlge strand 22 gauge pvc
> insulated wire.  My trusty meter read 3.58 mH.  Boy was I surprised!  Such
> a difference from my two 1 1/2" by 10" PVC air core chokes wound with
> hundreds of turns of magnet wire.  It took two of those to equal one of the
> toriod cores.  Anyway, I am new to winding toroid cores.  I've read a bit
> on insulating the core and inter-layer insulation.  If I were to increase
> the turns to double the inductance, the wire would get bunched.  Is it a
> problem if the turns touch each other? Is this where I would want to go to
> another layer?  Also, is the wire I'm using sufficient?  I could use two
> toroids per HV leg instead of using more windings on one.  Well, I guess
> any information would would be of great help.
> Thanks,
> Kevin Wahila

The spacing between windings is important, as the voltage developed
between adjacent windings can be quite large. Multi-layer coils
of this type can be real problems, as the inter LAYER voltage can
easily reach many kilovolts under certain conditions.

Keep in mind that when the coil is presented with an impulse, it will
respond by developing a large voltage across itself. Think in terms
of tens of kilovolts. If the voltage exceeds the breakdown rating
of the insulation then failure will often be catastrophic.

At these high voltages you want the windings insulated from the
core and from one another. You have to be extremely careful about
the END windings: if you get these too close together you will
experience an arc between these windings that will be really

You can use very thin WIRE for the coils, but try to keep the
insulation as thick as possible! High voltage probe wire works
well, though the insulation limits the number of turns you can
wind. 1" diameter cores are very small. Look around for the
larger cores if possible.

Hope this helps,
Fr. Thomas McGahee