Split solar system

I have an idea... I'm in the process of buying a travel trailer.  I cannot mount any additional solar panels to its roof, and I don't want to add any additional batteries because of the weight.

I have a tow vehicle that's a beast, though, with plenty of roof space.  So my thought is to mount solar and batteries on the tow vehicle, and then join the two with a high-current connection when I'm boondocking.

The trailer has a single 180W solar panel and two golf cart batteries; total around 200 Ah.

The tow vehicle has room for 600W (actually 1200W but that's overkill) and enough carrying capacity for another 600Ah of batteries.

I plan to join the two with a high-current connection that's fused at 75A.

The trailer and tow vehicle both have their own solar controllers and will work independently.  The tow vehicle batteries will also be charged from the vehicle alternator when the engine is running.

The purpose of this is to provide extended boondocking and be able to charge the tow vehicle batteries when driving.  That way I always have charged batteries even if I drop the trailer somewhere in the boondocks.

Anyone see any issues with this?  What sort of solar controllers and panels should I be using on the tow vehicle?  At a guess the trailer comes with a cheap PWM and I can buy whatever I need for the 600W array.


  • EstragonEstragon Registered Users Posts: 4,495 ✭✭✭✭✭
    I wouldn't regularly connect larger and smaller independent systems in parallel.  If one bank was at a low SOC, and the other full, when connected in parallel there could be some pretty large currents from the low one to the higher.  Charging and discharging imbalances between banks might also be an issue.

    Maybe something like a 1-2-none DC switch (with appropriate breakers), so one bank can be in regular use, and the other used as a reserve bank?
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • cptdondocptdondo Solar Expert Posts: 99 ✭✭✭
    edited February 2019 #3
    I thought about that.  The majority of the draw is in the trailer, with the smaller battery bank and the majority of the charge would be in tow vehicle.  So yeah, connecting the two would mean a big POP if the SOC in the trailer is low.

    A 1-2-none switch is not really practical for the above reasons - I want to be able to charge the small bank from the large one.

    I've thought about a DC-DC charger, but then I thought I'm overthinking things (which I have a tendency to do).....  Maybe a cutoff switch like a Blue Sea Battery Disconnect, connect the two together, turn the switch on, and let the breaker cycle until less than 75A is flowing?
  • cptdondocptdondo Solar Expert Posts: 99 ✭✭✭
    edited February 2019 #4
    Huh.  Anything like this available in North America?


    That would do it.

    HAH! This is available.


    Not sure I want to splurge that much but at least it's an option, especially if I figure out a way to add solar panels to the trailer (I'm worried about compromising the roof there).
  • littleharbor2littleharbor2 Solar Expert Posts: 1,639 ✭✭✭✭
    Maybe not the most efficient approach but you could connect your shore power cable to a pure sine wave inverter in the tow vehicle. As long as the systems are separate there shouldn't have any issues. This wont work if there is only one system. it would end up draining the battery trying to charge the batteries using... the batteries.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 540 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

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