Question on Dual battery system vs. battery chargers





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  1. #1
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    Default Question on Dual battery system vs. battery chargers

    Guys, forgive if I ask a dumb question, but this is something which had been puzzling me for a while and I am sure there is some genius (like Koebelwagen) on this forum that will be able to explain:

    In all threads around installation of a dual battery system, it is recommended that as thick as possible cabling be used (recommended not less than 16 mm) to ensure a good charge from the alternator/crank battery to the auxillary battery.

    This makes perfect sense to me as well but now the question: why is it then that battery chargers are equipped with such thin wiring and jumper clips as connectors whiilst they are doing the same job as the alternator to the auxillary battery?
    2007 Colt Rodeo 3000I V6 D/C 4x4
    Dual battery system
    57 mm freeflow system
    General Grabber AT3's
    Challenger Bundu Basher Off-road trailer aka Bos Parra

  2. #2
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    The alternator can supply whatever your rating is. Anything from 45-105A. The battery charger will have cables to match the charge rate. My charger is only rated at 10A, so why have a 16mm cable?
    LC 78 Troopie 1HD-FTE
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  3. #3
    4ePikanini Guest

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    In a practical sense you can think of it this way

    When the battery is fully charged the alternator bypasses the battery and delivers current to the vehicle where it is needed - hence the cable needing to be thick as the alternator (at times) supplies ALL of the current to the vehicle when running ( obviously an alternator can't start the car )

    In some vehicles ( please don't try this at home - I take no responsibility for your actions ) you can remove the + terminal and the car will still run and operate.

  4. #4
    4ePajero Guest

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    Quote Originally Posted by 4ePikanini View Post
    In a practical sense you can think of it this way

    When the battery is fully charged the alternator bypasses the battery and delivers current to the vehicle where it is needed - hence the cable needing to be thick as the alternator (at times) supplies ALL of the current to the vehicle when running ( obviously an alternator can't start the car )

    In some vehicles ( please don't try this at home - I take no responsibility for your actions ) you can remove the + terminal and the car will still run and operate.
    No!

    It has to do with voltage drop only!
    A lead/acid battery can be charged only if the voltage exceeds a specific minimum value.
    It the cables were short, as in a charger, you would need similar thickness cables/wires.

  5. #5
    4ePikanini Guest

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    Quote Originally Posted by 4ePajero View Post
    A lead/acid battery can be charged only if the voltage exceeds a specific minimum value.
    I agree


    Quote Originally Posted by 4ePajero View Post
    It the cables were short, as in a charger, you would need similar thickness cables/wires.
    I agree for two reasons

    1. You don't want voltage drop
    2. High current demands thick cables

    Hence my statement

    Quote Originally Posted by 4ePikanini View Post
    ..... hence the cable needing to be thick as the alternator (at times) supplies ALL of the current to the vehicle when running .....
    Or am I all confused in the fact that the alternator does not supply current to the electrical systems at times

    I based my responses on THIS stating that the alternator provides current.

  6. #6
    4ePajero Guest

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    Ai! These kids!

    Voltage = potential difference.

    Current is the flow of electrons between two sources at different potentials

    Alternator capacity is the amount of current it can 'allow' when two sources which are at different potentials are connected with a conductor. Another way of putting it is the ability to maintain the potential difference as the flow increases.
    An alternator thus generates a potential, with a capacity to maintain that potential, up to a stated draw (current).



    A simple analogy:

    Voltage:
    Imagine a water tank at a specific level. The level of the water (the 'head') represents the voltage (potential energy)

    Cable / wire:
    The pipe that lets water out of the tank. The thicker the pipe, the less the losses to friction.

    Current:
    Flow rate of the water in a pipe.

    Parallel connection:
    More than one water tank at the same level. The capacity increases but not the 'head'.

    Series connection:
    More than one water tank stacked one above the other, effectively increasing the 'head'.

    Voltage drop:
    Imagine a water tank with a 1mm dia outlet pipe. The 'head' at the outlet of the pipe is less than the 'head' at the open surface (due to friction losses).
    Same for a thin conduit.

  7. #7
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    Oom 4E!
    Welcome back...
    (You were missed)

    Thank You for that explanation...
    89 110 V8

    A closed mouth gathers no foot

  8. #8
    4ePajero Guest

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    Quote Originally Posted by scottys_sa View Post
    Oom 4E!
    Welcome back...
    (You were missed)
    Just provoked by all the BS posted lately.

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