[Elecraft] K3 Suddenly died

[Richard Fjeld]

My comments about using the 12V jack for measuring were directed to a 
K3/100.
I should have added that.


-----Original Message----- 
From: Richard Fjeld
Sent: Monday, October 07, 2013 12:22 AM
To: elecraft at mailman.qth.net
Subject: Re: [Elecraft] K3 Suddenly died

When we think of wire gauge requirements for amperage needs, we need to
remember the amperage rating for wire is given for house voltage, typically
~117 volts AC (in the US).  For lower voltage at 13.8 VDC, we need larger
wire
size (smaller gauge number).  What often saves us is short lead lengths.
Still, if one measures the voltage drop of a conductor under load by using
a DMM with a test lead at each end of the wire, a drop will be seen if the
wire size is not adequate for the load.   (Emphasis on 'under load'.)

The voltage drop across a resistance (in this case a conductor) is directly
proportional to the amount of current flow through the resistance.  At idle
current, very little voltage drop will be measured in the resistance of the
conductor.

The 12V jack on the back of the radio cannot be used to accurately measure
voltage drop in the power cable, but the voltage measured during key-down
will be approximately 1.4 volts less than the PS voltage if the cable is
good.
An RCA plug can be wired to make the test connections safely.

Dick, n0ce




-----Original Message----- 
From: Lewis Phelps
Sent: Sunday, October 06, 2013 2:43 PM
To: elecraft at mailman.qth.net List
Subject: Re: [Elecraft] K3 Suddenly died

Thanks for input.  We can all stand down on this one.

The problem turned out to be a power cable after all.

I was using a 3' power cable assembled with fairly light wire (16 gauge).
Over time, the wire had flexed sufficiently at the exit from the APP pin
that it began to fray. Fraying let to higher resistance, which led to more
voltage drop under load, which led to further decay of the wire-pin joint.

At the point I reported the problem, the power cord was still showing
nominal voltage when not connected to the rig. But (apparently) resistance
had risen to the point where the K3 wasn't getting sufficient voltage.  All
this eventually became clear when the wire was completely cooked, broken,
and charred on the end.

I shudda tried a different power cord sooner.

Lesson learned:  don't use 16 smaller gauge wire with Anderson Power Pole
connectors, even if you double the wire to fill up the void in the pin.
It's still a single stranded wire where it exits from the pin, and the
smaller wire size is more vulnerable to flexing, no matter how low the
current demand of the load it's carrying. Eventually, this wire can (and
did) become a 1 amp fuse.

73,

Lew N6LEW

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