On Thu, Feb 5, 2009 at 6:56 AM, John McKown <john_3000@...> wrote:
>
> --- In chordite@yahoogroups.com, Tony Godshall <togo@...> wrote:
>
>> Are you saying that if you switch AC this doesn't happen?
>
> ===================================
>
> I think the transfers tend to cancel somewhat. Here's something on the
> subject:
>
> "Since the contact interface acts as a resistor, the heat produced by the
> closed contacts is proportional to the voltage across them and the current
> through them. Temperature rise of clean contacts is negligible, but when the
> contacts start to separate, the number of contacting asperities decreases.
> As the last contacting asperity decreases its contact area, contact
> resistance increases until contact voltage reaches melting potential (about
> 0.5 V for most metals). Molten metal bridges the separating surfaces and
> finally breaks. During this process some material may transfer between
> contacts, especially if direct current is interrupted."

Interesting

I guess hall effect switches would then be immune since there's no actual
contact being broken.

--
Best Regards.
Please keep in touch.
This is unedited.
P-)