sizing of blocking diode (and by pass diode)

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  • shadeson
    Junior Member
    • Jul 2016
    • 3
    #1

    sizing of blocking diode (and by pass diode)

    Hi everybody
    I am trying to understand how I should size the blocking diods in a system where I aim for 90 volts from panels put in parallell. I would like one blocking diod per string of series. Then there can be 2,3 or 4 strings in parallell. Each string will generate 6-7 Amps. So how do choose blocking diodes? Should the Vrrm be a specific one or should it just be able to withstand 100V and 10 A ?

    The next question which I believe I already found the answer to is that the 100w panels that lacks bypass diodes should have a by pass diode that has a Vrrm that at least equals the Vcshorcut
    That is about is about 23V so a Vrrm=25volt ...but that is hard to find so I am guessing I have to choose Vrrm=35V diodes.


    Any help is much welcome!

    PS the attached picture show 4 panels in series but I am actually as I wrote looking at 5 in series but it is the same principle
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    • Mike90250
      Moderator
      • May 2009
      • 16020
      #2
      forget blocking diodes, most of the the modern charge controllers in the last 30 years provide that function.
      Bypass diodes prevent a panel from being totally shut down from stray shadows and such.
      Here's a link to an article about bypass diodes
      Access to this page has been denied
      http://www.digikey.com/en/articles/techzone/2012/dec/active-bypass-diodes-improve-solar-panel-efficiency-and-performance
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        • shadeson
          Junior Member
          • Jul 2016
          • 3
          #3
          Great - thanks for your answer.
          Yes I am aware of the built in function in the regulators BUT when you have a system of several groups in parallell (more than the 2 pairs on the picture) could'nt there be dangerous inbalances when shadowing or break down of panels or several panels in one group ?

            Comment

            • bcroe
              Solar Fanatic
              • Jan 2012
              • 5198
              #4
              Originally posted by shadeson
              Great - thanks for your answer.
              Yes I am aware of the built in function in the regulators BUT when you have a system of several groups in parallell (more than the 2 pairs on the picture) could'nt there be dangerous inbalances when shadowing or break down of panels or several panels in one group ?
              Even a shaded panel will continue to put out a voltage (at greatly reduced current capability) that will prevent back current from other
              strings. For a failure situation, fuses are required, not blocking diodes. Fuses have the advantage of lower forward drop and a safe
              open circuit failure mode, not a short. Bruce Roe

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