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Bypass Diode Enigma

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  • Bypass Diode Enigma

    Hello all,

    I am finishing 3 identical panels rated at 80 Watts, 24 Volts, & 3.5 Amps. I have installed junction boxes on 2 of them and am in the process of configuring the installation of the diodes. When each panel is tested in optimum solar conditions they produce about 26.5 Volts each. When I install the Back Power Blocking Diode the voltage is reduced by only a few Volts. (apparently normal result) However, when I install the Bypass Diode it is a totally different story. With the Bypass Diode installed the voltage drops to 0.5 Volts. What is going on? I tried changing diodes on both panels because I thought it could be a faulty diode but I got the same results. The type of diodes I am using are these: JF 10SQ050 & DOI 15SQ045. I tried finding the specs online with no luck but I believe they are about 150 Volts and 10 Amps. I noticed that when I was changing diodes while the panels where producing power there was little sparks when the diode made contact with the proper terminal when there should not be any sparks at all if it is touching the correct terminal. The side of the diode with the silver bar is hooked up to the positive terminal and the other side to the negative. By the way I am using a multimeter to test the voltage. Perhaps there is a special way to test the voltage when the bypass diode is installed. Please help!

  • #2
    Originally posted by solar noob View Post
    Hello all,

    I am finishing 3 identical panels rated at 80 Watts, 24 Volts, & 3.5 Amps. I have installed junction boxes on 2 of them and am in the process of configuring the installation of the diodes. When each panel is tested in optimum solar conditions they produce about 26.5 Volts each. When I install the Back Power Blocking Diode the voltage is reduced by only a few Volts. (apparently normal result) However, when I install the Bypass Diode it is a totally different story. With the Bypass Diode installed the voltage drops to 0.5 Volts. What is going on? I tried changing diodes on both panels because I thought it could be a faulty diode but I got the same results. The type of diodes I am using are these: JF 10SQ050 & DOI 15SQ045 I tried finding the specs online with no luck but I believe they are about 150 Volts and 10 Amps. I noticed that when I was changing diodes while the panels where producing power there was little sparks when the diode made contact with the proper terminal when there should not be any sparks at all if it is touching the correct terminal. The side of the diode with the silver bar is hooked up to the positive terminal and the other side to the negative. By the way I am using a multimeter to test the voltage. perhaps there is a special way to test the voltage when the bypass diode is installed. Please help!
    You are putting the bypass diodes in backwards!

    The bypass diodes should only be conducting when current is being forced through the set of cells in the positive direction while they are not getting enough sun to deliver that current on their own.

    When the group of cells is producing current, the bypass diode should be blocking, not conducting.

    If you draw the position of all of the diodes (bypass and blocking) out in a line from the - of the panel to the + of the panel, the bypass diodes should be pointing the same way as the blocking diode, toward the + side of the inverter or battery.
    SunnyBoy 3000 US, 18 BP Solar 175B panels.

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    • #3
      I will try putting the direction of the diode in the opposite way next time the sun is out. But I am pretty sure that I have it in the correct direction. Thanks.

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      • #4
        Originally posted by solar noob View Post
        I will try putting the direction of the diode in the opposite way next time the sun is out. But I am pretty sure that I have it in the correct direction. Thanks.
        If you are putting them in in the correct direction, then the diodes are blown. Check them with an ohmmeter.
        The reading should be low when you connect the red and black meter leads to the diode in one direction and high when you connect them in the other direction. If the measurements are equal and low in both directions, you do not have diodes any more.
        SunnyBoy 3000 US, 18 BP Solar 175B panels.

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        • #5
          Solar not so Enigma

          I tried what you said and it gave me better results but not what I was looking for. Then I began to ponder about the whole assembly of my project to find out if I had mixed up the polarity some where. Turns out that I was under the impression the entire time that the front of the cells where positive. Then it hit me! Light passes though the cell and is converted to electricity, meaning the back is positive and the front is negative. I checked online and sure enough. Wow thats pretty embarrassing. This blunder has set me back about a week and a half. Anyways, sorry to bother with such a foolish predicament. Thanks for your help though. I would have probably been baffled for another month or so without it.

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          • #6
            Originally posted by solar noob View Post
            Light passes though the cell and is converted to electricity, meaning the back is positive and the front is negative.
            Glad to hear that you are back on track!
            Although your mental image of the light passing through the cell to be converted to electricity may help you remember which face is which polarity, it has nothing to do with the way the cells actually work.
            If you shine light on the back instead of the front, the polarity will be unchanged. (Although less light will get through the coating on the back to get to the active area of the cell!)
            SunnyBoy 3000 US, 18 BP Solar 175B panels.

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            • #7
              Originally posted by solar noob View Post
              I tried what you said and it gave me better results but not what I was looking for. Then I began to ponder about the whole assembly of my project to find out if I had mixed up the polarity some where. Turns out that I was under the impression the entire time that the front of the cells where positive. Then it hit me! Light passes though the cell and is converted to electricity, meaning the back is positive and the front is negative. I checked online and sure enough. Wow thats pretty embarrassing. This blunder has set me back about a week and a half. Anyways, sorry to bother with such a foolish predicament. Thanks for your help though. I would have probably been baffled for another month or so without it.
              A few notes there:

              1) The direction of light doesn't matter. Some panels are designed to generate from both sides and the polarity doesn't change.
              2) If photons were electrons instead, and moved from the front to the back of the cell, the back would be negative. Electrons carry negative, not positive, charge.

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