battery loading

[Jim Bunnell]

I'm doing some wiring to my 26M. I have two batteries, starter and house, which charge through a combiner but output into separate circuits. How do you divide the load - specifically, do I put the VHF, depth sounder, autopilot and GPS on the house circuit (reserving starting power but reducing evening lighting and electronics) or with the starter? Thanks in advance for your advice.

[Don T]

Hello:
I put the load on the house battery because my whole purpose in using 2 batteries is to have a reserve that has no chance to be drawn dead. Others have used 2 batteries connected as one big bank and regulate how much power they use. A technique that would work with one battery too. There was a long thread not too long ago about batteries and systems.

[Paul S]

That last message was from me

Paul

[mike]

Others have used 2 batteries connected as one big bank and regulate how much power they use. A technique that would work with one battery too.

My setup is a variation of this. I felt it was a waste of space and weight to have a battery that was only used for starting the motor, considering the fact that I have a battery monitor that lets me accurately see how much power has been drawn. So, I have two identical AGMs (separate, not connected as one bank). Battery 2 is wired directly to the motor, but it is also, along with Battery 1, wired to a battery selector switch that feeds the house panel.

So, either battery can supply house power. When Battery 2 reaches about 50% discharged, I can then switch house power to Battery 1, reserving the power remaining in Battery 2 for starting. To confirm that there would be ample power for starting, I did a test... I discharged Battery 2 to about 65% discharged, significantly more than I would under normal circumstances. I then cranked the motor several times for about 4 or 5 seconds each time (without throttle added or the choke turned on, so that it would not start, simulating a "difficult" starting situation). After this, the motor still started fine.

The two are also connected with a combiner for simultaneous charging while motoring.

This setup is obviously more complicated than simply having one large bank that is both for starting and for house power, but I like being able to "save" one battery for starting, once it has been halfway discharged for house power. And, it's not as foolproof as having a dedicated starting battery, but this was a tradeoff I was willing to make in order to provide more house power without adding a 3rd battery.

--Mike