Zinc Pennies (was: Alarms, etc.)

From: JT McBride (James.McBride@GDEsystems.COM)
Date: Fri Apr 19 1996 - 18:15:43 EDT


Ned Vogler:
>Thanks all for responding to my question about the screws holding the horn
>for my alarm system. I think that I'll probably use a combination of all
>the ideas I received, I'll use stainless steel button-head machine screws,
...
>stainless hardware, and some silicone?? Jim Mcbride had mentioned something
>about using a penny as an anode, what's the benefit / significance here??

Corrosion problems may vary. I have little here in Southern California, except
for some experience with marine applications. Stainless steel is NOT steel,
at least in electrovoltaic terms; it's nickel. Stainless works great in
fiberglass and wood, but not in aluminum or steel (well, okay, it's better than
a lot of things, but not for critical applications).

There's also good reason not to try to seal things up completely with silicone.
You'll never get a perfect seal, but you can do an effective job of keeping
the junction wet (ie. rusting) for a lot longer than the rest of the structure.

I recommended the penny idea (although I am NOT advocating defacing the currency)
because zinc acts as a sacrificial anode - it will corrode away, but save any
iron or steel it's electrically connected to. Strips of zinc can be cut and made
into washers, but pennies happen to be round... Any penny minted after 1983
(maybe '81) is zinc with a thin copper plating. They're also cheap - only a
penny a piece! The secret service may frown on this though.

In reality, I doubt there will be any problem with just leaving the metal screws
where they are - as long as you're not cutting up your hands washing the wheel
wells (people bother doing that for trucks, sigh). If a machine screw is used,
be sure to use threadlock (Loctite or similar) or a Nyloc nut.

From sunny San Diego,

Jim
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