Charging a deep cycle battery
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  1. #1
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    Can one charge a deep cycle battery with an
    alternator in quick time. I have a trickle
    charger but this takes long, so seeing that
    a car battery gets powerd up quick with an
    alternator, why could one not connect 2 deep
    cycle batteries to a small engine that pulls an
    alternator which charges the battery faster,
    so 1/2 hr later I can use it again. (electric
    outboard) It doesnt feel right or would it work?
    I don't like unnatural noise in the bush so
    the genset will only run a fraction of the time.
    Brain fart?
    Andy

  2. #2
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    That depends on teh battery. And how long you insist it needs to work before replacement.

    Auto batteries are designed to dump current, long life is not a part of the design. Auto alternators do indeed dump charge back in at a relatively high rate.

    If the "deep cycle" battery is a traction type battery (golf cart), it will probably dump and accept charge at a higher rate than a battery designed for a solar charge setup. (I use golf cart ones in my solar setup...)

    If you want to be back in biz fully charged in 1/2 hour after a discharge to dead, that isn't good for lifetime.

    You can charge anytime at 1/10 of capacity (C/10), which would be 10A for a 100AH battery.

    Charging at C/3 is starting to push the ordinary battery. Much of that and you will need to replace sooner.

    What you want is charging at 2C, which is mighty darn fast.

    If you are using a regular "marine deep cycle", which is almost an auto battery with a new name, go ahead. They don't cost that much, and even if you can only do it 100 times instead of 1000, maybe that's OK.

    Don't discharge lower than 20 or 30% remaining (70 to 80% used) if you want lifetime.

  3. #3
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    I have a large (27M, I believe) deep cycle marine battery in my truck bed to power a winch for launching RC sailplanes. It's hooked up to the truck's charging system with a resistor (several brake light bulbs in parallel) to limit the charge rate to about 8 amps. When the battery is down a bit, the bulbs will glow dimly until the charge rate drops down to a couple amps.

    The battery is about seven years old now, and it still works fine. That's a lot longer than the first one lasted. It was hooked up without the resistor or an ampmeter, and probably charged at a much higher rate.

    Roger

  4. #4
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    AAhhh!, Roger, is that where your BB handle came from?

  5. #5
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    Not sure about the high current charging, But one thing to watch is the heat of the battery. If it gets too hot, the plates will warp and then the battery is toast. Batteries generate heat weather discharging or charging. Heat kills.

    Dave J

  6. #6
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    Yeah the heat thing.....it won't get much hotter than boiling water, but either the heat, or the rate of charge, whichever....its not good for the battery.

    If you do much high current discharging you will feel the heat. SAme with 2C charging.....with a 60 AH battery, that would be basically a 120A charge.

    There will be a bunch of gassing at that charge rate....that tends to lead to internal connection damage.

    As far as warpage, it seems to happen, but I don't quite see how it can be heat....given the "water" all around the plates (grids, really). Even though its acid, it still should boil around 220F or so.

    Best I can figure is that the paste is converted to sulphate or charged back fast enough that it does not happen evenly over the gridwork of the "plate", and stresses from the changing volume of the paste warp the grid.

  7. #7
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    If you use your trolling motor that much, I'd get two sets of batteries. That way one set could always be on a charger/maintainer. High charge rates ruins batteries.


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