Michael Ross via EV wrote:
I can't for the life of me figure out why a highly resistive dielectric
grease (mentioned by others) is a better choice than a conductive grease...
The grease is only filling the gaps (asperities) between the two metals.
There is no grease at the contact points -- it's squeezed out by the
high pressure.
noalox is essentially a conductive grease given the Zn content.
Marketeers make a big deal about how "conductive" their grease is
(sticking the probes of a multimeter into it, etc.) That just marketing
BS. The "conductive" grease is still many orders of magnitude less
conductive than the metals. Its conductivity is meanigless compared to
the metal-to-metal contact.
If you really do exclude the moisture then the zinc would be redundant,
seems like.
Like Bill says, the zinc particles are supposed to act as a sacrificial
anode (corrode first) in case water does manage to get into the joint.
With aluminum, you just cannot expose bare un-oxidixed metal, it is not
possible to do this
I agree. But you can reduce the thickness of this coating so it is
effectively gone.
Be interesting if someone has compared greased un-sanded to greased and
sanded.
I've done so, and so has Bill Dube' -- probably others. I agree
completely with Bill; sanding and noalox (or just about any grease) works.
I suppose if you used really fine grit paper you might actually improve
intimate mechanical contact, but I have my doubts.
Well, I'm not talking about heavy sanding that removes any noticeable
amount of metal. I'm just polishing the surface, to remove the dull
finish and make it look "shiny".
I admit I have not yet used any cells with aluminum terminals...
I have a group of used Thundersky cells, but I have not used them yet.
That will be a good test case.
I find it depressing to see how badly designed the terminals are on
these cells. My first reaction was "what idiot would use aluminum for
high-current connections in a high harsh automotive environment?"
Besides the aluminum itself, the other issue to address is the screw or
both. Threads in aluminum tend to stick, gall, or seize. You get
erroneous torque readings, and can even tear out the threads without
ever achieving enough contact pressure. The grease helps here, too.
And, they tend to use any old thing for the interconnects between cells.
You wind up with a mish-mash of incompatible metals. Aluminum terminal
with a steel screw, holding a copper strap that may or may not be tin
plated, etc. The cells themselves provide the voltage to enhance
corrosion. Put them in a car where they get wet or dirty, and you have a
wonderful environment for corrosion!
--
The definition of research: Shoot the arrow first, and paint the target
around where it lands. -- David Van Baak
--
Lee Hart's EV projects are at http://www.sunrise-ev.com/LeesEVs.htm
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