Announcement

Collapse
No announcement yet.

Couple questions on batteries and bank size.

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

  • Couple questions on batteries and bank size.

    Got a couple questions for you. My battery bank is only 2 12v 114ah deep cycle batts in series for 24v. I have 1800 watts of solar, a midnite classic 150 and a couple cheap modified inverters. I'm having trouble wrapping my mind around the charge current. At 12v the manufacturer says not to charge over 10 amps so when i went to 24v can i charge at a higher amp rate like maybe 20amps? Im able to charge up to 70 amps. And my other question is if I'm pulling a lot out of the bank can I just crank up the input amps? So what ever I'm running off the inverter will be coming from the panels not so much off the batteries. Or does it not work that way Thanks for the help!!!!

  • #2
    Originally posted by Stansbery View Post
    Got a couple questions for you. My battery bank is only 2 12v 114ah deep cycle batts in series for 24v. I have 1800 watts of solar, a midnite classic 150 and a couple cheap modified inverters. I'm having trouble wrapping my mind around the charge current. At 12v the manufacturer says not to charge over 10 amps so when i went to 24v can i charge at a higher amp rate like maybe 20amps?
    No. If you have one battery, and the spec sheet limits it to 10A, max charge rate is 10A. If you have two in parallel (still 12V) then the limit is 20A with two matched batteries. If they are in series (24V) limit is still 10A.

    For 114ah I wouldn't go over 14 amps - but the manufacturer's data sheet is always the final word.

    Im able to charge up to 70 amps.
    You're not likely to see that level very often. But in any case, you have to limit it to what your batteries can accept (10A.)

    And my other question is if I'm pulling a lot out of the bank can I just crank up the input amps? So what ever I'm running off the inverter will be coming from the panels not so much off the batteries. Or does it not work that way Thanks for the help!!!!
    If your charge controller is limiting at 10 amps, and your inverter is pulling 5 amps and the battery is low, then the charge controller will supply 10 amps - 5 to the inverter and 5 to the battery.

    Comment


    • #3
      Thanks for the quick response!! What if my inverter is pulling lets say 15 amps. Can I turn my limit up on the classic above 10a to compensate for the higher amp draw? Thanks again for the help!!

      Comment


      • #4
        You have some issues, let's see if we can straighten you out.

        First, NO you cannot charge them at 20 amps as that is twice the maximum rate.

        Series Circuit Laws

        1. Same current flows through each component in series.
        2. Power and Voltage Adds

        So you put 2 12 volt 114 AH in series so you now have a 24 volt 114 AH battery. Both batteries have the exact same 10 amps flowing. So here comes the really bad news. Your batteries like most batteries have a maximum charge rate. For lead acid it is around C/8 to C/10 where C = the battery Amp Hour capacity. Well 114 AH / 10 hours = 11.4 amps, so your batteries max charge rate is about C/10.

        Ready for the bad news. that means you cannot use more than 250 watts of solar panels. You are slamming the things with 1800 watts which will produce 1800 watts / 24 volts = 75 amps or 700% more than safe.

        Even more bad news. You batteries are so weak with only have a C/10 max charge rate also means the cannot be discharged more than 10 amps without significant voltage loss. That means the maximum load or Inverter you can use is 10 amps x 24 volts = 240 watts.

        You need to get rid of those batteries, they are useless crap. Either that or loose 1600 watts of panels. Take your pick...

        Forget 12 volt batteries, batteries are not 12 volts. The minimum size battery you can run at 24 volts with 1800 watts is 700 AH. You will not be using 12 volt batteries. None exist at 700 AH as they would weigh 500 pounds each. No Sir you will be using 6 volt 700 AH batteries and will need four of them. They weigh about 250 pounds each.

        FWIW I advice you to disconnect your solar system from the batteries. You are risking serious damage and threat to life doing what you are doing. Just think spewing boiling hot acid everywhere. What you have is a pispoor design. You got the right controller for the panel wattage you have. But you really screwed up bad on batteries and will have to eat the cost.

        You can two ways with this. 24 or 48 volts

        For 24 volts, minimum batterry capacity is 700 AH
        For 48 volts a smarter idea is 350 AH

        There is no point in buying 14 more of those POS 12 volt batteries you have. Eat the loss and get what is required. Either 24 or 48 volt cost the same $2500.
        Last edited by Sunking; 08-16-2017, 07:46 PM.
        MSEE, PE

        Comment


        • #5
          Originally posted by Stansbery View Post
          Thanks for the quick response!! What if my inverter is pulling lets say 15 amps. Can I turn my limit up on the classic above 10a to compensate for the higher amp draw? Thanks again for the help!!
          Nope. Because as soon as the load on the inverter drops to 4 amps, you are overcharging them. The "right" way to do what you want is to use a charge controller that can use a remote current sense to ensure that the current to the BATTERY never exceeds 10 amps - but the Classic does not support that.

          Comment


          • #6
            Disconnected!!! I did have my classic limiting the charge amps at 10A. I will be buying 6v batts very soon!!! Thanks for the help!

            Comment


            • #7
              Ok thanks jflory2.

              Comment


              • #8
                Originally posted by Stansbery View Post
                Disconnected!!! I did have my classic limiting the charge amps at 10A. I will be buying 6v batts very soon!!! Thanks for the help!
                I bet your controler was hot with fans running trying to shed 1600 watts of useless panels off. Panel voltage shot to virtually Voc.
                MSEE, PE

                Comment


                • #9
                  You can try to balance your risks. With 200ah 6v batteries, they should be able to take 25A charge, and if you limit amps to 35A. you could run loads at the same time.
                  Midnight also has the Whiz-Bang-Jr current sensor, and that measures battery current to control charging. I don't use one, so I'm not sure of the programming options it can be set for.
                  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


                  • #10
                    Actually no fans running, everything seemed fine. On the classic 150 it would let me limit the amps coming through the controller and it would automatically adjust the watts to the charge rate. I used the midnite solar sizing tool on their site and I am running 8 235w 24v panels 2 in series then 4 parallel. Gives me VOC. 73v and Batt charge current @ 28.8v 65.3A And I will be getting a wizbang jr after i get some batts.
                    Thanks for the replys guys!!

                    I was thinking of maybe 4 trojan t105re batts. Any thoughts on these?
                    Last edited by Stansbery; 08-16-2017, 09:14 PM.

                    Comment


                    • #11
                      Originally posted by Stansbery View Post
                      I was thinking of maybe 4 trojan t105re batts. Any thoughts on these?
                      Great batteries, but not for you. You need 600 AH min. T-105RE are 225 AH only 1/3 of what is required. It would take 12 T-105's.

                      Only thing Trojan has that would fit your needs is IND13-6 a 6-volt 695 AH battery. You got way more panel wattage than your battery wallet can afford. It you want to run 4 x T-105's you gotta cut panel wattage to 800 watts to limit charge current to 30 to 35 amps.

                      If you want to entertain 48 volts, then you can get by using T-105's, you would need 8 of them. Being Golf Cart Batteries can handle higher C-Rates. But honestly, even 8 x T-105's is a bit to small and not utilizing your panel full capabilities. At 48 volts will allow you to grow to 5000 watts, 1/2 that at 24 volts

                      You got two choices, New batteries or loose panels.
                      Last edited by Sunking; 08-16-2017, 11:37 PM.
                      MSEE, PE

                      Comment


                      • #12
                        Just making sure I'm getting this right. The smallest battery I can use is a 700ah battery? And then enough of them to be 24v? Something like 4 of the ind-13-6 Batts?

                        Comment


                        • #13
                          Originally posted by Stansbery View Post
                          Actually no fans running, everything seemed fine. On the classic 150 it would let me limit the amps coming through the controller and it would automatically adjust the watts to the charge rate. I used the midnite solar sizing tool on their site and I am running 8 235w 24v panels 2 in series then 4 parallel. Gives me VOC. 73v and Batt charge current @ 28.8v 65.3A And I will be getting a wizbang jr after i get some batts.
                          Thanks for the replys guys!!

                          I was thinking of maybe 4 trojan t105re batts. Any thoughts on these?
                          The current limiting function operates basically the same as the absorb or float function. No one is going to run around saying "disconnect the panels" any time a high power system goes into float. What you were doing was unconventional, and maybe not the most cost effective use of panels, but not dangerous.

                          As jflorey2 wrote, with proper controls that monitor current flow to the battery, you can do what you are thinking, making excess current available to operate daytime loads. You would have to home brew a solution with that charge controller, but at least it has a remote interface you could use to communicate with it, if you pursued the idea. Doing it wrong *is* dangerous, so you won't find much discussion here about how to go about it.
                          CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

                          Comment


                          • #14
                            Originally posted by Stansbery View Post
                            Just making sure I'm getting this right. The smallest battery I can use is a 700ah battery? And then enough of them to be 24v? Something like 4 of the ind-13-6 Batts?
                            Sure, if you want to be able to operate all your loads from batteries. If you want to just run daytime loads when excess power is available, there are ways to do that without going to such a big battery.
                            CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

                            Comment


                            • #15
                              Thanks for the help guys. I won't be doing anything that's dangerous!!! I will have the system off untill I get enough batteries to be proper and safe!! Thanks for all the help.

                              Comment

                              Working...
                              X