Melted J3 Connector on K2/100

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?
   
  Lee - K0WA
   


In our day and age it seems that Common Sense is in short supply.  If you don't have any Common Sense - get some and use it.  If you can't find any common sense, ask for help from somebody who has some common sense.
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[Ron D'Eau Claire-2]

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

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[Rick Dettinger-2]

So if you melted your Anderson connector, it had unusually high resistance
for some reason.
Ron AC7AC

-----------------------------------------
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.
Rick Dettinger
K7MW
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[Ron D'Eau Claire-2]

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.

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

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

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