Battery banks

[Maine Sail]

so your saying a 375 ah battery will only produce 18.75 amps for 20 h

Yes, absolutely. At 77F it will deliver its capacity if it meets its spec... Course this is only after being fully charged and then discharged at a constant 18.75A at 77F to 10.5V....

Conversely at a 4.86A load that battery can deliver 486Ah or at a 135A load it will only deliver 135Ah's. That battery has a Peukerts constant of 1.50..

A 200Ah battery would sustain a 10A load for 20 hours or a 100Ah battery would sustain 5A for 20 hours, but using all the capacity takes you to 0% SOC so you really only have half of any battery for usable capacity or just 30-35% when off cruising........

 

[Bill Roosa]

So MS, lead acid would appear to be a real problematic way to store electrons
What is your opinion on Ni-Cad batteries? I am of the impression that they are substantially more robust. Can go much deeper in to SOC without harm, don't have the problem with bulk-acceptance-trickle as they don't have internal resistance dependent on the SOC like lead acid and can be left discharged with out harm.
Thoughts?
BTW we do understand your position on the newer battery chemistries but they tend to catch fire with out some special charging circuits.

 

[Johann]

So MS, lead acid would appear to be a real problematic way to store electrons.

Apparently not the Carbon Foam AGM if you cycle between 20% - 80% SOC. Then you can get close to 100% efficiency from your charge source, if I am reading the literature correctly...

 

[seadaddler]

I think trying to run AC off batteries even with out all the info and just hearing about smaller
AC units on there boats having a hard time cooling the boat and needing larger unit to make the boat cool for relief and bigger unit more power needed.
The smaller units are working very hard to barely cooling here in Florida.
I run my Gen when ever I need AC and not just for a hour or 2 and keeping it comfortable
means running it for many hours other wise it is just awful tease.
I run my AC most of the day here in Florida and at night turn some fans and most times
the fans are ok but some times just really Hot and my is OK but I am hot.
Nick

 

[JamesG161]

@Maine Sail you did a wonderfully clear and concise description of the "working capacity" of a cruising battery.

I would like to understand the re-charging effects to complete the discharge/charge cycle. I understand the charging raises the temperature of a battery above ambient temps, but lets leave that temp variation aside for the moment.

A 200Ah battery is only a 200Ah battery with a 10A load at 77F when continuously discharged to 10.5V at 10A.

Using the above as the example case.

the actual usable capacity, from a 200Ah battery bank, is 60-70Ah's

The usable capacity if say 60Ah of 200Ah, would give you 6 hours (60Ah/10A) before recharge is needed.
My Freedom 2000 charger is rated at 100A at 12VDC.
This would leave a difference of 90A to charge (100A - 10A load). Simplistically, you could recharge the usable capacity in 60/90 = 0.667 hours or 40 minutes (genset time).
Correct?
Jim...

PS: I suspect more like 60 minutes as the battery heats up and offers resistance to the 90A rating and higher 14+VDC charge potential.