Why grease battery terminals?

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

  1. diymostthings

    diymostthings Well-Known Member

    Couldn't wait any longer. I stuck my ohmeter probes (digital, autoranging) in a pot of grease and measured the resistance.
    I then cleaned up a battery terminal and clamp, (tapered) tightened, and measured the contact resistance.
    Thirdly, I dismantled the clamp, smeared grease over the post and clamp, retightened and measured that resistance.

    Anyone interested in the results?
    PTP
     
  2. Parpee

    Parpee Member

    "Anyone interested in the results?"

    No. But suspect that isn't going to make any difference to eternity of this thread.

    Poop Poop
     
  3. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    Oh, go on, then. Put us all out of our misery. :)

    Handyandy - really
     
  4. devil's advocate

    devil's advocate New Member

  5. devil's advocate

    devil's advocate New Member

    But I suspect: (1) Infinite (2) Pretty much zero (3) ditto...
     
  6. ban-all-sheds

    ban-all-sheds New Member

    This news just in.

    A man known to his friends as Peter the plumber was today rushed to hospital with severe burns following what a fire brigade spokesman described as "a grease fire" suddenly ignited in his garage.
     
  7. l00pd0g

    l00pd0g New Member

    I can't believe that a topic on greasing battery terminals has gone on for this long. Not having a go, I just find it bizzare.

    I'll shuffle off now ;)

    <u>Loops</u>
     
  8. diymostthings

    diymostthings Well-Known Member

    devil's advocate is absolutely spot on. Grease was over 3 megohm, ungreased terminals zero, greased terminals zero/flashing 1 ohm.
     
  9. wwwdot

    wwwdot New Member

    Very good description Tonks.

    Except:
    Every colour CRT has a metal screen with tiny
    holes

    The triniton has wires to achieve the same ends - to
    only allow the electron beam to excite the correct
    strip of phosphor.


    The wires in a trinitron tube are there to support the aperture grill which is the equivalent of the shadow mask. Difference being an aperture grill has vertical slots rather than holes. Rather than use 3 seperate guns for the RGB it use a single gun to excite the phospors which are arranged vertically as against pyramid fashion in the shadowmask tube.

    On most aperture grill monitors you can actually see the wires approx 1/4 and 3/4 the way down the screen running horizontally across the screen if you look closely enough at a plain background light colour
     
  10. TonkaToy

    TonkaToy New Member

    Actually wwwdot, Stoday was spot on - although you're right as well. Trinitron, PIL (precision-in-line, and other CRT technologies that use phosphor stripes rather than dots, use a tension mask (or aperture grill) rather than a shadowmask for beam guidance.

    The tension mask consists of a grill of very fine wires aligned vertically behind the face of the CRT. These do have 2 or 3 (depending on the screen size) horizontal support wires to give the grid dimensional stability.
     
  11. GettinBetter

    GettinBetter New Member

    Here's my twopence worth:
    You cant 'squeeze' out the 'grease' or whatever, because - the analogy is that of a pile of marbles, as you squeeze them, they would just move sideways (ooze out in the case of the grease) until they go down to one marble thick. Then that would be it. So there's no way a single molecule of grease will move sideways between two solid surfaces. This will leave a thin layer (i.e. one molecule thick) to resist current flow. But in the real world, because of the irregular surface finish of the battery terminals at that magnification, the pressure of the clamping action, and the malleability of the terminals, areas of the two metals will be touching, with the molecules of grease only filling the gaps where they don't touch, hence a low resistance reading when passing a small current to test.
     
  12. devil's advocate

    devil's advocate New Member

    Hi GettinBetter.

    Ok, I wasn't getting down to molecular level when I suggested all the grease was being squeezed out! I know from experience (ah, my old GT6...) that when the clamp is removed, the battery terminal will still feel greasy for a start!

    Do you think a one-molecule layer of grease will effectively 'conduct', or is there true metal-to-metal contact over most of the area?

    Cheers, DA.


    (This one will run and run...)
     
  13. GettinBetter

    GettinBetter New Member

    Well it's all relative really, and there are several things to consider. As posted before (by other people) grease, air, etc are known as insulators (i.e they have high resistance to electron flow), BUT all insulators conduct some electrons its just a matter of how few or how many, and that will also depend on the potential differences involved in the circuit (the higher the voltages the more electrons flow).
    Moving on to your next question.
    If the surface finish of the terminals is oxides free and mechanically clean, then the metal to metal contact will exceed that of the CSA of the adjoining conductors (or should do) and IMO is what one should be looking to achieve.
    I've heard a theory that actual metal to metal contact is effectively a weld, and that the only reason two pieces of the same metal don't join together is because of surface oxidisation prevents it. so if you could remove all the oxides then push the metals together you'd get a weld. Mmmm.... sounds good.
     
  14. Stoday

    Stoday New Member

    it. so if you could remove all the oxides then push
    the metals together you'd get a weld.

    Yes. It's called Friction welding and it's done in the car industry. One bar of metal is rotated at high speed and pressed into contact with a stationary piece. The friction heats up the joint and clears away the oxide. The advantage is that you don't have the high temperatures of normal welding so it causes less distortion.
     
  15. Stoday

    Stoday New Member

    There's also some types of dental gold inlay (not crowns, which are cast). After drilling the tooth, the dentist pushes gold foil into the hole and vibrates it. Gold does not oxydise and welds together under the vibrator. Bit like a builder consolidating earth, but the earth dosn't weld.
     
  16. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    Hmmm. Stoday, I think GB was saying that (in theory) that the two metals would be welded WITHOUT friction if all oxidation was removed.
    Anyway, how come then that RUST is the product of oxidation and that can weld two pieces of metal together ?

    Handyandy - really
     
  17. Stoday

    Stoday New Member

    That theory is out of date. They thought it a possibility before working in space - would a spanner weld to the nut? It dosn't work - you need some friction.
     
  18. ban-all-sheds

    ban-all-sheds New Member

    Sort of related, I guess - I once saw a demonstration piece of ultra-high quality/accuracy machining - it was a nut and bolt with surfaces so perfect that you couldn't tighten it up, there just wasn't enough friction between the threads. And if you held one component up, the other would screw itself in or out under gravity...
     
  19. devil's advocate

    devil's advocate New Member

    Hi handyandy.

    Rust doesn't weld the metals together - a weld involves use of the same material; an oxide is different.

    I recall (many years ago) seeing a demo in my engineering diploma course of two 'perfect' metal surfaces being 'welded' (that's what the lecturer called it) together by simply being slid over eachother by hand. It wasn't all that strong - it could be prised apart by hand too...
     
  20. Parpee

    Parpee Member

    "I recall (many years ago) seeing a demo in my engineering diploma course of two 'perfect' metal surfaces being 'welded' (that's what the lecturer called it) together by simply being slid over eachother by hand. It wasn't all that strong - it could be prised apart by hand too... "

    Hey DA, I once had an Alfasud built entirely out of welds like that!

    PP
     

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice