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Re: SCR's again

Subject: 
        Re: SCR's again
  Date: 
        Mon, 17 Mar 1997 18:56:57 -0500
  From: 
        "Robert W. Stephens" <rwstephens-at-headwaters-dot-com>
    To: 
        Tesla List <tesla-at-pupman-dot-com>


> Date:          Sun, 16 Mar 1997 23:02:48 -0600
> To:            tesla-at-poodle.pupman-dot-com
> Subject:       SCR's again
> From:          Tesla List <tesla-at-pupman-dot-com>

> 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

Gary,

How much is a bunch, and waddayawant?  If possible I'd swing for the 
lot.  Yes, swing!!! : )

rwstephens