Short circuit voltage and no amperage one one of four panels

Socratic MonologueSocratic Monologue Posts: 30Solar Expert ✭✭
I've read a number of forum posts with essentially the same title as mine, and got bogged down very quickly in technicalities that are far out of my knowledge set.  So here I am in the beginner's section.

I've had a 12v system on my detached garage for around 8 years.  Four 120w panels, two Morningstar PWM controllers in parallel charging 410 AH of golf cart batteries.  Works fine for me in general. 

It has been hard to keep the batteries charged lately, so I checked the panels with a DC clampmeter and found one panel not delivering amperage at all.  I disconnected the leads and measured ~20v from the panel.  I reattached the problem panel to the controller by itself (it had been attached in parallel with another identical panel) and it still outputs zero amps; its partner panel is putting out 8-9 amps today to charge low battery bank.  Each of the other two panels and the second charge controller are about the same (8-9 amps each)  The problem panel and its partner are Solarworld 120w 12v panels about 8 years old.

Is it obvious why this panel is not functioning? What should I do to further troubleshoot?

Comments

  • EstragonEstragon Posts: 2,838Registered Users ✭✭✭✭✭
    For a start, examine the panel very closely. Starting with the mc4 connectors, look for any signs of discolouration (especially black or brown) that would indicate spot overheating or water intrusion.

    Also, I'd look for signs of corrosion on the connectors.
    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
  • Socratic MonologueSocratic Monologue Posts: 30Solar Expert ✭✭
    I did poke around inside the junction box (no mc4 connectors), and there is a some darkening of the cable insulator near the end.  Looks more like heat than water to me, but I guess I might not be able to tell the difference.  Possibly simply a deteriorated connection inside the junction box?
  • BB.BB. Posts: 27,883Super Moderators, Administrators admin
    If you can open the junction box on the back of the panel, you might find loose or corroded connections.

    A few vendors have had mfg and design problems that made panels fail in 5 years.

    Look for light coffee Collee colored stain under the glass over the j-box on the rear of the panel. (Over heated wiring).

    Signs of water infiltration. Lifted bus wiring, burned cells, etc.

    About the only thing easy to fix are connections in a j-box with service access.

    Otherwise try for a warranty replacement or purchasea new one.

    Make sure the panel mounting frame does not flex or rack. Solar panels should not be stressed.

    On some occasions, partially shaded panels can causea bypass diode to overheat and fail. They are in the j-box. Can be replaced in j-box with access

    Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • EstragonEstragon Posts: 2,838Registered Users ✭✭✭✭✭
    A bit of corrosion at a connection or just looseness could certainly cause enough heat to darken insulation. The panel could look okay for open circuit voltage, and fail only with significant current flowing.
    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
  • littleharbor2littleharbor2 Posts: 1,027Solar Expert ✭✭✭✭
    If you can access the buss tabbing coming out of the rear of the panel into the junction box you might be able to load test the panel that way and eliminate the problem as being an internal (encapsulated) flaw/break which isn't easily fixed. The j-box connections, diodes or leads should be repairable.

    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.

  • Socratic MonologueSocratic Monologue Posts: 30Solar Expert ✭✭
    It was a matter of a bad connection due to corrosion in the junction box.  I stripped the wires back a bit and it seems to be operating normally.  I feel dumb for having asked for advice on this, but I don't (yet) know all the ways that PV panels act oddly compared to simple typical electrical circuits, and so I was really overthinking things.

    Thanks for all the advice.  It is really valuable to have this forum to depend on for even these little issues.
  • EstragonEstragon Posts: 2,838Registered Users ✭✭✭✭✭
    Don't feel dumb. None of us knows everything about everything. The point of a forum is kinda take a penny, leave a penny.
    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
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