[Elecraft] Melted J3 Connector on K2/100

[Ron D'Eau Claire]

Rick K7MW wrote:
And a relativly large voltage drop.  This would show up as a low voltage at
the rig.  This is why it is important to monitor the voltage at the rig.  If
there is an unexpected low voltage at the K2, the cause needs to be
determined.

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Very true, and notice Rick said RELATIVELY large voltage drop. A drop of
only 1/2 volt, from 13.8 to 13.3 V at 15 amps = 7.5 watts of heat being
generated. That's plenty of heat to melt a lot of plastic! 

I had a similar failure, but in my case it was with the fuse holder. When I
got my KPA100, Elecraft finally shorted me a part from a kit. I was missing
half of the fuse holder. I was building it over a holiday weekend and, not
wanting to delay power-up, I decided not to request and wait for the missing
part. There was a auto supply store nearby that surely could supply a
suitable in-line fuse holder. 

Several weeks after finishing my KPA100 and enjoying it on the air I was
surprised when my K2 power failed for a moment while transmitting at 100
watts. Then it was fine. A few minutes  later power went off again
momentarily. I started checking connectors. The Anderson at the back of the
rig was fine. The connections to the Astron 20 amp supply under the desk
were fine. Then I happened to touch the in-line fuse holder near the power
supply. It was HOT! Those fuse holders depend upon spring pressure to hold
the contacts against the ends of the fuse. For some reason this automotive
fuse holder didn't have good enough contact. The voltage drop was
negligible, at least when I had done the initial checkout, but apparently
and increased ever so slightly over time. As the resistance grew, so did the
heat. The heat was enough to soften the plastic holder. The spring inside
holding the contacts tight against the fuse by pushing against the holder
caused it to stretch when it got warm, making the contacts poorer and the
heat greater until the circuit opened. As soon as it cooled a bit, the
contact was regained temporarily. 

A better quality fuse holder fixed the problem. 

Ron AC7AC