Re: 100 amp battery charger to 250 amp battery bank? Any problems?
C/10 means Capacity in amp hours (Ah) divided by 10. Another way to express this is .1C or capacity times .1 or 1/10. So if the manufacturers of your batteries say the recommended charge rate is .1C and the max rate is .2C then you would try to charge at .1X250 or 25 amps with a max of .2X250 or 50 amps.
I don’t think max charge rate is as critical as it use to be but can still be quite critical. Chargers have basically three stages that charge the battery: Bulk, Absorption, and Float. The bulk stage brings the battery to around 80% state of charge (SOC) at high current levels. The absorption stage brings the SOC to 100% at a low current. The float charge is needed due to the battery’s self-discharge rate and keeps the battery at 100%.
A simple charge algorithm may look like this. The bulk stage provides a constant 10 amps until the terminal voltage reaches 13.9v. It then switches to the absorption stage and reduces the constant current to 3 amps until the voltage reaches 14.4v and then holds the voltage constant at 14.4v until current drops below .5 amps. It then switches to the float mode and provides no charge until terminal voltage drops below 13.6v and then provides a constant 1.5 amps until the voltage rises to 13.2v. It repeats this on/off float stage indefinitely.
The concern I would have about a 100 amp charger charging a 250 Ah battery bank would be that if it is not a smart charger that steps down the current multiple times during the bulk stage, it may switch from the high current bulk stage to the low current absorption stage long before the battery reached 80% SOC. In that case, it may never reach 100% SOC.
