Originally Posted by opie
I suppose you are right... Amp hours in are amp hours in.
BUT... If I only have say 1.5 hours to run my generator I can get more charge into 1 bank rather than both banks. Limiting ultimate cycle time on the batts and bring 1 bank up closer to full than if I tried to charge all 4. All assuming that bulk charge cuts off around 90% of batt capacity.
I only have 60amp available for charging @ 14.6 bulk. I am going to remove the 8guage wire from the factory and replace it with 4gauge so the batts get full voltage from the charger.
OK...well you should and could upgrade to 90+ amps charging for a 420a/h system...but lets set that aside...and use an example.
1. You can either charge a 210 a/h bank or a 420 a/h bank. Lets assume you have depleted both to 50% and want to recharge in the time you have available and lets use 2 hours of charging to keep things easy!
2. So bank #1 needs 105 amp hours put back in. And bank 1+2 needs 210 amp hours put back in.
3. Lets further assume that your charging system goes into absorbtion stage at about 75% full and float stage at around 90% full.
4. In bank #1 you will be at 75% when you get to (.75x210=157.5ah)...or once you have added 52.5 amphours back in in bulk stage....LESS than one hour with a 60 amp charger. (FAR less with a proper sized charger...except that a SINGLE 210 a/h cannot take even your 60 amps during charging ...it will likely only take a max of 52 amps of charge current (25%). So in your first hour you will charge in bulk at 52 amps...THEN shift down to lower voltage absorbtion charging for the remainder of the time as resistance builds...so maybe 1/2 those amps on average if you are lucky. You'll never get to float so lets' disregard that...So you are left with 75 or 80 amp hours added in 2 hours to a single 210ah bank.
5. Now lets return to the bank #1+2 scenario.
Here we have a need to REPLACE 210 ah's ...in a 420ah bank. The 420 ah bank will be 75% full at 315 ah's. SO..we get to add 105 amp hours at bulk rate of 60 amps
due to the larger bank size...before the charges cycles to absorbtion. You can see that we'll be able to do around 1.75 hours of BULK charging at 60 amps and about .25 hours of absorbtion charging and so will add about 120amp hours to the BIG bank in the same amount of time . Again, the difference would be even more dramatic with a 90 amp charger since the big bank can use ALL of it and the little one can only use 52 amps or so in bulk phase.
Hope that clarifies.