Why grease battery terminals?

Discussion in 'Electricians' Talk' started by diymostthings, Mar 10, 2005.

  1. diymostthings

    diymostthings Well-Known Member

    Surely putting grease on battery posts will result in a very bad electrical connection - but that is what everyone recommends. My car battery posts are smothered in grease. Or are you meant to put the grease on AFTER you've tightened the connection?
    PTP
     
  2. Kev Cordina

    Kev Cordina New Member

    The grease will stop corrosion - a very fine layer between the post and the clamp won't affect the connection significantly.

    The idea is to stop the clamp and post corroding together and preventing removal.

    Kev
     
  3. devil's advocate

    devil's advocate New Member

    A thin smear is applied before assembly. When the terminal is fitted and tightened, the grease is squeezed out to leave the metals in good contact - but the grease leaves a perfect air and moisture seal around the touching parts.
     
  4. Stevemastic

    Stevemastic Member

    Or if you are worried about using lm grease there are some nice red & green sprays but you would need to own a big fleet to make it worth while.
     
  5. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    I think you are supposed to use Petroleum Jelly.
    This is more conductive than yer bog standard
    lithium grease, but has the same waterproofing
    capabilities.

    Handyandy - really
     
  6. Wscad

    Wscad New Member

    Use vasaline (not sure if spelling is correct)

    Not taking the mick here... but it works!

    Prepare.... apply & forget!
     
  7. Wscad

    Wscad New Member

    Yer just beat me Andy...but we are on the same page I think
     
  8. Stoday

    Stoday New Member

    Originally, batteries were not sealed as they are these days. They needed topping up from time-to-time with distilled water. Inevitably, you got some little splashes around the battery, which helped to terminals to corrode rapidly unless they were greased.

    With the sealed batteries we have these days, I think greasing the terminals is much less important, although if you need to remove a battery connection it's easier if it's greased.
     
  9. Hitch.

    Hitch. New Member

    I work on converting brand spanking new vehicles, they never come to us from the factory greased, nor sprayed.
     
  10. sinewave

    sinewave Screwfix Select

    > I work on converting brand spanking new vehicles,
    they never come to us from the factory greased, nor
    sprayed.


    That's cause they know your goin to rip em apart again!
     
  11. seylectric

    seylectric New Member

    I replaced the battery on my car (five year old Passat) recently and there was no sign of the terminals ever having been greased. I guess with sealed batteries it isn't considered to be necessary anymore.
     
  12. diymostthings

    diymostthings Well-Known Member

    Well I have to say that the answers so far are not very convincing. I learnt that there were insulators (e.g. glass, PVC, dry air, ebonite -remember that?) and conductors (e.g. copper, silver, lead, perfect vacuum etc.). Grease, an oil based product like plastic must therefore be an insulator. Even a thin film between the connectors surely will reduce the electrical contact. Has anyone ever stuck their continuity probes into a jar of vaseline?

    PTP
     
  13. devil's advocate

    devil's advocate New Member

    Hi PtheP.

    I refer you to my earlier post on this topic - the grease is squeezed out until the metals make perfect contact, but the surrounding 'grease' makes a perfect seal arround it (more so than if it was just smeared on afterwards.

    You are right; grease, petroleum jelly, (and perfect vacuums - where did you get that idea?) etc, are all nigh-on perfect insulators - their purpose is not to improve the connection, but to prevent it deteriorating afterwards.

    As has also been mentioned, it doesn't apply so much in these days of sealed batteries - but the acidic vapour from old, top-up, batts caused havoc with the surrounding metal.

    (Even new battery posts, whilst not covered in grease, are still 'greasey'!_
     
  14. Stoday

    Stoday New Member

    Pure water is an insulator too.
     
  15. devil's advocate

    devil's advocate New Member

    Pure water won't freeze, either.

    At least that's what Kurt Vonnegut said.
     
  16. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    I think you are supposed to use Petroleum Jelly.
    This is more conductive than yer bog standard
    lithium grease, but has the same waterproofing
    capabilities.

    Handyandy - really

    The reason I said this, is because in a car handbook(I've read all the books of all my previous cars), it recommends that you use petroleum jelly(exact words). I presumed that it might have more conductive properties than grease. No book I've read has ever recommended grease.

    It might be worth noting that another reason for smearing with this stuff is to prevent the battery leaking voltage across the terminals, especially when damp (look at your battery on a misty morning). A damp battery(unprotected) will do this, but protecting with petroleum jelly will prevent it. And yes, I have tested this theory.

    Handyandy - really
     
  17. diymostthings

    diymostthings Well-Known Member

    OK devil's advocate - yes I have to reluctantly agree you may be right. I still find it hard to imagine all the grease being squeezed out of the joint.

    As for a perfect vacuum being a conductor - do you know how the cathode ray tube in your tele works? (or do you remember valves?)

    Thanks all. Got the answer now.

    PTP
     
  18. Stoday

    Stoday New Member

    Conductors don't need a heated cathode to boil off electrons like CRTs and valves do.
     
  19. diymostthings

    diymostthings Well-Known Member

    Conductors need a plus and minus at each end to get a current flowing. A heated cathode is just another minus and the anode another plus.
     
  20. handyman 2

    handyman 2 New Member

    The reason why battery terminals were greased was to protect them from the corrosive gases given off from unsealed batteries whilst they were charging.
    These gases are released and contain an element of Sulphuric Acid which can corrode the connectors on the battery.

    It's not as important using a sealed battery as effectively there should be no leakage but some people still grease them as a matter of habit

    If you do decide to then before making your connection to the battery, first smear petroleum jelly (eg Vaseline) over the terminal post then wipe the excess around the connector/post after tightning.
    Petroleum jelly does not absorb water over time as some greases do which is why it is preferential.
    And for those of you who do have corrosion on a terminal - it looks like an off white crust, simply pour boiling water over the treminal/connector to remove it ans then once dry, give it a smear :)
     

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