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  • Blocking diode getting hot

    Hi,

    I was wondering if anyone could help me with a problem as I am new to solar panels.
    I have installed a 80w solar panel to a boat with a marlec wind/solar regulator. The details from marlec stated a blocking diode was needed. I installed one to the positive side of the solar panel ( p600d rectifier) that should be capable of doing the job. My question is should the diode be getting extremely hot. Too hot touch when there is full sunlight. The wires have not started to melt yet but I am getting concerned. I have seen diodes with heat sinks but sure for a 80w panel this would be over kill. Have I done something wrong or is this normal with diodes?

    Any help would be great,

    thanks

    Jamie

  • #2
    Originally posted by J4mie82 View Post
    Hi,

    I was wondering if anyone could help me with a problem as I am new to solar panels.
    I have installed a 80w solar panel to a boat with a marlec wind/solar regulator. The details from marlec stated a blocking diode was needed. I installed one to the positive side of the solar panel ( p600d rectifier) that should be capable of doing the job. My question is should the diode be getting extremely hot. Too hot touch when there is full sunlight. The wires have not started to melt yet but I am getting concerned. I have seen diodes with heat sinks but sure for a 80w panel this would be over kill. Have I done something wrong or is this normal with diodes?

    Any help would be great,

    thanks

    Jamie
    The diode is too small for the amount of current you are putting through it.
    It should be a low voltage (Schottky) diode. If it is a standard rectifier diode it will have a forward drop under load of about 1V. If your panel puts out 6A then it will dissipate ~7 watts and will for sure need a heat sink.
    Get a better diode and maybe a heat sink for it.
    A modern PV/RE type charge controller will have the diode function built in.
    SunnyBoy 3000 US, 18 BP Solar 175B panels.

    Comment


    • #3
      You diode current rating is too low is my guess. It makes it to physically small to dissipate the amount heat generated. It is also guaranteed to fail from excess current. Easy fix get one sized appropriately.
      MSEE, PE

      Comment


      • #4
        What type if Schottky diode should I get? I'm not to clued up on diodes and specs. I have a 80w solar panel with max amp about 4/5 amps. That's why I thought a P600d would be fine having a 6 amp/200v rating.

        Comment


        • #5
          Originally posted by J4mie82 View Post
          What type if Schottky diode should I get? I'm not to clued up on diodes and specs. I have a 80w solar panel with max amp about 4/5 amps. That's why I thought a P600d would be fine having a 6 amp/200v rating.
          The P600D is a standard silicon rectifier diode, and at its rated current of 6A will typically have a forward voltage drop of 1.1V. That makes nearly 8 watts that have to be eliminated either by air convection around the diode or by conduction down the leads.
          It is not at all surprising that the diode gets too hot to touch, even though it may survive that operation just fine.
          The diode will operate at up to 175C (ouch) although at that temperature it can handle essentially zero current.

          I would look for a Schottky diode with a rating of at least 10A to preserve a low voltage drop.
          Something like this: https://cdn-reichelt.de/documents/da...10100%23ON.pdf will waste only 4 watts at 6A and can be bolted to a heat sink (could be just a simple aluminum plate) to reduce the temperature.
          SunnyBoy 3000 US, 18 BP Solar 175B panels.

          Comment


          • #6
            Thanks for all the advice, I have unclipped the solar panel for now till I get the correct diode.

            I'm still a bit confused on what all the specs mean. I understood that the diode allowed the current produced from the solar panel to pass through to the battery with little resistance meaning little heat?
            Then at night when the voltage of the the solar panel drops below the battery voltage the current from the battery is pushed into the solar panel. This is why a diode is used to block the current using the high resistance properties of the diode. Shouldn't the diode be hotter at night if it's causing the most resistance then?

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            • #7
              Will this diode be ok

              http://www.amazon.co.uk/gp/aw/d/B00C...&pi=SX200_QL40

              Comment


              • #8
                A stadard silicon diode drops .7 v across it in passing the current from panel to charge controller.. example panel output 19.7v voltage on output side of diode will be 19v..

                Diodes are very useful in doing this in many applications.. and can be connected in series to give a fairly accurate voltage reduction of any amount..

                If you are using any reasonable charge controller it should have the diode already built in..

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                • #9
                  Originally posted by Sunny Solar View Post
                  A stadard silicon diode drops .7 v across it in passing the current from panel to charge controller.. example panel output 19.7v voltage on output side of diode will be 19v..

                  Diodes are very useful in doing this in many applications.. and can be connected in series to give a fairly accurate voltage reduction of any amount..

                  If you are using any reasonable charge controller it should have the diode already built in..


                  The charge controller I am using is primarily designed for a wind turbine which shunts power back to slow the blades on the turbine when the battery is full.

                  Will diode work?
                  http://www.maplin.co.uk/p/mbrf1645-1...ectifier-n25cc

                  Comment


                  • #10
                    Originally posted by J4mie82 View Post
                    Shouldn't the diode be hotter at night if it's causing the most resistance then?
                    If its resistance to (reverse) current flow is high enough (which it is) then there will be virtually no current flowing and therefore the I2R losses will be insignificantly small.

                    --mapmaker
                    ob 3524, FM60, ePanel, 4 L16, 4 x 235 watt panels

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                    • #11
                      New diode

                      I received my new Schottky diode in the post and will install it today. The diode will be fitted I between two sections of wire. Is it ok to just solder the terminals on? Will this diode also get hot? I have a small heat sink to attach but this is only 3cm by 5cm.

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                      • #12
                        If this diode works, the next thing to figure out is if this marlec regulator (with your diode) does a good job of maintaining your batteries.

                        As inetdog mentioned, modern, configurable charge controllers do not need external diodes. The purpose of a charge controller is to properly maintain the battery. The battery is the heart of the system. It may be foolish to go cheap on the charge controller.

                        I'm not familiar with Marlec Regulators... I looked at Marlec's web site... I didn't see much technical information on their charge regulator. I have no idea how well this regulator will treat your battery... Do you? Are you sure this charge regulator is worth the effort you are putting into this endeavor?

                        --mapmaker
                        ob 3524, FM60, ePanel, 4 L16, 4 x 235 watt panels

                        Comment


                        • #13
                          Originally posted by mapmaker View Post
                          If this diode works, the next thing to figure out is if this marlec regulator (with your diode) does a good job of maintaining your batteries.

                          As inetdog mentioned, modern, configurable charge controllers do not need external diodes. The purpose of a charge controller is to properly maintain the battery. The battery is the heart of the system. It may be foolish to go cheap on the charge controller.

                          I'm not familiar with Marlec Regulators... I looked at Marlec's web site... I didn't see much technical information on their charge regulator. I have no idea how well this regulator will treat your battery... Do you? Are you sure this charge regulator is worth the effort you are putting into this endeavor?


                          Haha you're trying to get me worried now. I think the charge controller is old but have checked it when it with a multimeter and the regulator cuts in at the right voltage and also trickle charges at the right voltage 14.4v

                          I have checked what voltage the battery starts to gas at with a wall charger and it does not gas 14.4 volts. I also have the wind turbine I am currently fabricating parts for specific to this regulator so don't really want to change.

                          I have put the link to the exact model I am using.

                          I run a 45w tv, 2 strips of 0.5a LEDs, and a water pump off a 88ah battery. The tv is only used for 4 hours a day. The lights an water pump are only used sparingly so don't add up to much. The setup is only used at weekends. I would like to use the tv for a lot longer and therefore want to use the turbine for winter months.

                          Thanks for the info. I am a biology teacher haha so only really go up to gcse physics

                          http://www.marlec.co.uk/wp-content/u...ers-Manual.pdf
                          Last edited by inetdog; 08-15-2014, 01:00 PM. Reason: fixed quote tag

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                          • #14
                            A diode of the proper size, is most likely NOT going to be able to be soldered in, it will have bolt/lug connections. It WILL need a heatsink.

                            80W @ 12V is about 7 amps..... into a .5V drop across a Schottky diode Volts x Amps = 4 watts. Not a trifle amount of power to dissipate.
                            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

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                            • #15
                              There is now a way to cool that "diode" and perhaps waste less energy. The idea is to replace the diode with a MOSFET
                              transistor, which has an inherent diode. Then an additional circuit is added to turn on the MOSFET whenever the inherent
                              diode is forwarded biased, tuning the MOSFET into a very low resistance short (depending on its size). Of course it must
                              be turned off if current tries to reverse, to preserve the diode function. An LM74610-Q1 attached to an appropriate 'FET
                              is available to do the function, providing the reverse voltage doesn't exceed 45V. I have built such systems with
                              capabilities of 72V and 90A, with good results. Bruce Roe

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