Re: [Paddlewise] Filling battery compartment with vaseline?

There seems to be a bit of confusion on this list regarding the
function of "leaking" battery compartments, both in GPS receivers and
in VHF alkaline battery trays. It is not difficult to design a AA
battery compartment that is completely watertight. I have a $10 diving
flashlight that uses AA batteries and is watertight to 2000 feet. Why,
then, are there so many examples of electronic gear that are designed
to have leaking AA battery compartments? On reason is to avoid
explosion. As alkaline batteries are used, the corrosion of the
electrode in the electrolyte causes hygrogen gas to be released. To
quote from the NIOSH factsheet on "Exploding Flashlights", many
battery compartments "are constructed to allow leakage" of hydrogen
gas. This is not the only way to deal with the problem. Instead, "some
manufacturers of equipment with air- and water-tight battery compartments
have incorporated safeguards to prevent H2 accumulation. For example,
one-way relief valves may be incorporated in battery compartments to
allow H2 to escape. Or, chemicals may be used to absorb or recombine
H2."  (It is this latter design that my diving flashlight uses.)

It is an easy matter to modify a battery compartment to make it
watertight. But before you do so, make sure that you consider why the
compartment was designed to leak in the first place (to
vent hydrogen gas), and be sure to include a gas-absorbing chip,
one-way relief valve, or other design modification so that you do not
transform your GPS receiver into an exploding GPS receiver.

The NIOSH factsheet can be found at the following URLs:
http://www.usfa.fema.gov/alerts/flashlgt.htm
http://www.cdc.gov/niosh/fact0002.html

Dan Hagen


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