Battery info for a technosaur

[2sticks]

I have waded through many posts regarding charging systems (solar, wind, dockside etc.)and have questions about battery size and number needed. The vessel is an Oday 32 with the normal compliment of interior lighting, nav. lights (soon to be LED on all counts) Adler Barbour cold machine and stereo. Not heavily equipped with using devices. Not being terribly knowledgable about electrical in general, I'm seeking guidance before the expense of a suitable battery bank. I currently have two gel batteries of unknown origin or condition which seem to discharge rather quickly. What is the consensus concerning size number and perhaps type best suited to our needs? The boat will be cruising away from the dock at regular intervals with needs for self sufficiency for 60 to 90 days at a time. The plan calls for 100 w solar panel and a wind charger also. any advice will certainly be appreciated.

Thanks in advance, Darrell

 

[Ralph Johnstone]

Looking at one single part of your battery question, the most important piece of the equation (IMHO) is a remote alternator regulator.

Simply put, this little device will give your alternator a healthy kick in the butt and get it to work changing you batteries. As you'll probably find on your present alternator, it's set for an output voltage which is neither too high to cause your batteries to boil but just high enough to charge a starting battery. Not really what you want for deep cycle batteries. These require a high voltage (14.7V) which will put lots of amperage into the battery when they are deeply discharged, but drop the voltage down to a safe level (13.2V) once the battery is fully charged.

Several years ago I installed a Balmar ARS-5 remote alternator regulator for the 55 amp alternator on on the Yanmar 2GM20F. Whereas I used to get a fixed 14.2V pushing 10-15 amps into the batteries and only getting to 80% state of charge (SOC), I now get 14.7V pushing 30-40 amps CONTINUOUSLY into the batteries and eventually getting to 100% SOC, My house batteries are 230 amp-hour and suit us very well for a similar load and sailing to what you have.

 

[2sticks]

Surely someone has preferences!!

 

[Maine Sail]

Surely someone has preferences!!

You really need to know your average daily use before sizing a battry bank and charging systems. To know your daily use an "energy budget" can be an okay tool but not very accurate. The best way to determine daily averages is to install a Battery Monitor such as the Victron BMV-600.

Figure that about 30--35% of the banks Ah capacity will be actual usable capacity when away from the dock. This is cycling the bank between 50% SOC to 80-85% SOC. Compare that to daily use in Ah's then overlay that on how many days you want to go without hearing an engine..

For example if you use 90Ah's per day then a minimum bank size would be about 300Ah for 30% usable capacity for ONE DAY'S use..

Getting back to 100% SOC takes a LONG time due to declining acceptance rates as a battery nears full. Unless you turn off the loads and let the solar go to work when off cruising you will be cycling through about 30-35% of a battery banks total Ah capacity.

This would still mean you need to replace 90Ah's every day so you would want a charge system that can do that in the shortest time possible.. AGM & GEL can be recharged faster than flooded but come with some high upfront costs. Flooded batteries can be recharged at about 20-25% of "C" or the 20 hour capacity or about 75A for a 300Ah bank. If you go to 450Ah then those same flooded batts could be charged at roughly 110A...

 

[Bill1565]

Maine is right. You need to work out your needs first. You will need a battery monitor later if you get one now, it will help with figuring your needs. Personally I dislike xantrex like victron.