Re: Overvoltage Protector Update

Posted by John Huggins, kx4o on Aug 23, 2010; 6:10pm
URL: http://elecraft.85.s1.nabble.com/Overvoltage-Protector-tp5445892p5453656.html

Nice circuit.  Since this is meant to help protect the K3 from faulty
power supplies, this begs the question of what abuse can the K3 (or K2)
take from the power bus.

As an automotive power bus is a terrible awful place, will the K3 design
tolerate these typical values found on a vehicle power rail:

- Steady State Voltage between 12.5 to 15 Vdc,
- Upper and lower ripple of +/- 1 Vpeak riding on the Steady State values,
- Surge values between 9 and 20 Vdc for 600 ms,
- Spikes of +/- 125 Volts peaking for 70 uS falling to steady state levels
after 1 ms,

?

> I've updated the drawing to include construction notes and a mechanical
> sketch:
>
> http://www.ssec.wisc.edu/~scotte/hr/OVP.pdf
>
>
> The large heat sink, I know, will seem to some like overkill.  To me, an
> extra 20 bucks seems like cheap insurance.  See the notes.
>
> As W8JI notes, a simpler circuit just uses a zener diode to drive the SCR.
>  I chose the more complex version to allow the trip point to be set close
> to the operating voltage.  The K3, for example, has a maximum rating of
> 15.0 V, too close to 13.8 for the simpler circuit.
>
> At the moment, all the parts are available from Digi-Key.
>
> Scott  K9MA
>
>
>
>
> On Aug 20, 2010, at 3:00 PM, Scott Ellington wrote:
>
>> Some power supplies, like the Samlex SEC 1235, have no built-in

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