RE: [TCML] First (or maybe 2nd) light on my medium-sized SG coil

["Lau, Gary" <Gary.Lau@xxxxxx>]

It's not even clear that maximizing peak primary current by minimizing inductance is a good thing.  Assuming that Fpri=Fsec is maintained, a lower primary inductance will indeed maximize primary current, but this also increases spark gap losses.  The experience of myself and others is that higher inductance primary coils give better performance.  Granted, primary resistive losses may be greater, but apparently not as great as the higher gap losses with low inductance primaries.

Regards, Gary Lau
MA, USA

> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> Behalf Of bartb
> Sent: Sunday, April 20, 2008 2:20 PM
> To: Tesla Coil Mailing List
> Subject: Re: [TCML] First (or maybe 2nd) light on my medium-sized SG coil
>
> If you want high peak currents, reduce the surge impedance as Z =
> sqrt(Lp/Cp). Less L or more C will decrease surge impedance and increase
> current as Ip = Vp/Z.
>
>  From my reasoning, lead inductance can be an issue regarding it's
> length, but it is dependent on the ratio of primary to lead inductance.
> For my coil, that ratio is 29.8. If I double the length (from 30" to
> 60") of lead wiring, that ratio drops to 13.3 (which puts the lead L as
> 7.5% of the total L). So for coils which use only a few primary turns
> (low inductance), the lead inductance can be significant and thus the
> length can have a significant effect on Ip (and tuning), but for those
> 10 to 15 turn coils, usually it's not a concern and lead inductance then
> has little effect on Ip. This is why I call out lead length and lead
> wire size in Javatc so that I can account for it and apply it into the
> total L. In many cases, it has little effect, but in some cases it does.
>
> I don't think it's right to say lead length makes little difference or
> that lead length must be kept short due to Ip. Both are generalizations
> and it really should be put into perspective to the coil itself. I think
> it is of course good practice to keep it short. But on really tiny
> coils, even short lengths can have an impact.
>
> Take care,
> Bart
>
>
> Lau, Gary wrote:
> > I'm all for keeping tap leads and all tank circuit wiring as direct and tidy as
> possible, but doing so in the name minimizing inductance to not impede current
> peaks doesn't make sense to me.
> >
> > Any additional inductance in tap wiring would simply be that much more
> inductance in the primary circuit, so tapping slightly inward on the primary inductor
> would compensate.  Additional inductance in wiring may not couple strongly to the
> secondary, so it might be referred to as off-axis inductance.  But this is not a loss
> and is not undesirable; it just means that the secondary may need to be lowered
> slightly to compensate for a very marginally lower coupling.  Off-axis inductors are
> sometimes used for fine tuning the primary.
> >
> > Unnecessarily lengthy tank circuit wiring may result in RESISTIVE losses
> however, and for THAT reason should be kept as direct as possible.  Resistive
> losses are truly losses and cannot be compensated for.  I don't mean to nit-pick, but
> it's important to keep our reasoning straight.
> >
> > Regards, Gary Lau
> > MA, USA
> >
> >
> >
> >> -----Original Message-----
> >> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> >> Behalf Of DC Cox
> >> Sent: Saturday, April 19, 2008 4:28 PM
> >> To: Tesla Coil Mailing List
> >> Subject: Re: [TCML] First (or maybe 2nd) light on my medium-sized SG coil
> >>
> >> The tap lead should be short such that it adds only minimal inductance to
> >> the LC tank circuit.  Any additional inductance in the tank circuit circuit
> >> is undesireable as inductance always acts to impede the current max peaks,
> >> and we need to keep these max curents high as the magnetic field coupling
> >> the sec coil depends on high current to produce powerful magnetic fields
> >> that contain a lot of energy.
> >>
> >>
> > <snip>
> >
> >> Safety first and happy coiling!
> >>
> >> Regards,
> >>
> >> Dr. Resonance
> >>
> >
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> >
> >
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