2 bank inboard charger 3 batteries

[sparky15]

So I have a 16 ft vessel, one battery to start the outboard one battery for elec/acc and the third up front only for the trolling motor. I have a two bank inboard charger and I want one bank going to the start battery and to hook the elec/acc battery in parallel with the tolling motor battery to charge em.
My concern is once I hook my 15 ft marinco inboard extension from the acc. batt. To the trolling batt. It will start pulling to much juice across the 12awg extension wire(ment for charging)once the trolling battery is dead. Do I need a double pole single throw switch to disconnect the wires for when in use or will it be ok??
Thanks in advance!


If I could draw a pic I would
One bank for start batt, second bank both for acc. Batt. And trolling motor batt.

 

[fucawi]

Re: 2 bank inboard charger 3 batteries

if you connect a discharged battery to a fully charged one then there will be a current flow into the discharged one...you should never discharge below 10.8v . If this current flow could be excessive you could fit a fuse or measure with a meter with one up and the other down. Next question is what is the output of your charger ? 5A 10 A ....if so would not worry about the cables its that inital surge that may blow a fuse

 

[John_S]

Re: 2 bank inboard charger 3 batteries

I don't like putting batteries in parrellel, but if you have to, I would think you are better off doing it with the start and acc battery. Typically they are installed with a switch that lets you switch between them or run in parrellel. If you don't already have one, that may be a better option then trolling battery with acc battery. In emergencies, you can use the acc battery to start your boat.

 

[j_martin]

Re: 2 bank inboard charger 3 batteries

When battery chargers were both bulky and expensive, having a switch to parallel batteries for charging was "the thing". Now we're tearing that unnecessary source of failure out of the old bass boats and replacing them with $35 chargers for the extra battery.

I have a dual bank charger and an automotive small charger in my boat. I just back it in the garage, plug it in, and forget it.

 

[sparky15]

Re: 2 bank inboard charger 3 batteries

Charger on output says dual 12v @ 8 amps, the theory behind leaving the start batt. On its own bank was so that nothing else would draw from it except starting the motor. I didnt want any of the batt. In parallel but after looking at how I would hook up the dual charger to three batteries

I wanted a batt up front only for the troll motor, one in a compartment back right, and the other in compartment in back left now im kinda leaning to either getting a 3 bank charger or just a single charger for the third batt. Convenience equals more money....again

Fucawi~ the extension wires are both fused 40A out of the box, Im just concerned that when (i know ill drain it) the troll batt drains it will then start pulling from the batt on the other end of the charger extension. And alway pop those fuses and/or have a voltage drop over the 12awg wires im pretty sure the extension wires are made just to extend one of the banks, not to add a second battery on one of the banks.

 

[fucawi]

Re: 2 bank inboard charger 3 batteries

voltage drop is not as important as you think when charging as when charged the current will tend to zero and hence no voltage drop.
To be honest a third charger or change over switch is the prefered option ..I mean a change over switch for the charge current out the charger rather than a big rotary battery switch