Ask PYS: Power

John, on Nov 10, 2010 asked:

I have a 46 foot Ocean Alexander trawler. I'm frustrated that I have to run my 8kW AC generator most of the time just to recharge my 1600 amp hours (AH) AGM house battery bank. What's your recommendation for recharging more quickly? By the way, my charger is a 100 amp unit.

Hi John,

Let's assume your house bank is properly sized for a day's use and therefore uses 1/3 of 1600 AH while you cruise extensively. Consequently, you have to replenish approximately 500 AH every day. Since your battery bank is so large, the acceptance charge rate (40% of battery bank for AGM) is not a limiting factor. You want to be able to limit generator run time to a couple of hours per day and maximize AC generator capacity. A standard approach to achieve this would be to ADD two new 100A three-stage DC chargers to your system and to wire all three chargers in parallel for a combined output of 300A. Each charger will poll the house bank voltage and adjust its amperage output accordingly.