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  • #61
    Just to give a restart/review for this extensive thread:

    1. If you cannot charge your batteries fully if you limit your charging to the current and voltage limits the battery manufacturer recommends, you are screwed. :People with very low sun hour numbers (high latitude, for example) will need to use batteries such as AGM which will accept charging at a higher rate.
    2. If you can stay withing the battery manufacturer's parameters but end up tripping the inverter as a result, then a voltage dropping diode may work for you, but an elegant solution will use a relay to switch the diode out of the circuit when the batteries are not being charged. The extra power to actuate the relay (Normally Closed contacts in parallel with diode) can easily be spared during charging. No diode drop and no relay drain when pulling down the batteries after the PV has cut off.
    SunnyBoy 3000 US, 18 BP Solar 175B panels.

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    • #62
      Originally posted by inetdog View Post
      Just to give a restart/review for this extensive thread:

      1. If you cannot charge your batteries fully if you limit your charging to the current and voltage limits the battery manufacturer recommends, you are screwed. :People with very low sun hour numbers (high latitude, for example) will need to use batteries such as AGM which will accept charging at a higher rate.
      2. If you can stay withing the battery manufacturer's parameters but end up tripping the inverter as a result, then a voltage dropping diode may work for you, but an elegant solution will use a relay to switch the diode out of the circuit when the batteries are not being charged. The extra power to actuate the relay (Normally Closed contacts in parallel with diode) can easily be spared during charging. No diode drop and no relay drain when pulling down the batteries after the PV has cut off.
      Another approach is use an MOSFET transistor which looks like a diode when biased off. When the
      diode is conducting (backward for the FET), you can apply turn on bias, and the drop will become
      the FET resistance. Power to turn on essentially zero, resistance can be managed. The bias will
      need to be removed if current reverses. I have equipment working this way at 90A. Bruce Roe

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      • #63
        I followed this older discussion on inverter tripping problems, unfortunately, I made an uneducated mistake and invested in a DC/AC 1000W inverter (Go Power) never realizing that it's max input power is limited to 15V. I charge my batteries with MPPT-60 Morningstar with temperature sensor and commonly see well over 15v coming out from the controller on colder mornings. This trips the inverter and requires a manual reset of the unit - this is not convenient at all as the equipment is located outside.
        I noticed the last comment on use of MOSFET as opposed to a simple diode to avoid power losses. There was another earlier poster proposing the use of high voltage LDO: http://www.solarpaneltalk.com/showth...ll=1#post42154
        Would you please be so kind and let me know more about implementation of such solution? My electrical/electronic knowledge is quite minimal and I wouldn't be able to design this on my own. Unfortunately, I am not in a position to invest in another, better quality inverter at this time.

        Thanks a lot!!
        Joe

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        • #64
          The proposed solution with the MOSFET (or other better semiconductor type available now) was not to try to regulate the voltage using a series pass element but simply to turn the voltage dropping diode on and off as needed. You would still need a high power diode in parallel with the MOSFET.
          SunnyBoy 3000 US, 18 BP Solar 175B panels.

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          • #65
            Right, I was not correct in saying "as opposed to a simple diode" instead of "in parallel" - this shows how limited my ele knowledge is. Nevertheless, could you please advise on a design involving the diode and MOSFET (or other better semiconductor) in parallel to turn the voltage dropping diode on and off (preferably adjustable)

            Thanks a lot.
            Joe

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            • #66
              I believe the intent here is to add a series diode or 2 to the circuit, to reduce the peak voltage
              a bit. Such diodes could be shorted when not required, to improve efficiency. Shorting could
              be done with a robust switch or relay. Just how you'll control them isn't obvious.

              One approach I have used in designs up to 60V and 90A, is to use N channel MOSFETs as
              switchable diodes; the control power could be a 9V battery which will last shelf life.

              If you short the MOSFET gate to the source, the source to drain wil appear as a diode, with
              conduction in the reverse direction from normal linear operation: the source more positive
              than the drain. This diode may be shorted out by turning on the MOSFET, by connecting the
              neg of the 9V to the source and the pos to the gate, instead of the short. The only voltage
              drop will be across the S-D resistance. Paralleling MOSFETs works since they have a positive
              temp coefficient.

              Of course an on MOSFET becomes a short in either direction between S-D. That may not
              matter here. You could also use external diodes to be shorted, seems like a waste. Bruce Roe

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              • #67
                Never mind.

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