Auxillary charing with 2005 HPDI twins

[DannyMart]

I have a pair of 2005 200 HPDI engines rigged to 2 batteries with 2 battery switches. Stbd battery runs on position 1 on switch 1 and port battery on position 2 on 2nd battery switch for normal use. I was told this would isolate each battery and I've never had a power problem on the water. Both batteries are connected to a "smart" charger when the boat is not in use. I run group 27 wet cell combined deep cycle/starting batteries with the highest CCA I can find (Interstate). The radio and GPS/sonar runs off of panel directly connected to battery #2.

I just found out there is a an auxiliary charging circuit option on my engines. I would like to add a 3rd battery for house use as I plan on adding a second sonar unit, radio and USB charging outlet. Will that work with the aux circuit? Should both engines be connected via the aux circuit to the 3rd house battery? If both engine batteries died and I want to use the house battery for starting, how should it be wired or would it just be easier to use jumper cables?

Forgive my ignorance on the topic. I am not the handiest guy with a wrench. Up till now, I have just paid to have work done on the boat & engines, but now that I'm retired, I'd like to learn more about maintaining the boat and engines.

[boscoe99]

You can do as you suggest. Either connect one or both of the isolator charging leads to the third battery.

If it were me, I would simply buy a Yandina Combiner (or two) and simply make all of the necessary connections at the batteries. Same results. Cost may be less. Easier installation.

The combiner will charge the third battery at any time the motor is running. Stop the motor and the batteries are disconnected from each other. Run the third battery to depletion if you want. The start battery will remain fully charged. Start the motor. Both batteries will be connected so that each is recharged. Each according to its own need.

[DannyMart]

You can do as you suggest. Either connect one or both of the isolator charging leads to the third battery.

If it were me, I would simply buy a Yandina Combiner (or two) and simply make all of the necessary connections at the batteries. Same results. Cost may be less. Easier installation.

The combiner will charge the third battery at any time the motor is running. Stop the motor and the batteries are disconnected from each other. Run the third battery to depletion if you want. The start battery will remain fully charged. Start the motor. Both batteries will be connected so that each is recharged. Each according to its own need.

Great suggestion. If one uses the aux charging route, are the starting batteries receiving fewer amps? I assume the engine has a max amp output of let's say 60 amps at wot. If 20 amps are going to the aux circuit, does that leave only 40 amps for the starting battery attached to that engine? Would the same issue be present with a combiner?

[fairdeal]

Since you already have two 1-2-both-off switches,
below is a scheme to add one more switch with the house battery,
and have a means to combine or isolate each:



the schematic is from Blue Sea, who sell a similar device to the Yandina Boscoe mentioned -
so it shows their device -
but the wiring would be similar.

You don't "lose out" on any amperage, not using the Aux output cable -

its not "extra" power - just "isolated" from the main battery cable.