Ethergore said:
I wish you would have had a few more hours of driving. I have a feeling the charging rate would stay slowing down pretty quickly once the battery was at a higher state of charge and really needed the voltage. I would also like to know what voltage you are getting at your aux battery when your battery is 50% or more discharged. At that point my separator will cycle on and off as my truck battery dumps everything it has in to the aux battery.
Thanks for your time and input.
Ethergore - This might answer some of your questions:
I did notice a few things during my second trip studying truck charging of the camper battery.
On my trip back home, the camper battery bank was at around 94% to start the journey. I had used the solar to get my battery closer to full.
The truck charging setup actually did a nice job topping it off.
On my trip home, 2.5 hours later, my voltage was up to 14.2 volts and the amps were less than 1. The trimetric showed 100% of charge.
With the truck running still, I measured the truck battery and the truck's aux battery. They both tested 14.4 volts. Inside the camper we stayed at 14.2 volts. Only a 0.2 volt drop was significantly better than I would have guessed on my first trip (however this is at really low amps so you'd expect voltage drop not to be too much).
Once enough battery % had been recovered, the setup if given enough time can provide enough voltage to get to 100%.
I'm sure adding a higher gauge wire or dual alternators would really speed this up by letting more power being sent to the camper, but it's much better than I first thought.
There have been some good links here about battery charging. I'm certainly no expert but my understanding is that as batteries are heavily discharged they accept more amps at a lower voltage. As the approach full charge they need higher voltage as the amps decrease to complete the charge cycle. The truck charging setup does a decent job of doing just that.
Anyway, here's my summary of charging the camper by amps:
IOTA with 4 stage - up to 27-30 amps/hour
Truck with FWC setup - up to 14-17 amps/hour
Solar (depending on setup, sunlight, etc) - 4-6 amps/hour per 100 watts of solar
Hope that answers some questions so many of us have had with charging.