Announcement

Collapse
No announcement yet.

Bypass and blocking diodes

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Bypass and blocking diodes

    I understand these perform different functions. What I cannot ascertain is whether or not the diodes are actually the same piece of kit, just installed differently? I have two BP 350 Solar 50W panels that I will connect in parallel. These, together with a wind generator will charge a 4x115AH battery bank thru a fused charge controller.
    I need 9A 45v 'bypass' diodes on each panel plus 5A 45v 'blocking' diodes.
    OK, I have identified the 'blocking' diode I need (SB540) - it's a straightforward axial schottky 'power' diode.
    When it comes to a 'bypass' diode I become confused (by the terminology) because no manufacturer I have checked lists their diodes as 'bypass'. Is this because 'bypass' simply refers to the actual function to which a regular 9A 45v 'power' diode is being used?
    I welcome the advice that your learned community can offer me.
    Many thanks,
    Geoff

  • #2
    Originally posted by Geoff Nebel View Post
    I understand these perform different functions. What I cannot ascertain is whether or not the diodes are actually the same piece of kit, just installed differently? I have two BP 350 Solar 50W panels that I will connect in parallel. These, together with a wind generator will charge a 4x115AH battery bank thru a fused charge controller.
    I need 9A 45v 'bypass' diodes on each panel plus 5A 45v 'blocking' diodes.
    OK, I have identified the 'blocking' diode I need (SB540) - it's a straightforward axial schottky 'power' diode.
    When it comes to a 'bypass' diode I become confused (by the terminology) because no manufacturer I have checked lists their diodes as 'bypass'. Is this because 'bypass' simply refers to the actual function to which a regular 9A 45v 'power' diode is being used?
    I welcome the advice that your learned community can offer me.
    Many thanks,
    Geoff
    1. Usually blocking diodes are not required, since the blocking function is part of the Charge Controller.
    2. Bypass diodes often do not have to withstand as high a reverse voltage as blocking diodes, and only have to carry the Isc current of the one panel they are attached to (as long as there are not higher current panels in a series string). It is just as important to have a low voltage drop for a bypass diode, or maybe even more important since there may be two or three bypass diodes active when a panel is shaded.
    If you are not in a situation where there is partial shade on one or more panels in a series string, you will not be using the bypass diodes much if at all. In that case, the voltage drop of the bypass diode is not as important and cheaper non-Schottyk diodes may be OK.
    SunnyBoy 3000 US, 18 BP Solar 175B panels.

    Comment


    • #3
      Originally posted by inetdog View Post
      1. Usually blocking diodes are not required, since the blocking function is part of the Charge Controller.
      2. Bypass diodes often do not have to withstand as high a reverse voltage as blocking diodes, and only have to carry the Isc current of the one panel they are attached to (as long as there are not higher current panels in a series string). It is just as important to have a low voltage drop for a bypass diode, or maybe even more important since there may be two or three bypass diodes active when a panel is shaded.
      If you are not in a situation where there is partial shade on one or more panels in a series string, you will not be using the bypass diodes much if at all. In that case, the voltage drop of the bypass diode is not as important and cheaper non-Schottyk diodes may be OK.
      Thank you for your reply.
      There is partial shade on both panels during the day.
      I understand the functions of blocking and bypass diodes.
      I agree that in a simple single module and regulator system, a separate blocking diode is not normally required since one is normally incorporated into the regulator.
      However, when more than one module or a module and another charge source (eg wind generator in my case) are directly connected in parallel, a blocking diode is required in each series string of solar modules. I'm ok with the use of and have identified the correct blocking diodes I require.
      My uncertainty is simply what should I use as bypass diodes? BP advise that a 9A 45V Schottky axial diode should be fitted (BP have pulled out of PV panel manufacture and I have not been able to get any info from them).
      My question is simple: Will a regular Schottky 9A 12V axial power diode be OK to fit as a bypass diode?
      Thanks

      Comment


      • #4
        bypass diodes get wired (3 or 4 of them) into the middle of the PV array. Sometimes they are embedded in the tab wires as SMD diodes, or sometimes in the J-box on the back of the panel. If there are no provisions for them, they are very tough to add.
        Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
        || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
        || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

        solar: http://tinyurl.com/LMR-Solar
        gen: http://tinyurl.com/LMR-Lister

        Comment


        • #5
          Originally posted by Mike90250 View Post
          bypass diodes get wired (3 or 4 of them) into the middle of the PV array. Sometimes they are embedded in the tab wires as SMD diodes, or sometimes in the J-box on the back of the panel. If there are no provisions for them, they are very tough to add.
          Thanks Mike,
          There is provision in the junction box on the underside of the panels.
          Are you able to advise if a particular Schottky 9A 45 diode - I have identified one ref. VS90SQ045 - be ok to use as a bypass diode?

          Comment


          • #6
            hard to do better than a $2 diode. It's a wire lead part, and if your panels are more than a couple of amps, you may want to figure how to heat sink it, 5A @ .5V = 2.5 watts you need to dissipate in a hot box on the roof. It's DC, so any switching speed spec is irrelevant.

            http://www.digikey.com/product-detai...Q045-ND/352059
            Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
            || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
            || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

            solar: http://tinyurl.com/LMR-Solar
            gen: http://tinyurl.com/LMR-Lister

            Comment


            • #7
              Originally posted by Mike90250 View Post
              hard to do better than a $2 diode. It's a wire lead part, and if your panels are more than a couple of amps, you may want to figure how to heat sink it, 5A @ .5V = 2.5 watts you need to dissipate in a hot box on the roof. It's DC, so any switching speed spec is irrelevant.
              Reminder: For Schottky diodes (and diodes in general) be sure to use the current versus voltage curve of the diode to get the voltage drop to use when calculating power, not just the "nominal" forward voltage drop.

              In this case, the maximum forward voltage drop at maximum rated current was used:
              Voltage - Forward (Vf) (Max) @ If 480mV @ 9A
              SunnyBoy 3000 US, 18 BP Solar 175B panels.

              Comment


              • #8
                Originally posted by Mike90250 View Post
                hard to do better than a $2 diode. It's a wire lead part, and if your panels are more than a couple of amps, you may want to figure how to heat sink it, 5A @ .5V = 2.5 watts you need to dissipate in a hot box on the roof. It's DC, so any switching speed spec is irrelevant.

                http://www.digikey.com/product-detai...Q045-ND/352059
                I reckoned two bucks was pretty good too. Thanks Mike

                Comment


                • #9
                  Originally posted by inetdog View Post
                  Reminder: For Schottky diodes (and diodes in general) be sure to use the current versus voltage curve of the diode to get the voltage drop to use when calculating power, not just the "nominal" forward voltage drop.
                  Thanks Inetdog

                  Comment

                  Working...
                  X