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Re: Secondary form-factor
From: Adam[SMTP:absmith-at-tiac-dot-net]
Sent: Tuesday, October 28, 1997 3:39 PM
To: Tesla List
Subject: Re: Secondary form-factor
> I my haste, I may have over done it with my secondary coil. It is
> wound on 4" PVC waste pipe, 4' long, approx. 1500 turns. Is this coil
> too long and thin?
Yeah, that's way too long. Most people who build on 4" PVC end up with a
coil between 18" and 26" high, depending on what gauge wire they are
using. In general, if you want a coil with a lower frequency, it is
better to start with a wider form so that the secondary is within the
strong area of the field from the primary (these coils are magnetically
coupled remember).
> If so, I could (shudder) slice off about 1' and use the 1' length as
> the secondary for an air-core transformer I'm thinking about making.
If I were you, I would either try this as a bipolar coil with the
secondary horizontal and the primary at the center, or drink some rum and
bite hard on a stick while you <yikes> saw it in half.
> Scenario 1:
>
> 2 microwave transformers, producing 4200V, 60Hz
> 4' secondary
> 0.01 uF cap., 30 kV
>
> Scenario 2:
>
> 15kV, 60ma solid state power supply (air core tranny driven at 4-20kHz)
> 3' secondary
> 0.01 uF cap., 30 kV
>
> Which scenario would is most attractive? (From a big whopping spark
> standpoint, of course ;)
I'm not quite sure what you are trying to accomplish with these supplies.
You are not going to be able to build a 15kV -at- 60mA air core transformer
that will run efficiently at 4-20kHz. Iron/Ferrite core is a must in
this frequency range.
Besides, what do you have against 60Hz? 60Hz works fine giving the
secondary a chance to resonate for about 1/120th of a second between hits
from the caps. Plus, neon sign transformers are cheap (often free) and
provide the 15kV 60mA you are looking for, from a single easy-to-hook-up
black box.
On the downside, 15kV AC from any source is going to stress your 30kV
cap. If the cap is rated 30kVDC, it could very easily fail (depends on
the type of capacitor, and the manufacturer's margin of safety in the
rating). I would use a 12,000V supply max with this capacitor, and even
that is still a risk. If you must run at 15kV, use a cap rated at 50kV
or higher (or caps in series), and choose the capacitance value
appropriate to the required tank resonance frequency, and to match your
transformer's output impedance, wherever possible. HV pulse caps are
expensive (I just found this out) and it's certainly worth buying the
highest voltage rating you can afford, especially for use with High-Q
resonant circuits like Tesla primaries.
-Adam
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Adam Smith
absmith-at-tiac-dot-net
Epoch, Inc. Digital Music Project
www.tiac-dot-net/users/absmith/ Now with MP3! Musik. Macht. Macintosh.
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