Wattage difference at controller

m1noel
m1noel Registered Users Posts: 1 ✭
in Caravan, Recreational Vehicle, and Marine Power Systems #1
I have 5-100W panels on the roof of my RV with a Renogy 40A controller.  Everything has been fine until this week.  The controller is showing panels connected but only at 12.2-12.5 volts and 0 watts.  If I disconnect the wires, my multi tester shows 19-21V coming from the panel.  I have tried 3 different controllers now with the same result, no charge.  I have checked the connections between panels and each panel individually.  I cannot figure this out and am losing sleep trying to come up with the solution.
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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #2
    Are you hooking up the controller to the battery first? This is generally required to establish system voltage.

    Are the batteries full and can't receive more charge? Though the voltage would indicate they aren't...
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,626 admin
    #3
    Which model of controller?
    Sounds like all panels connected in series?
    Any current?
    To pull the panels down to 12.5 volts sounds like apem controller on a relatively discharged 12 volt battery back?
    As Photowhit says connect controller to battery first then connect the array.
    Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #4
    My first thought is there is a bad " high resistance" connection somewhere in the common wiring that feeds the controller  which allows voltage to be measured, but can't pass any current. Assuming this is a PWM controller given the panel output voltage  being 19-21 VOC connect the array to a load such as 2 × 12V lamps in series to verify there's is actually output,  a digital multimeter is not the best tool for fault finding as they have extremely high input impedance, a load is needed to force the failure point into fault.

    Usually when there is a high resistance connection, there will be signs of heat damage, pay attention to all screw type connections with multi stranded wire, the strands have a tendency to creep when crimp ferrules are not used. Check all circuit breakers and or fuses with a load connected, as mentioned above, by checking for voltage across the device, there should be no voltage, ensure all connections are sound. As the fault is common to all the panels, I would start on the common wiring first,

    Should the system have an MPPT controller, there are different tests, details are so important when asking for help.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #5
    m1noel said:
    I have 5-100W panels on the roof of my RV ...

    I have checked the connections between panels and each panel individually. 
    I went back to see why Bill thought the panels were connected in series. Saw the above...

    If your panels are connected in series you will need a MPPT type charge controllers, assuming somewhat standard 100 watt 12 volt nominal panels. 
    Best Solar Panels For RV 2021 or Camper Van Buyer Guide
    If you have an inexpensive PWM charge controller, typical of this application, the panels would need to be wired in parallel.

    If you have a more expensive MPPT type charge controller, they can be connected in series.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,626 admin
    edited June 2021 #6
    I was wondering if in series because of how "easily" the array voltage was pulled to 12.5 volts... And if there was a single "bad connection" or bad panel, that would also account for "crashing" to 12 volts and zero amps... In parallel, a single connection fault at the panels would not do this (unless is was from combiner to controller).

    Admittedly, that is a weak argument... But why I raised the questions (PWM, MPPT, Series or Parallel, etc.).

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