Wiring on-board charger through battery isolator - why?

Willhound

Got the new on board charger from the dealer today to replace the one that was D.O.A. when boat delivered. Went to hook it up and found that the original had been hooked to a distribution block which then looks like it runs to the battery isolator on the positive sides, and the grounds to a common ground somewhere. Maybe somewhere up near the battery switch? I see only one set of leads going to the house battery that look like charging loop. The starter battery has two serious looking leads (pos and neg) that seem to go towards the engine block.
The new charger came with ring terminals that were too big to go on the distribution block and I didn't have anything else available so I was tempted to bypass all that and hook the leads from the new on-board charger directly to the batteries, but was afraid of messing something up. I did temporarily just to confirm the charger was working, but will have to pick up some proper size ring terminals to go back to the distribution block and put everything back the way it was. Seems like a complicated way to wire the charger and for what reason?

Dream_Inn

Think of the isolator as a one-way valve.  It allows you to charge all the batteries at once and also isolating them so one does not discharge the other.

Willhound

I understand that from the alternator perspective . But doesn't the twin bank charger do the same thing? Or just a redundancy?

Willhound

Further to the issue of whether to connect through the isolator or not, as per the Promariner website "If you are charging 1 or 2 batteries with a 3 bank charger, you will need to connect all the leads on the 1 or 2 batteries. At no time should the charger be run without all the leads being connected to a battery(s)."
And this being a three bank charger (I plan on adding a third battery soon) I'm wondering how this would work if running through the isolator.
Any harm if I skip wiring the charger through the isolator as per current set up and just wire direct to batteries? Alternator would still be charging through isolator.

Cableguy Greg

The alternator output goes to the input lug of the isolator. The outputs of the isolator go to the batteries. The charger outputs are connected to the outputs of the isolator, thus charging the batteries and not using the isolator.

If you add a third battery, where are you going to place it? More than likely you are going to put in on the house side of the boat. If you do that, you can't connect it to the third output of the charger. What you are doing is making the house battery, one really large battery by wiring them in parallel. The dual bank charger will still charge the house batteries as one. The triple charger won't be utilized well in this situation. If you had twin engines with two starting batteries and a house bank, then you would need a triple bank charger.

frenchship

Agreed with Cableguy

J3ff

Cableguy Greg said:

The alternator output goes to the input lug of the isolator. The outputs of the isolator go to the batteries. The charger outputs are connected to the outputs of the isolator, thus charging the batteries and not using the isolator.

If you add a third battery, where are you going to place it? More than likely you are going to put in on the house side of the boat. If you do that, you can't connect it to the third output of the charger. What you are doing is making the house battery, one really large battery by wiring them in parallel. The dual bank charger will still charge the house batteries as one. The triple charger won't be utilized well in this situation. If you had twin engines with two starting batteries and a house bank, then you would need a triple bank charger.

Like this?
:P 

Willhound

Thanks @Cableguy Greg. what you said here       "The alternator output goes to the input lug of the isolator. The outputs of the isolator go to the batteries. The charger outputs are connected to the outputs of the isolator, thus charging the batteries and not using the isolator. "   makes it clear to me. What they did was run the feeds from the on-board charger to the out posts on the isolator, I suppose to cut down on wire and connections to the battery.

As far as the new on-board charger, I will be adding a second house battery in parallel as you point out and I had requested a 3-bank charger as the replacememt from the dealer since the Pro Sport + from ProMariner can be hooked to three batteries, even if two of them are in parallel. Somehow the charger can sense the parallel connection, but treat each battery separately with it's own charge and maintenance profile. Easier on the charger and better for the batteries this way. At least according to ProMariner. But makes sense to me.

In which case I will have to wire the charger directly to the batteries since there are only two circuits at the isolator. I'll strip the two feeds from the charger location to the isolator back to a good location and cap them.

So the starter battery and two house batteries in parallel will be charged through the isolator when on alternator, and directly through the charger to each battery when on shore power.
Make sense?

Stodge

The last battery charger I hooked up had instructions to connect the output directly to the battery banks.  I get why they might be confused and use the issolator since the alternator output goes there, but that's because you (likely) have 3 battery banks (port starter, starboard starter and house) but only 2 alternators.  

Given 3 battery banks you want a charger with 3 charging banks.  With that combination I'd be going direct from charger to battery bank.  At least that my $0.02, which in Canada has to be $0.05 since you got rid of pennies.  

Willhound

Yeah, at least a nickel!
Original charger was wired with a distinct harness and everything. Looks stock. 
One alternator as single engine but I will be adding a second house battery so the three bank charger will go directly to batteries.  Here is what isolator looks like currently. 
So the way this was wired was from charger to output posts on isolator using a distribution block.

Which you can see I've now removed. Will have to cap the positive leads from the area this was mounted at since they are connected to the positive outputs on the isolator.