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Re: [TCML] mini Tesla coil specs
This could be of some help to You guys:
http://scopeboy.com/tesla/t4spec.html
I am just wondering if IGBT "gap" + primary of a very low impedance are more loosy than in normal spark gaps coils at typical Tesla coil frequencies.
Dex
--- pbbrodie@xxxxxxxxxxxxx wrote:
From: "Paul Brodie" <pbbrodie@xxxxxxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Subject: Re: [TCML] mini Tesla coil specs
Date: Sun, 8 Nov 2009 16:59:14 -0500
Unfortunately, the http://home.hiwaay.net/~eburwell link is no longer
active. :-(
Paul
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
>
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