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Re: SCR spark gap results are in!

Original poster: "S&JY" <youngsters@xxxxxxxxxxxxxxx>

Several years ago, another coiler reported design details and schematics of
an SCR driven coil, at least 8 pages worth with many photos.  It was a
magnifier that resonated at 78 kHz.  If you do a search for "SCR coils
stuff", you will find this URL:  http://home.hiwaay.net/~eburwell/
Unfortunately, the link no longer works, but it appears the coiler was E
Burwell.

He said "I'm pumping 1000A pulses through an 80A SCR.  Strong gate drive and
the saturable inductor are the key.  The saturable inductor in my setup is a
HUGE ferrite toroid.  It buy me 2 uSs before the core saturates.  The
current rises to 32A at which point the core saturates.  The inductance
drops dramatically and the current then rises to 1000A in 2.5 uS."  The 8
pages I saved don't say how well the coil performed.  The drive circuit was
a LMC555 timer followed by an IRF521 feeding a pulse transformer.  The SCR
was a T500.  I don't have the complete schematic or enough info to replicate
his work, so please don't bother to ask me for more detail - I don't have
it.

Perhaps SCR technology has advanced in the intervening years to allow higher
frequency TCs.  If anyone has more detail about Burwell's SCR coil, please
share it.
--Steve Y.

----- Original Message -----
From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Thursday, December 02, 2004 6:06 PM
Subject: RE: SCR spark gap results are in!


> Original poster: "Derek Woodroffe" <tesla@xxxxxxxxxxxxxxx>
>
> Hi,
> Please forgive my lack of knowledge on this thread I'm new to TCML.
>
> Re SCR turn off times, If you ran the SCR with a suitable reverse
> diode you should be able to use the coil in a similar way to an IGBT in an
> OLTC. Discharge the primary cap into the primary, let it ring up with the
> reverse diode taking the -ve swings , turn off when ring up is complete.
>
>   The slow turn off times are not as important as they can be over a
number
> of cycles (the ring up time of the coil) so slower devices could be used.
>
> The problem you may be having with SCR's is that their slow turn on
> time will limit the power you can get into the first bang, but if you have
> got 1us turn on time SCR's as long as they can handle the dv/dt I don't
see
> that as an issue.
>
> Derek Woodroffe.
>
>
>
>