Re: Protecting NSTs

• To: tesla-at-pupman-dot-com
• Subject: Re: Protecting NSTs
• From: "Malcolm Watts" <malcolm.watts-at-wnp.ac.nz> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
• Date: Mon, 27 Sep 1999 03:44:03 -0600
• Approved: twftesla-at-uswest-dot-net
• Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

Hi Marco,

> Original Poster: "Marco Denicolai" <Marco.Denicolai-at-tellabs.fi> 
> 
> Hello.
> 
> If with "fullwave" you mean a bridge (4 diodes), actually a single
> series diode is enough.

Indeed I did mean a fullwave bridge. All the  NSTs I've seen have a 
centre-tap in the secondary. I don't know how you'd get a fullwave 
output from anything using a single diode?
 
> 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?

It's always there isn't it?

 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 transformer magnetic shunt starting to affect? 

Umm - well actually the shunting does limit the current as long as the 
transformer output isn't resonated with a capacitor and then the 
current can only rise if it is allowed to ring up over more than a 
quarter (half?) a cycle?

I think the issue of concern if there is any would be the parasitic 
capacitance present at the terminals discharging through the 
diode/s and gap. However, all rectifiers I know of are designed to 
take peak repetitive currents well above their average ratings. I'd be 
surprised if this is an issue for a NST supply. ?

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.

?  Not sure how this relates. 

> 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 allow max 2X voltage buildup.

How's the quasi-resonant supply going? I've just resumed work on 
my DC charger also.

Regards,
Malcolm

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