At 12:35 PM 11/19/2009, you wrote:
>
>If anyone is interested I've posted a circuit and veroboard layout
>for a tested and working crowbar circuit based on the MC3423 chip on
>the blog for my Wittman Tailwind build. Total parts cost around $5.
>
>http://tailwindbuild.blogspot.com/2009/11/15th-november-2009-overvoltage-crowbar.html
>
>Click on the pics/diagrams to enlarge
>
>The variable resistor allows the crowbar voltage to be set as
>required and compensates for differences in the internal reference
>voltage on the MC3423.
Some thoughts based on lessons-learned:
You need to select the trip time delay capacitor
for something on the order of 50-100 milliseconds.
Further, depending on how "twitchy" the SCR is,
you may experience nuisance triggers of the SCR
due to very low energy but fast rise-time
noises on the bus. These are effectively dealt
with by tying a 10 ohm resistor from SCR gate
to ground (which may mean a commensurate increase
in gate drive requirements from the MC3423).
Bob . . .
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