Announcement

Collapse
No announcement yet.

How charge controllers stop battery discharge

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

  • How charge controllers stop battery discharge

    I am a little confused about something and I hope one of you pros can help.

    So my charge controller is supposed to keep my battery from overdischarging and from over charging. I understand how overcharge protection works because the cc will stop charging the battery when it is full. What I am cinfused about is the discharge protection.

    If I have it setup correctly, then there is nothing between the inverter and the cc to stop stop discharge. So I have the chain like this: Solar pane to CC>> CC to battery>>battery to inverter>>Inverter to load. It seems to me that in order to stop the battery from discharging at a certain point, there would have to be something to cut off the electricity between the battery and the inverter.

    So how can a CC prevent over-discharge? Do I have my system wired completely wrong?

    This instructable says connect the inverter to the charge controller, but that is a heavier load than a light, especially if I have my devices running on the inverter. So that doesn't seem right.
    http://www.instructables.com/id/Solar-Power-System/

    Last edited by wpmasterdesign; 04-21-2017, 05:34 PM.

  • #2
    The only way for the CC to prevent over discharge would be for it to have the ONLY load(s) connected to the load terminals on the CC. Most better controllers don't even have this feature. It is intended to control lighting or some other small loads. While they are supposed to disconnect from the battery in the event of over discharge to protect your battery they are initially meant to turn on a lighting circuit for a preset amount of time. The load terminals are generally limited to the amp rating of the controller. Most all solar systems will have larger load requirements than a simple lighting circuit and thus make the load terminals nearly useless.
    2.2kw Suntech mono, Classic 200, NEW Trace SW4024

    Comment


    • #3
      So you could either add an external Low Voltage Disconnect (LVD) relay or program the LOAD terminal for a reasonable lower limit voltage and use it to drive a relay to cut off the real load connected to the battery through the relay.
      SunnyBoy 3000 US, 18 BP Solar 175B panels.

      Comment


      • #4
        Thats kinda what I was thinking guys. Since I use small modular "as needed" units, I think I am better off doing it how I do now and that is to simply disconnect the battery from the controller when I am not using the power. Thanks for clarifyin!

        Comment


        • #5
          Doesn't your inverter have a low voltage cutoff? Mine do. If the voltage drops too low the inverter will shutoff stopping the discharge.

          Comment


          • #6
            My inverter will set off an alarm when voltage hits about 10.6, and will cut off when voltage hits 10.5.
            The only problem with that is that although you can go as low as 10.5 (50%), everthing I ever read says you should not go below 11.9 (80%) for better battery life.

            Comment


            • #7
              When your batteries are less than full and you hit them with a heavy surge load from the inverter the voltage will sag , then recover. If the LVD on the inverter were say, 11.5 volts then you would be tripping it all the time at anything above idle.
              2.2kw Suntech mono, Classic 200, NEW Trace SW4024

              Comment


              • #8
                Well like I said, due to what I have been told by so many, I never let my batterry drop under 11.9. But I suspect you are correct.

                Comment


                • #9
                  Originally posted by inetdog View Post
                  So you could either add an external Low Voltage Disconnect (LVD) relay or program the LOAD terminal for a reasonable lower limit voltage and use it to drive a relay to cut off the real load connected to the battery through the relay.
                  Thanks so much for this info. Do you know where one can acquire one of these devices that suppirts 100A and ~24V shutoff? Had a difficult time tracking anything down...

                  Comment


                  • #10
                    Way back in the day, didn't they used to say that the charge controller prevented battery discharge back through the panels at night? Could that be what the OP read?

                    Comment


                    • #11
                      You are on the right track - the inverter's own low voltage disconnect is a last-ditch effort to prevent immediate damage. So an external low-voltage disconnect is needed prior to that to be more conservative. Probably the easiest thing to do is re-engineer your system so you never pull more than 50% capacity regularly. A larger battery might be the easiest way to control this.

                      And yes, disconnect the inverter when not in use as many will draw some amount of idle current.

                      Comment


                      • #12
                        Originally posted by wpmasterdesign View Post
                        My inverter will set off an alarm when voltage hits about 10.6, and will cut off when voltage hits 10.5.
                        The only problem with that is that although you can go as low as 10.5 (50%), everthing I ever read says you should not go below 11.9 (80%) for better battery life.
                        That's because they are intended to cut power based on voltage sag instead of theoretical state of charge voltage.

                        WWW

                        Comment


                        • #13
                          Originally posted by wpmasterdesign View Post
                          My inverter will set off an alarm when voltage hits about 10.6, and will cut off when voltage hits 10.5.
                          The only problem with that is that although you can go as low as 10.5 (50%), everthing I ever read says you should not go below 11.9 (80%) for better battery life.
                          11.9 volts is Open Circuit Voltage on a rested battery. That has nothing to do with a loaded battery.

                          I can take a new fully charged 12 volt batter, and make it read 7.2 volts. In fact that is a Industry Test to determine Cranking Amps. Hit a starting battery with 500 amp load and the voltage will crash. So when you see a 12 volt battery with a CA of 500 amps, that 500 amp sis delivered at 7.2 volts on a 12 volt battery. Take the load off, and the battery recovers to 12.6 volts fful charged OCV.

                          10.5 volts on a 12 volt battery under load is 100% discharged. Disconnect the battery, let it rest, and it will recover to 11.9 volts. 10.5 is industry standard to keep your Inverter from destroying the battery. You do not want to raise that voltage. If you do and hit the battery with a heavy load, your Inverter is going to Falsely Trip Off-Line from under voltage when there is nothing wrong except your battery is not sized correctly.

                          MSEE, PE

                          Comment


                          • #14
                            Originally posted by AzRoute66 View Post
                            Way back in the day, didn't they used to say that the charge controller prevented battery discharge back through the panels at night? Could that be what the OP read?
                            Could be, but it's not. The OP was asking about how to prevent the inverter from over discharging the batteries.
                            then there is nothing between the inverter and the cc to stop stop discharge.
                            Charge controllers still prevent back-feed into PV panels at night.

                            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


                            • #15
                              Charge controllers do two things and two things only:

                              Prevent back feed at night
                              Tries it best to charge batteries and does a poor job of it.
                              MSEE, PE

                              Comment

                              Working...
                              X