Re: [TCML] Single-ended NST, wiring

[mddeming@xxxxxxx]

Kits are made as cheap, fast, and carelessly as possible. Any damage caused by them is the liability of the builder under the blanket disclaimer they are sold under. Just like Russian roulette and unprotected sex, getting away with doing something is not proof of its inherent safety. 

Matt D




-----Original Message-----
From: jhowson4 <jhowson4@xxxxxxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Sent: Tue, Mar 5, 2013 7:14 pm
Subject: Re: [TCML] Single-ended NST, wiring


Hmmm. I wonder why this configuration is so prevalent in the small kit coils 
available from information unlimited and in the larger ones used at resonance 
research and the like then. For the purpose of limiting that voltage rise 
perhaps? If the dangers are reasonably high, then one would think the kits would 
be engineered away from this configuration. Heck the little information 
unlimited BTC-30 I built years ago, does not even have an RF ground, it just 
uses the house ground, with no problems I might add. 



Thanks, 
John "Jay" Howson IV 


"Why thank you, I will be happy to take those electrons off your hands." 

----- Original Message -----
From: "Jim Lux" <jimlux@xxxxxxxxxxxxx> 
To: tesla@xxxxxxxxxx 
Sent: Tuesday, March 5, 2013 10:45:17 AM 
Subject: Re: [TCML] Single-ended NST, wiring 

On 3/5/13 7:08 AM, Jim Lux wrote: 
> On 3/5/13 5:42 AM, jhowson4@xxxxxxxxxxx wrote: 
>> alright so apparently i missed something all these years. 
>> 
>> I thought you wanted to separate the two grounds and because the HV 
>> was grounded you should only use the RF ground in that system, but 
>> apparently not, you use both. 
>> 
>> You want to connect the ground on your transformer to the house 
>> ground, make your circuit like you have shone, and connect the 
>> bottom/inner turn of your primary to the base of your secondary. 
> 
> No.. there is no good reason to connect primary to secondary. Some 
> people do it for historical reasons, but for the vast majority of cases 
> this isn't a good idea. 
> 
> If you are using a Neon Sign transformer, or anything with a grounded 
> centertap, connecting primary and secondary as you describe is 
> DANGEROUS. On a typical NST driven primary, both ends of the primary 
> are "hot" relative to ground. 
> 



I missed the reference to the single ended NST with one end grounded. 
In that case, the danger is not as high. 

However, you generally do not want the primary connected directly to the 
secondary in any case: the spark from the secondary is a nice low 
impedance, and you don't want to make it easier to have 
someone/something hit by a spark connected to a HV source with more current. 

In typical cases, of course, the substantial impedance of the secondary 
winding would be in series as well, but there are cases of injury (and 
death?) when a connection was made between the primary winding and a 
person via a streamer. So that pushes for making the primary winding 
generally "isolated" from ground, so that if something "grounded" (e.g. 
a person) happens to touch it, the hazard is less. 

OTOH, you want some non-infinite impedance from primary to ground to 
limit the voltage rise between HV windings in the transformer and the 
core. 

> 
>> The NST (4kV, 50mA) for my SGTC is a single end type with one of its 
>> secondary winding ends attached to the metal casing. 
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