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Re: Filter Torroids Question

Hi Glenn,

> The torroids from Hosfelt arrived today (item T-250-B).
> My question is, has there been a discussion or consensus
> over what type of wire to wind these with?
> Without a lot of thought, I fit 20 turns of 12ga solid
> THHN house wire on one of them before realizing that the
> wire is only rated at 600v.  If anyone wants to know,
> this measured out at exactly 80uh with the LCR meter.

Well, the idea is to get the inductance up as high as possible,
while avoiding burn-out due to a high voltage gradient between
the turns.  I have used 24 gauge solid hook-up wire to wind these
same toroids.  With 50 turns of this wire on a single layer, I
get 540 uH.  However, I feel I need to get to at least 2 mH,
preferable 4-5 mH.  So, instead of using 4 of these in series a
side, I am going to try to layer a toroid with some plastic and
polyurethane paint insulating between layers.  In that way, I can
get the number of toroids down per side of the tank circuit.

As far as the size of the wire to use, 24 gauge solid hook-up wire
should be plenty big.  We are always talking about less than 1 Amp
from the transformer.  24 gauge wire can handle that with no problem.
Using a larger wire size limits the number of turns you can get on
the toroid.

As far as the voltage rating on the wire, you shouldn't need to worry
too much.  These ferite toroids are non-conductive.  The main worry is
the voltage drop between turns of wire.  For the sake of argument, let's
say that we have 15 Kv of RF superimposed on the 60 Hz supply that we
are trying to filter out.  Let's also suppose we have enough inductance
to cause a 90% drop of the RF voltage across the inductor, ie 13.5 KV.
If you have a single layer of 50 turns, you will have a drop of 270 volts
per turn.  So, with 600 volt insulation, you will have no problem.  The
real problem comes in when you try to layer a toroid winding, instead of
a single layer.  If it took 4 layers to get you to the inductance value
you need, you could say you have about 25% of the total voltage drop
between layers.  That's about 3500 volts between layers.  Now you have a
problem.  This problem should be able to be solved by placing unsulating
material between layers of the inductor.  I am working on this now.
Another thing I am planning on doing is to use 2 toroids per side in
series, each of about 2 mH in value.  That is about 3.5 layers of 24 gauge
hook-up wire.  By using 2 in series, I will divide the drop up between 7-8
total layers, or only about 7000 volts per toroid.  This should be much
easier to handle without burn-out.

Hope that provides some insight,
Scotty