Electrical hacking (was Re: [Techtalk] [OT] charging USB
devicewithout a PC)
almut-behrens at gmx.net
Tue Apr 15 00:22:15 EST 2003
On Mon, Apr 14, 2003 at 10:22:12AM -0500, Alvin Goats wrote:
> Avoid moisture, sweating, conductive oils, fresh paint or finger nail
> polish (finger nail polish is a good conformal coating, but the acetone
> in it is a little conductive).
the term "conductive oils" in that paragraph somehow caught my
attention, because it reminds me of a somewhat unpleasant episode
that happened a long time ago, when I was still aiming to become an
engineer. At the time, I sort of learned the embarrassing way, that
there (supposedly?) is no such thing as a conductive oil. It was in
a discussion among several chemistry/engineering students, where the
topic had somehow shifted to liquid conductors that would not dry out.
With my general tendency to not keep my mouth shut when it would be
more appropriate to do so, I suggested that there might be some special
oil with that property. Almost instantly, all the guys started laughing
and making ridicule of me, and everyone (except blushing me) was having
a hell of a good time -- I still remember that quite well, as they
made me feel like a stupid little girl who had just been asking for
flammable water ;(
In an attempt at ego-repairing, I tried hard to come up with anything
that would - even remotely - resemble an electrically conductive oily
substance. Yet my investigations failed .
Anyway, that episode is long over and done... yet, I'd still be curious
as to whether there really are conductive oils (you know, that would -
in hindsight - give me that warm, ego-soothing "see, I told you..."
 I came across so-called "contact oils" used for electro-motor
brushes, power pickups and other sliding contacts. However, the oil
itself is - as any oil - a very good insulator. As far as I learned,
those work by a combination of the following three factors: (a)
preventing corrosion, (b) polishing the metal surface and thus
maximizing the contact area (at the microscopic level), (c) leaving
nothing but an ultra-thin film of oil between the contacts (nanometer
range), so that even the lowest voltage can "spark through" this
dielectricum to inititate the flow of current.
In addition to that, there seem to be several techniques for testing
oil contamination (from acids, moisture, metal particles) which are
based on changes in the conductive properties of the oil -- yet this
seems to be more like "slightly reducing the dielectric strength",
still far far away from the conductiveness of metals, graphite, carbon
P.S. sorry for taking that thread even further off-topic...
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