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Old 05-10-2015, 10:55 AM   #1
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Optimal Configuration?

I'm rethinking the 12 volt system on Stella and still new to all this.

Currently we have three battery banks and a Xantrex Truecharge2 40. There are two 8D AGMs in both of the main banks. Each of these banks independently starts one of the mains and also serves house loads. The third "bank" is a single 8D AGM for the genset exclusively (which seems like overkill). The 4 engine/house batteries--which are dead--have (had) 980 amp hours combined, which seemed ample, and tons of cranking amps. The genset AGM still has some life left.

Each of the three banks appears to be independently charged by the Xantrex.

I'm not completely comfortable with the Xantrex, both from things I've read and due to swelling of the AGM cases that may be due to overcharging. So I'm thinking of replacing it with a Magnum MS 2812 inverter charger.

It appears that the Magnum only charges a single bank. (True?)

I'm virtually certain I'll stick with AGMs but might go with easier to handle 6-volt AGM golf cart batts for engines and house. The two main banks, in their original Defever configuration, are outboard of each engine and I prefer to keep them there (except when it's time to move them).

Assuming the banks stay where they are physically, what would be the optimal configuration electrically? Am I looking at a new Magnum plus a separate charger or battery combiner or something else? All ideas much appreciated.
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Old 05-10-2015, 11:10 AM   #2
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In my opinion the optimal confiiguration for batteries is...

1. A house bank
2. Separate engine starting batteries for each engine
3. Separate generator starting battery

Again, in my opinion optimal charging is...

1. A charger large enough to charge the house bank in a reasonable amount of time.
2. A "no action required" method of automatically keeping the engine and gen set batteries topped off.


My opinion of optimal battery interconnections...

1. The ability to move the house loads to an engine battery in an emergency
2. The ability to start and run each engine from a battery other than its dedicated start battery in an emergency.
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Old 05-10-2015, 12:28 PM   #3
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I agree with everything Kevin posted. I think it's important to have a dedicated start battery separate from the dedicated house bank. Also, I think we tend to grossly oversize our start batteries on many engines.

Many boats, like yours, share the roles of house/start. Many of us can easily start on a Group 31, but we have an 8D for start. With a dedicated start battery (or pair of start batts) eliminating the multi-role, it can be appropriately downsized.
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Old 05-10-2015, 01:10 PM   #4
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I once owned a Defever 45 PH with your exact battery configuration. This is what I did and I never saw a downside:

Replaced the 4 8D's with 12 GC's and make them a single house/start bank. This gives you over 1200 AH's. The generator is your backup if you are forgetful enough to discharge this huge bank enough that your engine won't start. I never let SOC go below 80%.

Installed a Magnum 2800 inverter/charger with the monitor panel so you can observe SOC. That prevents you from overly discharging your house batteries.

Combined the engine alternators so they act as a single alternator along with an external regulator. Balmar has the products for this.

Not having a separate start battery makes sense if you have a small house bank but with 1200 AH's I wouldn't worry about it.

The way the Defever batteries are configured makes this the only sensible way to go in my opinion.
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Old 05-10-2015, 01:38 PM   #5
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A lot of overkill in most boats when it comes to starting batts. Lots of ways to optimize, with some good ideas above.

A few things I've learned on my boat and others: A single grp 31 is fine for starting most engines up to 8 liters. But you do want a backup either to house bank or if twin boat, to other engine batt. A manual or electric parallel switch works fine here.

Nothing wrong with gennie sharing a batt with an engine. No need for a separate gennie batt. Disable the gennie charge circuit and let the batt charger maintain the engine/gennie batt. It's on when gennie is on, and some gennie charge circuits have poor volt control. Not so much an issue if gennie has a car alt, those are ok.

If you have a huge house bank, get an inverter/charger for it alone. Get a separate charger for engine/gen batt or batts. This charger can be quite small like 20A as there is very little charging needed, just maintaining.

On twin engine boats, I don't like both engines sharing a single batt bank like Tiara does. It does work, but there can be glitches and loss of redundancy.

If you are going to depend on main engine alt to charge a big house bank, the regulator needs to limit output to prevent alt from overheating.
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Old 05-10-2015, 04:37 PM   #6
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I agree with Ksanders premise. In our boat, each engine has its own starting bank and each generator (2) has its own starting bank. The engine banks are 24VDC and the generator banks are 12VDC. We have a 12 battery house bank providing 24VDC with 660 amp hrs. In addition, all comm/nav equipment is powered by its own 12VDC 2 battery bank. All batteries are charged through inverter/chargers when on shore or generator power and through Balmar alternators on each engine when running. The generator batteries are charged through a charger when 120V is available or by the alternator on each generator. Any combination of all banks can be done to power engine start if any bank fails. Sounds complicated but it really isn't and provides redundancy all the way around.
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Old 05-11-2015, 06:39 AM   #7
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The big advantage for AGM is their ability to absorb more charge than LA in a shorter time.

Can you BLAST charge them too use this advantage ?Is this your normal operation?

If not why pay extra?
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Old 05-11-2015, 06:50 AM   #8
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I appreciate all the replies--lots to process here.

Fred, I lean toward AGMs more for limited off-gassing and maintenance -- along with freeze resistance and (theoretically, at least) longer life.
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Old 05-11-2015, 09:43 AM   #9
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Quote:
Originally Posted by angus99 View Post
I appreciate all the replies--lots to process here.

Fred, I lean toward AGMs more for limited off-gassing and maintenance -- along with freeze resistance and (theoretically, at least) longer life.
Regarding AGM's

One of the big challenges I have with AGM's and one of the big reasons I'll never own an agm for a house bank is the simple fact that if you drain them all the way down inadvertantly they are ruined.

I could stand corrected here but that happened to me in my excursion. I bought a set of AGM's for something over $400 if memory is correct. Then less than a week later I inadvertantly left the key on overnight. The batteries were ruined. When I asked the battery shop about this they indicated that is a well known issue with AGM's.

On my boat, I had a situation where my shore power went inoperative while I was away for an extended time, due to harbor personnel fault. When I arrived on the boat the batteries were flat. I was pissed. I turned on my inverter/charger and it would not start working due to low voltage so I then turned on my trusty Charles Industry backup charger. It got the lead acid batteries kick started. That was 3 seasons ago. They are still running fine.
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Old 05-11-2015, 09:53 AM   #10
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angus; Good recommendations above but I suggest the opposite. Since all this is new to you just replace the starting batteries with inexpensive wet cell batts and go boating. Four years from now you will know what you really need for your cruising style and will have had ample time to learn the deficiencies of the current set up and what, if anything, you want to do with it.
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Old 05-12-2015, 08:58 AM   #11
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Quote:
Originally Posted by angus99 View Post
Currently we have three battery banks and a Xantrex Truecharge2 40. There are two 8D AGMs in both of the main banks. Each of these banks independently starts one of the mains and also serves house loads. The third "bank" is a single 8D AGM for the genset exclusively (which seems like overkill).

Our set-up, and most of the boats built by our brand over time, is similar.

Our boat apparently started life with only two G29s on each main bank, and it looked like the PO added a G27 to each. As necessary, I replaced each with 3x G31 Odyssey AGMs... and the oldest bank is now entering it's 10th season.

Now that I know more about what I'm doing -- maybe -- I intend to replace that oldest bank with 4x AGM GCs when it becomes necessary, since that will also give me enough CCAs/MCAs to start than engine.

Your plan to replace the 8Ds with GCs sounds like your easiest way to go boating.

Yes, an 8D to start a genset sounds like way overkill. The CCA/MCA specs would be in your manual, but I'd bet a G24 or similar would likely work. We switched ours to an Odyssey G34, works fine.

-Chris
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