RV solar panel tow vehicle charging combo

System
System Posts: 2,511 admin
in Solar Beginners Corner #1
Acquired a travel trailer with a solar panel. The cables go directly from the solar panel to the battery as does the charge hook up from the tow vehicle. There is no flow controller and I am wondering if one is necessary. I would expect when the tow vehicle is running there would be some sort of competing charge or "backwash" to the solar panel??
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #2
    Re: RV solar panel tow vehicle charging combo

    The Solar should have a 3stage charge controller, that delivers nearly 14.5V to the deep cycle battery.

    There should be an isolation diode/ interlock in the trailer connector harness (or in the tow vehicle) so that if you leave a light on in the trailer, you don't run the starting battery flat. The idea is that when the engine is running, the alternator can charge the towed battery at 13.8V. This is lower than the normal solar charging.

    The Solar panel should just add to the power coming from the alternator, and there should be an on-board charge controller that prevents back feed to the solar panel (towing at night)
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
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  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    #3
    Re: RV solar panel tow vehicle charging combo
    BobFar wrote: »
    Acquired a travel trailer with a solar panel. The cables go directly from the solar panel to the battery as does the charge hook up from the tow vehicle. There is no flow controller and I am wondering if one is necessary. I would expect when the tow vehicle is running there would be some sort of competing charge or "backwash" to the solar panel??
    Thanks

    Commercial solar panels have a "backflow" diode to prevent them from sucking electricity from the battery in darkness. Since the panel (almost certainly) puts out more voltage than the truck's charging system, that diode would be big enough to prevent the backwash you are talking about.

    I might worry that the solar panel is dumping more voltage into the truck's electrical system than it is designed to handle, instead of vice versa.


    The simple setup you've got could, of course, be improved, but as long as the solar panel isn't big enough to boil the battery dry, there's probably no hazard to it the way it is.

    Yes, there should be an isolator between the truck's charging system and the trailer's battery - just like an aux battery in a motorhome - to keep the trailer from draining the truck's engine battery. But some older motorhomes (I bought one recently) just used a solenoid switch instead of a true isolator. On mine, the two batteries are connected together when the key is on, but when the key is off they aren't, and the motorhome loads are all connected to the aux battery. (I will be changing this out for an isolator in the near future - and definitely before I add a solar panel.)

    And yes, your battery will be charged better, and last longer if you add a charge controller between the solar panel and the trailer battery. That is IF the solar panel is even big enough to charge the trailer battery properly.

    The main drawback to what you've described, is that the truck can charge up the trailer battery to say 13.8 volts or so, then the solar panel can pump that up even more...and without a solar charge controller that panel doesn't know when to stop, and it could overcharge the battery and "boil it dry".
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