From: Tothwolf
The conductivity of tin/lead solder is simply higher
than that of the
wire and terminal alone
I think you meant 'resistance', not "conductivity", right?
Can you tell what size the wire is?
Sorry, I'm not good at telling those larger sizes apart. I looked on the
insulation to see if it said, and all it gave was some manufacturer data, and
a 600V rating.
Maybe they used too large of terminal for the wire and
the crimped
connection is bad?
I can verify that the opening in the terminal was 'full' of wire - i.e. wire
and terminal were size-matched.
I honestly don't think that it was the wire-terminal connection that caused
the problem. For one, the insulation on the wire right up at the terminal
shows no damage (it's still nice and flexible, I can put thumbnail prints in
it - unlike the insulation on the terminal, which was extremely brittle (I
wound up cutting the insulation off the terminal with a Dremel to check out
the crimp - replaced with heat-shrink), and if the wire-terminal connection
had been bad, I'd have expected the wire there to get pretty hot. Also, when I
pulled the terminal off the lug, melted solder from the terminal-PCB
connection had run down onto the lug, and you can see the shape of the
terminal in it. So either i) they soldered the lug onto the PCB after the
terminal had been placed on the lug (very unlikely), or the solder melted from
the overheat. (Some overheat!) Would that much heat from a poor wire-terminal
joint have made it to the PCB? Anyway, given both of these, I suspect it was
either the terminal-tab connection, or the tab-PCB connection.
Is that
terminal a dual crimped type with a separate insulation crimp?
If you look into the
end of the connector, there would be a secondary
crimp grabbing the wire's insulation.
I _think_ it's double crimped, but it's not 100.00% definite. Most of the other
terminals, all the smaller ones, are very definitely double crimped. The handful
of other large ones (from the full-wave bridge to the heat-sink/bus-bar) look
a lot like this one - strong indications of a double crimp, but not absolutely
positive.
At the very least, the pc board mount tab should be
resoldered.
Yep, did that - although I'm a tiny bit worried that I got a cold solder
joint on the pins, the solder didn't really flow up them the way it should.
There may be burned gunk (probably from the old rosin) on them; I may remove
the existing solder, and take corrective action.
(What I'm going to do first is turn the thing on with a bunch of Minimum Load
Modules in it, and run it for a while, and monitor the temperature of the
connection.)
Noel