Re. DC powered tesla coil (fwd)

---------- Forwarded message ----------
Date: Tue, 21 Jul 98 09:04:43 EDT
From: Gary Lau  21-Jul-1998 0807 <lau-at-hdecad.ENET.dec-dot-com>
To: tesla-at-pupman-dot-com
Subject: Re. DC powered tesla coil (fwd)

>From: Max Di Tommaso <sistemi-at-mail.matav.hu>
>Hi all,
>I just joined the list. As a beginner, I have my load of questions to
>ask to you expert coilers (I confess, haven't built a working one yet!).
>1. I was wondering about charging the tank cap with DC voltage supplied
>by a neon transformer and a half or full-wave rectifier. This would
>allow charging larger caps with smaller transformer because the spark
>gap wouldn't fire 50 or 60 times per second but less frequently, let's
>say every second. 

Any neon transformer can charge up a suitable capacitor every half-cycle
just fine without resorting to DC.  I have only heard of going down to 30
gap firings per second, no slower.  It you do attempt to go slower, the
character of the sparks will not be as good, as a spark depends upon a recent
previous spark to ionize the channel, so that a continuous channel forms.
Once per second won't work well, though it might be interesting to see what

Most capacitors used with small neon transformers (20-30mA) start around .004
uF.  With this value, it can be charged from zero to the transformer's peak
voltage in one half cycle.  If you were to size a capacitor such that it would 
charge at 30 mA for one second, you would need something like a 2uF capacitor.
Besides the cap being HUGE, you'd be hard pressed to create a primary inductor
that would resonate with that at the same frequency as a reasonable secondary.

>I guess that the peak power delivered to the coil
>shouldn't be much different as it depends, IMO, on the peak voltage
>before the spark gap fires and not how often this occurs. Is that
>correct? Any other parameter unchanged, does the repetition rate of the
>tank cap discharge affect the quality (lenght, brightness, etc) of the
>streamers jumping out the toroid?

I think you want to talk about the average power.  The peak power would be very
different.  The peak primary voltage will be the same regardless since you're
charging the cap up to the same transformer voltage, either a big cap once per
second, or a small cap 120 times per second.  

>2. I happen to have some inductive ballast of the type used with
>fluorescent tubes. Can they have any use in coiling (perhaps as RF

I've heard of no Tesla coil applications for ballasts.  The insulation is only
good for a few hundred volts, not the 30KV++ required for protection network
chokes, and the resistance is too high for use as AC mains RFI chokes.

>Thanks to everyone for any opinion. (English is not my native language,
>so please excuse my mistakes).

What mistakes?  Your English, grammar, and spelling is perfect and far better
than a lot of the native posters on this list!

>Max Di Tommaso

Regards, Gary Lau
Waltham, MA USA