Charging /flooded lead acid battery off of a solar panel/ sealed AGM system.

Why use a Solar Panel?

Get an Electronic Battery Isolator and use your engine alternator to keep the battery charged. Your engine running 15 minute generates more power than a 100 watt panel can generate in several days. A 100 wat panel mounted on a van is not going to keep that battery charged up and meet your needs.

That MPPT charge controller may get confused if you used a jumper wire between your spare FLA and your AGM because it would really not know what voltage is for the battery that needs to be charge. Also like two tanks of water that are connected to each other the battery charge will balance out just like the two water tanks. So basically you will discharge your AGM into your FLA which uses up the AGM's life.

I would disconnect the AGM before I connected the spare FLA and let that 100 watt panel charge each battery individually but depending on the Ah rating of that spare FLA battery a single 100 watt panel may not perform a good charge.

You could follow Sunkings advice and use teh engine alternator to keep both batteries charged since that 100 watt panel at best has maybe 5.5 amps of charging ability for a couple of hours a day. It might be better to save your money by not purchasing the 100 watt panel and CC

The battery Isolator sounds interesting. I usually have to travel between the campgrounds and the lake and travel to hunting areas and only stay in one place for no more than 4 days. By upping my AGM house battery to 70 Ah my furnace should run a few days.

How long would it take the vehicle alternator to charge a 50% depleted 70 AH battery. Could I wire in a switch to divert the line to the house battery to charge the boat battery?

Depends on the vehicle. A 35A alternator will take much longer to recharge a battery than a 120A alternator. Larger vehicles have larger alternators. Also depends on conditions, rain, night, wipers, lights siphon off some of the charge power, and it's not available to the battery.
For simple math, a 100Ah AGM battery could be safely charged at 20A. (20% of it's capacity). if the battery was half depleted, it would take 110% to replace the 50Ah consumed, so 50ah / 22 = 2.3 hours IF the alternator was set to the right voltage for charging an AGM battery.

So not only installing an isolator I also have to reduce the amperage to 15 amps for a 70 AH battery.

The battery generally is ok in an automotive system, as it's always nearly full, and doesn't pull much from the alternator. But when you have a discharged battery, it can really stress the alternator while charging, You may have to get a fancy Controller or Isolator. Balmar makes some

I got a better question and answer for you.

How long would it take 100 watt panel mounted flat on top of your van? .

At best you may replace 10 AH per day, so 3 to 4 days with a panel assuming absolutely no clouds or any kind of shade from sunrise to sunset.

Alternator depends on size and what is running at the time, but 30 minutes to 2 hours.

I guess I'll find out. I'm going to set it up with the battery Isolator, according to the furnace manufacturer I should get three nights of heat with a 70 ah battery. We are going to buy a 100w. portable solar panel for my wife's Pleasure Way so I'll borrow it if it looks like I will be stationary for a longer period of time.

Thank you for all the help

In RV circles, using your vehicle to charge your battery is often considered the last resort. Firing up your 200+ horsepower engine to use as a battery charger is hardly the most economical way to do it. But when in a pinch, you do what you need to do. Your alternator can indeed make a lot of amps but it needs to try and push it through what is likely no bigger than 10 gauge wiring over a relatively long wire length. Folks that want to rely on their alternator for fast charging will upgrade the wiring between the alternator and trailer wire harness to something much bigger to make better use of it.

Depending on just how much furnace use you'll have in one night, I would not count on more than one night with your single 70 ah battery. A furnace fan draws around 7 A DC. Your 100 watt panel will definitely help though, and I if it is in the sun for most of the day you'll get more than 10 ah put back in. Our old camper had a similar setup and we could easily go for 4-day weekends with no battery issues. Always furnace at night in Montana mountains and the panel was mounted fixed and flat on the roof.

You have 280 watt panel, not 100 watts. A 100 watt panel generates 5.5 amps of current. With a 4 Sun Hour day on paper generates 22 AH. But that assumes optimum orientation, tilt angle, no shade, and does not account for charge efficiency. 10 to 15 AH at best. If you use a MPPT controller you can get a little more of 30% and get up to 20 AH.

I agree with you if you are parked for several days, running the engine at idle is not the best solution. That is why any off-gridder needs a generator. But when you are driving, nothing better or faster than an Electronic Isolator. Just 15 minutes does more than a week of solar panels.

Our old camper is what referring to. It came with a single 100 watt panel installed by the previous owner and a single group 24 dual purpose battery. It inspired us to put new solar on our next camper which is the 280 watts I'm now running with 2 GC 6V batteries.

Project completed.

Finished the project a couple of days ago and have been testing it. I think I have a winner. I can run the Fantastic Roof vent fan for over 10 hours and not even use half the batteries power. I ran them down to nearly depleted 11.8v and charged them completely by the time I got to town (16 miles). The battery isolator keeps the starting battery full first the automatically starts to charge the cabin batteries and when the engine is shut down it isolates the two systems so running the furnace and cabin lights or roof vent won't discharge the starting battery. I will be adding a port to be able to add a portable 100w. solar panel for extended stays at remote sights.

Heater installation the white pipe is the cold air return, I raised it off the floor to eliminate picking up debris, the brown tube is the heat duct to the cabin. The wood box is the battery and wiring box.



The battery box and wiring, I left enough room for another battery if needed.



View from the cabin, heat outlet into the cabin, battery box with v. gauge and charging ports.



I did add two LED interior cabin lights also.

If you spot anything that might be amiss with the installation shout it out.

I would take the wiring OUT of the battery box. If you charge with enough amps to bubble the electrolyte, acid fumes will destroy the wiring parts (fuse holders etc.)

In the future you should replace those 12 volt batteries with 2 series wired 6 volt golf cart batteries. In the meantime your positive charging line and load should both be on the same diagonal corner from the negative line and load, forcing somewhat equal charge/discharge from both batteries.