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  • from12v to 24v with same items ....

    hi all again....
    I don't know if this topic can be here or any moderator can transfere it to suitable place ,
    the question is :
    if I have 12v system ( 12v panels , going to mppt charge controller 60amp sconnected to 2x battery each 200amh connected parallel ( bank 400amh), SO...
    will it work if I use step up transformer from 12v to 24v fitted between panels and charge controller ??( I mean to keep the 12v panels without change )
    putting in mind I will connect the 2x battery in series to be 24v system.

  • #2
    Originally posted by zolar View Post
    hi all again....
    I don't know if this topic can be here or any moderator can transfere it to suitable place ,
    the question is :
    if I have 12v system ( 12v panels , going to mppt charge controller 60amp sconnected to 2x battery each 200amh connected parallel ( bank 400amh), SO...
    will it work if I use step up transformer from 12v to 24v fitted between panels and charge controller ??( I mean to keep the 12v panels without change )
    putting in mind I will connect the 2x battery in series to be 24v system.
    You can wire your "12v' panels in series which should provide a voltage high enough to charge a 24v battery system.

    The key is having an MPPT CC which usually allows a higher input voltage and will still charge a 12V or 24V battery without any issues.

    One thing to remember is trying to generate a C/10 charge rate for an FLA type battery. You can go a little higher or lower but that C/10 is optimum.

    So for a 2 x 12v 200Ah battery system wired in parallel you get a 12v 400Ah system needed about 40 amps (400Ah/10).

    Or you can wire those 2 x 12V 200Ah batteries in series and get a 24V 200Ah system needing about 20 amps (200Ah/10) for charging.

    Comment


    • #3
      thanks suneagle for reply,
      actually not fully understand , let me try answer you :
      about connecting the panels in series to get 24v , I know that but as I said I want to keep them without change (i wanted them providing 12v ) ,
      about the CC mppt wont be important if I double the battery bank ?
      also my batteries are GEL and I may increase the panel ,or connecting them in series as I said .
      finally I am asking this just to know if it could work? cuz the question after that will be:
      HOW ABOUT IF I PUT THAT STEPUP TRANSFORMER AFTER BATTERIES ? IF I KEEP MY SYSTEM 12v AND AFTER TRANSFORMER 24v THEN INVERTER ON 24v AND so on.

      Comment


      • #4
        Originally posted by zolar View Post
        thanks suneagle for reply,
        actually not fully understand , let me try answer you :
        about connecting the panels in series to get 24v , I know that but as I said I want to keep them without change (i wanted them providing 12v ) ,
        about the CC mppt wont be important if I double the battery bank ?
        also my batteries are GEL and I may increase the panel ,or connecting them in series as I said .
        finally I am asking this just to know if it could work? cuz the question after that will be:
        HOW ABOUT IF I PUT THAT STEPUP TRANSFORMER AFTER BATTERIES ? IF I KEEP MY SYSTEM 12v AND AFTER TRANSFORMER 24v THEN INVERTER ON 24v AND so on.
        A quality MPPT CC will provide the correct charging voltage to the battery as long as the voltage from the pv panels exceeds the desired battery voltage.

        ie. For a 12V battery the input to the CC needs to be > 16V. For a 24V battery the input need to be > 32V. So if the input voltage was over 24V the CC will still regulate the charging voltage down to match the 12V battery voltage.

        If you want to use a 24V interter then you should have a 24V battery. Using a step-up transformer (12V - 24V) may work a few times but it is inefficient and not the best practice. It is better to just match the battery voltage to the inverter input voltage.

        Comment


        • #5
          ok ,suneagle thanks a lot , I just wanted to do that so I can have more battery capacity bank when connecting the 2 batteries as parallel so they will be more storage than I connect them series to get 24v ,,, so if they are parallel with 12v with 400amh then after battery , I use the stepup transformer from 12v to 24v going to inverter , so the amperage consumption will be lower in 24v than 12v...
          . ( sorry I think I am not explaining clearly )
          Last edited by zolar; 11-22-2018, 12:15 PM.

          Comment


          • #6
            Zolar,

            your batteries will yield the same amount of energy regardless of whether you connect them in series or parallel.

            Series: 24 volts x 200 amp/hours = 4800watt/hours

            Parallel: 12 volts x 400 amp/hours = 4800watt/hours.

            The advantage to using the 24volt battery is that a given load draws half the current compared to a 12 volt system.

            Example: a 480 watt load will draw 20 amps from a 24 volt battery and 40 amps from a 12 volt battery.

            Lower current means lower voltage drop. This allows smaller conductors and $ savings.

            I highly recommend the battery stickies in the forum. Especially the battery/inverter sizing sticky.

            Comment


            • #7
              Another detail.....

              You need to decide on whether you are going with a 12 volt or 24 volt battery bank and then buy a suitable inverter to match.

              Transformers only work with AC. With a DC system there do exist "buck/boost" converters that will convert 12 volts DC to 24 volts. That would not be a practical solution in your application. Stick with an inverter specific to your batteries.

              Comment


              • #8
                hi steve and thanks for your post ,
                and what you said about amps consumption vary depend on voltage, its absolutely right and I know that ,,, HERE IS THE SPOT , and THATS WHY I am saying this
                connecting the 2 batteries parallel as 400amps will be more storage than connecting them series as 200amps only .
                BUT ,,, BUT ,,,,BUT,,, installing the stepup transformer between the batteries and inverter will give the voltage of 24v with more storage and the load will depend on voltage which is just before the inverter ( which means consumption is half than if it was 12V ) and the result ofcourse I gain more time running my load.
                sorry guys may be I can't say my idea clearly . ( my bad English )

                Comment


                • #9
                  Zolar,

                  I think that you are missing the point.

                  The storage capacity of a 12 volt 400 a/h battery bank is exactly the same as a 24 volt 200 amp/hour battery bank.

                  P=I x E.....

                  Comment


                  • #10
                    And, again, transformers DO NOT work with DC.

                    Comment


                    • #11
                      hi steve again ,,thanks again and sorry for bothering ....
                      brother lets say it step by step and its only 2 steps .,,,,
                      believe me I got your point but that point only equal if the load using12v with 400amh batteries or 24v with 200amh batteries.
                      IF YOU ARE WITH ME TILL HERE TELL ME ( OK ) please

                      Comment


                      • #12
                        Here is where thinking in terms of Watts or Watthours may make it easier.
                        12x400 = 4800 Watthours
                        24x200 = 4800 Watthours

                        Comment


                        • #13
                          thanks ampster for your post ,
                          brother if you read the topic from beginning you will see that :
                          the rule you wrote , I said many times that i know it ,,,, suneagle explained it ,,,,, ,also pnw_steve said that more than once.
                          that's why I want some one who go with me step by step.
                          the only thing may stop me from trying to understand is what pnw_steve said that ( transformers do not work with dc ) .
                          anyway generally I will say it again trying my best explaining and I hope will be clear ( may be due to my bad English I couldn't deliver the idea ):

                          guys I am with you all and I am sure of what you all said that for a certain load wattage " higher voltage less amps consumption"
                          please say yes you agree for that .....
                          now I am saying while using 2x batteries of 200 amh each connected parallel as 12v to be total storage of 400amh ,
                          OK?
                          no need to reduce the storage to 200 amh when I connect them in parallel to use 24v.
                          I keep my system as it is and I step up the voltage to 24v by using that transformer putting it after batteries and before the inverter ( the load will deal with 24v not 12v and the storage is still as 400 amh not reduced to 200 amh .
                          I don't think I can make more clearly than that

                          Comment


                          • #14
                            You are trying to fool Ohms Law if you think you can double your power.
                            In your example you are correct that the storage remains at 400ah. What Ohms law tells us is if you put a 1 Amp 24v load on that device it will have to pull over 2 Amps out of that 12 volt source in order to provide 24 volts. You cannot fool the laws of physics. In other words your 400ah battery will drain twice as fast.
                            Last edited by Ampster; 11-23-2018, 09:13 AM.

                            Comment


                            • #15
                              Originally posted by zolar View Post
                              I keep my system as it is and I step up the voltage to 24v by using that transformer putting it after batteries and before the inverter ( the load will deal with 24v not 12v and the storage is still as 400 amh not reduced to 200 amh .
                              I don't think I can make more clearly than that
                              The only thing you are making crystal clear is you do not understand one word of what you are being told, and you have no idea what you are talking about or doing. You are trapped inside a 12 volt toy box.

                              Example say you have 4 x 12-volt 200 AH batteries. With those 4 batteries, they can be configured for a 12, 24, and 48 volt system. Given that you would opt for 48 volt system, or maybe 24 volts because it is the least expensive and highest efficiency.

                              As for power, all three configurations have the exact same capacity in Watt Hours:

                              1. 12 volts @ 800 AH = 9600 watt hours
                              2. 24 volts @ 400 AH = 9600 watt hours
                              3. 48 volts @ 200 AH = 9600 watt hours.

                              Lastly there is NO SUCH THING as a DC TRANSFORMER. They do not exist as it is IMPOSSIBLE. Get that through your head and quit wasting everyone time.
                              MSEE, PE

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