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Re: [TCML] (no subject)

Thanks, I have 2 other Tesla coils now biggest 12kv@ 50ma

Sent from my Verizon, Samsung Galaxy Tablet
-------- Original message --------From: Carl Noggle <cn8@xxxxxxx> Date: 8/15/17  1:08 PM  (GMT-06:00) To: Tesla Coil Mailing List <tesla@xxxxxxxxxx> Subject: Re: [TCML] (no subject) 
Jim, as usual, speaketh the TRVTH.

An 8kV transformer will charge a capacitor to close to 12 kV, which is 
fine for a Tesla coil.  Your cap should be rated for at least 30kV, 
since it will be charged both positively and negatively, and should have 
some slack on top of that.  That will work for a rectified coil too, 
since the voltage will stay on one side of zero.  My coil runs on 9 kV, 
with 50kV rated caps.  If you go much above 15 kV of operating voltage, 
you will encounter unauthorized arcs, sparks and coronas which will 
require a new level of high voltage art and finesse.

Excellent advice to build a coil with one NST for starters.

--- Carl

On 8/15/2017 10:01 AM, jimlux wrote:
> On 8/15/17 9:11 AM, Jeff Allen wrote:
>> Hello All, I have 8000vdc transformer at 1 amp. Do i need to use a 
>> voltage
>> doubler to get up around 16000v? Can some one explain the differance 
>> useing
>> ac or dc voltage for the Tesla? Im looking to build a large Tesla and 
>> big
>> arckes. Thanks
> is it 8kV DC, or AC?  Most transformers put out AC but sometimes they 
> are packaged with an integral rectifier.
> For a first coil, I'd start with a (iron core) neon sign transformer, 
> build that up and get through all the peculiarities of building a coil.
> But DC is a bit trickier to use - WIth AC, the circuit is pretty 
> simple - the supply voltage charges a primary capacitor until the 
> spark gap breaks down connecting it to the primary inductor.  That 
> resonant LC is coupled magnetically to the LC secondary circuit, the 
> energy transfers from primary to secondary, the voltage comes up on 
> the secondary and you get sparks.
> With AC, the supply goes through zero periodically, so the spark gap 
> "turns off" naturally.  With DC, you have to help it along -typically 
> by using a series inductor and a big HV diode - so now, you not only 
> have your HV supply, the primary capacitor and primary inductor, but 
> you have a "charging inductor" and a HV diode (that has to take a 
> pretty abusive environment... no 1N4001 in this application<grin>)
> with 8kVA, you're also most likely looking at needing a rotary gap - 
> while people have built static gap coils at that power level, it's 
> tricky - probably a blast gap of some sort (high velocity air to "blow 
> out" the spark between half cycles, or at least cool the elecrodes).
> Hence the suggestion to try a lower power NST based coil with a static 
> gap so you get the "feel" of tuning and stuff on something that won't 
> outright kill out or start a fire or spread shrapnel from a rotary gap 
> or worse if something goes wrong.
> Or, find someone near you who's built coils before so they can give 
> you advice.
> You'll also need a suitable primary capacitor - with 8kV you're going 
> to need a healthy HV capacitor that can take the RF current - current 
> techniques are "repurposed" and derated pulse discharge capacitors 
> from companies like Maxwell Labs/General Atomic OR series parallel 
> strings of high current polypropylene dielectric snubber capacitors.
> Neither of these is cheap at this power level (hundreds of $)
> Do you want a doubler?  That kind of depends - 8 kV is certainly 
> enough to make sure the spark gap breaks down, but you're also 
> doubling the current. Most AC coils run at 14-15kVrms which is about 
> 20kV peak.  But building a high power doubler is no trivial matter 
> either.
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