Inverter system failure

kansaskansas Solar Expert Posts: 100 ✭✭
My solar system is 4 years old.  It consists of 2 Kyocera 140 watt 12 volt panels; Morningstar ProStar 30 amp 12/24 charge controller: and a Morningstar SureSine 300 watt Sine Wave Inverter. The service panel is a Midnite Big Baby Box with Midnite VDC breakers for the panels to controller circuit; controller to battery circuit; and battery to inverter circuit.  The batteries to inverter circuit is also protected by a 110 amp DC fuse. The system sees only occasional and limited use and the two USREGC2 battery are very rarely discharged below 90% as measured by a Trimetric TM-2025. The inverter has a remote off/ on switch.  Other than a high voltage disconnect on a very cold and sunny day several years ago, the system has worked without a hitch. 

A couple of days ago the inverter shut down.  The demand on the inverter at the time of the shut down was low and no breakers tripped.  The AC Output LED and the Status LED on the inverter were both red, indicating (per the manual) an Inverter or System Fault.  I shut the entire system down and, per the inverter manual, disconnected all wiring to the inverter and removed the cover to check the fuses, all of which were intact. After putting everything back together and restarting the system the inverter worked as it always has.  A day later it failed again, again showing both red lights.

When I then began to shut the system down for a second time by first flipping the panels to controller circuit breaker, the inverter came back to life.  That didn't make sense to me and I suspected a loose connection of some kind.  I went ahead and shut things down and checked for loose connections.  I was able to get a feeble squeak out of two of the breaker terminal, but I would say everything was dead tight. A day and a half later the inverter shut down for the third time and the shutdown was again remedied by flipping and resetting the panels to charge controller circuit breaker.  When the inverter is on and working properly it is unaffected by opening the panels to controller circuit. Opening and closing the inverter to battery circuit would not restart the inverter after these failures.

Any ideas as to what's going on?  The system components are housed in a tightly closed cabinet in a cellar under my cabin. They get cold but rarely as cold as freezing, never get hot and are not subjected to high humidity.  The SureSine is hardened against harsh environments anyway and looks brand new, inside and out.  I would conclude that the inverter need repair (is that possible?) or replacement if not for its behavior in response to the panel to controller circuit.  Should I replace the panels/ controller circuit breaker?  It doesn't make sense to me. 

Thanks - Bill

Two 140 watt Kyocera panels, wired in parallel; Ironridge top of pole mount; two 6 volt, 242 AH US batteries, wired in series; Morningstar ProStar 30 charge controller and SureSine 300 inverter; Trimetric 2025-A meter; IOTA DLS-45 charger, Honda EG3500X generator; Aermotor 702 water pumping windmill.


  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    edited November 2018 #2
    Do you have 12 VDC (10.5 to 15.0 volts) to the inverter DC input terminals?

    Flip the configuration switches on the bottom of the inverter (standby, minimum voltage, etc.)... Just to make sure the contacts are mating properly.

    Check all of the terminals from battery to AC inverter input... Tight and clean, no browning (not getting hot from dirty/loose connections). No corrosion (I have had a few main panel problems because rain water followed the wires down to bus bar/breaker connections--and corrosion).

    Without an AC load, does the inverter start and stay running? (standby power? good 12 VDC to inverter input?).


    I should add that ~5 years to repair and 10+ years is a "good life" for power electronics. Anything over ~5 years old can be difficult to repair (difficult to get parts--It is surprising how fast stuff is obsoleted in the electronics world--Sometimes down to 18 months of production).
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • EstragonEstragon Registered Users Posts: 4,495 ✭✭✭✭✭
    A couple of things to check/try...

    1.  What is the DC voltage at the inverter DC terminals?  Check +ive to -ive, and each to ground terminal.  

    2.  Turn off inverter to battery breaker.  Disconnect the switch circuit and the AC output circuits.  Set dip switch 1 to disable search mode if not already so set.  Turn on DC breaker.  Any lights?  Check AC terminals for voltage.  Turn DC off.  Jumper the switch terminals to force AC on.  Turn DC on.  Any lights?  Check AC terminals for voltage.

    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
  • mcgivormcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    Since the fault is cleared by disconnecting the PV,  it's likely there is a problem on the PV circuit. We're the panels exposed to sun, if so what voltage output is measured both open circuit and when connected to the battery.  When connected to the battery is there current flow, dose the battery voltage increase, is the battery receiving a charge? Measure voltage on the PV input as well as output whilst charging the PV voltage should be slightly higher. Check all external wiring as being exposed to the elements and perhaps rodents could be the source.
    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.
  • kansaskansas Solar Expert Posts: 100 ✭✭
    Good ideas.  I'll let you know my progress.
    Two 140 watt Kyocera panels, wired in parallel; Ironridge top of pole mount; two 6 volt, 242 AH US batteries, wired in series; Morningstar ProStar 30 charge controller and SureSine 300 inverter; Trimetric 2025-A meter; IOTA DLS-45 charger, Honda EG3500X generator; Aermotor 702 water pumping windmill.
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