Dual 6 volt GC2 batteries and charging characteristics

[busterbrown73]

We just returned home to Michigan from a 24 day trip around the southwest. This was the first big test of our new dual 6 volt battery bank (upgraded from a single group 24 12 volt).

As I have really no experience with charging behaviors of a serial 6 volt setup, I'm looking to see if I need to upgrade the OEM converter charger on my travel trailer. This is what I noticed during our trip.

1. Started with a fully charged 13.3 volt bank on the morning of our departure after plugged into shore power for 48 hours. The Duracell (215 amp hour) flooded batteries are brand new.

2. After using typical appliances through a dry camping night, (DC inverter for television/fan, furnace, led lights, LPG fridge, and water pump), the bank would drop to 12.4 to 12.6 volts. We would run our 3700 watt inverter generator for 5 to 6 hours during the next day to allow the converter to recharge the bank. I thought it was preforming as expected except that the converter would charge to about 12.8 to 12.9 volts. I never got back to 13.3 volts until we plugged into shore power at a full hookup campground.

3. On several legs of the journey, we would leave the dry camp location without running the generator in the morning and drive 4 or 5 hours to our next camp site. I checked the volts on arrival at the new site and my TV would barely provide a recharge (12.5 to maybe 12.6). The previous group 24 12 volt would be completely charged after just a couple of hours of running the truck. (Obviously, I have much more amp hours with the GC2s).

My concerns are:

1. Is my OEM converter the bottleneck in my coach's recharging capabilities?
2. For a dual 6-volt in-series battery bank (flooded), what should I expect as a full charge? I've read 13.3 volts as being 100% as a float charge but absorption voltage could be much higher.
3. Will a true 4 stage converter charger (bulk, absorption, float, equalize) help maximize battery usability and increase overall battery life?
4. If a new converter is needed, what size (amp) is preferred? Are converter/inverter types recommended as I see the price point goes much higher? Realistically, I would like to see a full charge after a couple hours of generator use.
5. Is a larger battery bank crippled by the inadequate charging abilities of the converter?

[time2roll]

In 3 hours your charging voltage should be 14.3+ volts. 13.3 is a trickle charge.

Consider this PD-60-14.8 converter made for GC batteries.

http://www.bestconverter.com/PD-9260C-148-60-Amp

[2oldman]

What is the amp rating of your converter?

It's good to remember that 2-6v batteries are just one big 12v in two parts. It's that simple. Charging is the same, assuming your wiring is adequate and clean.

busterbrown73 wrote:
2.... (DC inverter for television/fan, furnace, led lights, LPG fridge, and water pump),

FYI.. the only thing on that list that runs on the inverter is the television.

3. Yes, a true 4 stage is better. 55 amps should be good.

If your 215amp-hour 'battery' has been drawn down to 50%, you need to replenish 107ah, which is at least 2 hours on a 55a charger. This also assumes you've used big enough wire from the converter to the batteries. Many of us use a tri-metric (I think) meter to measure amps in and out. A bit more accurate than voltage.

5. Yeah, too small of a charger takes forever.

All this said, it's common with us boondockers that we never get a 100% charge except on shore power. Reason is, flooded batteries take much longer than you think due to the absorption phase. I have Lithium batteries which don't have this problem.