Submerged batteries work??!!

Discussion in 'General Electronics Chat' started by BenThere, Nov 27, 2006.

  1. BenThere

    Thread Starter New Member

    Nov 27, 2006
    3
    0
    Hello, Crazy question here.

    During a camping trip last weekend, we awoke to find the stern of our boat submerged by a viscious tide (and a poor anchoring strategy). The battery was completely underwater for a good few hours. We're thinking we're screwed.

    I can see that the thing might be sealed well enough to prevent a chemical reaction but why wouldn't it just short itself right out across the poles in the water?

    It started up like nothing ever happened.

    How is that? Can someone explain?

    Thank You, Ben
     
  2. wireaddict

    Senior Member

    Nov 1, 2006
    133
    0
    Hi Ben. It appears that your battery is sealed; water [particularly salt water] in the cells would dilute & contaminate the acid. Other considerations are the resistance of the water & the condition of the battery. A good 55 A/hr. battery can supply 5 amps for 11 hours before it's discharged. Water, even salt water, isn't enough of a conductor to immediately short it out or discharge it like the starter would. Once, we left a door open in our Tahoe all night [9 or 10 hrs.] so the interior lights were on that long, too. We had similar thoughts as you did, but it also started normally. Good thing you didn't get water in the engine.

    Dave
     
  3. BenThere

    Thread Starter New Member

    Nov 27, 2006
    3
    0
    Thanks for the reply!!

    I figured the water would just create an immediate short and the battery would be ruined pretty much immediately. Glad I was wrong.
     
  4. Dave

    Retired Moderator

    Nov 17, 2003
    6,960
    143
    The issue of how good a conductor water is is dependant on the salt content of the water (amongst other things but lets assume salt is the primary constituent of sea water). Pure water is a poor conductor (resistivity of typically 2.5e5 Ohm-m for ambient conditions), however salt acts as an ionic compound in the water because cations and anions are freed from their respective bondings as part of the dissolution process. It is the amount of these ions that determine the conductivity, where increased numbers of ions (i.e. a greater salt concentration) represents a lower resistivity and higher conductivity.

    Dave
     
  5. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    You might have had a discharged battery, but the terminal post were too small for a heavy current flow. Because the electrons have to attach to an ion in the water, and then move to the anode to sustain current, the mutually repulsive effect of the negative charges around the area of the anode post creates what amounts to a high rsistance.
     
  6. BenThere

    Thread Starter New Member

    Nov 27, 2006
    3
    0
    Thanks for the replies. I didn't mean to mimick your moniker, beenthere. I signed on before I noticed you and I always use BenThere if it's available.

    Thanks again, Ben
     
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