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Who is right about what dual batteries do?

Discussion in 'The Garage' started by Poohbair, Nov 13, 2004.

  1. Poohbair

    Poohbair 1/2 ton status

    Jan 30, 2003
    Likes Received:
    Ellensburg, WA
    I really know nothing about electricity... I am a retard when it comes to things of the sort. My friend is going to setup dual batteries in his 72 and was talking about finding the simplest way to do it.
    While in the discussion, one guy says that if you hook 2 batteries together (+ to + and - to -) that it doubles your battery amp output... for instance if you had 2 500 CCA batteries that you would now have 1000 CCA's?
    I was thinking that you would still have 500 CCA's, but have 500 CCA's for twice as long...

    What REALLY happens when you hook 2 batteries together like this?
  2. Eric M.

    Eric M. 1/2 ton status

    Dec 10, 2001
    Likes Received:
    Oakland, CA
    I think it is a mathmatical problem. 500 for twice as long, 1000 for the same amount of time, 250 for 4 times as long. Basically, you are doubling what you have in relation to the various properties.

    I think.

    Eric M.
  3. dremu

    dremu Officious Thread Derailer Premium Member GMOTM Winner

    Feb 27, 2000
    Likes Received:
    East of San Francisco
    Mmm. Both right. CCA is cold, so at firing time ... and assuming your wiring can take it, you would get 1000CCA from two 500CCA batteries in parallel (+ to + and - to -.) This was more or less how the factory dual battery option worked -- a must for those in Minnesota, for instance /forums/images/graemlins/laugh.gif

    A 500 CCA battery will more or less give you 50Ah (amp-hours)-- that is, 1A draw for 50 hours. No, it will not give you 50A for 1 hour /forums/images/graemlins/smile.gif

    Two of them in parallel, as above, would give you 1A for 100 hours, so they would in sum be rated for 100Ah. (So yeah, Eric, you're right too.)

    Note to real EE's: I'm fudging, as you know as well as I do that this is all approximations and doesn't take into account wiring, etc etc. It's the general principle. (I am not a "real" EE /forums/images/graemlins/smile.gif

    -- A
  4. Pookster

    Pookster 1/2 ton status

    Nov 21, 2000
    Likes Received:
    NYC, NY, USA
    your both correct, it just dpeend son how your "looking" at things- When you put two batteries in parallel, (as discribed) the voltage doesnt change, but the capacity doubles- hence, you are really getting 1000CCA instead of just 500. Given the same load, you would get a theoretical "double" run time. hook them in series, you've upped the voltage, but kept current the same. CCA's are really simply just ameasure of how much current the battery can give. Thats why A volt meter is not the greatest tester of batteries as compared to a load test.

    However, I assume you might want dual batteries for other options, such as a winch- in this case, dual 500 batteries will outperform a single 1000. two 500's will more readily give out the juice you need.
  5. wasted wages

    wasted wages 3/4 ton status

    Dec 3, 2003
    Likes Received:
    Dallas Texas
    [ QUOTE ]
    What REALLY happens when you hook 2 batteries together like this

    [/ QUOTE ]

    you end up with 2 dead batteries out in the middle of nowhere!!!! /forums/images/graemlins/whistling.gif /forums/images/graemlins/whistling.gif /forums/images/graemlins/whistling.gif

    Just kidding,,,,, /forums/images/graemlins/waytogo.gif /forums/images/graemlins/waytogo.gif

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