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In an idea world perhaps but in real life this is not the case.
Best,
JJ
At 09:04 AM 5/23/2001, Olaf Trygve Berglihn wrote:
>Jarrod Jablonski <JJ@Ha*.ne*> writes:
>
> > Captured o-rings are dangerous due to combustion from battery off
> > gassing and are not recommended.
>
>This is an issue when charging, but not really when discharging. Also,
>the lead-gel YUASA batteries used (don't have it here in front of me,
>but I think it is YUASA), are able to absorb the gas produced to a
>certain degree.
>
>The basic chemical reaction is as follows:
>
>[anode] PbO_2 + 4H^+ + SO_4^{2-} = PbSO_4 + 2H2O
>[cathode] Pb + SO_4^{2-} = PbSO_4 + 2e^-
>[overall] PbO_2 + 2H_2SO_4 + Pb = 2PbSO_4 + 2H2O
>
>Direction of equilibrium reactions:
> ---> Discharge
> <--- Charge
>
>During the final stage of the charging cycle there are competing
>chemical reactions taking place. Water is decomposed to produce
>hydrogen and oxygen gases. The charging efficiency drops dramatically
>at this stage. The presence of bubbles causes a stirring action of the
>acid, thus sulphuric acid is then mixed within the electrolyte.
>
>During the final stage of charging or under overcharge condition, the
>charging energy is consumed for electrolytic decomposition of
>water. Oxygen is released as gas from the positive plate into the
>sealed cell compartment. The oxygen then rapidly diffuses through the
>separator or cracks in the gel. The oxygen reacts with the moist
>negative active material to form lead oxide. The oxidation of the
>negative causes a slight depolarization and inhibits the release of
>Hydrogen gas. The lead oxide reacts to form lead sulphate that on
>further charge changes to form lead and sulphuric acid. This results
>in no loss of oxygen or hydrogen and therefore eliminates the need to
>add H_2O.
>
>Now, for the discharge part, there is no production of gaseous
>hydrogen, and any (unlikely) hydrogen leaking out was most probably
>produced by overcharge.
>
>Bottom line is: Do not overcharge - a decent charger will prevent
>it. Let the battery sit for a while after charging before you close
>the lid. Vent a canister that has not been used for a while.
>
>Gas in the canister that has leaked from the sealed battery during
>dive is highly improbable, and I see no special reason to have a
>o-ring system that can act as a relief for an explosion in the
>canister that will not happen. I do not think this represent a danger
>for a battery that has been well vented during charging and set to
>rest before use.
>
>Please correct me if I missed something out here (is has been a while
>since I graduated chem. eng.). Do you have any examples of hydrogen
>gas trapped in the sealed battery that has caused explosion in a
>canister - i.e. if the battery was vented during charging.
>
>Saying this, I have not yet had a leak in my apollo 14, and I'm
>looking forward to going diving the next four days with my repaired
>Goodman handle.
>
>Olaf
>--
>Olaf Trygve Berglihn <olafb@pv*.or*>
Jarrod Jablonski
President-
Global Underwater Explorers
CEO Halcyon Manufacturing/Extreme Exposure
GUE (www.gue.com) is a non-profit educational, research, and exploratory
organization with hundreds of dedicated members around the world.
Halcyon manufacturing (www.halcyon.net) and Extreme Exposure
(www.extreme-exposure.com) produce some of the scuba industry's most novel
and robust diving equipment designed by many of diving's most active
explorers.
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