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Re: Oil-immersed RFCs


From: 	DR.RESONANCE[SMTP:DR.RESONANCE-at-next-wave-dot-net]
Sent: 	Sunday, August 31, 1997 9:41 PM
To: 	Tesla List
Subject: 	Re: Oil-immersed RFCs

To: Felix

The oil immersion is not necessary.  The peak spikes are no where near 60
kv IF you keep the spark gap in parallel with the feed transformer.  At
sparking this represents a short across the transformer and the spikes are
usually below 20 KV in smaller systems.  A standard 6 inch long piece of 1
1/2 inch dia plastic (delrin, etc) works fine -- cut 1/2 inch deep x 1/4
inch wide notches and space them 1/4 inch apart.  Wind #24 or 26 AWG into
each notch which gives approx 100 turns per notch.  Wind 5-6 notches so you
have a 500-600 turn inductor.  Use a small HF toroid wound with 10-12 turns
of #16-18 AWG PVC insulated wire.  Use this in series with the aircore
inductor with the ferrite core toroid attached to the xmfr bushing. 
Additional protection can be provided by a 10 to 100 Ohm resistor (25-50 w)
in series with these two inductors.  We have never had one of the above
described systems fail in over 30 years of active coil building --- and we
only lost two neons -- actually probably because they were used and perhaps
bad to start with.

DR.RESONANCE-at-next-wave-dot-net


> 
> 
> From: 	Felix[SMTP:73374.1547-at-CompuServe.COM]
> Sent: 	Sunday, August 31, 1997 2:15 PM
> To: 	tesla-at-pupman-dot-com
> Subject: 	Oil-immersed RFCs
> 
> Tom,
> In your RFCs, is the number of 'slices' of winding driven much more by 
> breakdown voltage than by inductance requirements? I've been looking at
>  solenoid formulas and wire tables and offer this line of thought:
>      Using no. 22 wire, which gave about 35 tpi on my Tesla secondary,
one of
> your slices of winding would have about 35 layers in its 1-in radial
depth.
> Postulating a two-slice RFC facing 60 kv spikes, we get roughly 1 kv per 
> layer of winding or, as you point out, 2 kv between the ends of adjacent 
> layers---or easily 5 kv if the layers are not laid down absolutely evenly
> and some wires slip down into a lower layer
>   Now 2 to 5 kv sounds to me like a lot for the few mils of enamel on my
no.
>  22 Phelps-Dodge Thermaleze, although I know volts/mil are higher for 
> insulation in thin layers.
>    This suggests that the choice of RFC wire gauge may be more critical
than
> it looks at first sight. I've never seen data on breakdown voltage of
> enameled wires in the 22 to 28 ga region, far less at the high
frequencies
> of interest, but if for instance the insulation breakdown were about the
> same over this range of wire gauges, then the thinner wire would be 
> better due to fewer volts per layer.
> I also notice that Tesla secondaries with 500 to 1000 turns and several
feet
>  of arc evidently achieve turn-to-turn breakdowns of 0.5 kv or more, and
in 
> the literature I haven't seen any concern about needing heavier secondary

> wire at higher arc length. This suggests that for our RFCs, something
around
>  1 kv between any two adjacent wires may be OK. This would call for
dividing 
> the total inductance of each RFC into about two to five 'slices',
depending 
> on how precisely your electric drill technique can place and separate the

> layers. As a by-product it would also give the several millihenries that
some
>  coilers favor.
> How does all this sound to you?
> The fun thing about coiling is that the circuit diagram can be so simple
in
> appearance, yet conceal so many unexpected subtleties.
>     Regards, Felix
> 
>