Model Forum / Radio Controlled / Air Models / January 2007

Here is a dissertation on the subject of black wire corrosion:

The black wire syndrome is an occurrence in battery packs (Ni-Cds) where the
negative wire becomes corroded (turns from shinny copper to blue-black).
This is the result of either a shorted cell in the pack, the normal wear out
failure mode of Ni-Cds, or cell reversal when a pack is left under load for
an extended period. The sealing mechanism of a Ni-Cd cell depends to some
degree on maintaining a potential across the seal interface. Once this
potential goes to zero the cell undergoes what is called creep leakage. With
other cells in a pack at some potential above zero the leakage (electrolyte)
is "driven" along the negative lead. It can travel for some distance making
the wire impossible to solder and at the same time greatly reducing its
ability to carry current and even worse, makes the wire somewhat brittle. A
switch left on in a plane or transmitter for several months can cause this
creepage to go all the way to the switch itself, destroying the battery lead
as well as the switch harness. There is no cure. The effected lead,
connector, switch harness must be replaced. This leakage creep takes time so
periodic inspection of the packs, making sure that there are no shorted
cells insures against the problem.  The cells should also be inspected for
any evidence of white powder (electrolyte mixed with carbon dioxide in the
air to form potassium carbonate). In humid conditions this can revert back
to mobile electrolyte free to creep along the negative lead. Some "salting"
as this white powder is referred to, does not necessarily mean that the cell
has leaked. There may have been some slight amount of residual electrolyte
left on the cell during the manufacturing process. This can be removed with
simple household vinegar and then washed with water after which it is dried
by applying a little warmth from your heat gun..

My bad, Sr. fingers. You are right it is KOH, not KOK (whatever that is).

It is electrochemically driven so it is usually seen on the negative side.

Long dissertation follows:
The black wire syndrome is an occurrence in battery packs (Ni-Cds) where the
negative wire becomes corroded (turns from shinny copper to blue-black).
This is the result of either a shorted cell in the pack, the normal wear out
failure mode of Ni-Cds, or cell reversal when a pack is left under load for
an extended period. The sealing mechanism of a Ni-Cd cell depends to some
degree on maintaining a potential across the seal interface. Once this
potential goes to zero the cell undergoes what is called creep leakage. With
other cells in a pack at some potential above zero the leakage (electrolyte)
is "driven" along the negative lead. It can travel for some distance making
the wire impossible to solder and at the same time greatly reducing its
ability to carry current and even worse, makes the wire somewhat brittle. A
switch left on in a plane or transmitter for several months can cause this
creepage to go all the way to the switch itself, destroying the battery lead
as well as the switch harness. There is no cure. The effected lead,
connector, switch harness must be replaced. This leakage creep takes time so
periodic inspection of the packs, making sure that there are no shorted
cells insures against the problem.  The cells should also be inspected for
any evidence of white powder (electrolyte mixed with carbon dioxide in the
air to form potassium carbonate). In humid conditions this can revert back
to mobile electrolyte free to creep along the negative lead. Some "salting"
as this white powder is referred to, does not necessarily mean that the cell
has leaked. There may have been some slight amount of residual electrolyte
left on the cell during the manufacturing process. This can be removed with
simple household vinegar and then washed with water after which it is dried
by applying a little warmth from your heat gun..

Red S.
Red's R/C Battery Clinic
http://www.rcbatteryclinic.com
Check us out for "revolting" information.

Don't mean to shatter your universe here.. but you can get black wire
corrosion on any negative wire on a DC circuit that's had the exposed part
of the wire exposed to moisture.

Motorcycles get it in their rear light and indicator earth wiring, the wires
that are about the furthest away from the battery on the bike.. and it's a
lead acid battery on the bike not ni-cads... well some are sealed gell
cells,

but i'm just trying to say black wire corrosion is not exclusive amoungst
modelers who use ni-cad batteries,

i've had it on vehicle trailer sockets, sensor wires on engines, the wiring
from a cheap solar panel,

it's always the negative wire that's affected, and in all cases the wires
connections had been exposed to moisture, on motorcycles it's the rear light
assembly, and on cars the trailer socket assembly as they are behind the
rear wheels and thus get all the road spray,

the solar panel wasnt sealed underneath, so moisture got to it easily.