Adding and charging a 3rd domestic battery to a bv44

[elias]

Merry Christmas to all!

I m thinking of adding an extra battery to the domestic bank ( consists of 2 * 140AH Bosch batteries , installed 8/2019). Charging  is achieved by 120 w panel through a pwm charger - Greece summer, motor alternator - 2 hours per day average and AC- 10 hours per week .
 I have 2 alternatives in mind.

1. Installing a similar 140 AH, parallel conect it with the rest , so nothing changes but i ll have a 6month gap battery age, and less space in the lockers ( any photos of someone with similar arrangement would be highly appreciated.
2. Install a 60-70 ah battery , devote only loads from WC electric motor and shower drain pumps and charge though a SECOND PWM charge controller parallel to the other one . Less space needed , no risk of different aged batteries. Here rise a question , can PWM controllers installed parralel in the same PV array but deliver current to different battery banks? From a search i did , in theory is possible. Any ideas or experinces?

[IslandAlchemy]

Personally speaking, I would just add a third battery into the house bank.

[Sitesurfer]

Although I am sure that someone more electrically opinionated than myself will be along shortly, I'd have to concur that simply adding another battery on to the bank and moving to the next job seems like a far more sensible choice to me.

I'm a believer in the 'simple electrics = less grief' school of thought.

[sy_Anniina]

I would vote also for the simplest parallel option. I have myself 2x 180Ah + 1x 220Ah AGM leisure batteries (IIRC) on a single bank placed under salon settee. Even bow thruster and windlass are powered by this bank.

Could not find a photo unfortunately.

BR,

Tommi
s/y Anniina

[elias]

Thanks for all yor answers , and for me too the easiest is to keep it simple but i want to save some space.But how you created a bank with 2x 180Ah + 1x 220Ah AGM ? I thought that only same capacity batteries can be used to create a bank.

[sy_Anniina]

All the batteries on a bank should have same chemistry, so you shouldn't mix wet cells, gel, agm together. Some say you should even stick with same manufacturer and type, which is what I did.

Different capacities of same battery models just have different plate areas, which is effectively the same thing as connecting batteries parallel.

Having grossly different capacities on a system that doesn't have good star connection may create problems due to uneven discharge..

Web is full of battery informaation, many pieces also false... One of my favourite quite informative sites is batteryuniversity.com

BR,

Tommi

[elias]

Actually after many lines of reading I bumped into this

"""The charge-discharge testing of a 24V battery with two
very dissimilar strings formed by 4 monoblocs
6CP100 (6V/100Ah C10) and 12 cells
2CP550(2V/550Ah C10) showed that the currents
flowing from and to the individual strings are
principally governed by the string impedance and
independent of the installed string capacity.
Such “asymmetrical” batteries can be operated quite
successfully and yield nearly their complete cycle life
potential when deep discharges to 100% d.o.d C3 are
carried out.
If power outages cause only shallow discharges then
the “low” impedance string furnishes an overproportional
share of the Ah discharged and may thus
suffer in terms of achievable cycle life.
However if these shallow discharges are infrequent
(»50 to 100/year) then the ultimate battery life will be
governed mostly by calendar or elapsed service time
considerations and not by exhaustion of its cycle life
capital."""
The background to that is batteries for telephone exchanges/basestations.
http://neuralfibre.com/paul/wp-content/uploads/2007/05/can-we-now-sin.pdf

So I think I m going for a simple parallel addition of a same type battery

Thanks a lot for saving me some hours of work !!!

[Salty]

Although I am sure that someone more electrically opinionated than myself will be along shortly, etc.
.
.

I echo Sitesurfer’s comment, but for what it’s worth, I fitted an extra bank of batteries onboard to power an electronic antifouling system.

My original system consisted of two 140a/h domestic batteries + a 90a/h engine start battery. This system has a mains electricity powered battery charging system that can be used during those very rare occasions when I use a marina berth, but as I use a swinging mooring throughout the spring/summer/autumn season, the mains charger is rarely used except when the boat is ashore over winter.

I fitted a 12 volt battery powered antifouling system back in the winter of 2014/2015, and installed two approx 100a/h batteries. This system is wired in totally independently of the domestic and engine start batteries and of all other 12 volt systems, and remains switched on 24/7 throughout the season, but is off throughout the winter while the boat is ashore. In order to keep the antifouling batteries and the two domestics charged I have two 100 watt solar panels feeding a Marlec charge controller. This controller has outputs to two independent battery systems. One charge output feeds the domestic batteries while the other output feeds the batteries for the antifouling system. My engine start battery gets nothing from this system, but my experience has been that the engine starter battery needs and gets very little by way of charging other than when the engine is used during departure and subsequent re-entry into port. The engine start battery was also changed for new during the same winter of 2014/15. Occasionally during the winter months ashore I will switch on the mains battery charger, and that feeds the two domestic batteries and the engine start battery.
Up to now this arrangement has worked well enough, though I have noticed that the two domestic batteries of late are beginning to look a little low after I’ve spent a night onboard during the winter months, though much depends on the amount of sunshine the solar panels get during the daytime where this winter has had very cloudy daytime periods where the solar panels have produced very little charge, and also how much the onboard heater is used, particularly during the hours of darkness.

[elias]

Wow
“12 volt battery powered antifouling system”
I didn’t know the existence of such system !

So I ll skip this 2 solar controller experiment and stick with another battery in the same bank . Thank you all