With all due respect, Roy's post reminded me of the many on-line articles I have read that claim a 100Ah battery at 50% soc can be charged full in 2 1/2 hours using a 20a charger. The thinking is: 50Ah / 20a = 2 1/2 hrs, so it would take 2 1/2 hours.
So let's take a look:
First of all, a 100Ah battery is capable of taking far more than a measly 20 amps at 50% soc. For example, my 215's max out my 45 amper until they are over 80%, before amps taper. Anything less than the 20a is a result of too low a charging voltage. I.E; dial that charger up to 14.8 and just see if the charger doesn't max out at or above it's 20a limit.
At 50% dod, that's (-)50Ah. 50-80% is 30Ah. At sufficient voltage, the charger will be maxed out at its current limit of 20 amps from 50-80%, thus taking 1 hour 30 minutes to replace those 30Ah's. And as I have learned recently, the remaining 20% / 20Ah's will take even longer than 1 1/2 hours. Why? Because when amps taper, they tend to do a bit of a nose dive. But at the very best, in this example, the amps will average out at about 10-12 amps during that 80-100% charge cycle. So, at an average of say 11a, it would take about 1 hour 50 minutes to replace only 20Ah's, whereas it only took 1 hour 30 minutes to replace 30Ah's. So that's a total of 3 hours 20 minutes... Way above the purported 2 hours 30 minutes.
If you lower that voltage from 14.8v to 13.6 during the absorption / constant voltage stage, the amps will drop drastically, and that 3 hours 20 minutes will likely more than double!
Now let's apply these figures to a 400Ah bank (4-12's in parallel), using a 40a b&d 1093:
50% dod = (-)200Ah; 50-80% = 120Ah. The 1093 will be maxed out at its 40a limit from 50-80%, so that will take 3 hours. The remaining 20% / 80Ah will take approximately 3 hours 40 minutes, (80Ah / 22a (average) = 3.6+ hrs), (double that if at 13.6V) for a grand total of 6 hours 40 minutes, to 11 hours! Now remember, if there is a 900w genset, running at near full bore this 6 1/2+ hours, that's roughly a gallon of gas per charge cycle, ( X how many cycles/week?), not to mention the wear and tear on that poor genset.
The OP needs to use either a smaller (split) bank or the larger genset and charger. And BTW, I'm in somewhat of the same boat with my 430Ah bank and my eu2000i 1600w genset, which can only power a 60-70a non pfc charger. I'd use a 100 amper in a heartbeat, if I could.
