On Thu, Apr 5, 2018 at 1:47 PM, Van Horn, David <
david.vanhorn@backcountryaccess.com> wrote:

>
> High energy capacitive discharge is fairly well trodden ground. See if an=
y
> of these give you some food for thought.
> http://www.electricstuff.co.uk/destructotron.html
> http://www.capturedlightning.com/frames/shrinkergallery.html
> https://hackaday.com/2012/09/28/how-a-quarter-shrinker-works/
>
>
> These are primarily "one shot" applications, I need tens of pulses per
> second.
>
>
I designed and built a few of these for my day job (larger capacitor maker
you would recognize). They are "hockey puck" SCRs with multiple diodes in
parallel to catch the ring back. I used single SCRs as it made the design
much easier. You need to know how much di/dt you want to handle. I started
with these (there are probably better parts on the market now):

https://www.vishay.com/thyristors/list/product-94414/

These have good voltage handling and are capable of 1000 A/us of current
rise. To get the max di/dt out of an SCR you need to drive the gate as hard
as possible. For the Vishay SCR I used a microchip mosfet driver at around
20V if I recall correctly. To manage di/dt I use inductance in the circuit,
which is usually just extra wire. Using v=3DL(di/dt) you can work out how
much inductance you'll need to protect the SCR. To measure wire inductance
I just back calculated the ringing frequency with my known capacitance
after firing the circuit with a low voltage.

The device sheets always specify "non repetitive" and so far I'm not sure
what that means exactly. They are happy with large currents at 5 to 15Hz
with some factor of safety in the di/dt limit. The largest di/dt happens at
the beginning of the sinusoidal discharge.

This is an LT spice circuit that track really well with "real life"

https://i.imgur.com/bWBy5N6.png

For timing the discharges I used a PIC that's controlled by UART.

Interesting SCR stuff:

http://educypedia.karadimov.info/library/an1008.pdf
https://www.dynexsemi.com/assets/downloads/dnx_an4999.pdf


Also, SBE (not my employer) is using a physical discharge contact for their
large capacitor work:

http://www.sbelectronics.com/wp-content/uploads/2009/11/PMC2006-presentatio=
n.pdf
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