[Elecraft] Overvoltage Protector Update

[Scott Ellington]

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 overvoltage 
 protection.  All regulated power supplies are capable of producing much more 
 than their normal output voltage if any one of a number of things fails.  
 Linear supplies are particularly susceptible, since the pass transistor can 
 short.  
 
 While Elecraft assures me that the K3 can survive an overvoltage with minimal 
 damage, I prefer to be on the safe side.   So I designed a crowbar circuit, 
 which can be used with any 12 V power supply up to 30A.  If the voltage 
 exceeds the trip point (14-16 V), it will short the power supply output and, 
 if necessary, blow a fuse.
 
 http://www.ssec.wisc.edu/~scotte/hr/OVP.pdf
 
 I haven't built this one yet, but a very similar one I built in 1984 worked 
 fine.
 
 73,
 
 Scott  K9MA
 
 
 

Scott Ellington
Madison, Wisconsin
USA



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Re: [Elecraft] Overvoltage Protector Update

[John Huggins, kx4o]

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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