12V RV installation

Hello, i just bought two solar panels for my rv.
The panels are in a different size and have different voltage.
thats why i need 2 solar controllers.


I am using 120W on Voltronic MPP 165 DUO Digital  
and 60 W on Voltronic MPP 165 DUO Digital

I just have a question about the installation from the Controller to the Battery.

At the moment i have this installation




from both Controllers is going a plus and minus cable to the battery.
But is it also possible to connect it like this?


That would be a "nicer" installation and less cables in the rv.
Sorry for the beginner question.

Hope someone can help me.

Thanks
aspn


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Comments

  • littleharbor2littleharbor2 Solar Expert Posts: 635 ✭✭✭✭
    As long as the Vmp. of the panels is close you can parallel wire them and use one controller.

    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, 700 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

  • EstragonEstragon Registered Users Posts: 1,416 ✭✭✭✭
    The short answer is yes.

    The longer answer has a "but". The first issue is wire size. You need to make sure the wire carrying the combined current from the two controllers is heavy enough to carry the combined current. You would effectively be making the controller on the right battery terminals into a battery buss bar.

    You should also have a properly sized fuse/breaker protecting the circuits, one for the heavier wire from buss to battery, and a smaller one between controllers.

    If there is much voltage drop between the left and right controllers, there could be an issue where the right hand controller "sees" a different battery state of charge than the left. In that case, the left controller may want to supply absorb voltage too long. Probably not a big deal, but something to watch for.

    As LH2 said, if the panels were close in Vmp, a single controller would suffice. You said they have different voltages though. I'm a bit surprised a 60w and 120w would be anything other than ~18Vmp. If they were, I'd use a single PWM controller, and call it a day.
    Off-grid.  
    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
  • aspnaspn Registered Users Posts: 3
    Good morning, thanks for your answers.

    The 110W has 18,56V (Vmp) 21,9V (Voc)
    and the 60 W has 20,88(Vmp) 24,64V(Voc)

    I think the bigger problem is that the panels are placed on different spots on the van. That one is getting less light in the late hours than the other and then its more of a problem i think?

  • mcgivormcgivor Registered Users Posts: 1,190 ✭✭✭✭
    Having both  panels in parallel, using one controller should be fine, if one has less sun it simply would contribute less with little or no effect on the other, much lIke having a shaded panel in a parrallel array.

      1500W, 6× Schutten 250W Poly panels , Schneider 150 60 CC, Schneider SW 2524 inverter, 8×T105 GC 24V nominal 

  • BB.BB. Super Moderators Posts: 26,758 admin
    Two things. Pick a clear noon day--Set up the panels (same angle, facing sun) and run three tests. Panel A output, Panel B output, Panel A+B output. See what the difference is (small difference, use one controller). Note, the battery bank has to be fairly discharged/have a large constant load. If the battery is >~80% state of charge and the controller is at Absorb (~14.75 volts or so), then the battery will be limiting the charging current, not the panels+configuration questions.

    Second, if you have two (or more) charge controllers), I highly suggest that you do the first wiring. Each controller has its own "home run" to the battery bank. When you connect them in series (like #2), the added current and voltage drop can reduce charging current. And, some charge controllers do behave a bit squirrelly if they are connected to a "noisy" output--The noise from one controller can confuse the other controller and reduce the charging current.

    And lastly, you should have fuses/breakers for all + wires that leave the battery bank (especially if you have a larger battery bank and/or smaller diameter wires). You want the fuse to blow vs the wiring get hot and possibly start a fire if there is a short circuit somewhere.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • aspnaspn Registered Users Posts: 3
    Great forum!!!
    Thank you all for your tips.
    @BB I will try that tomorrow.

    Cheers,
    Pat
  • EstragonEstragon Registered Users Posts: 1,416 ✭✭✭✭
    @BB.

    I have 2 charge controllers (2 classic 150s), soon to be 3 (adding a Morningstar PWM with vertically mounted panels to float over winter), all connected or to be connected to battery +/- buss bars. Also a couple of inverters. It seems to work okay.

    The (parallel?) connection on the controller on the right in the second diagram seem to me as being not so different than a battery buss bar. When adding the PWM, should I be going directly to the battery, or add to the busses?
    Off-grid.  
    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
  • BB.BB. Super Moderators Posts: 26,758 admin
    It does depend on the wiring back to the battery bank. Longer run of smaller diameter wire is worse.

    And battery bus bar/common connections have lower resistance to the battery bank  (which also acts like a large filter capacitor which helps reduce controller cross-talk).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • EstragonEstragon Registered Users Posts: 1,416 ✭✭✭✭
    IIRC the wire to the bank from buss is 4/0 and ~6', which, assuming good connections, should be pretty low resistance. So if I'm understanding correctly, the bank should still act as a capacitor even though the controllers are connected to a common buss?
    Off-grid.  
    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
  • BB.BB. Super Moderators Posts: 26,758 admin
    There is also the inductance of the wiring. A capacitor at one end, the "long" inductive wiring, and low resistance makes for a "High Q" oscillator. Hit that with square waves (PWM from charge controller) and you can have a nice oscillator.

    Not saying that will be a problem here. Just an example of what can happen.  Bundle tying the plus and minus called together lowers the cable inductance (which helps move the natural frequency higher. ... and out of resonates ).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • EstragonEstragon Registered Users Posts: 1,416 ✭✭✭✭
    Ok, thanks. Will have to do some reading before finalizing the wiring on the new PWM and panels. Bundling the +/- wires to the bank would mean putting the batteries in a U shape instead of the straight line with +/- at each end, which the box may not accomodate.
    Off-grid.  
    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
  • BB.BB. Super Moderators Posts: 26,758 admin
    You do the best you can with what you have.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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