three battery system w/ twin engines and large house battery

[foca1]

I have a pair of 2003 Yamaha 150 HPDIs I would like to connect to a set of 3 batteries. One battery for each engine and a third "house" battery. Actually the house battery will be 3 deep cycle batteries in parallel.

I've seen discussions on using 2 of those automatic charge relays (ACR) so that each starting battery charges then charges the house battery charges. My problem is that once both engines charge their respective starting batteries, and the ACR circuit connects both "alternators" to the house battery, you now have connected the "alternators" togeter. I thought that was a no-no because it would burn-out the charging system.

1)
Am I wrong here?

2)
Should I be concerned with current limiting the "alternator" since I have such a large house battery bank?

I use the term "alternator" to really mean the Rectifier/Regulator. Maybe the yamaha regulator has more "smarts" than I'm aware of.

3)
Is it still possible to burn-out the rectifier/regulator if the battery is accidentally disconnected?

I have also read somewhere that there is a secondary output from the regulator.

4)
How is that different from the primary regulator output?

5)
Where do I attach my wire for the secondary output? or where is that wire lead?

If for so reason go back to older 2-cycle outboard engines, would I need to re-wire my electrical system?

I'm so confused, any insight would be helpful.

Thanks

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Twin 2003 Yamaha 150 HPDI, 1990 Center console Scarab Sportster

[VectorPat]

Your engine does have a built in isolator. Look in the pan of the engine where the harnesses all connect. There should be a 10gauge wire with a quick connect laying in there some that is not connected to anything. This is the aux. output. It can by connected to a house battery's positive terminal and tie the ground back to the cranking battery. You have a 45amp alternator. It will charge which ever battery is lowest. So if you house battery is dead, your cranking battery may not get much of anything. Connecting both engine togather wont kill the alternators but can cause one engine to stop charging as it will see the higher voltage from the other alternator. I would try splitting the system in 2. Keeping the engines seperate. If you tax these charging systems too much you will have running issue as these motor reley very heavily on battery voltage.

[mendo]

I agree, keep them separate.

I would hook both motors to a Battery Isolation Switch that will allow you to choose between which motor you want to charge the house battery, use one or the other.

[STV_Keith]

The ACR's, like the Blue Sea Systems 7610 isolate the "backflow" of power from one charging system to the other. I run that setup on my rig.

Each motor's battery is connected to it's own ACR, then the output of the ACR's are tied together and run to the house batteries. The ACR's allow the starting batteries to be charged first, by their respective motors, then the house batteries get charged. The two starting batteries are isolated from each other, as our the house batteries from the other two.

[Riverman]

ACRs are superior to isolators in that there is no voltage drop across them. Less voltage drop = more charging voltage. There is a smaller one here that will work as well.

[VectorPat]

There is no voltage loss using the engines isolator. I do agree that the boat mounted isolators do usually have a voltage drop.

[foca1]

Thanks for the inputs! It has help me come to a decision. Looks like I'm worried about nothing since Yamaha has done a really nice job with the AUX output, but it's a shame the mating harness is $35 a piece (boats.net). I plan to do a little experimenting using one or both AUX outputs from the engine to the house battery. I think they are diode protected, but nobody seems to know for sure. If you're not experimenting... then you're not learning!