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Paralleling batteries for my 12V trolling motor


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Paralleling same voltage batteries increases total ah ampere hours. Ampere hours is same thing as battery capacity. While charging such parallel batteries no wire connection change is required. Treat it as one battery. All else is a myth.

 

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Hooking up batteries in series or parallel the batteries should only be done with identical make and specification of battery or you will have issues.    

In my application I am connecting two new and identical batteries 27DC-180 (MCA=1,000, RES=175, Ah=105) in parallel with #2AWG with crimped and shrink wrapped jumpers.  I am connecting each bank of my ProSport 2-bank onboard battery charger to a battery.   

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Regardless of series or parallel circuits, depending on the application. The circuit is only as strong as the weakest battery. Yes brand new identical batteries are the best to start with; but after some time, even these batteries need to be tested individually. Making sure they have all survived being discharged and recharged numerous times. Here's a good example of what I'm saying. My golf cart we use at our trailer is a 36 volt system. 6, 6volt batteries connected in series. Being a used cart I replace all the 6 batteries with the same make and size. The cart worked perfectly for about 5 years; using a self regulating charger. After that the carts running time slowly decreased to the point that at a full charge, we wouldn't get a weekend out of that charge. Being a mechanic I have equipment to test batteries. After allowing the battery pack to fully charge, I performed a discharge test on the pack and it seemed to pass but barely. Disconnected the batteries from each other, charged and tested them individually and found that 2 of the batteries were not accepting a charge properly. They quickly fell well below the manufacturer's rating during a load test. After only replacing those 2 batteries the cart ran as intended. Yes eventually I replace all the batteries again; but by doing so I added a few year worth of use with the original batteries that I installed.   

Dan.   

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15 hours ago, Salmon Catcher said:

Battery Capacity, battery power, battery AH ampere hours is same thing. Benefit of paralleling batteries is to increase total battery power. Two batteries in parallel will run your trolling motor longer then one. That is the benefit.

Theres math involved and Im sure a graph somewhere that will show you running a more powerful 24 system will outperform a 12v system with more AH and reserve capacity. This is the main thing here, if you are carrying two group 31's in the boat anyways you should be running them for 24v.

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1 hour ago, AKRISONER said:

Theres math involved and Im sure a graph somewhere that will show you running a more powerful 24 system will outperform a 12v system with more AH and reserve capacity. This is the main thing here, if you are carrying two group 31's in the boat anyways you should be running them for 24v.

You are correct.  At the similar Ah rating a series rated 24V system will out perform a 12V system.  The have a 12V system and wiring them in parallel this is the best solution for what I am running - short of dripping $3k for a new trolling motor.    

 

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All chart plotters, sonars, radars, downriggers run on 12 volts DC. What is the point complicating electric circuit wiring it to 24V?  No matter how you connect your batteries in series or parallel you will have same total capacity=total power=combined ampere hours.  Can not violate formula Power= Voltage * Current

If you need some exotic voltage like 18DC,  use dc to ac inverter and ac to 18V dc supply. That complicates circuit and introduces more potential problem down the road. I would not run my critical navigation equipment on such power source.

 

  

 

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The higher voltage systems can supply same amount of power with smaller power loss due to wire resistance. This is why most high power AC lines feeding  large industrial consumers are at 24 000 volts. 24K transformer outside each plant drops it down to 600V fed inside the building.

If you run large electric motor at 100A current at 600V you need finger size copper wire. On a high side 24kv of this step down transformer you have  only 2.5 A current and only requires telephone size copper wire to run this motor.

Talking about boat application this power loss over boat el wiring is miniscule. Not worth discussion.

Keep in mind: two 12v  batteries in series for 24v if one of them goes bad it will drag overall performance. If one battery goes open (internally) you loose your power.

Two batteries in parallel if one goes (open) you still have power from a good one. Redundancy.

There is no redundancy in 24V configuration for two 12v batteries.

 

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9 hours ago, Salmon Catcher said:

All chart plotters, sonars, radars, downriggers run on 12 volts DC. What is the point complicating electric circuit wiring it to 24V?  No matter how you connect your batteries in series or parallel you will have same total capacity=total power=combined ampere hours.  Can not violate formula Power= Voltage * Current

If you need some exotic voltage like 18DC,  use dc to ac inverter and ac to 18V dc supply. That complicates circuit and introduces more potential problem down the road. I would not run my critical navigation equipment on such power source.

 

  

 

Who said anything about the guy rewiring his boat for 24V?   We're talking trolling motors here.  Some guys mentioned he'd be better off running a 24V setup, vs a 12V setup.  But, as the OP stated, that's not in the cards so he'll be simply increasing the capacity of his 12V setup by adding an additional battery.     

 

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9 hours ago, BillM said:

Who said anything about the guy rewiring his boat for 24V?   We're talking trolling motors here.  Some guys mentioned he'd be better off running a 24V setup, vs a 12V setup.  But, as the OP stated, that's not in the cards so he'll be simply increasing the capacity of his 12V setup by adding an additional battery.     

 

Not to hijack the thread, but since it is being brought up…you should see the insanity around going 24v now for guys running livescope/mega live etc etc.

im personally a big time believer in over gauging, looming and really clean dedicated runs to avoid line loss for your electrical installation. Garmin even shows you by displaying the unit’s voltage plain as day what kind of line loss you experiencing  but I’m not a believer in the whole 24v Bull.

by the way, If you wire your marine electronics into your boat’s bus fuse block, you’ve just waisted all of that money. My father is the “function” over “form” type being an old farmer…sure as turd, he’s running the exact same electronics set up as me and his looks like absolute garbage and there’s a disaster of interference all over his livescope and 2d sonar. I offered to rewire it all for him because I enjoy dc wiring and use his boat regularly, but as far as he is concerned, he did a great job because the thing turns on! Can’t ever tell your old man nothing lol

Edited by AKRISONER
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As you mentioned above, most modern electronics display dc voltage it is feeding on. Just bought cigarette lighter plug with dc voltage display. While all your gadgets are down when starting engine this meter shows how low your battery dips down at starting time. This cranking voltage should not go lower than 10V. If it does you have undercharged battery or it starts to go lazy and may need replacement soon. Being busiest fishing charter on Lake Ontario with 700+ fishing hours every season all my gear must run A+.  Tight lines. Capt. Bob, Salmon Catcher Fishing Charters

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