Announcement

Collapse
No announcement yet.

battery bank

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

  • battery bank

    In stalling a off grid system and my installer wants to use 8x EnergyCell 200GH 12v Front terminal VLRA/AGM for the battery bank how does that sound you all?
    wayne

  • #2
    Like a really bad idea. You want to avoid parallel battery systems.
    MSEE, PE

    Comment


    • #3
      If he is proposing two strings of 4 batteries to make up a 48V system, you might get away with it but it is not optimal.
      But if it is a 12V system, that if far to many batteries in parallel, as Sunking stated.
      SunnyBoy 3000 US, 18 BP Solar 175B panels.

      Comment


      • #4
        it is 2 strings of 4 to make 48 volts. whats recommended then please advise?

        Comment


        • #5
          Originally posted by wkobe88822 View Post
          it is 2 strings of 4 to make 48 volts. whats recommended then please advise?
          Two strings of four is not outrageous, given the availability of batter configurations.
          But if you could find 6V batteries of twice the AH capacity you could put 8 of them in a single string to get your 48 volts.
          Really big banks will use as low as two volt batteries to avoid paralleling multiple strings.
          The weight and size of the battery will be roughly proportional to the number of watt-hours it can store, so going to 1/2 the voltage allows you to go to twice the AH rating.

          At some point, when you end up needing a forklift to maneuver your 2V batteries, you have to break down and start putting strings in parallel.
          SunnyBoy 3000 US, 18 BP Solar 175B panels.

          Comment


          • #6
            So please help me under stand how lower voltage higher amp hr is better? not sure i understand

            Comment


            • #7
              Originally posted by wkobe88822 View Post
              So please help me under stand how lower voltage higher amp hr is better? not sure i understand
              Lower voltage, higher amp hour lets you put the batteries all into one series string.

              For example, your Energy Cell 200GH are 12V, 191AH. When you put them into two strings you get a 48V bank with 382AH capacity.
              If you got 6V batteries at 382AH each (hypothetically, since you have less choice in AGM batteries than you do with FLA), you would still use 8 of them but would put them in one series string of 8=382AH capacity to make up your battery bank.

              The problem with batteries in parallel is that one string or the other will always have a little different resistance and will take/supply more than its share of charging/discharging current. That will become a maintenance problem and will reduce overall battery bank life.

              Now at first impression, somebody who though that you were using the 8 batteries all in parallel to make a 12V bank would call your installer crazy. The details count.
              SunnyBoy 3000 US, 18 BP Solar 175B panels.

              Comment


              • #8
                so how does amps X volt = watts play in to all of this stuff. I can ask installer for any config i want as long as it stays in my budget? We changed the battery to this to get RE batteries 12x OUTBACK POWER ENERGYCELL 200RE, 12V 178AH AGM BATTERY but if there is something better you could recommend that would be great.

                Comment


                • #9
                  Originally posted by wkobe88822 View Post
                  so how does amps X volt = watts play in to all of this stuff.
                  Batteries have stored energy in units of Watt Hours = Voltage x Amp Hours

                  So how much energy does a 6 volt 200 AH battery have?
                  How much energy does a 12 volt 100 AH have?
                  How much does a 24 volt 50 AH have?
                  How much does a 48 volt 25 ah have?

                  How about a 2 volt 4000 AH used in telephone offices? How about 24 of those 4000 AH batteries at 48 volts


                  MSEE, PE

                  Comment


                  • #10
                    Ok that kind of answered my question so the reason to go lower volt batteries is to have a more stable battery bank but 12 volts at 200 amp hours will have more power stored than a 6 volt 200 amp hour battery.

                    Comment


                    • #11
                      Originally posted by wkobe88822 View Post
                      Ok that kind of answered my question so the reason to go lower volt batteries is to have a more stable battery bank but 12 volts at 200 amp hours will have more power stored than a 6 volt 200 amp hour battery.
                      Yes, twice as much energy. Energy is measured in watt-hours. Power is measured in watts.
                      A 6V 200AH battery would be half the size of the 12V 200AH one. So the eight batteries at 6V 400AH would take up about the same total space as the eight 12V 200AH.
                      SunnyBoy 3000 US, 18 BP Solar 175B panels.

                      Comment


                      • #12
                        Originally posted by wkobe88822 View Post
                        Ok that kind of answered my question so the reason to go lower volt batteries is to have a more stable battery bank but 12 volts at 200 amp hours will have more power stored than a 6 volt 200 amp hour battery.
                        Well you are starting to see some light, bu tnot quite there yet. It comes down to weight and performance.

                        On the performance side, parallel batteries cycle life is cut drastically because one strin gof batteries end up doing most of the work. Enough for that.

                        Weight is the main reason, Energy has mass meaning it takes a specific volume and weight to store a unit of energy. Lead Acid batteries Specific Energy Density of roughly 100 pounds per Kwh. So 12 volt 100 AH battery weighs around 120 pounds. A 6 volt 200 AH battery weighs in around 60 pounds.. About the largest 12 volt battery you can buy is 200 AH or 240 pounds.
                        MSEE, PE

                        Comment


                        • #13
                          Originally posted by Sunking View Post
                          Well you are starting to see some light, bu tnot quite there yet. It comes down to weight and performance.

                          On the performance side, parallel batteries cycle life is cut drastically because one strin gof batteries end up doing most of the work. Enough for that.

                          Weight is the main reason, Energy has mass meaning it takes a specific volume and weight to store a unit of energy. Lead Acid batteries Specific Energy Density of roughly 100 pounds per Kwh. So 12 volt 100 AH battery weighs around 120 pounds. A 6 volt 200 AH battery weighs in around 60 pounds.. About the largest 12 volt battery you can buy is 200 AH or 240 pounds.
                          Sunking, correct me if I am wrong but that doesn't add up.

                          Both batteries produce 1.2 kWh ( 12v x 100Ah = 1.2kWh, 6v x 200Ah = 1.2kWh) so they should weight the same. Is the weight related to the voltage as well as the Ah rating of a battery?

                          I agree a 6v 200Ah battery weighs around 60 pounds because I have a couple of 6v 232Ah for my RC and they weight about 66 pounds each.
                          Last edited by SunEagle; 09-20-2014, 10:02 AM. Reason: added last sentence

                          Comment


                          • #14
                            Originally posted by SunEagle View Post
                            Is the weight related to the voltage as well as the Ah rating of a battery?
                            Kwh is the common denominator, not voltage or AH. What I am trying to point out the largest 12 volt battery you can buy is about 200 AH . Well they do make Rail Road 12 volt batteries up to 350 AH but those weigh in at around 300 pounds and not something a home owner is equipped to deal with.

                            So the point here is let's say you want a 1000 AH battery. Forget voltage for a second just 1000 AH battery string. How do you do that? Well if using a 12 volt volt battery forces you to make 5 parallel string using 200 AH batteries. To get 1000 AH batteries means you have to use lower voltage batteries. A 12 volt 1000 AH battery would weigh in around 700 pounds and thus do not exist. However there are numerous 1000 AH 2 volt batteries and they weigh in around a manageable 120 pounds.

                            FWIW 2-volt batteries comes in as large as 6000 AH, the kind they use in ships and submarines. A 2 volt 6000 AH battery weighs 750 to 900 pounds. As a caveat a USN Navy Sea Wolf Class uses 400 volt 6000 AH battery or 160,000 pounds of batteries in the engine room, and another slightly smaller string in for Environmental.
                            MSEE, PE

                            Comment


                            • #15
                              Originally posted by Sunking View Post
                              Kwh is the common denominator, not voltage or AH. What I am trying to point out the largest 12 volt battery you can buy is about 200 AH . Well they do make Rail Road 12 volt batteries up to 350 AH but those weigh in at around 300 pounds and not something a home owner is equipped to deal with.

                              So the point here is let's say you want a 1000 AH battery. Forget voltage for a second just 1000 AH battery string. How do you do that? Well if using a 12 volt volt battery forces you to make 5 parallel string using 200 AH batteries. To get 1000 AH batteries means you have to use lower voltage batteries. A 12 volt 1000 AH battery would weigh in around 700 pounds and thus do not exist. However there are numerous 1000 AH 2 volt batteries and they weigh in around a manageable 120 pounds.

                              FWIW 2-volt batteries comes in as large as 6000 AH, the kind they use in ships and submarines. A 2 volt 6000 AH battery weighs 750 to 900 pounds. As a caveat a USN Navy Sea Wolf Class uses 400 volt 6000 AH battery or 160,000 pounds of batteries in the engine room, and another slightly smaller string in for Environmental.
                              Now that is a pretty heavy battery system.

                              I understand there is a relationship between the battery voltage, weight and Ah. What I was trying to figure out is the math to determine the weight of a battery and got confused when you stated it was related to 100 pounds per kWh the battery could produce. Both a 12v 100Ah battery and 6v 200Ah battery produce 1.2kWh so they should weight the same but don't.

                              Comment

                              Working...
                              X