14 Sep
2014
14 Sep
'14
2:59 p.m.
This is very interesting... I had participated in a similar discussion on
what is more a tradesperson's board some months ago; it's fun to get the
perspective of some engineers and computer guys here.
I personally was trained that soldering is typically the superior method SO
LONG AS YOU ARE DOING IT CORRECTLY.
Unfortunately, most folks aren't as good at soldering as they think ... :|
I think the consensus on the trades board (mechanics, electricians, etc)
was that while you could achieve good, long-lasting results with both
techniques, given the proper tool, the crimp was more fool-proof, easy to
teach and will give the most consistent results... I can see that, sure,
it's much easier to just tell a technician, strip the wire this far, stick
it in this lug, work the crimper through it's entire range of motion...
easier than, you know, heat the surface not the solder, make sure it's not
beading up, this is how you recognize a good solder joint and don't forget
to put some heat shrink up the wire before you splice em together!
I switch off as the situation dictates... I have a nice Hakko iron as well
as a Crimpmaster with like 15 different die sets (I found someone selling
like every single one, and I stocked up! anyone got a line on MMJ plugs??)
and generally if I don't expect to ever want to change the connection, or
if I am splicing or attaching very small wire (~26 ga) where there isn't
really an appropriate lug size (and I don't want Scotchloks everywhere) I
will solder; I will crimp lugs if I'm doing something more temporary, or if
I deliberately need to attach to something that takes lugs e.g. a terminal
strip, etc.
The [Ideal] Crimpmaster is a nice tool and not too expensive... maybe $40
for the handle and $15-25 for each specific die set you want. You don't
have to go and shell out $400 for the AMP crimper or the Deutsch crimper or
whatever... There are many knock-offs of the Crimpmaster that take the same
dies... probably even cheaper if you need the price point to be lower yet.
Nothing wrong with doubling up the techniques; crimp then solder... I've
done this more than once... when I wanted to REALLY make sure it wasn't
gonna come apart.
In this particular scenario where you are trying to assumedly connect a
wiring harness to a terminal strip on a power supply (?) I'd probably just
crimp it.
All this talk about the skin effect and where AC vs DC travels on the
conductor is tickling my memory but it's been so long... I'm not even gonna
lie, I'd have to refer back to my e-mag textbook on that one, LOL. But,
Noel, I think you are correct?
Best,
Sean
On Sun, Sep 14, 2014 at 6:46 AM, Noel Chiappa <jnc at mercury.lcs.mit.edu>
wrote:
First, thanks to everyone for the help; this is really
a puzzler for me,
and I
really appreciate the assistance. Anyway, on to substance (several replies
all
packaged into one to minimize list traffic - and sorry the result is a bit
of
a tome):
From: Tothwolf
What caused the excessive current draw though? Is
there a marginal
part
on the pc board? You shouldn't be seeing that
much current draw
though
a pc board.
I realized after I posted is that your first question is the $64K question
-
and I don't know the answer. I suppose it could (broadly) be one of four
things:
- The previous owner tried to draw too much power (although the boards
that were plugged in when I bought it shouldn't have done that - I
haven't
sat down to calculate the total draw, and compare it with what the PS can
supply, but the card cage was less than half full of stock items)
- There's a fault (e.g. partial short), or faulty component, somewhere
in the power supply
- The connector is under-specified for the current it could be/was asked
to carry
- There's a poor connection somewhere in the connector system, further
dividable into:
-- The wire<->terminal joint
-- The terminal<->lug joint
-- The lug<->PCB joint
I agree that without knowing the original cause, and correcting it, the
problem could recur - but I don't think I can (at this remove) work out
which
one it was. So I can take some corrective action(s), but I don't think I
can
be sure I got the orignal cause...
The first question that comes to mind for me, is
the terminal even
original to the chassis or did someone replace it at some point in
the
field?
Well, I'd have said 'original' (it has the look/feel of original work), but
looking closely, I cannot be sure. It's the only connector of that type in
the
PS - the other +5V lines are i) soldered to the tips of the rectifiers in
the
full-wave bridge, and ii) use crimped bolt-on type terminals (i.e. not the
push-on tabs) for the rest. Those latter do have the same colour and
general
look as this one, _but_ the crimping marks on their insulators are more
distinct. (Perhaps the heat removed them on this one?)
If it was a poor wire<->terminal connection, could that really have melted
the solder on the lug<->PCB joint?
Is that terminal a dual crimped type with a
separate insulation
crimp?
Sorry, how would I tell?
The .250 tab type terminal on the board is likely
made by either AMP
or
Molex and would probably be pretty easy to source
as a replacement
part.
I read this to mean you think I should replace the soldered on tab
(presumably
as well as the crimped terminal on the wire)?
Done correctly, using the right compression dies
and tools, crimped
connections are always far more secure and reliable both mechanically
and electrically
Alas, while I have a fairly well-equipped shop, it doesn't run to the
right compression dies and tools...
From: Chuck Guzis
You may want to consider a standard PCB screw lug
Well, I'd have to modify the PCB, which I'm loathe to do. The current tab
uses
two round pins to make the connection to the PCB, which I suppose I could
cut
into a slot, but there are other components in the immediate vicinity
(seems
odd for such a high-current connection, but...)
From: Paul Koning
Solder helps keep things mechanically sound, but
for high current
connections a well executed crimp is probably better.
Really? I thought that while AC was carried in the skin of a conductor, DC
was
carried spread evenly throughout, so I assume(d) that the wider
cross-section
of a soldered connection would allow it to carry more current.
Perhaps the industries that stopped using soldered connections in favour of
crimped did so because with hand-soldering, you can get variation (and also
of course bad solder joints), whereas with a crimp it's pretty uniform from
joint to joint?
What I would do is pull the old lug off, clean
off the wire, and
crimp
on a new lug
Ah, to make sure I understand, you're talking about replacing the terminal
attached to the wire, right? (I tend to think of the 'lug' as the
spade-shaped thing soldered onto the board.)
with a good quality (commercial grade, not Radio
Shack) ratchet crimp
tool.
And if I don't have such a tool... ?
If it's done right it should be on very
tight; if you can pull it off
without serious force it's either the wrong size lug or the wrong
tool.
You're talking about the wire into the terminal here, right? Yes, I've
always made sure a crimped wire _cannot_ be pulled loose (whatever size
connector).
FWIW, the terminal onto the lug is a pretty tight fit, too - I can wiggle
it
with my fingers, but to get it off I'm going to need some mechanical help.
Noel