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  • Depth Of Discharrge and Charge Controllers

    Hi everybody,

    I've a question regarding Charge Controllers and Depth Of Discharge. When sizing a Off Grid PV System and the Battery bank you have to make a decision about Depth Of Discharge. I do understand the relation between DOD and Cycle life of batteries. My question is if you designed the system with a DOD of 50%. How does the Charge Controller knows when to stop discharging at 50%? Is it a setting on every charge controller or? Please help me out on this. Most appriciated.

  • #2
    If you are going to set it, it would be on the inverter. The CC controls charging not discharging
    OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

    Comment


    • Bendesa1962
      Bendesa1962 commented
      Editing a comment
      Well I'm confused now. Not sure if you are correct. Please check this out http://www.voltaicsystems.com/blog/s...ry-protection/

    • ButchDeal
      ButchDeal commented
      Editing a comment
      Those are tiny little systems. You posted in the bimodal system section. This is about house sized systems. The charge controller on these systems only controls charging from solar. The inverter/charger controls the level of discharge and the grid based charging.

  • #3
    Ok I see wrong forum. Sorry about that. I'm new here. I'm going to repost it in the Off Grid Section Thanks for your replies

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    • ButchDeal
      ButchDeal commented
      Editing a comment
      Sorry but it will be the exact same answer for off grid. The web page you linked is about tiny systems. Of grid is similar to bimodal in the way they work.

  • #4
    That's my understanding. But I'm not sure if I agree with your answer to be honest butch. I know charge controlllers can be set to minimum charge rates for the battery and the connection between the battery bank and the inverter goes trough the charge controller right?

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    • #5
      That is your mistake right there. Do not run the connection for the inverter through the charge controller. Unless you have a very small inverter the connection is not rated for the amps.
      OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

      Comment


      • #6
        Originally posted by Bendesa1962 View Post
        ..... I know charge controlllers can be set to minimum charge rates for the battery
        MAXIMUM rate is the RECHARGE setting, so if you have over-paneled your system to insure cloudy winter harvest, you don't cook the batteries in the summer.
        Controllers control charge RATE


        and the connection between the battery bank and the inverter goes trough the charge controller right?
        Wrong. Inverter gets wired to battery just like the controller gets wired to the battery (each with the appropriate gauge wire and fuses)

        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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        • #7
          ok Well thanks a lot so far everyone. I'm not sure yet if I have the whole picture. If neccesary I get back on it. Once again thanks for your answers i do appriciate it

          Comment


          • #8
            Originally posted by ButchDeal View Post
            That is your mistake right there. Do not run the connection for the inverter through the charge controller. Unless you have a very small inverter the connection is not rated for the amps.
            +1

            The fact that many (especially small) CCs have a set of LOAD terminals does not mean that is the place to connect the inverter.
            Some CCs double as solar lighting controllers and use the LOAD terminals to turn the lights on when the sun goes down and turn them off at a programmed time or when the battery voltage drops too low.

            Bendesa1962:
            If you want to try to use the LOAD terminals to serve as a Low Voltage Disconnect (LVD) for your inverter you can use LOAD to drive a relay that opens and closes a contactor in the DC leads to the inverter. Unfortunately many of the CCs that have LOAD terminals have a fixed LVD voltage setting that is far too low for proper battery protection.
            SunnyBoy 3000 US, 18 BP Solar 175B panels.

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            • #9
              It is rather difficult to determine the exact charge state of the battery just from a voltage measurement. The voltage will depend to some degree upon the amount of load at the time, at rest will be different, so will at even a slight charge. I have a load that draws 10 times the current at startup so a time element also has to be included. Inverters have a low voltage shutdown voltage and that is primarily to protect the inverter from poor wiring. Those voltages are as low as 10.5 volts which will for sure destroy a battery over time. In my system I don't want tp drop below 80% and I use a microprocessor to monitor the state of charge. My functions only operate during the day and they won't start unless the voltage is well over 13V. It is understandable you think think that you have asked a simple question. Setting that dropout voltage depends on what your typical loads are and how critical they are to run. Sometimes it is ok to sacrifice battery life.

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              • #10
                Originally posted by Bendesa1962 View Post
                ok Well thanks a lot so far everyone. I'm not sure yet if I have the whole picture.
                Trust us, you do not have a clue.
                MSEE, PE

                Comment


                • #11
                  Hi there,

                  Regarding your question, I think you need to manually switch off the load ensure you only discharged 50%.

                  Sometimes you may not need to manually switch off the load if you have an automatic controller such as a photosensor for street lighting systems. Thats what I did in my house. I oversized the battery to get a 50% DOD based on 11 hours operation and used a photosensor and DC LED lamps.

                  hope that helps.

                  Comment


                  • #12
                    Hi Boss,
                    Regarding the DOD and SOC charge % calculation the manufacturer use simply measurement relation between current voltage temperature and battery profile. the shunt resistance plays important roll when measure the battery DOD and SOC. For DOD and SOC use to trigger the relay to start up and OFF the GENSET the best controller is ELTEK. But it will give you better result when use high capacity battery like 1500AH/2v-48VDC. and for the 1500AH battery the 1% will be 15Amp which will decrease after certain time period and so on. the time period calculation is based of Battery voltage, current passed through shunt, Battery temperature and battery profile......

                    Thanks,

                    Barca

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