battery charging question

  • chippee
    sw wi
    Posts: 488
    April 13, 2003 at 11:48 pm #1243214

    I have a 12 volt trolling motor but have hooked up 2 batteries to it to hopefully give me longer lasting power. I have them hooked up inline,positive to pos. and neg to neg, when i charge i charge one battery only thinking it will flow through the system. i did this all last year but fried my front battery but the second battery was fine, so this year i tried charging a pos. post on one battery and a neg. post on the other, but my lasting power did not seem to compare to last year. any ideas on the right way to do this?

    gimpy
    Owatonna, Minnesota
    Posts: 149
    April 14, 2003 at 1:23 am #264008

    If you havent already, buy a automatic charger. They are nice cause they tell you when there done charging. Do one at a time. I dont know if i exactly answered your question, but this might help, I am no expert.

    Gianni
    Cedar Rapids, IA
    Posts: 2063
    April 14, 2003 at 2:56 am #264023

    In theory, you had it right before. In practice, what you’re trying to do is impossible. The batteries should be hooked in parallel (pos to pos), as hooking them in series (pos to neg) will give you 24V and likely fry your motor before too long.

    Unfortunately, the batteries will never be identical in every way, and so when one starts to go, it will take the other down. You will have lots of current leakage problems between the batteries as they attempt to stabilize, etc. Another sort of odd phenomena associated with electric motors is the feedback voltage that is generated by the armiture in the field once the motor is spinning – my first thoughts would be that it would have a different effect on the two batteries, even though they are shorted.

    It is possible to build something that automatically isolates the two batteris and uses both to supply current to the trolling motor, but such a system would be prohibitively expensive (making 24v and 36v motors was apparently much easier).

    The best option would be to run one battery until it’s dead, then hook up the other. Then you don’t have to worry about any of the problems above. I think someone like Guest builds a two-battery switch that has four positions (1, 2, both, off). Then you could switch at the turn of a switch.

    richardsmith
    Owatonna Mn 55060
    Posts: 174
    April 14, 2003 at 3:02 am #264026

    Hi Den ! I also have been running a 12volt system in my boat for years with two batteries hooked togeather to make 1 big 12volt ! In my experience I have always charged the batteries as one unit and have never had a problem ! I use an automatic 10/2 on board battery charger which I leave plugged in all the time the boat is out of the water ! A little hint,always buy the battery with the most reserve capasity, the more the better !! This is just my experience with a 12volt system.

    Richard (Smitty)

    Keep a tight line !!!

    bassbaron
    eldridge, ia
    Posts: 709
    April 18, 2003 at 2:25 am #264490

    Speaking of batteries- does it hurt to leave them on charge all the time or should I go a day on, then some time off? I have an on board dual pro charger and use 2 x 12 volt optima batteries. I dont want to “overcharge” them and Im not sure if the dual pro is a trickle or a float charger. (Does this make a difference?) I can tell you that when charging there are 4 red lights for full charge, then when it is “done” a green light comes on. I bought my boat used with the charger on it and dont have the manual for the charger.
    I probably should have asked this 4 months ago when i put it away for the winter, but sometimes my trips are few and far between so it will be useful knowledge. Thanks.

    By the way, I have a maxxum 74 lb, and ran it on 75% for 15 hours in my garage with no apparent loss of power on these batteries just to see if they run as advertised. So far (1 year) i have been very happy with them.

    jon_jordan
    St. Paul, Mn
    Posts: 10908
    April 18, 2003 at 2:41 am #264493

    Quote:

    By the way, I have a maxxum 74 lb, and ran it on 75% for 15 hours in my garage with no apparent loss of power on these batteries just to see if they run as advertised. So far (1 year) i have been very happy with them.

    I hope you had that motor in a garbage can full of water or something!! The motor depends on the cooling effect of water to keep from over heating the coils in the motor. I’m sure you did or that motor would be cooked. Just pointing that out to anyone who may try the same thing!

    Jon J.

    bassbaron
    eldridge, ia
    Posts: 709
    April 18, 2003 at 3:07 am #264497

    yes- i put in in a tub of water, i probably should have posted that to save from blowing everyones motors. Thanks.

    Gianni
    Cedar Rapids, IA
    Posts: 2063
    April 18, 2003 at 3:39 am #264500

    Contact the manufacturer of the charger – dollars to donuts they will send you a new copy of the manual for the unit if you give them a model number.

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