Re: dc drive forT-coil and S-gap replacement?

From: 	Greg Leyh[SMTP:lod-at-pacbell-dot-net]
Sent: 	Wednesday, January 07, 1998 6:19 AM
To: 	Tesla List
Subject: 	Re: dc drive forT-coil and S-gap replacement?

solva-wijnschenk wrote:

> I am too wondering wether it is possibel to drive a teslacoil with dc
> and without a unaccurate sparkgab.
> First: Would it be worth to try to rectify the output of a 20-25 KV NST
> with High Voltage Bridge rectifier consisting of several 1Amp, 10000 V
> diodes switched in series and feeding the HV capacitor?

Much of the advantage of a DC coil is lost on 60Hz single-phase systems,
since a large filter cap would be required.  A switched-mode cap charger
would be the best way to use single-phase on a DC coil.

> Second:
> does anybody know some scheme's for sparkgap replacement by HV-triacs.
> This would be a great way to synchronize the 'gap' on the
> resonancefrequency by for example triggering the triacs via shuntvoltage
> of a (very low!!, high Watt) resistor placed in the primary circuit?

My preferred topology for a single-phase coil would feature 
the following technology:

Prime power - 10kW offline switched, HV capacitor charger 
   - 4W/cu.in., weight 75 lbs
   - no 60Hz xfmr
   - operates from 110V to 250V, DC to 400Hz
   - break rates to 400 BPS

Primary switch - Modified GTO
   - no moving parts
   - higher efficiency
   - ultimate quenching capability
   - much lower primary impedance(and therefore voltage) possible

The coil itself would have a coupling between 0.25 and 0.35,
given the quenching ability of the GTO stack.  Any energy that 
was not absorbed by the arc would be actively switched back 
from the secondary into the primary capacitor bank, thus reducing 
considerably the actual demand from the prime power source.  The
power factor would be around 0.98, due to the linear charging 
ramp on the pri cap bank.