After considerable research I came up with a solution that I really like and thought I would share as it is frustratingly difficult to track down this info, so maybe this can help someone else down the road.
The problem: the truck camper was wired into the trailer harness aux power by the installers and it would not charge the batteries at all(due to regenerative braking and low battery volts) so I would get about 2.5 days of capacity running the refrigerator, water pump and misc lights. Drawing down the batteries this low would surely reduce the life span so I needed a better solution.
Specifically we use our camper for exploring the west for day hikes, long weekends and recently a week long trip to Yosemite and Great Basin national park. Meaning: we don't stay in one place for more than a few days at a time so I don't need a full off the grid solution/capacity that keeps the batteries charged between sunny days = a lot of panels. I need something that charges the batteries between the stops and extends the capacity when not moving.
The solution: A 150 watt solar panel and a 20 amp battery to battery charger on my truck/camper and after several trips solution/design provide out nicely. The Ford f150 v6 turbo has a 110amp alternator that the b2b charger uses to generate its 20amps of charging power.
I ended up with a kyocera 150 watt 12v/8amp panel, Bogart tm2030 battery monitor and a sc2030 charger controller and a Sterling marine grade(waterproof) 20amp 12v battery to battery charge to support my 12 volt system - 2 220ah 6v batteries. I also upgraded the battery wiring to 2/0(for future inverter), compression lugs, blue sea switch, anl fuse and 6 gauge wire for chargers. (Research voltage drop to understand you can lose power in the wires and reduce the efficiency of your system)
The panel mounts are designed with 1/4 turn camlocs so that I can quickly remove and use an extension cable to have the flexibility to set the panel in the sun should I need the extra power because the truck is in the shade. I could see this need if we set up a basecamp and used the motorcycle for exploring.
Here is how I landed on this design - first thing you discover when researching lead acid batteries is that almost all charging profiles look like this.
Chargers pump in as many amps as available and then as the battery reaches say 85-90% fully charged the amps start to tail off as the resistance goes up. Meaning you can have all the amps in the world from a lot of panels but the batteries will not use them.
My setup will pump in 26 amps, from solar and b2b charger, for about an hour when the batteries are partially discharged. After 1-2 hours the amps drop down to about 6 and it can stay there for hours as it tops off the batteries and over charges per the Bogart recommended charging profile. I know this because I put the battery monitor on a long line so I can put inside the truck cab to watch how all this works. At some point I will just mount inside the camper as I will not have to monitor because I know it works.
One interesting fact I learned about the b2b charger from Sterling is that they have a override for new vehicles that have a regenerative braking scheme to help with gas mileage. I guess new vehicles run the battery low and when you step on the brakes, the cpu tells the alternator to go full tilt and charge the vehicle battery during braking so that you are not using engine power to drive the alternator as much(fuel savings). I saw this behaviour when I first installed the b2b charger before I had the solar panel. I was not seeing any amps going into the battery until I stepped on the brake and then it would shoot up to 20 amps until I let off the brakes. I installed the extra wire from Sterling to a keyed fuse so that it would know to charge regardless vehicle charging scheme.
Now that I have seen how this design works I think I would go with a bigger b2b charge to get the bulk of the amps in sooner so the solar has more time to work during the top off phase. I had a brief email exchange with Sterling and they said the 60amp model would be fine as you will need a bigger alternator if you go with their 120amp model. I selected the marine version as I wanted to mount on vehicle but they make no waterproof versions to go inside your camper/vehicle but I have limited space and this setup allows me to tow and charge with same charger if ever needed. This would mean you could start the vehicle and pump in a lot of amps in a short period should you need it and not have to run the vehicle very long.
Yosemite Trip Results:
In general we seem to use 30-60 amps a night depending on if we are using our 12v mattress heater on cold nights and have had no problem recharging over 100%. During our Yosemite trip, the vehicle sat for roughly 2.5 days in lower pines campground and only had about 1 hour of sun before going into the shade, ie we had a little extra capacity but was getting close to running out of power. The last day we drove around for a few hours exploring and was able to put enough amps in so that overnight we had no issues maintaining the refrigerator. The next day we had a 8 hour drive to next stop and within 3 hours of driving the system was fully charged. For the next day we explored and did not really have to worry about charge as the following day was our return trip of 10 hours of driving. The return trip ended up being in clouds almost the whole time and when we arrived home the batteries were 100%, which would not have happened if 100% solar, regardless of how many panels I had.
Solar Only Test Results:
I pulled out 11% overnight and let the solar panel charge during the day with good exposure the system was full charged by the end of the day.
So for about $750 I will never have to worry about capacity again and know my batteries will last a lot longer.
Anyway hope this helps someone as I spent way too much time learning all of these details.
The problem: the truck camper was wired into the trailer harness aux power by the installers and it would not charge the batteries at all(due to regenerative braking and low battery volts) so I would get about 2.5 days of capacity running the refrigerator, water pump and misc lights. Drawing down the batteries this low would surely reduce the life span so I needed a better solution.
Specifically we use our camper for exploring the west for day hikes, long weekends and recently a week long trip to Yosemite and Great Basin national park. Meaning: we don't stay in one place for more than a few days at a time so I don't need a full off the grid solution/capacity that keeps the batteries charged between sunny days = a lot of panels. I need something that charges the batteries between the stops and extends the capacity when not moving.
The solution: A 150 watt solar panel and a 20 amp battery to battery charger on my truck/camper and after several trips solution/design provide out nicely. The Ford f150 v6 turbo has a 110amp alternator that the b2b charger uses to generate its 20amps of charging power.
I ended up with a kyocera 150 watt 12v/8amp panel, Bogart tm2030 battery monitor and a sc2030 charger controller and a Sterling marine grade(waterproof) 20amp 12v battery to battery charge to support my 12 volt system - 2 220ah 6v batteries. I also upgraded the battery wiring to 2/0(for future inverter), compression lugs, blue sea switch, anl fuse and 6 gauge wire for chargers. (Research voltage drop to understand you can lose power in the wires and reduce the efficiency of your system)
The panel mounts are designed with 1/4 turn camlocs so that I can quickly remove and use an extension cable to have the flexibility to set the panel in the sun should I need the extra power because the truck is in the shade. I could see this need if we set up a basecamp and used the motorcycle for exploring.
Here is how I landed on this design - first thing you discover when researching lead acid batteries is that almost all charging profiles look like this.
Chargers pump in as many amps as available and then as the battery reaches say 85-90% fully charged the amps start to tail off as the resistance goes up. Meaning you can have all the amps in the world from a lot of panels but the batteries will not use them.
My setup will pump in 26 amps, from solar and b2b charger, for about an hour when the batteries are partially discharged. After 1-2 hours the amps drop down to about 6 and it can stay there for hours as it tops off the batteries and over charges per the Bogart recommended charging profile. I know this because I put the battery monitor on a long line so I can put inside the truck cab to watch how all this works. At some point I will just mount inside the camper as I will not have to monitor because I know it works.
One interesting fact I learned about the b2b charger from Sterling is that they have a override for new vehicles that have a regenerative braking scheme to help with gas mileage. I guess new vehicles run the battery low and when you step on the brakes, the cpu tells the alternator to go full tilt and charge the vehicle battery during braking so that you are not using engine power to drive the alternator as much(fuel savings). I saw this behaviour when I first installed the b2b charger before I had the solar panel. I was not seeing any amps going into the battery until I stepped on the brake and then it would shoot up to 20 amps until I let off the brakes. I installed the extra wire from Sterling to a keyed fuse so that it would know to charge regardless vehicle charging scheme.
Now that I have seen how this design works I think I would go with a bigger b2b charge to get the bulk of the amps in sooner so the solar has more time to work during the top off phase. I had a brief email exchange with Sterling and they said the 60amp model would be fine as you will need a bigger alternator if you go with their 120amp model. I selected the marine version as I wanted to mount on vehicle but they make no waterproof versions to go inside your camper/vehicle but I have limited space and this setup allows me to tow and charge with same charger if ever needed. This would mean you could start the vehicle and pump in a lot of amps in a short period should you need it and not have to run the vehicle very long.
Yosemite Trip Results:
In general we seem to use 30-60 amps a night depending on if we are using our 12v mattress heater on cold nights and have had no problem recharging over 100%. During our Yosemite trip, the vehicle sat for roughly 2.5 days in lower pines campground and only had about 1 hour of sun before going into the shade, ie we had a little extra capacity but was getting close to running out of power. The last day we drove around for a few hours exploring and was able to put enough amps in so that overnight we had no issues maintaining the refrigerator. The next day we had a 8 hour drive to next stop and within 3 hours of driving the system was fully charged. For the next day we explored and did not really have to worry about charge as the following day was our return trip of 10 hours of driving. The return trip ended up being in clouds almost the whole time and when we arrived home the batteries were 100%, which would not have happened if 100% solar, regardless of how many panels I had.
Solar Only Test Results:
I pulled out 11% overnight and let the solar panel charge during the day with good exposure the system was full charged by the end of the day.
So for about $750 I will never have to worry about capacity again and know my batteries will last a lot longer.
Anyway hope this helps someone as I spent way too much time learning all of these details.
