battery wiring question, 12v trolling motor and start battery

Discussion in 'Boat Tips' started by Catfish Pursuit, Jun 8, 2009.

  1. Catfish Pursuit

    Catfish Pursuit New Member

    Messages:
    1,081
    State:
    Missouri
    Here's what I have. Big battery for my 12 volt 50 pound thrust trolling motor and another big battery that I run for my starting/sonar/bilge/livewell/running lights. I have never had a problem with running the start battery down, even after 8 hours of fishing with livewell and sonar up and running full time. I was charging my trolling motor battery and a neighbor came over and said I should just wire the two batteries together so they will both be charged all the time. The batteries are both in the back side by side. He said to just run a short cable positive to positive, then another negative to negative and my alternator would charge them both. Anyone ever done this? My alternator is a 50 amp. Thanks, Chris
     
  2. SkipEye

    SkipEye Well-Known Member

    Messages:
    7,525
    State:
    Winfield, MO
    Name:
    Darryl
    That is termed PARALLELING your batteries. And yes, it will increase your ampacity and also allow the alternator to charge both batteries.

    One caution though, this should only be done with two batteries of similiar size AND CONDITION.
     

  3. Catfish Pursuit

    Catfish Pursuit New Member

    Messages:
    1,081
    State:
    Missouri
    Thanks! My start battery is not quite as big as my trolling motor battery so I may just leave them as they are. Most I've ever ran the trolling motor battery down was to 70% so not that big of a deal. Thanks again! Chris
     
  4. tswebb71

    tswebb71 New Member

    Messages:
    405
    State:
    So. IL
    Since we are talking about batteries, I have a question. I have a 24 volt trolling motor where they are wired + to - and - to + with the trolling motor coming off the + on one battery and the - on the other. Is it possible to hook another 12v device to ONE of the batteries while using both of them to run my trolling motor or will I burn something up?

    Thanks
     
  5. Grimpuppy

    Grimpuppy New Member

    Messages:
    3,556
    State:
    Concordia, KS
    Scott - If you hook into the Pos and Neg of ONE battery it is still only 12V, even though you have it wired in series for 24v with another battery. You won't burn anything up.
     
  6. JEFFRODAMIS

    JEFFRODAMIS New Member

    Messages:
    2,537
    State:
    TEXAS
    Installing hydraulics on cars ive ran the switch box (12 volt) off the first battery in a series of a 48 volt system and been fine, but i usually rin it off the engine's battery. this would be my only experience in doing something like what your were asking
     
  7. boombalaty

    boombalaty New Member

    Messages:
    1,536
    State:
    Kansas
    I would recommend using a battery isolator. It will allow both batteries to be charged by the alternator but the draw on each will be separate. This way if you are on the water for long periods of time you never have to worry about your trolling motor causing you to be stranded. You can get an isolator at any boat supplier and they are very easy to install.
     
  8. boombalaty

    boombalaty New Member

    Messages:
    1,536
    State:
    Kansas
    Yes you can do the 12-24 volt thing. If you are paralleling 2 batteries without an alternator it is important to use two similar batteries. If they are not one can become dependent on the other causing one to fail. I have been in 12 volt audio industry for about 15 years and have seen this many times with multi battery systems. An isolator is money well spent. Just my 2cents:wink:
     
  9. tswebb71

    tswebb71 New Member

    Messages:
    405
    State:
    So. IL
    That was my thinking but I just didn't know if it work if they were wired in tandem for the trolling motor. Thank you.
     
  10. SkipEye

    SkipEye Well-Known Member

    Messages:
    7,525
    State:
    Winfield, MO
    Name:
    Darryl
    If you are running 12v accessories off of your 24v batt system ALWAYS use the lower battery bank.

    If you wire something to the upper bank (other than the 24v trolling motor) you may end up melting some wires. There are devices whether you realize it or not that are grounded to your boat hull. If one of these is on the lower bank and one on the upper bank you'll have a 12v difference of potential on your grounds and something is gonna smoke somewhere. This is for an aluminum hull of course.

    Two that I know of are your stereo chassis (even if you do not connect ground to the lug on the chassis rear). The other is your VHF antenna, you'll find that the mount is at ground potential.

    Ask me how I know this. :smile2:
     
  11. nick81

    nick81 New Member

    Messages:
    99
    State:
    south carolina
    yes...what you can do is make a jumper to go from neg. on one to pos. on the other.