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Re: SCR's

Subject: 
        Re: SCR's
  Date: 
        Sat, 15 Mar 1997 12:37:33 -0700
  From: 
        "DR.RESONANCE" <DR.RESONANCE-at-next-wave-dot-net>
    To: 
        "Tesla List" <tesla-at-pupman-dot-com>


To:  Bill Noble

Noted your post on the SCR's and automotive ignition coils.  

The peak currents and nasty ringing seems to damage many solid state
device
when used with auto induction coils.  We have used these circuits also
but
always rate all devices for at least 5 times the expectly (or scoped)
peak
potentials and currents.  It may look strange to use hockey pucks in a
massive copper clamp with these devices but at least they never seem to
fail.

A friend and our group are also trying a novel approach to using these
coils.  We are going to fire another SCR system into the coil as soon as
it
hits the peak from the first system.  The second system will be reverse
polarity in attempt to cancel the first energy wave out and will be
dumped
about 4-10 microseconds later than the first.  Our thought is the di/dt
will go to zero much faster with less ringing and give us a greater fall
which should produce a higher output potential.

We are doing our first experiments on an common Accel "super coil" which
is
a 60 KV coil available for about $35.00 at automotive racing stores.  I
also talked to Dr. Jacobs of Jacobs Electronics about using one of their
coils in our testing applications.

Also noted the msn-dot-com post -- any chance you're from the Madison,
Wisconsin area??

DR.RESONANCE-at-next-wave-dot-net


----------
> From: Tesla List <tesla-at-pupman-dot-com>
> To: tesla-at-poodle.pupman-dot-com
> Subject: RE: SCR's
> Date: Saturday,March 15,1997 7:13 AM
> 
> Subject: 
>         RE: SCR's
>   Date: 
>         Sat, 15 Mar 97 11:29:02 UT
>   From: 
>         "William Noble" <William_B_Noble-at-msn-dot-com>
>     To: 
>         "Tesla List" <tesla-at-pupman-dot-com>
> 
> 
> I used to build electronic ignitions for cars - I would charge a 1 to 2 
> microfarad capacitor to about 450 V, The capacitor, an SCR,and the coil 
> primary made up the HV circuit.  When the breaker points opened, I would 
> trigger the SCR, dumping the capacitor into the primary of the ignition
> coil.  
> The coil would ring, shutting the SCR off, and the capacitor would start 
> charging again.  The Delta Mark 10 ignition uses a similar circuit. 
> This is a 
> lot like a tesla coil (and the spark from the ignition coil would jump
> about 4 
> inches), which is why I started thinking about SCRs - clearly in the
> above 
> circuit there is a pretty fast current rise - of course it depends on
> the 
> reactance of the automotive ignition coil (I used a 6V coil).
> 
> (snip)
> >
> >I'm not sure that SCR's can switch fast enough. I tried using MOSFET's
to
> >switch large currents into a primary (no capacitor - instead I drove the
> >switch at the resonance frequency. I got a 2" spark and I killed 4 or 5
> >FET's - the problem was that as the voltage rose in the secondary -
> >it was fed back to the primary. Result overvoltage killing the FET's.
> >
> >FET's have very low on resistances, 0.1 ohm, switch very fast
> >ie 50nS and handle high peak currents (40A), and they can be switched
> >off. Unfourtunately you would need a lot of them to handle 1000A at
> >10kV - back to the spark gap lads.
> >
> Have fun,
> >
> >Alan Sharp (UK)