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Old 01-06-2011, 20:43   #1
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Charging Large House Bank Under Way

My boat a 49’ DeFever had a total of 5 8D flooded batteries, 2 for the port engine 2 for the starboard and 1 for the 12.5 kw generator. There was no dedicated house bank. The boat came with a 40 amp charger that has 3 outputs and charged each of the 3 banks. The boat also had a 400 watt inverter. We just purchased the boat this past November and I am trying to set the boat up for extended cruising with a lot of nights spent at anchor.

I have removed all but 1 of the 8Ds and will use that battery to start both of the Perkins 135 hp engines.

I purchased a group 31 flooded battery to start the generator.

I am in the process of installing a new house bank of batteries and inverter/charger. The batteries that I have just finished building a rack for are Full River 415 amp hour AGM 6 volt batteries. This will give me a 12v 1245 AH house bank. I also have purchased a Magnum 2800 watt inverter with built in 125 a charger.

I need help deciding how to charge the house bank while under way. The twin Perkins each have a 70 amp alternator with built in regulator. I want to install a large alternator with smart charger but I am running out of money for now so I need to use the original alternators for now. I could use one alternator to charge the starting battery which it should do with no trouble and the other to charge the house bank. I am concerned that the stock alternator may overheat trying to charge the large house bank of low resistance AGM batteries. If I don’t burn up the alternator I am concerned that the alternator with its internal regulator might over charge the AGM batteries. I wish I had paid attention to the float voltage of the alternator before I started removing batteries. Full River says that if the batteries are at 104 deg F to Charge at 14.34 Volts and to Float at 13.29 Volts. The engine room will probably be slightly more than 104 degrees after running several hours during the summer.

I could let both alternators charge the starting battery and use the C160n combiner and the high voltage cutout feature to limit the charging voltage to 14.2 volts to the house bank. The 2 stock alternators combined will probably only put out about 100 amps after they get hot so I think the combiner would be ok.

I could use an echo type charger between the starting and house bank. Help on how to best charge the house bank under way is appreciated.

Thanks for your help,
Shay Slass

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Old 03-06-2011, 11:38   #2
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I have three bank system as well, one house, two start. I wired the alternators to charge the house bank and two Blue Seas automatic charge relays downstream from it for the start banks. Once the house bank hits the correct voltage, the ACRs open up and combine all three for charging. Fairly simple. This way, the bank that gets used the most gets charged first.

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Old 03-06-2011, 13:21   #3
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Re: Charging Large House Bank Under Way

Check out the Dual Alternator Controller from Ample Power.
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Old 06-06-2011, 08:37   #4
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Re: Charging Large House Bank Under Way

My house bank is only a bit larger than yours at 1350 AH, also made of 6v AGM's in series parallel.

I charge with a Penntex (large frame) 200A alternator - using a Balmar ARS-5 programmable regulator. - I purposely dumb down the alternator(via the regulator) to 175A max, which keeps things running plenty cool.

My motor is a Cummins 5.9 with a serpentine belt which provides plenty of belt to run the alternator - don't know how your Perkins is set up, but anything over 110A will require 2 belts or a serpentine - you may also have to consider side loading bearings on water pumps etc. if using old style belts.

As my boat is a single, I use a Digital duo (echo charge) unit for recharging the grp 31 start battery.

In your case, why not put a large frame alt(ebay $200) on one of your motors with a good programable regulator - (which you will need to give those AGM's the slightly elevated voltage they need to charge right - contact Fullrivers engineering rep for the exact specs for your batteries)
mine spec'd out to:

Bulk 14.8v
Absor 14.7v
Float 13.7v

Leave the stock alt on your other engine to recharge the start battery - it does not need a 3 stage regulator.

my system works great for our use - I can anchor up to 6 days without starting the motor if desired and still have 60% SOC. Normally we are recharging at 80% SOC and can fully recharge in 4-5 hrs cruising including float.

good luck
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Old 06-06-2011, 09:03   #5
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Re: Charging Large House Bank Under Way

Let one alternator charge the main crank battery, the other the genny battery, and use the genny to charge the house bank via the inverter/charger... Faster, easier, better!
Any fool with a big enough checkbook can BUY a boat; it takes a SPECIAL type of fool to build his own! -Capngeo
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Old 06-06-2011, 09:17   #6
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Re: Charging Large House Bank Under Way

Just keep in mind if you eventually go to larger alternators: my experience is that over 75 amp alternators should have dual belts. (assuming you have V belts) I have run 100 amp alternators with single belts and it is doable, but with a good regulator that works the alternator hard, you eat up belts fast and create a lot of belt dust. If those are Motorola Alternators, they can be modded to use an external regulator. Maybe with two alternators and a gen also, you are fine without spending more money. I assume there is an important reason you are going so large on the battery bank....many people forget that you have to refill it somehow! ...and it's a slow long haul putting that many amps back in...batteries heat up, charge rates go down etc. Lets say you motor for 8 hours or overnight for 24 hours and get them full. Then you reach landfall and stay in a harbor for 2 weeks. Unless you recharge daily, how will you replenish? or will you live with your batteries undercharged and just top them off at an undercharged level daily?

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