AGM Battery Bank Configuration

[Exile]

Originally Posted by witzgall

Here is a scenario:

You sit at anchor for 4 days, enjoying the serenity. Then you need to move, and
It is a motorsail situation. So you run the motor for eight hours. Regular basis, maybe not, but it certainly will happen sometime, and that alternator will fry in short order if subjected to that kind of stress.

One other option, upgrade your alternator, move the 8D over to the house, and then get a simple echo charge unit to charge the starter battery. No more "1-2- both" situation. Make the starter battery an AGM or GEL, and it will be very happy for a long time.

I hear ya. Now that I think about it (remarkable when that happens), the Xantrex "smart charger" has nothing to do with charging the batts when the eng is running. Instead, one eng alt provides DC current to the eng batt (one 8D), & the other alt provides DC current to the house batts (two 8D's). Each alt has its own built-in regulator to prevent overcharging. When producing 110 a/c current with the Xantrex from shore power or via the generator, the Xantrex itself is supposed to regulate the current going into the batts. From keeping tabs on the Xantrex monitor, this is exactly what it appears to be doing. The genset batt gets charged off what you guys are calling an echo charger (BEP relay) from one of the 8D's.

As far as switches go, there is a 1-2-All selector for the house bank, and then the eng & gen batts. each have their own on-off switch. The switches are only for utilization, however, i.e. all batts will charge all the time regardless of what position the switches are in. I always leave the house switch to "All" unless I want to check voltage on individual batts. I think this set-up is pretty standard, no? (to the extent anything is "standard" on a boat). The one problem I see is not being able to shut down the charge to the batts when charging off the engine. Should there be a fault with one of the engine alts, there would be no way to avoid frying a batt while motoring out of the serene anchorage (short of disconnecting cables, that is).

To the extent it may be possible to answer without seeing a wiring diagram, I'm just wondering if I can maintain the existing charging set-up but bring the 3rd (eng start) 8D into service as an additional house batt. At this point, I'm not too concerned about which batt to use to start the engine. If this is possible, then the same two eng alts will charge the same three 8D's, and the Xantrex would also work the same off a/c power. Make any sense??

[witzgall]

Yuu cannot charge a battery bank with two alternators, unless they are both controlled by the same regulator. If they have separate regulators, they will "Fool" each other as to the voltage of the bank, and mess charging up. Balmar (and others?) make special regulators to charge from two alternators simultaneously.

Chris

[Exile]

Originally Posted by witzgall

Yuu cannot charge a battery bank with two alternators, unless they are both controlled by the same regulator. If they have separate regulators, they will "Fool" each other as to the voltage of the bank, and mess charging up. Balmar (and others?) make special regulators to charge from two alternators simultaneously.

Chris

No, no - I said (or meant to say) that I was charging two separate banks, each with their own alternator. One alt charges the eng start bank (one 8D), & the other alt charges the house bank (two 8D's). Both alts run off the engine.

[Pete7]

That is getting complicated. Since you are running the genny to maintain the fridge freezer each day then it should also be used to top up the batteries.

Pete

[Exile]

Originally Posted by Pete7

That is getting complicated. Since you are running the genny to maintain the fridge freezer each day then it should also be used to top up the batteries.

Pete

Almost always is, unless I also happen to be motoring. But then I have a very efficient engine-driven fridge so it's rare that I would run both at the same time. If I had to do all over again, I would have opted for a boat with fewer systems and therefore a lot less complexity. The boat fit so many other criteria that we had that I knew it would work out well. It has been a lengthy process understanding how & why everything works, a process that I am know will be ongoing. Always difficult to come to conclusions via the internet, but this thread & many others sure have helped! Thank you.

Dan