Electrical techie question I've been meaning to ask for ages

Discussion in 'Tech/Mech General' started by GeriatricWanderer, Mar 18, 2015.

  1. GeriatricWanderer

    GeriatricWanderer Funster

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    Battery terminal corrosion - why only (mostly) on the negative pole?
     
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  2. Lenny HB

    Lenny HB Funster

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    Two reasons, one is you get a reaction that causes electrons to flow when you put two dissimilar metals together, battery terminals are lead the connectors are either copper or brass. 2nd reason is that when the battery acid comes in contact with the connectors you get a reaction which creates corrosion. You tend to get far less terminal corrosion with fully sealed batteries.
    Cars always used to be positive earth they changed to negative earth as the positive terminal corrosion used to be very bad on positive earth cars, it was something to do with electron flow can't remember exactly.
     
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  3. Portland

    Portland Funster

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    To clean it correctly brush it off and then run boiling water over it. This will change it to copper sulphate and then use either a brand product or old fashioned vasaline to help keep the reaction down
     
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  4. John Laidler

    John Laidler Funster

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    That's a very good question! It might be due to dissimilar metals, but should it then not happen on both terminals? However, the positive terminal is often well shrouded so it may be surrounded by drier air than the exposed negative terminal.
     
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  5. scotjimland

    scotjimland Funster Life Member

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    Corrosion happens when there is a flow of electrons between the +ve post and the -ve .. across the top of the battery..
    you can only get a flow if the top of the battery is damp or wet, usually from acid that has escaped as mist from the cells during heavy charging .. you will never or rarely see it on sealed or maintenance free batteries ..

    the same corrosion that can get also get on the battery screwed-rod J bolts and clamp.. the electrons are flowing to earth via the clamp.

    Nothing to do with dissimilar metals
     
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  6. Wildman

    Wildman Read Only Funster

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  7. scotjimland

    scotjimland Funster Life Member

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    Googling provides this explanation

    Corrosion Of Battery Terminals: Explanation, Cleaning & Prevention
    http://benignblog.com/2013/05/why-b...e-causes-composition-cleaning-prevention.html

    Causes And Compounds Formation:

    In case of sealed lead acid battery (also known as SLA battery or dry battery), corrosion happens when electrolyte makes its way out to battery terminals through any leaks or joints. In case of flooded lead acid batteries (wet batteries), electrolyte can jump out while carelessly pouring water into cells. Also, fumes of sulphuric acid which is a part of electrolyte and actually responsible for corrosion keeps arising out of vents of flooded lead acid batteries when battery is charging or hot. Overcharging heats up the battery and heat increases the volume of electrolyte filled inside it. This electrolyte can leak out of vents of overcharged flooded lead acid battery if it is topped up with too much water and also SLA batteries through loose joints.Posts of lead acid batteries are mostly made from lead. Lead itself is a stable metal. Its reaction with sulphuric acid is very slow. If contact happens at battery posts, the compound which is formed as a result of reaction is lead sulphate ( PbSO4 ). The chemical reaction between lead and sulphuric acid is accordingly:

    Pb (s) + H2SO4 (aq) → PbSO4 (aq) + H2 (g)
     
  8. John Laidler

    John Laidler Funster

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    I did quite a lot of Googling before my answer above and I couldn't find a convincing explanation why it should happen mostly to the negative terminal either! It may be some sort of "electroplating" (wrong word!) effect which affects the cathode and not the anode but what the exact mechanism is for the formation of white lead oxide, for example, on one terminal rather than the other still escapes. I can see why things will corrode when wet and in the presence of acid but why only one terminal? Unless one is wetter than the other because it is not shrouded, which was my first guess.
     
  9. scotjimland

    scotjimland Funster Life Member

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    not just one terminal as you can see from these examples.. plenty more images if you google..

    [​IMG]

    [​IMG]

    upload_2015-3-18_16-11-16.jpeg
     
  10. GeriatricWanderer

    GeriatricWanderer Funster

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    Where's Mr Mott?
    I bet he'd have a thousand words to say on the subject and be quite harsh on any poster who had got it wrong!
     
  11. gus-lopez

    gus-lopez Funster

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    Anyone who allows them to get in to that state should be made to walk forever more !:)
     
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