I used my volt meter recently to check my two, 6-volt batteries state of charge. I have been curious as to how well my truck would charge my batteries after a time of dry camping. Here is what I found:
6.39 volts (100%) before camping trip.
6.19 volts (70%) after two days of dry camping.
6.37 volts (100%) hooked up but isolated after 2-hour drive.
This recharging number surprised me. I thought it would take more than one-hours drive to charge the batteries from one day's camping.
I am attempting to figure out how long I need to travel between campgrounds, and still keep my batteries fully charged.
My truck takes a good 6 hours to recharge my dual 6V batteries after a couple of days of camping. I never am able to gt them to the same level that the converter does.
Your diesel has a much higher output from the alternator than I do, but I think you may be measuring the static(surface) charge present when batteries are exposed to charging voltage for a brief time. To get an accurate check, turn something on with a moderate current draw for a few minutes. Something like a powered vent or CRT television. Then measure with everything off.
Okay, I turned on a light and fan for a minute or two, then turned them off and checked the voltage: 6.33 (90%) that sounds better. Can I assume one more hour of driving would bring it up to 100%, or does it take longer the closer it gets to fully charged?
Charging a battery bank is somewhat like a frog on a log who can jump 1/2 to the end of the log in any jump. Every jump takes about the same time but the amp-hours returned to the battery become smaller and smaller.
This is a good topic. In a recent Trailer Life(or was it Motorehome?) tech issues section the author would not commit to a drive time charge rate. All he did was try to steer you to another product(s).
It would be nice if someone could come up with a reasonable time. Is it 100 miles or 500 miles? Is it one hour or 10 hours? I'm sure all vehicles are not the same, but still?
I figure, off the top of my head, my rig should be charged after a couple of hours drive. No real basis for this though.