[Prev][Next][Index][Thread]

Re: 2 simple questions



-- BEGIN included message





At 08:33 AM 3/10/97 -0600, you wrote:
>Return-Path: <tesla-request-at-pupman-dot-com>
>Received: from ns-1.csn-dot-net ([199.117.27.21]) by mail.stic-dot-net
>          (post.office MTA v2.0 0813 ID# 0-10265) with ESMTP id AAA63
>          for <tesla-at-stic-dot-net>; Mon, 10 Mar 1997 01:31:25 -0600
>Received: from poodle.pupman-dot-com (slist-at-pupman-dot-com [204.133.95.34])
>	by ns-1.csn-dot-net (8.8.5/8.8.5) with ESMTP id AAA10633
>	for <tesla-at-stic-dot-net>; Mon, 10 Mar 1997 00:31:20 -0700 (MST)
>Received: (from slist-at-localhost) by poodle.pupman-dot-com (8.7.6/8.7.1) id
AAA23652; Mon, 10 Mar 1997 00:30:47 -0700
>X-Envelope-From: William_B_Noble-at-msn-dot-com  Mon Mar 10 00:30:47 1997
>Received: from ns-1.csn-dot-net (nameserv [199.117.27.21]) by poodle.pupman-dot-com
(8.7.6/8.7.1) with ESMTP id AAA23635 for <tesla-at-pupman-dot-com>; Mon, 10 Mar
1997 00:30:44 -0700
>Received: from upsmot02.msn-dot-com (upsmot02.msn-dot-com [204.95.110.79])
>	by ns-1.csn-dot-net (8.8.5/8.8.5) with SMTP id WAA09214
>	for <tesla-at-pupman-dot-com>; Sun, 9 Mar 1997 22:42:19 -0700 (MST)
>Received: from upmajb06 ([204.95.110.89]) by upsmot02.msn-dot-com
(8.6.8.1/Configuration 4) with SMTP id VAA08412 for <tesla-at-pupman-dot-com>; Sun,
9 Mar 1997 21:35:25 -0800
>Date: Sun, 9 Mar 97 18:43:11 UT
>From: "William Noble" <William_B_Noble-at-msn-dot-com>
>Message-Id: <UPMAIL09.199703100536550993-at-msn-dot-com>
>To: "Tesla List" <tesla-at-pupman-dot-com>
>Subject: 2 simple questions
>
>1. how do you decide what diameter tubing to use for primaries - I am building 
>a small coil, and I bought a box of 3/8 tubing, but several persons 
>recommended 1/4.  I won't be messing with the tubing for a couple of weeks so 
>there is plenty of time to return it and get the smaller (cheaper) stuff.
>
>2. A more technical question.  I don't understand the need for the HV primary 
>voltage.  As best I can figure out, what drives the output is primary current, 
>not voltage - after all, there is no way you will have 15KV across a copper 
>buss bar - what you are doing, it seems to me, is creating a big pulse that 
>then resonates back and forth through a tank circuit made up of the primary 
>and the capacitor (whilst the spark gap conducts), and the primary only 
>(higher freq osc) when the spark gap is not conducting.
>
>So, why can't I just charge up a farad or so of "computer type" electrolytics 
>to 100VDC and then dump the charge through a 1,000 amp SCR into the primary 
>directly????  Has anyone tried this??  I would imagine having a LC circuit of 
>the tubing for the L, and a suitable AC capacitor, as a tank circuit.  Then, 
>the SCR and the capacitor bank would share a common ground with the tank 
>circuit.  The SCR would fire, dumping charge, and then the reverse current 
>would shut off the SCR.  The pulse would resonate in the tank for a while, 
>then you would fire the SCR again.   A crude schematic is represented below:
>			  Gate Drive
>			 /
>			/
>   L-----|---------------SCR----------||||||||||||||||||||||||||  ------ +++   
> 
>   L      C                                  CCCCCCCCCCCC     charging circuit
>   L-----|____________________|||||||||||||||||||||||||||_____- - -
>
>This would seem to have several benefits over a spark gap interrupter - lower 
>loss, faster switching, lower (hence safer) primary voltages, and lower cost 
>primary power supply.  Comments???
>
>
William,

It would work, but for a lot of things.  First, the farad plus computer caps
are made for hour long charge/discharge times.  Second the same caps are
incredibly inductive which would ruin the primary tank system's surge
impedance even if they could charge and recharge fast enough. (which they
can't).  The spark (voltage) out is a actually a function of the RATE OF
CURRENT delivery with respect to time.  We require lots of current in a tiny
period of time to get lots of voltage rise from the secondary.  We also need
to recharge  the capacitor in milliseconds and dump it in microseconds.
Fiinally, to resonate a 1 farad capacitor at even a low frequency of 100khz
we would require about .000006 turns in the primary.  Not conducive to
critical tune.   All of the above militates against any low voltage scenario
with big caps producing any sort of viable continuos operation Tesla coil.

Richard Hull, TCBOR






-- END included message