Solar for Tow Vehicle question

I've got a 5W on my Ford Ranger's dash that sits for 6-8 months at a time. Been working great. Have a 5W on a Toyota MR2 Spyder that has kept it up to snuff for over a year (wife's daughter's car - semi abandoned). The Toyota, the panel had to be outside the vehicle - too much attenuation behind the windshield. The toyota will otherwise drain the battery too low in 6 weeks.

Hard to suggest the wattage without knowing the battery drain due to radio and other devices connected. With battery disconnected 2W is enough to stop self-discharge. With radio on standby... who knows? Maybe 10W, maybe 20W. Shouldn't need more than 20W.

Having said this, I would not leave anything connected on any vehicle left unattended for a week, this includes solar charger. Instead, I would either install a cut-off switch and disconnect the battery - or just do nothing if it's only a week. When fully charged and disconnected, truck battery can be left for at least 4-6 weeks.

Small charger under windshield may fail when it's hot - plastic casing just melts down, or fail due to corrosion or cr-appy Chinese quality, and you have a truck full of gas.

Bigger charger outside would have panels in aluminum frames and normally would include a controller which can fail, or connections would fail, and there is a higher current than in small chargers so there is more fire risk - not from the panel and controller but from a spark on temporary clamps on battery or cig lighter.

RoyB wrote:
Alot of folks would get something that lays in the windshield area and just plug the solar panel into the cigarette lighter socket. I used to do that all the time with my 99 TJ Jeep.

The newer cars and trucks seem to have the cigarette lighter on their ignition key-off timer so if that is the game plan be sure you have access to a constant connection to the batteries.

I have three such cigarette lights available from the console area of my truck. The only one that is HOT all the time is the one inside the console storage section between the seats..

Just a caution to think about...
Roy Ken

This is just the type he is considering. I told him he needs to figure out the drain first. My suggestion was to start with the aftermarket radio that is in it. That is usually the place where you have issues. I have seen so many incorrectly installed by kids and have had to be rewired. I used to do a lot of auto wiring and electronics installs of varying types. Never had battery problems. He is dead set on a solar set though. I also recommended just getting a battery cutoff like we have on our campers. Just cut off the batteries.

If a vehicles batteries are in good condition, you can just unhook the ground cable to remove any parasitic loads and the battery will hold its charge for months.
I had a '57 Ford in storage for 8 years and it only got started twice a year. It never failed to start and the battery kept its charge with no problem.

Worked in a boat shop..we just disconnected the battery and put the boats away for 6 months here in the Northeast. Batteries in good shape start right up.

There is a parasitic drain from stuff like the radio to keep the clock going.

If one wanted a fairly inexpensive kit, I wonder about getting the Harbor Freight solar panel setup, as well as a MPPT controller (some no-name Chinese ones are fairly decent as per YouTube videos, others are junk), so the batteries can trickle/float charge indefinitely. That way, one can set up the panels, attach the charger to the battery, and pretty much forget about it until the vehicle is needed again.

Several months? With a constant parasitic drain on them?

I think I would find out what is draining his batteries and fix that first. Truck should be able to sit for several months with no battery problems. In the mean time disconnecting negative battery lead will stop ALL drain

If the truck won't sit for 6 or 8 weeks and then start something is wrong with the truck and he should fix it.

Does the trailer have solar? Are they connected?
I use the trailer solar to keep all the batteries charged including the truck.

Otherwise 5 to 10 watts per battery and with your low sun I would stick to the high side in winter.

If a vehicles batteries are in good condition, you can just unhook the ground cable to remove any parasitic loads and the battery will hold its charge for months.
I had a '57 Ford in storage for 8 years and it only got started twice a year. It never failed to start and the battery kept its charge with no problem.