[Elecraft] Melted J3 Connector on K2/100

[Ron D'Eau Claire]

Lee, KOWA wrote:


Well, I was giving the K2/100 heck (100 watts) on 40 meters tonight into a
nice load (1.2) and things start stinking a little when I turn it back over
to the other station.  I had been sending code at around 18 wpm for about 10
minutes.  I am running a Astron switching power supply.  Then the rig shut
off and did not come on again.  The heat sink was not all that hot, but I
noticed the large gauge wire and the fuse holder was warmer than what I
would expect.  The 20 amp fuse was not blown.
   
  I pulled the Anderson Power pole plugs....and the RED side of the plug is
melted while the black plug is not.  The RED Anderson Power Pole connector
on the K2 is also slighly deformed from melting.  I took the K2 over to
another supply on the bench and the K2 came up.
   
  Looking at the schmatic....I must have drawn to much current for the
connectors.  Hardly seems to be plausible.  What do you experts think here?

-------------------------------

You should have been drawing something like 15 to 18 amps, peak key down,
from the power supply at 100 watts. Sending CW, that's likely something in
the range of 10 amps on average (the sending speed has nothing to do with
the duty cycle: 2 wpm and 200 wpm with the same Morse text has the same duty
cycle). 

That certainly should not overhead those Anderson connectors or damage the
K2. It sounds like it's a problem at the connector, since the rig works FB
once you connect it to another cable. 

The way a cable connector overheats is by the resistance in the connection
at the terminals. If the resistance were zero, you could draw millions of
amps through it and it'd stay perfectly cool. Unfortunately, the resistance
might be very low compared to what we're used to, but it's no where near
zero! So there is always some heating of the connector and wire. That's what
the amperage rating is based upon for both connectors and wire: the amount
of resistance they show. 

So if you melted your Anderson connector, it had unusually high resistance
for some reason. I can think of two reasons for that:

1) What I'd consider the most likely is a bad contact between the two halves
of the connector when they were mated. That's easy to make happen with an
Anderson connector *if* you fail to push the contacts all the way forward in
the housing! If they aren't all the way in, the tabs will just touch over a
small area, producing a relatively poor connection that will heat up badly.
The KPA100 manual advises making sure the wires cannot be pulled back out.
That's one way to ensure the terminals are fully inserted. 

If you'd like to see photographs of properly (and improperly) inserted
Anderson connector terminals, download a copy of the Transverter Assembly
Manual for the XV432 Transverter. That's the Assembly Manual, not the XV
Owner's Manual. Properly and improperly installed terminals in Anderson
connectors are shown in photographs in Figure 27 on Page 33.

2) The other possibility is a bad connection between the cable wire and the
terminal in the connector. That's why the manual advises soldering, not just
crimping, the cable to the connector. A little bit of resistance right there
can turn the assembly into a powerful heating element that will cause a lot
of trouble. Be sure your wires are securely soldered to the terminals. 

Ron AC7AC