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Re: [TCML] mini Tesla coil specs

Herr Zap was responding to me but I really appreciate you providing that information. I am using (6) 1200 volt 95 amp SCR's I bought for $4 total that I certainly don't mind sacrificing (frying) while attempting this project. The SCR's are also already mounted on a nice large heatsink. I will definitely take a look at Mr. Burwell's site and see what I can glean from what he has already accomplished. I'm sure it is going to save me all sorts of trouble. Thanks again!
Think Positive

----- Original Message ----- 
From: "S&JY" <youngs@xxxxxxxxx>
To: "'Tesla Coil Mailing List'" <tesla@xxxxxxxxxx>
Sent: Sunday, November 08, 2009 1:03 PM
Subject: RE: [TCML] mini Tesla coil specs

> Herr Zap,
> Here is a description of one SCR driven TC, circa 2000:
> Original Poster: "Eddie Burwell" <eburwell@xxxxxxxxxx> 
> Well, from my experiments with SCR based coils IGBTs look like the hot
> ticket. IGBTs like SCRs are four layer devices and have "fixed" voltage
> drops. This means the power lost in the switching device goes up linearly
> with increasing current rather than I^2R as does a mosfet. The IGBTs have
> some nice advantages over SCRs namely they turn on fast and they can be
> switched off.
>   I tried using saturable reactors to effectively speed up the turn on time
> of the SCRs which works but causes other problems ( like holding the SCR on
> for an excessive period of time.) So I ditched the saturable reactors and
> went to a 365A 1800V 60uS Tq SCR. This sucker is rated for 8000A peak. This
> works OK except that the SCR doesn't turn off until the primary cap is
> almost empty. No first notch quenching:-(. In order to get first notch with
> a 100KHz coil a Tq of 5uS would be necessary. Unfortunately 5uS SCR are kind
> of rare and don't usually exceed 600v.  As you head towards lower voltages
> and higher currents and more capacitance keeping the inductance low enough
> to hit the target resonance frequency becomes difficult. Not to mention how
> absurdly careful you need to be in order to minimize parasitic inductance.
> If your cap has as much inductance as your primary then your primary will
> only see half the voltage. This sort of thing can happen when your primary
> has only one turn.  So higher voltage is better! 
>  A 1200V IGBT is sufficiently fast and can be turned off, but there remains
> one question. How far can they be pushed past their current rating for a
> pulse? A 100A SCR can do 1000A for a brief pulse. Could a 45A IGBT make it
> to 450A? The ratings on IRG4PH50U say 45A cont. 180A peak but there is no
> indication in the data sheet as to how the max peak current relates to the
> with of a pulse (for infrequent pulses). If They can hit 450A look out!
>  With my last experiments in solid state coiling I could pull about 18"
> with a 1 joule cap fired 400 times per second. The SCR was barely warm.
> quality caps are an absolute necessity! I started with some CDE SCRN222s.
> Their internal connections were so poor the terminals got hot although the
> rest of the cap was cool. With 10 joules per bang an IGBT coil should start
> to really perform!
> To see my outdated web page with some of my early work look at:
> http://home.hiwaay.net/~eburwell
> Oh yeah.. IGBTs typically have internal anti-parallel diodes rated for the
> same current as the IGBT. Convenient..
> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
> Of Quarkster
> Sent: Friday, November 06, 2009 10:50 AM
> To: Tesla Coil Mailing List
> Subject: Re: [TCML] mini Tesla coil specs
> Hi Paul -
> Since you had also mentioned driving a coil with a SISG switch, I wasn't 
> sure if "SRC" might be a new type of power switching circuit that you might 
> have discovered somewhere. I suspected that you might have meant SCR, but I 
> thought it would be better to ask for clarification.
> In some industrial power-control systems, strings of series-connected SCRs 
> are used to obtain the high standoff voltage ratings required. Large arrays 
> of series-connected high-voltage, high-current SCRs have shown up on eBay 
> that have power ratings of hundreds of KW. However, I think these are 
> primarily used in pulse-width-modulation power control of resistive loads. 
> SCRs typically have rather slow turn-on and turn-off characteristics, 
> compared to IGBTs or MOSFETs, so they are not optimum for any application 
> that requires high-frequency switching.
> Over the years, there has been a fair amount of discussion on the TCML 
> concerning the use of SCRs as switches in Tesla coil primary circuits 
> (search the TCML archives at www.pupman.com). However, I don't recall anyone
> ever actually building a SCR-commutated Tesla coil. (If anyone is aware of a
> Tesla coil that successfully used SCRs as a primary switch, please speak 
> up!)
> SCRs are used very successfully to drive high-voltage generators based on 
> iron-core automotive ignition coils, but this is quite different than a 
> resonant Tesla coil.
> Regards,
> Herr Zapp
> ----- Original Message ----- 
> From: "Paul Brodie" <pbbrodie@xxxxxxxxxxxxx>
> To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
> Sent: Thursday, November 05, 2009 9:40 PM
> Subject: Re: [TCML] mini Tesla coil specs
>> Sorry, Herr Zap.
>> Simply a typographical error. I am legally blind and I normally write with
>> 18 type size. It is very difficult for me to see what is on the screen 
>> when I write with small type like this. I have set it to do it 
>> automatically when I write with HTML. Please excuse the error. By the way,
>> even though I am using plain text, is there any reason I can't use a 
>> larger type size when writing to the TCML? I suppose I should be asking 
>> Chip but in a way, I am. ;-)
>> Thanks for pointing out the error. That made my question rather confusing,
>> I suppose.
>> Paul
>> Think Positive
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