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Battery Charger size for 2 Group 31 Batteries in Parallel

Discussion in 'Electronics' started by CaboFly, Nov 6, 2022.

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  1. CaboFly, Nov 6, 2022
    #1
    CaboFly

    CaboFly Member

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    I plan on adding a dedicated battery bank for my Scotty downriggers and JL stereo system. I was going to utilize house bank but downriggers would have to go thru converter being 12v only and their amp draw would then max converter with current electronics pushing it over. Could add another converter but don't want to push house bank too hard and both stereo amp and downriggers pull a lot of juice. My gut tells me just adding a 12v bank and charger for these new items is prudent strategy. Q is should I go with a 25 amp charger or 40 amp charger. The 210 amp hours of both group 31's combined seems to indicate either would be ok but I am not sure what would make one better than the other. Appreciate any input. Also my house bank is 4 group 31's on a 45amp charger. If you think adding a new converter would be better solution open to that idea as well. I just like idea of heavy stereo and downrigger use not impacting my primary dc system.

    Thanks.
  2. Capt Ralph, Nov 6, 2022
    #2
    Capt Ralph

    Capt Ralph Senior Member

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    I assume you run your gen-set all the time. So, your charger would always be charging.
    So, How many amps would the down riggers and stereo draw would answer the charger size.

    Now, ammonia on your parade; Those down riggers will induce noise on the batteries, My cause static thru your stereo.
  3. DOCKMASTER, Nov 6, 2022
    #3
    DOCKMASTER

    DOCKMASTER Senior Member

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    Why do you think your downriggers pull so much amperage? I have four Cannon Tournament Pro downriggers and they don’t pull much on my house bank. Even though the draw is a little bit they only run for a short time so I’m surprised you are worried about them. Of course, I have a gen running and battery charger going all the time. But I assume if you are using downriggers then you are trolling and have an engine alternator going?
  4. CaboFly, Nov 6, 2022
    #4
    CaboFly

    CaboFly Member

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    Yes Gen always running. The noise from downriggers is partly why I liked using dedicated bank so my electronics were not impacted. The percentage of time I would be fishing and jamming the stereo would not be significant but occasional. Open to suggestions as always. Max draw on downriggers when running is 19.5 amps each.
  5. Capt Ralph, Nov 6, 2022
    #5
    Capt Ralph

    Capt Ralph Senior Member

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    I recall (from past Cabo threads) Cabos have an unique (strange) battery system where the house bank is not charged by the engine alternators.
    This may be on CaboFly's mind.

    I have no idea what downrigers draw in amps but I have learned that some big sterio amps can put a hurting on a battery quickly. A few years ago, I assisted in installing these monster amps on ski boats. Wow, dead batteries in no time with key off on the sand bar.

    Good thing a second battery and ACR was installed.
    On an older ski boat, had to install a larger alternator to keep the amp running.
    Freaking to loud for me but the spoiled (SFB) deaf kids loved it.
    Last edited: Nov 6, 2022
  6. CaboFly, Nov 6, 2022
    #6
    CaboFly

    CaboFly Member

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    Not worried about house bank handling downriggers more so my boat is 24v and my Newmar converter for 12v dc is 40 continous 50 amp intermittent.

    Ironically on my last boat I ran downriggers off converter and when fishing my nmea 2k would on occasion cycle power which I imagine is voltage related with downriggers on converter and max load. On this refit I am either going to add seperate converter or add 12v battery bank with dedicated charger. Trying to determine which option is best.
  7. Capt Ralph, Nov 6, 2022
    #7
    Capt Ralph

    Capt Ralph Senior Member

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    I vote for a good battery or two and based on the current draw, the larger (or more) charger.
    In the old days we called them converter/chargers. The charger would more or less supplement the amp draw then charge the batteries when all was calm. ie ole Raritan converter/chargers that we still use.
    The newer chargers will work the same way but when all settles down, their charge program/profile does a better job in a float mode.
    Yes, keep the electronics separate from the noise and surges of the DCv motors.
    Still not sure of your stereo amp. Where it should go. How loud do you need that noise. I'm convinced fish don't like it.
  8. CaboFly, Nov 6, 2022
    #8
    CaboFly

    CaboFly Member

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    The stereo system won't be massive. Just something for occasional tunes. Would like to use with new bank on 12v as I like knowing it won't impact House system and if downrigger use creates a hum I just won't play stereo when salmon fishing which would be rare anyway. Also amp location is much closer to new 12v bank than House 24v bank.
  9. Capt J, Nov 7, 2022
    #9
    Capt J

    Capt J Senior Member

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    It depends on how many amps you will be drawing from the battery bank. How many amps does the stereo draw? Given the price difference between most 25 and 40 amp battery chargers, if the stereo has a decent sized amp, I would go with the 40 amp charger.
  10. cleanslate, Nov 7, 2022
    #10
    cleanslate

    cleanslate Senior Member

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    I would go with the two batteries ,Group 31 you say, and a 25 amp charger. And no converter.

    You are already charging four group 31s batteries with a 40/45 amp charger which is working fine.
    Mine pea brain says if you cut things in half , two group 31 batteries and half your current charger ,25 amp or so...That should do the trick. Small charger takes up less space and AC amps also...