Adding a panel to existing camper

HI. Been off grid for 16 years. Not completely ignorant but.... I bought a truck camper that has a 100 watt panel. Cheesy 7 amp controller and former owner put in 4 marine batteries. I just got a 30 amp charger and I have a 75 watt orphaned panel I want to add...keeping it mobile. Just started to look at how the existing 12v panel is wired. It goes from 8ga to 10 and then I think to 12. I'm probably going to bring 8ga all the way to the new controller but I'm not sure whether to tie the 75 watt one into it. I'm very remote in Mexico and don't have too many parts options. What's the simplest way to tie them together til I can get a combiner box? Ideally I'd like to have some way of just plugging in the mobile panel. 


  • mike95490mike95490 Solar Expert Posts: 9,274 ✭✭✭✭✭
    10ga is good for 30A , so I think using that is fine.   I'd simply parallel the new panel with the old. 175V @ 12V is 14A so a new controller would be required
    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 ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    gen: ,

  • bajarickbajarick Registered Users Posts: 5 ✭✭
    Thanks. Just got the new controller. Looking for an easy way to connect the two panels together but don't know exactly where and how to do it. 
  • BB.BB. Super Moderators, Administrators Posts: 31,683 admin
    edited November 2020 #4
    What brand/model (link?) of solar charge controller did you purchase.

    If you got a PWM type (usually less expensive)--Then you would connect the panels in parallel... + to + and - to - .... That keeps the Vmp-array at ~17.5 volts (for a 12 volt battery on a PWM controller). You do not need a combiner box with this... You could simply cut the wires and wire nut all three + connections together (panel 1, panel 2, and charge controller). And do the same for the negative terminals (put the wire nuts in a J-Box to keep out water and animals).

    If you have an MPPT controller, you usually would connect the two panel in series. Again you can cut and wire nut connections in a Jbox.

    If your panels have the original MC4 connectors, there are jumpers and junction blocks that you can buy:'


    PS: What are the Vmp and Imp of your two panels? To put them in parallel, the output voltage Vmp should be within 10% or better.

    If installing them in series, then the Imp current should be within 10% or better.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • bajarickbajarick Registered Users Posts: 5 ✭✭
    Thanks for replies! Woke up last night and thought of the mc4 connectors. I got a Renogy?  pwm 30amp charger. Panels are close enough. I'll check into what options the mc4 connectors will give me. 
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