Message text written by Steve Daniels
>So here's something I've been wondering about. Do coils get
weaker with age? They have no moving parts, and you'd think that
they'd either work or not.
<
Steve,
Coils are constructed of copper wires insulated with a varnish or enamal
coating. Varnish or enamal coated wire is used because the thickness of
the isulation is minimal and higher winding densities can be achieved than
with plastic coated wire. Typically, the finished coils are then varnished
again. The varnish can and does break down over time and you can get
winding to winding shorts between adjacent wires that will manifest
themselves as reduced perfoemance and higher than normal primary current.
Add to this the fact that coils are encapsulated in epoxy. Epoxy is rather
expensive (on the order of $10 (US) per Lb - 21 euro/Kg) so some
manufacturers (most or all?) will pour in some sand (this is not just beach
sand but carefully graded sand of uniform gain size) before the
encapsulation. If the epoxy does not fully impregnate the sand there will
be loose granules that can abrade the wire as well leading to premature
failure.
That said, may I make the observation that many coils have lasted 40 years
or more without any appearent loss of performance.
So can a coil's performance degrade over time? Yes it can but the
occurance is more of a random nature. For this reason the coil should be
considered a potential source of an existing problem but should not
necessarily be a routine maintenence item.
Drive your British car (my new salutation)
Dave
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