On 2/3/2016 3:33 PM, wrote:
Irv Finkleman wrote:
Here's a situation I haven't encountered before
and which I know little about.

I am building a magnetic loop antenna and have
an assembly which includes a capacitor and drive motor ideally suited
for the antenna. My problem is that the assembly is welded to an
aluminum mount. I want to attach a copper tubing loop to the mount
which will connect the loop to the motor driven capacitor.

My concern is the matter of dissimilar metals i.e. copper and aluminum
being joined. I would prefer to be able to bolt the assembly to the
copper tubing using star washers to reduce the joint resistance.

Here are my concerns:
1. What about rectification at the dissimilar metals joint? Is it going
to cause problems? Is it of any real concern?

3. Can the copper be welded to the aluminum mount for better joint
conduction? This is a last resort for me as it would mean taking the
assembly to a place where the welding, if possible, could be done.

Thanks in advance for any comments or suggestions which would be greatly
welcomed.

Irv, VE6BP
RADIATE OR DIE TRYING!!

Yes, there is a problem with aluminum to copper connections.

There are various "greases" to solve the problem.


That grease is widely used where aluminum power wiring comes in from a
pole and connects to a lug in a meter. And for that matter when I have
bought wiring panels (I mean the box where your power fuses or circuit
breakers live) they have come with a sticker saying the grease must be
used wherever wire other than copper connects to the panel.
Bob, WA9D

Bob Wilson wrote:
On 2/3/2016 3:33 PM, wrote:
Irv Finkleman wrote:
Here's a situation I haven't encountered before
and which I know little about.

I am building a magnetic loop antenna and have
an assembly which includes a capacitor and drive motor ideally suited
for the antenna. My problem is that the assembly is welded to an
aluminum mount. I want to attach a copper tubing loop to the mount
which will connect the loop to the motor driven capacitor.

My concern is the matter of dissimilar metals i.e. copper and aluminum
being joined. I would prefer to be able to bolt the assembly to the
copper tubing using star washers to reduce the joint resistance.

Here are my concerns:
1. What about rectification at the dissimilar metals joint? Is it going
to cause problems? Is it of any real concern?

3. Can the copper be welded to the aluminum mount for better joint
conduction? This is a last resort for me as it would mean taking the
assembly to a place where the welding, if possible, could be done.

Thanks in advance for any comments or suggestions which would be greatly
welcomed.

Irv, VE6BP
RADIATE OR DIE TRYING!!

Yes, there is a problem with aluminum to copper connections.

There are various "greases" to solve the problem.


That grease is widely used where aluminum power wiring comes in from a
pole and connects to a lug in a meter. And for that matter when I have
bought wiring panels (I mean the box where your power fuses or circuit
breakers live) they have come with a sticker saying the grease must be
used wherever wire other than copper connects to the panel.
Bob, WA9D

Yep, because aluminum to copper connections without the grease develop
resistive layers which get hot.

Also there is a problem with the differing coefficients of expansion
which loosens the connection and makes the problem worse over time.

The net result is aluminum/copper interfaces not done right tend to
burn down houses.

--
Jim Pennino

"Bob Wilson" wrote in message
...
Yes, there is a problem with aluminum to copper connections.

There are various "greases" to solve the problem.


That grease is widely used where aluminum power wiring comes in from a
pole and connects to a lug in a meter. And for that matter when I have
bought wiring panels (I mean the box where your power fuses or circuit
breakers live) they have come with a sticker saying the grease must be
used wherever wire other than copper connects to the panel.
Bob, WA9D

That grease is fine for inside a house where it does not get wet. Outside
for antennas it would probably wash off after a few rains. Then with the
wet conductors you get what is called galvanic corrosion.

The more distance in the chart it is, the faster this action is.
https://en.wikipedia.org/wiki/Galvanic_corrosion

You can buy stainless steel tape at most welding shops.
The tape is used to protect threads and valuable machined parts from weld slag. If you apply it to the copper, the aluminum will not corrode.
The problem with stainless steel is that it is an alloy and has a different dielectric constant than either the aluminum or the copper.

As one poster said, your efforts would be rewarded if you just used a larger diameter aluminum loop and forgot about the copper. Especially if you were going to install this antenna permanently in a place that was not easily accessible.

On 2/5/2016 9:31 AM, Channel Jumper wrote:
Ralph Mowery;851568 Wrote:
"Bob Wilson" wrote in message
...--
Yes, there is a problem with aluminum to copper connections.

There are various "greases" to solve the problem.

-
That grease is widely used where aluminum power wiring comes in from a

pole and connects to a lug in a meter. And for that matter when I have

bought wiring panels (I mean the box where your power fuses or circuit

breakers live) they have come with a sticker saying the grease must be

used wherever wire other than copper connects to the panel.
Bob, WA9D-

That grease is fine for inside a house where it does not get wet.
Outside
for antennas it would probably wash off after a few rains. Then with
the
wet conductors you get what is called galvanic corrosion.

The more distance in the chart it is, the faster this action is.
https://en.wikipedia.org/wiki/Galvanic_corrosion

You can buy stainless steel tape at most welding shops.
The tape is used to protect threads and valuable machined parts from
weld slag. If you apply it to the copper, the aluminum will not
corrode.
The problem with stainless steel is that it is an alloy and has a
different dielectric constant than either the aluminum or the copper.

I don't want to be pedantic, but the dielectric constant is of virtually
no impact. The important properties of conductors used in a loop
antenna are conductivity (resistivity) and permeability. Even so, an
adequately thin piece of material will have little impact on the
properties of the loop. The real issue is that welding any of these
materials will be difficult.


As one poster said, your efforts would be rewarded if you just used a
larger diameter aluminum loop and forgot about the copper. Especially
if you were going to install this antenna permanently in a place that
was not easily accessible.

1+

Aluminum is your friend. Light and corrosion resistant, it weathers
very well if you keep it from contact with certain metals like copper.
Unlike many metals, on contact with air aluminum creates a thin very
tough barrier of aluminum oxide that prevents further corrosion in most
situations.

--

Rick

Channel Jumper wrote:

Ralph Mowery;851568 Wrote:
"Bob Wilson" wrote in message
...--
Yes, there is a problem with aluminum to copper connections.

There are various "greases" to solve the problem.

-
That grease is widely used where aluminum power wiring comes in from a

pole and connects to a lug in a meter. And for that matter when I have

bought wiring panels (I mean the box where your power fuses or circuit

breakers live) they have come with a sticker saying the grease must be

used wherever wire other than copper connects to the panel.
Bob, WA9D-

That grease is fine for inside a house where it does not get wet.
Outside
for antennas it would probably wash off after a few rains. Then with
the
wet conductors you get what is called galvanic corrosion.

The more distance in the chart it is, the faster this action is.
https://en.wikipedia.org/wiki/Galvanic_corrosion

You can buy stainless steel tape at most welding shops.
The tape is used to protect threads and valuable machined parts from
weld slag. If you apply it to the copper, the aluminum will not
corrode.
The problem with stainless steel is that it is an alloy and has a
different dielectric constant than either the aluminum or the copper.

To be a bit simplistic, metals don't have a real dielectric constant.

The issue with dissimilar metal connections is the electropotential
difference between the metals in the presence of an electrolyte.

This means that if you can keep all electrolytes, which water is,
from the connection, nothing will happen.

As air contains water, keeping all water out is problematic.

The greases do two things; they contain conductive particles to minimize
the electropotential difference of the contact and provide a barrier to
keep water out.

Coating the copper end of a connection with solder also helps greatly
as it raises the anodic index from the -0.35 of copper to -0.65 which
is a LOT closer to the anodic index of most aluminum alloys.


--
Jim Pennino