House Batteries Question

[Maine Sail]

That seems contrary to the geometry of the system. If the batteries were wider, the heal angle would have a more pronounced effect. However, as they are taller rather than wider, the heal angle is irrelevant. The only exception might be in an absurd case where the batteries were many feet taller.

It is the plates inside the battery that often get taller but the case stays the same. In other words a 215Ah - 225Ah GC2 has slightly shorter plates than does a 240Ah GC2 but they both share the same case. This can mean less room for healing before the plates can uncover. On-board installed cell orientation, to minimize plates uncovering, is still critical with any flooded battery and is an ABYC requirement with regard to flooded batteries. Some battery makers just try to stuff too many Ah's into a small case and it is not always optimal on a sailboat..

 

[Gunni]

Now would be a good time to say that AGM batteries don’t have this problem of lead uncovered by sloshing sulphuric acid. Get ‘em to fit, lay ‘em on their side, heck, pitch-pole’m!

 

[Ward H]

I recognize that the thread title says "house batteries". Does it apply to the "start" bank as well? I'm faced with replacing 3 12v deep cycle batts. 2 House and 1 Start. Is there an advantage to use a different 12v battery for starting and maybe 4 6v GC batts for House? I have a Sterling Pro Charger Ultra 40 and I have a question out to the manuf to see if each output can handle different type batteries with their associated banks. They have not replied.

A different chemistry means FLA, AGM or Gel, not 6V and 12V. If all your batteries are flooded lead acid, no problem.
The charger will just see two 12V banks.
Since your house bank and starter bank are different size you might be better with an ACR between the two banks and connect the charger just to the house bank. The ACR will direct the charge to the start.

 

[Justin_NSA]

Good stuff guys. I'm going to raise this with Sterling when I reach them. At least I know I can optimize each bank.

 

[Maine Sail]

Good stuff guys. I'm going to raise this with Sterling when I reach them. At least I know I can optimize each bank.

For dockside charging, and mixed chemistries, the Sterling BCM or Battery Chemisty Module is a great solution:
Sterling Power Battery Chemistry Module

The best solution for mixed chemistries, and one that works with all charge sources (alt, solar, wind, fuel cell, hydro, battery charger etc.), would be the Sterling Power DC to DC battery to battery chargers.
Sterling Power DC to DC Battery to Battery Charger BB1230

 

[Gunni]

For 7 years I ran a 12vdc AGM as my starter battery, and 2 FLA 4D 12vdc batteries and did it off one of those old OEM Sentry battery chargers. That starter AGM is still in service, the 4Ds replaced with 4 31XT AGM. I believe the reason the starter batter is not a problem with even a dumb charger is that it never leaves float. Charge demands are nominal. If you never use your starter battery as anything other than backup, no concerns with any chemistry.

 

[Bill Roosa]

start vs house. A starter is not nearly as hard on a battery as a long hair with a 1000W blow dryer.
With a 50 HP engine the starter is rated at around 50 amps. Cold start cranking of 10 seconds (a loooong crank) means 50A*10sec*1 hour/3600sec=(a wopping)0.14 Ah
A 1000W hair dryer draws 1000W/12volt=83.3Amps (before losses in the inverter so actually draws more!!!!!). If she (yea I'm bald and sexist) drys her hair for 5 minutes that gives
83.3A*5 min*1 h/60min=6.9 Ah or 6.9/0.14=69 times the Ah load

I've used 2-6 volt for a long time now and they handle starting the engine just fine.
So the real question is do you actually need a dedicated start battery or can you just divide you house bank into 2 and only isolate when you think the reefer (or other loads) will drain the both house banks overnight or on that long sail to the point where you will not be able to start the motor afterword?

 

[Bill Roosa]

A larger (start converted to deep cycle) house bank also has advantages in both charging and longevity as the resulting bigger Ah bank does not get discharged as deeply (all other things being equal)
FWIW