Altenator Charging 2 in parallel? Bad?
 

My boat is set up like So:
I have 3 switches one for each motor, and one for genny.

1 Bat for just the genny on its own switch.
1 bat connected to position (1) on either engines switch.
1 Bat connected to position (2) on either engines switch.

So when running each motor is charging its own battery.


I am going to add a battery to Position (2) connecting 2 group 27's in parallel for one big house battery.

Will the port alternator charge both battery's ok? i know slower, but will it hurt the alternator?

it will charge both batts....only issue you may run into is if one of the battery's has a bad cell...it can drain and ruin the other batt its connected to....i would install a battery isoaltor and let it do the switching between what ever battery need to be charged.

I personally like the alternators to only charge the starting batts and only charge house deep cycle batts off of shorepower.

While this is fine the charger will do that. when at a dock.

but lets say you run somewhere and anchor for the day, and the house is on the 2 27 tied together.

I have a battery to start the engines off of. but why would you not point one of the engines back at the set and let them get some juice that the motor provides?

the other motor is plenty for the other starting only battery.

Or what happends if you point BOTH motors to the same battery/batteris (when tied) does this help? or hurt?

It hurts, one alt will always be stronger then the other no matter how exact they are built...and it will back-feed the other one and eventually ruin the regulator inside and you will need to buy an new alt or have it rebuilt....
Not to say that it cant be done...but you get into different things like blocking diodes, voltage sensing equipment or battery isolators etc....

Good to know, thanks fort he input. I expected that but have to ask when talking this subject, and thinking of all the possibility's.

What about adding a battery combiner? I don't know how difficult it would be with the twin engines..

I've been reading alot about this lately, as I plan to add a 3rd battery to my rig. I currently have 1 battery for each motor.

I'm going the Blue Seas ACR route. ...and after doing some reading, that would be my suggestion to you, as well. About $80, a battery, and some 8g wire. Simple install.

What Charge Sources will an ACR work with? An ACR will work with all charge sources, including an alternator, AC charger, or solar panel. However, low current charge sources might not produce the voltage rise required to force the ACR to combine.

this would be bad in a float mode.. then you have one hot bat, and one not hot bat in parallel.


These are more of a smarter isolator. which is great when you want to keep one battery up and let your stereo or what ever kill the other one. But in my application. I want both batterys to function as one, all the time. ONE BIG Battery. if i kill it, thats still fine. i can charge it, I still have a separate starting battery that I can fire up with on both motors, and another battery that will start the genny and then the battery charger will charge all 4. but when sitting for a day, and night that one big battery needs to be ONE so it keep going for the fridge and stuff. the ACR would disconnect the second battery from the stuff I have it connected to in the first place as soon as it started seeing the voltage drop below a point, then its saves the other battery. I dont want to save it. i want them to die together, a LONG slow death haha.