Question\Discussion on Charging New house Bank

Mich350

Current Status:  2008 350 EC with the Inteli-Power PD2040 (40amp) charger, house bank two 27 group deep cycles (Guessing Ah for each at 80).  Both batteries are now 3 seasons old.  Plus 2 starting batteries that are good.  Day on the lake power consumption is radio\amp(40 Amps ), galley fridge (6amps), cockpit fridge(6amps), and occassional use of lights and water pump during each hour (3amps).  Total typical usage is 55 Amps per hour at max when radio is on all the time.
Needless to say we kill the house bank to 50% or below in 3 hours, this is a PITA for me since I know I am shortening the battery life and using the generator more then I want too.  Because of this I am going to goto 3 group 31 deep cycles on the house bank.  At roughly 100 - 110 Ah per batery i'll be around 300 Ah and double my current capacity.

The questions I have are regarding charging the battery banks via the PD2040 charger (whether on dock or genset power) vs the engine alternators.

Questions:
1)  How does the charger decide which of the three banks to charge between Star Starter, port Starter and House Bank (how does it allocate its 40 amps)? 

2)  When the engines are running and alternators spinning at enough rpm to produce charge, they are each rated at 70 amps.  Are all 70 amps available say at 2000 rpm?  How is the alternator power shared or divided between the battery banks?


With the above answers I can then calculate the mins\hours needed to recharge the batteries based on the amount of discharge they are at.

Note:  I am sticking with the flooded wet batteries for now.  The PD2040 charging rates for the phases are for led acid wet cell batteries.  I believe if I was going to go to AGMs I would also need to update charger.

Grahamu

I'm not familiar with PD2040 but if it is a smart charger  it will send most of it's charge to the battery with the lowest voltage and the charge amperage will gradually reduce as the voltage increases. The alternators are probably sensing the voltage of it's start battery and although the isolator will distribute the charge to where it's needed the actual charge amperage available will be lower due to the sensing. On some boats with large house banks the alternator is made to sense this battery rather than the engine battery and therefore put out a larger charge amperage. I have 4 6Volt golf cart batteries and have never been below 12 volts on an overnight anchorage.

Cableguy Greg

I would consider replacing that charger. It is now 14 or more years old. My PD2020 crapped out 4 years ago, which was original to my 2008 boat. I replaced it with the ProMariner ProNautic charger, which is a smart charger. I have had much better charges with this charger over the original one. 

YYZRC

I think your estimates of the fridge amp draw are optimistic. Assuming they are the original Waeco fridges, they are pigs, especially in the dead of summer. 

As @Grahamu stated, the isolator will be inefficient unless you have a newer digital model like the ProIsoCharge. I agree with @Cableguy Greg that the original charger is due for replacement. I would get a ProNautic 1250. 

I run 3 group 31 AGM house with the ProNautic 1240. I always run the genny at some point to cool the cabin and/or to cook so there is a period of charging with that. I also have a small solar array. 

Grahamu

I should clarify my earlier post in that one of the first items to be changed during last winter's project was the charger and isolator. I also installed a Pronautic 1240P along with a standard isolator. I must also admit I do not run the stereo system when anchoring out for the night due to the high current draw of the amps (74 amps at max output). Instead I have a Bluetooth Rechargeable Bose speaker connected to my phone or tablet. I run my genset for an hour at breakfast and another hour at dinnertime to re-charge everything and cooking.