[TowerTalk] Copper grounding bus bar

[Dan Zimmerman N3OX]

"solder through the heavy oil film, and you
can get the solder to bond the aluminum and copper together.    Have never
tried it, but it would be interesting to try."

I DID try it last year sometime, but even if we could trust solder
joints in lightning service at all, I'd never trust the resulting
joint between copper and aluminum to any sort of service where
reliability was even a MINOR concern (of course, I get the idea that
you're talking more of an aside than anything having to do with an
actual ground system )

In fact, I tried it and at the prompting of people on this reflector,
I think, I did some destructive testing.  I'd made a post excitedly
claiming I could solder to aluminum and got many comments that I
should check into that a little more.

If you give it a little tug, you think it's well bonded.  If you pull
HARD the whole solder blob comes off the aluminum in one piece and
leaves only a little residue.

Now, that said, it is an interesting technique because if you get
yourself in a position where you really must make a non-critical
connection between aluminum and copper and don't have mechanical means
(I don't know when this would be ;-) ) the initial bond DOES have some
mechanical strength and makes good electrical contact...

Without some real quantitative tests, I wouldn't make the assertion
that it has *any* advantage over bolting the wire down with joint
compound.  It is SUPER cool to see the solder lay down like it has wet
the aluminum (and maybe it has, but the resulting bond is not like the
one you get on copper)

I decided with the help of advice from here that in my intended
application (copper antenna wires to homebrew aluminum flashing
capacitors), I'd just bolt it down with stainless hardware.

I still have a question in my mind whether solder + bolting would be
better than just bolting, but I doubt it.  Adding a couple of other
metals to that electrochemical soup probably isn't a good thing.

If you want to try it and run it through some tests it's really easy
to solder #14 copper wire to aluminum flashing under oil... in fact, I
seem to remember doing it without the oil.  I used a big drop of
solder and lots of flux and scraped the aluminum with the soldering
gun tip really hard.  Then you've got something to play with.  Run a
bunch of current through it and measure the voltage drop relative to a
similar bolted connection.  Build two of each and measure them before
and after sitting inside and outside for a month, stuff like that.

But I'd never consider getting it anywhere near anything critical or
up on top of a tower vs. long standing, proven methods with lots of
professional testing.

 73,
Dan