Small boat lithium battery system

[LaughingGull]

Hi all,
Wondering if I could get some feedback. My boat, Laughing Gull, is a 32' sailboat. I plan on doing some extended cruising and so I want to upgrade to lithium.
I currently have two group 27 AGM dual purpose batteries wired with a 1,2,Both switch. The existing alternator is an internally regulated 55amp Hatachi mounted on a 3GM30F. The system I have works well enough for my existing power needs, but now I am adding refrigeration to the system.

My questions are:

1. When using a DC to DC charger, should there be a lead battery in line between the alternator and lithium battery? Or can a DC-DC charger be wired directly to a lithium battery without the need of a lead battery? I am considering installing two Dakota 135 dual purpose batteries that will in effect replace my AGMs and at the same time provide more than double the power.

2. Is an alternator upgrade in my future? The main source of charging will be the alternator. I want the ability to charge the batteries as quickly as possible without excessively compromising the engine, thus I am looking for a "best fit" alternator. Maybe the alternator I have now will do the job but where it is internally regulated, I just don't know.

3. Lastly, does anyone have experience with the use of two DC to DC chargers in an effort to get the most out of your alternator and decrease the time needed to run the engine to charge batteries? I see that Victron offers a 12v 30amp charger. If I install two of these in parallel does this mean a 60amp alternator will keep up? And just to help me understand, if I installed three of these chargers will a 100amp alternator keep up?

There's a lot to unpack here.
Thanks for your help in advance.

[SV_Wanderer]

One option you might consider is to replace the starting battery with a lithium one; Dakota is who we went with as well, replacing 4 6V golf cart batteries with six 135ah Dakotas for the house bank, and one more for the starting. They make a number of options (including these) that can serve as starting batteries (and have BMS designed for doing so). That would let you sidestep the DC-DC charging issue.

However, I suspect you’ll need to switch to an external regulator at the very least. We have a larger alternator (120amp) on a Beta 25, and needed a Balmar regulator, brush box, and cooling fan.

[barnakiel]

A 55 A alt is good enough for batteries up to about 200 Ah (house). No need to add starter bat Ah as this one gets discharged only very little each time.


For house batteries, I would concentrate on a shore charger (when docked) and a solar or wind system (when anchored and sailing). Running the engine just to charge the house battery is errrrr .... well. Oh my. Noisy and not nice in such a small boat.


We have cruised probably quite extensively and always with just plain banana car starter batteries. If ever I wanted MORE of anything it was only ever of generating power, not storing it. Now to address this I upgraded our solar panels from 75W (2003) to 410W (today).


So my 2 c . Probably not much use for yous but I say it anyways.


Have fun.


b.

[Reeve21]

A modest solar installation should keep up with your refrigerator without the complication of changing battery chemistry, and if you have room to add another AGM that would be insurance against cloudy/rainy days.


Got to go hitch my horse to the buggy now......

[ggarrouste]

external regulator or the VRC-200 by https://nordkyndesign.com/product/no...ce-controller/ which looks like a very interesting approach for controling the output of an alternator.