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  • Diodes in junction box

    I am searching for a new junction box. Some have double the amount of diodes. Does it matter? do the amount of diodes correspond to the wattage of the panel?
    I have a 175W 24V panel missing the junction box. I tried a box rated from 200W -300W. It has 6 diodes. I only got 11.7V. When I tested the busbars before putting the junction box on I was getting 32.7V.
    Can someone please explain how the diodes and junction box work, or which way the current flows (diagram). Sometimes it is better to understand how it works than be told how to do it.
    Thanks.
    Last edited by steff503; 08-17-2018, 05:49 AM.

  • #2
    11.7A....32.7A??? surely you are referring to volts, not amps.

    You must have something connected wrong. Sounds like you are only getting voltage from 1/3 of your panel . A 72 cell panel will be split up by the diodes into 3 banks of 24 cells.

    There's others here who can give a clearer explanation of how diodes work to bypass shaded sections of your panel. There's a chance some of the diodes are connected backwards.as they are directional.
    Last edited by littleharbor; 08-16-2018, 08:45 AM.
    2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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    • #3
      HA, Yes Volts. When I test the bus bars coming out of the panel, it has no junction box, I get 32.7 V. When I hook up the junction box, I get 11.7 V.

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      • #4
        Diodes have an Anode (+) and a Cathode (-). The Cathode (-) is marked by a stripe, a dot, or a small cut on one end of the housing, or some other means.

        An easy way to remember how diodes hook up is to hook the - side (which is marked) to the + of whatever it is.

        So in a junction box, the blocking diode hooks across the - and + leads coming out. And the - side goes to the + lead.

        This works for both bypass and blocking diodes.

        As far as how they work........well they only let current flow one way through them. You can test this with a volt-ohm meter.

        Blocking diodes only let current flow OUT of a solar panel......and prevent current from flowing IN.

        ByPass diodes are a little tricky, but what they do is let current flow AROUND some of the cells in a panel. That's why you have several diodes in some junction boxes.

        The panel is split internally into sections, and each section has a bypass diode, so if say a big ass leaf falls on the panel and blocks a cell, the current can flow around the section that cell is in.

        Hope that helps

        z
        Last edited by Zardiw; 03-31-2019, 11:08 AM.

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