[TCML] First (or maybe 2nd) light on my medium-sized SG coil
bartb at classictesla.com
Sun Apr 20 12:20:18 MDT 2008
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.
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 at pupman.com [mailto:tesla-bounces at pupman.com] 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.
>> Safety first and happy coiling!
>> Dr. Resonance
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