[Elecraft] K3 power switching.

[G4GNX]

Forgive me Fred, but so far I've not been able to locate those components on 
the schematics. Do you know which page they're on?

It's also possible that the zener had failed previously, so this time it 
didn't cause the fuse to trip. On the other hand, what sort of fuse is it, 
mechanical, thermal or electronic? As we all known, chips are the fastest 
fuse on multiple legs and given a gross voltage overload, I doubt that a 
mechanical or thermal fuse would be fast enough.

I'd prefer to see a full-blown crowbar circuit at the start of the power 
circuit and of course the same in the PSU although I do admit to having 
defeated a crowbar once. I'd built a 12V 10A variable PSU which would go up 
to 15V before the crowbar tripped in and the regulator then saw the overload 
and shut the output down. For some reason I had connected the PSU across a 
car battery and then absent mindedly increased the PSU voltage past 15V at 
which point the crowbar shorted the output, but of course car batteries 
don't care about that, so considerable current hit the crowbar and destroyed 
it! No other damage, so I replaced the thyristor and learned from the 
experience. :-)

73,

Alan. G4GNX

-----Original Message----- 
From: Fred Townsend
Sent: Wednesday, May 13, 2015 7:36 AM
To: G4GNX ; Elecraft Reflector
Subject: Re: [Elecraft] K3 power switching.

Alan the power circuit on the K3 is very robust and is protected from over 
voltage. There is a 15 volt zener that should trip a self resetting 6A fuse. 
It may be that zener over heated and shorted but even so there should not be 
smoke.

I agree your psu should be set so it can not exceed 14.8 volts.

73
Fred, AE6QL