SCR's again

To: tesla-at-poodle.pupman-dot-com
Subject: SCR's again
From: Tesla List <tesla-at-stic-dot-net>
Date: Sun, 16 Mar 1997 23:02:48 -0600
Approved: tesla-at-stic-dot-net
Subject: 
           SCR's again
      Date: 
           Sun, 16 Mar 1997 21:16:15 -0800
      From: 
           gweaver-at-earthlink-dot-net
        To: 
           Tesla List <tesla-at-pupman-dot-com>
References: 
           1


Tesla List wrote:
> 
> 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)


I found a bunch of 600 volt 300 amp SCR's at the scrap yard.  The
aluminum heat sink that was attached to these SCR's weighed about 5
lbs.  Do you think the HV feed back will kill one of these?  If anyone
is interested in experementing I will let these go real cheap. I'm
talking 98% below retail price.

Gary Weaver