OP here to finally report back on some real world results from last July when I was dry camping in the Adirondacks in very dense shade and I had to use my voltage boosting contraption.
After 2 days of getting no charging from my solar panels (hopeless in my 100% shaded site) I hooked up my contraption and it worked out fairly well - once I figured out the process.
So with my 2 Group 24 batteries down about 60 AHs, I was able to transfer about 40-50 AHs into the TT batteries in a few hours. Yes it was labor intensive (fun for me) to set it up, monitor it and tweak the voltage setting over time. I have a Turnigy meter and a sears DC clamp on ammeter. The goal was to pump about 30 AHs from the truck battery to the TT batteries with the truck turned off, then let the truck idle for 20 minutes to quickly charge the truck battery and repeat till done.
I would first let the voltage booster run for an hour or so without the truck running. I first set the boost voltage to something like 13.6 volts and it would pump 15 or 20 Amps into the TT batteries - but it would soon blow the fuse on my truck 7-pin charging wire - so I hooked up jumper cables between the truck battery and the contraption.
With the jumper cables connected to the voltage booster, I could let the voltage booster run for an hour or so at 30 amps charging from the TV battery to the TT battery. Amps would taper to 10 or less and I would have to increase the voltage set point on the booster to raise it back to 30 or so Amps. All without the truck running.
After transferring about 30 AHs from the TV to TT batteries, I would start the truck and let it idle for 20 minutes while keeping the contraption running. The truck battery was accepting something like 70 Amps from the alternator when I first started the truck.
So basically, I was slowly moving Amps from the TV to the TT (at about 20 Amps), and periodically quickly recharging the TV battery with the truck alternator (at about 70 Amps). And later that day, I would drive the truck on some errands for an hour or so to get the truck battery more fully charged.
Lesson Learned: a current-limited voltage booster would be better. If I had used a current limited voltage booster I could have set the output to 14.4V with a 20 Amp max output. Then I would only have to remember to start the truck every 60 or 90 minutes for 20 minutes and not have to monitor the amps and adjust the voltage when they tapered.
I did this same procedure every 2 or 3 days to keep the batteries charged enough to keep the the propane fridge, water heater and LED lights working for our 8 day stay.
Ed
