Re: Protecting NSTs


If with "fullwave" you mean a bridge (4 diodes), actually a single series diode
is enough.

Questions that should get an answer before trying this solution:

1. That diode will see the short circuit current of the transformer when the
spark gap fires. How fast is the magnetic shunt build in the NST?
2. The NST secondary inductance will also act as a current rise delay (delay,
not limiter): which effect is faster, current rise due to the secondary
inductance terminating its influence or current decrease due the the
magnetic shunt starting to affect?
3. What is the maximum quench time of the spark gap used? That could be so fast
to limit by itself the current rise at the transformer side.

The easiest thing to do would be to simulate with MicroSim the whole thing,
inserting actual values for NST inductance and primary capacitor. You can find
something about what I did at
http://www.saunalahti.fi/dncmrc/thorguid.htm#b5-1-1. There is no NST there but
the idea is the same: inductor to limit the current (1.5H !) and diode the
max 2X voltage buildup.


Tesla List <tesla-at-pupman-dot-com> on 22.09.99 14:46:13

To:   tesla-at-pupman-dot-com
cc:    (bcc: Marco Denicolai/MARTIS)
Subject:  Protecting NSTs

Original Poster: "Malcolm Watts" <malcolm.watts-at-wnp.ac.nz>

Hi all,
           I have a suggestion for preventing resonant charging when
using a NST that was inspired by a question put to the Tesla-2 list.
Inserting a fullwave rectifier between the transformer and primary
cap should do the job since it prevents the cap discharging back
into the transformer and allowing the secondary to resonantly swing
to ever higher voltages. It won't stop the peak cap voltage from
reaching 2x the RMS transformer voltage but that is as far as it can
go. In other words, if you use a fullwave bridge and your static gap
is set wide enough to prevent firing, you know your transformer is in
danger. It *may* also block gap transients from reaching the
transformer if the diodes are ultra fast types perhaps (speculation).