Battery acid and salt water

Discussion in 'OnBoard Electronics & Controls' started by chabrenas, Jan 15, 2009.

  1. chabrenas
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    chabrenas Mike K-H

    Many books and articles warn that allowing battery acid to come in contact with salt water will give off chlorine. My chemistry is very, very rusty, but I don't see why the chlorine ions shouldn't remain in solution. However, letting salt water get into a battery seems likely to result in chlorine being given off at one or other part of the charge/discharge cycle. Anyone here qualified to tell me the true story?
     
  2. mydauphin
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    mydauphin Senior Member

    Interesting, that is something to that you will only know if you test it. It will probably generate portions of Sodium sulfate and hydrochloric acid. It will release some sulfur acid and a little chlorine gas. But it should not be violent and chlorine will be the least of your problems. Or it could just dilute acid and just generate some sodium sulfate. Also depends on temperature. Try it and let me know.
     
  3. chabrenas
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    chabrenas Mike K-H

    I think sodium sulphate is rather less soluble than the other salts obtainable from the mix, so I suppose some could precipitate out, causing chlorine to be given off to restore the balance.

    It seems pointless to do my own experiments when someone who knows their chemistry well should be able to predict the result. Of course, sulphuric acid and salt water swilling around the cabin floor or the bilges is likely to encounter the occasional bits of copper, alloy, brass, alulinium, etc., in close enough proximity to form a cell that might increase the cahnces of producing chlorine gas.
     
  4. CDK
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    CDK retired engineer

    Mydauphin is correct, the stronger acid makes a salt with the available sodium, the chlorine forms an acid with the freed hydrogen. But since seawater contains just 2-3% salt, the main effect is that the acid is diluted. If this happens inside a battery it is much more complicated because the lead becomes involved.
    But it surely ruins the battery.
     
  5. chabrenas
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    chabrenas Mike K-H

    While they remain in solution, you can't talk about the ions pairing off as HCl and NaSO4, but some NaSO4 may precipitate out if it isn't a very soluble salt.

    Ruining a battery is a repairable process, but humans can't inhale much chlorine and still remain repairable, so I'm trying to find out whether the chlorine story is a myth, or whether there are specific conditions in which it can be released.

    It sounds to me as though spilling sulphuric acid into a wet battery box, or even into the bilges, is not going to release chlorine, but I have that niggling worry about what could happen if the (now somewhat diluted) mix surrounded a couple of dissimilar metals down there...
     
  6. mydauphin
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    mydauphin Senior Member

    I think discussion is pointless, you shouldn't put seawater in batteries or breath the chlorine. That is why I use gel batteries and they are outside living space. Is there another reason for this discussion then may be we can go further.
     
  7. Fanie
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    Fanie Fanie

    If a yacht overturn and battery acid is to mix with sea water your concern is not the small amount of chlorine, you may or may not even notice, but what is a concern is the battery acid is going to burn your skin ears and eyes and bugger almost everything els up it comes in contact with.

    As mydauphin suggested, use SLA batteries. Worst that can happen with them is generating a bit of hydrogen before going flat if the situation isn't resolved, which sounds like the boat has sunk already.

    There are different types of chlorine, some are more dangerous than others, a chemical expert should be able to explain the different types and where they are found, ie pool chlorine is different from chlorine you get when burning PVC.

    A special combination you could try is mixing pool chlorine with brake flood. In about 5 mins you would be scattered all over the boat. So don't bleed the boat's brakes in the pool I say :D
     
  8. marshmat
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    marshmat Senior Member

    Having worked at pools a while back, I think it's safe to say that mixing pool chlorine with just about anything other than water is not a particularly smart move!

    (Since we're on a chemistry binge: the unstabilized, granular variety is usually calcium hypochlorite, and public pools sometimes use sodium or lithium hypochlorite in solid or near-saturated-solution form. The "hockey pucks" used in backyard pools are most often stabilized trichloro-s-triazinetrione, or trichloroisocyanuric acid. Nobody uses pure gaseous anymore, for obvious reasons.)

    I would have to actually sit down with an inorganic chemistry handbook and do the calculation to answer your question about chlorine release, chabrenas. I do know that chlorine gas is released if an electric current is passed through saltwater- I've smoked people out of a lab that way once, while testing an MHD pump. As to getting battery acid in the bilges- yup, that'll be very very bad for any equipment or fittings down there, as well as for any person who dares to enter.
     
  9. chabrenas
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    chabrenas Mike K-H

    When I say chlorine, I mean the gas Cl2, not bleaching and sterilising agents that release chlorine ions in solution.

    I agree entirely with those who say use Gel or AGM batteries (they weren't available when I did most of my offshore racing), but looking around forums and sales pages suggests that the vast majority of boaters still use flooded cell lead-acid batteries, just as most of them use crappy cables and connectors.

    I am writing a series of blog posts about marine electrics that I hope will prove useful, but it's no use just telling people what I think is good practice when it looks as if the vast majority if the boating world doesn't follow it - for various reasons, including a few old wives' tales. I need to debunk the rubbish and give good reasons for following best practice, even if it costs a bit more to do so.

    One of my problems is that a lot of the literature on Gel/AGM batteries is about their use in 'float' (standby power) environments, not deep cycle marine environments. Some of the best articles are on manufacturers' sites, but they are written to promote a product line.

    I'd appreciate input about people's own knowledge and experience, and links to authoritative articles on the Web.
     
  10. Fanie
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    Fanie Fanie

    The rule with batteries in any kind of waters is simple. Keep them dry and the terminals out of the water. As far as I know you get spillproof battery boxes where you can ride the battries in.

    Before fancy welders like we have today they used batteries to weld with. One must never underestimate to power of these every day used luxuries, even the small ones can be deadly when they explode.

    There was a time one had to hand crank an engine to get it started. Can you imagine the Yamaha with a crank kandle ;)

    Matt - Since the AWB used chlorine and brake fluid to make bombs with, it became news so everyone here now knows how to do it cheaply :D They did warn housewives who buys groceries not to put the chlorine granuals in a bag with daddy's brake fluid, in the case of a leak it could be fun.

    He he... makes you look different at the female in the car next to you. Cant wait for the trafic light to change eh :D
     
  11. CDK
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    CDK retired engineer

    You may remember from the chemistry lessons that Cl, Br, J and F are the halogens, something very similar to hooligans. An aggressive bunch that reacts with almost anything and therefore are almost never found as elements.
    So the tale of Cl2 escaping is probably not true.

    Many years ago I got a telephone call from the marina that my boat was unusually deep in the water. When I arrived I found the engine bay flooded, cause by a small tear in a Mercruiser bellows, cut by an oyster shell quite near the surface. In a few weeks time the engine bay was filled until the valve covers of the engines.
    There were two fully charges batteries powering the electrolysis and total destruction of two hydraulic pumps, starters, alternators, ignition units and the complete wiring harness of two engines. Where the battery poles were, a crater had formed, so there was free interaction between seawater and battery acid, what were once heavy cables now were only empty hoses.
    Yet there wasn't even the faintest smell of chlorine...
     
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  12. chabrenas
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    chabrenas Mike K-H

    Thanks, CDK. Just the kind of tale I'm looking for. Anyone else got a story to tell? Or a chemistry lesson?

    PS Sorry about the boat... Hope the insurance paid up.
     
  13. CDK
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    CDK retired engineer

    They did!
    In fact they paid for original Merc spare parts, like $890 for an alternator. I found refurbished parts for less than 1/3 and when the job was done, I invested their bonus in an Apelco LCD radar.
    And the best automatic bilge pump I could find....
     
  14. chabrenas
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    chabrenas Mike K-H

    Howzit, Fanie. I'd forgotten about the AWB bomb-making technique, although I was back & forth through Mafikeng at the time.

    Biggest engine I've ever hand cranked was a 2 cylinder Volvo diesel in an S&S 34. Decompression cams on, wind up slowly, then flip the cam levers....But since you only need to do that when you're in the thick of it all and find the starter button doesn't work, you've only got one chance.
     

  15. Fanie
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    Fanie Fanie

    You were through Mafi-where ? :D

    I'm always scared that if you try and pull start one of these big outboard engines it may backfire and actually wind you the wrong way round, which would leave you with extremely long thin arms.

    We had a lister water pump on the farm when I was a kid. That was a real kicker.

    As for chemistry, I find that, and stuff like medical stuff very interesting, but to remember those terms... I guess I have a poor memory, is why there's guys like you all, and Google for if one really needs the specifics.
     
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