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Diodes for Mitsubishi 110 Watt 12v panels ?

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  • Diodes for Mitsubishi 110 Watt 12v panels ?

    Greetings experts and fellow novices. Question is how to identify replacement diodes for Mitsubishi 110w 12v panels. I "had" Five panels in parallel for an off grid 12v system. Xantrex C40 charge controller and two Xantrex DR2412 inverters for 220vac. Storage is five 12v AGM deep cycle RV / Marine batteries. I say "HAD" because Zeus and his lightning bolt took out one inverter, the charge controller and three of the five panels... I've replaced the entire system (except batteries) with new and current components but this morning it hit me.... Can I repair the three panels and add them to the new system? New system also 12v.

    I dug out the potting material in one of the panel junction boxes and sure enough, one of the two diodes inside it is destroyed. The bad diode is shorted no matter the panel in light or covered. Removing the diode changed the output of the panel about 15v in the shade of the covered porch with no load connected.

    NOTE: Before doing anything to the panel in full sun it supplied about 3v while the two good panels provide 17v +-.

    These panels have 36 cells, and two diodes. Any idea what specific diodes these are? Since the panels are installed in an area where there is no opportunity for shade, do I even need the diodes? If they are not needed, do I simply un-solder and remove them leaving an open circuit or do I replace them with a wire "short"?

    Thanks in advance,
    John,
    East Alabama

  • #2
    The diodes are each in parallel with half of the cells in the panel.
    Replacing the diode with a wire short will restore the shorted out condition you had with the failed diode in place, so no that is not the way to go.

    As long as you are running all of your panels in parallel rather than making up a series string and using an MPPT controller, the diodes are not serving any useful purpose.
    Any condition that would activate a diode would drop the voltage output of that panel so low that it would not contribute to battery charging anyway.
    SunnyBoy 3000 US, 18 BP Solar 175B panels.

    Comment


    • #3
      Originally posted by inetdog View Post
      The diodes are each in parallel with half of the cells in the panel.
      Replacing the diode with a wire short will restore the shorted out condition you had with the failed diode in place, so no that is not the way to go.

      As long as you are running all of your panels in parallel rather than making up a series string and using an MPPT controller, the diodes are not serving any useful purpose.
      Any condition that would activate a diode would drop the voltage output of that panel so low that it would not contribute to battery charging anyway.
      Inetdog: After reading your note about replacing a shorted diode with a wire I started laughing because... What the hek was I thinking?

      Is seems that I can just cut out the diodes because my installation is all 12volt panels in parallel with a MPPT controller and in an area where they are not subject to shade. Is that correct? Thank you for such a speedy response!

      John

      Comment


      • #4
        Originally posted by johnnybravo View Post
        Is seems that I can just cut out the diodes because my installation is all 12volt panels in parallel with a MPPT controller and in an area where they are not subject to shade. Is that correct?
        Yes.

        If you are feeling particularly organized, you might want to add a sticker or Sharpie note to the effect that the bypass diodes have been removed from those panels.

        Note that if there was also lightning damage to the cells themselves you may not be able to get the combination of full Vmp and full Imp from the panel. In that case it is probably not worth keeping.
        SunnyBoy 3000 US, 18 BP Solar 175B panels.

        Comment


        • #5
          Originally posted by inetdog View Post
          Yes.

          If you are feeling particularly organized, you might want to add a sticker or Sharpie note to the effect that the bypass diodes have been removed from those panels.

          Note that if there was also lightning damage to the cells themselves you may not be able to get the combination of full Vmp and full Imp from the panel. In that case it is probably not worth keeping.
          Inetdog : Thank you for the guidance. I'll report back on the performance of the panels after diodes removed and installed under load. I'm hoping to take advantage of the extra 500 watts. UH OH. Just hit me that my new C60 charge controller and DC breaker fuses will have to be upgraded to accommodate the extra current....

          Comment


          • #6
            Originally posted by johnnybravo View Post
            I dug out the potting material in one of the panel junction boxes and sure enough, one of the two diodes inside it is destroyed. The bad diode is shorted no matter the panel in light or covered. Removing the diode changed the output of the panel about 15v in the shade of the covered porch with no load connected.
            I'm familiar swith that problem when I attached my battery directly to my panels in reverse polarity. Ooops.

            What you are looking for a "solar Schottky diodes", as they have the least amount of forward voltage drop. You can find them at digikey, and many solar places. Even Amazon has them. Ideally get ones that are "matched", or just try to pair them up as close as you can when you inspect them with a multimeter.

            My suggestion is to over-size them in capacity to dissipate a bit more heat. Don't be stingy with the leads and cut them too short - but don't leave them too long to be a danger either.

            Comment


            • #7
              If you want to put the panels back in service, I'd recommend checking them out first.
              With the bad diodes removed, you could (under strong sun) check the short circuit
              current delivered to a connection to where EACH diode was. Or if they now put out
              plenty of open circuit voltage, connect in parallel with the others and compare
              output current using a clamp on ammeter. Do note IF current flows in the correct
              direction. Bruce Roe

              Comment


              • #8
                Bruce - Thanks for the good advice. Yesterday I removed (cut) the diodes out of the circuits and each panel now measures 17v under the porch facing outward towards heavy overcast/rain. When the sun comes out I'll first test each panel individually under load with an automotive head light. (Best I can do). I do have a clamp meter and can check current - good thinking.

                I appreciate all the advice and guidance. Gaining and additional 500 watts from what was considered trash is a windfall for me!

                Regards,
                John

                p.s. / Correction: The charge controller I have is a Xantrex C60. IT is PWM not MPPT. It's the closest replacement for the zapped out C40 that insurance would cover. I'll have to upgrade to a larger capacity charge controller. Any recommendations?

                My system:
                12v Kyocera 140w (five panels)
                12 foot Solar Tracking frame / home brew.
                Microcontroller tracking controller follows clock centered on solar noon instead of light sensors / home brew.
                Trace 100 amp combiner box.
                Xantrex C60 CC
                Xantrex Freedom SW3012 inverters (two stacked for 220vac)
                Onan 4000 watt genset with a gunked up carb.
                House has two separate AC breaker panels and wiring systems:
                (installed when house was built)
                White outlets = Commercial power
                Grey outlets = PV power (with manual switch to backfeed from commercial)
                Well pump switch to use commercial or PV power.

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