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  • Home Solar project

    Hi you previously helped me with my motor home solar panel project, which solved our problem. I have started a home project and once again would like your advice

    I currently have:
    4 x Sony 250w solar panels
    2 x 100ah Leisure batteries
    So my question
    should the panels be wired in series or parallel,if series what is the correct charge controller i should use
    Regards mike

  • #2
    Originally posted by mpryan View Post
    Hi you previously helped me with my motor home solar panel project, which solved our problem. I have started a home project and once again would like your advice

    I currently have:
    4 x Sony 250w solar panels
    2 x 100ah Leisure batteries
    So my question
    should the panels be wired in series or parallel,if series what is the correct charge controller i should use
    Regards mike
    With 1000 watts of panels and I assume a 12v battery system you will need an 80 amp MPPT type CC. (1000w / 12v = 83amps)

    The problem you might have is too fast a charge on that (again I assume) 12V 200Ah battery system. It would be happy with about 20amps of charging and you will have close to 80amps or a C/2.5 charge rate which will hurt your batteries.

    With 80amps of charging you can go up to a 960Ah battery (C/12) or as small as a 640Ah battery system (C/8).

    So either increase your battery system or loose 2 of those 250w panels.

    Comment


    • #3
      hi so if i use two of the 250w panels in series, with my two 100ah batteries, can i then use a 40ah charge controller at 12 v

      Comment


      • #4
        Originally posted by mpryan View Post
        hi so if i use two of the 250w panels in series, with my two 100ah batteries, can i then use a 40ah charge controller at 12 v
        500 watts with an MPPT CC can generate about 40 amps for a 12 volt battery system. The problem I see is that with only 200Ah of battery capacity you run the risk of charging it too quickly.

        By math on paper you could get a C/5 charge rate (200Ah / 40A = 5hour) which may be a little too aggressive for anything but AGM type batteries. It sounds like you have basic FLA type which should not be charged faster then a C/8 rate or in your case about 25 amps of charging. That calculates out to about 300 watts of panels (25A x 12V = 300W).

        What is the make and model of your CC?
        Last edited by SunEagle; 10-10-2018, 09:07 AM. Reason: added last question

        Comment


        • #5
          Im trying my first attempt at building a small Halloween display but its in the middle of nowhere so solar is going to power it. It originally took 3 1.5W watch batteries. Can I just use a 12V 1.5W Solar panel to power it? Will this step down the voltage and keep my battery from getting overjuiced? https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

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          • #6
            Who has popcorn.

            MSEE, PE

            Comment


            • #7
              Originally posted by mr2nr151 View Post
              Im trying my first attempt at building a small Halloween display but its in the middle of nowhere so solar is going to power it. It originally took 3 1.5W watch batteries. Can I just use a 12V 1.5W Solar panel to power it? Will this step down the voltage and keep my battery from getting overjuiced? https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
              Simple answer to a post with little to no information is NO.

              Most solar charge controllers will not work with "watch batteries".

              Try to determine the number of watt hours that display will use in a 24 hour period and then (maybe) we can size your solar / battery system.

              Comment


              • #8
                Sorry I'm using a 12V Battery. I know it's overkill. I just don't want to burn up my LED's So my main question is does it automatically step down voltage for the load. Or will I need another component.

                Comment


                • #9
                  Originally posted by mr2nr151 View Post
                  Sorry I'm using a 12V Battery. I know it's overkill. I just don't want to burn up my LED's So my main question is does it automatically step down voltage for the load. Or will I need another component.
                  The load will "see" the voltage provided by the battery. For example if the load requires only 5 volts to run then 12 volts may be too much.

                  A charge controller is designed to keep a 12 volt battery at or above it's rating. Most CC's may not have the ability to "step down" the voltage below what the battery requires although some may provide a 5V USB connection.

                  Comment


                  • #10
                    Many of the inexpensive controllers DO have USB outputs.

                    30 amp charge controller.jpg
                    2.2kw Suntech mono, Classic 200, NEW Trace SW4024

                    Comment


                    • #11
                      Originally posted by littleharbor View Post
                      Many of the inexpensive controllers DO have USB outputs.

                      30 amp charge controller.jpg
                      That may work but he would need to come up with a wiring device that converts the USB to power the load.

                      Again. I do not know exactly what the voltage requirement of the load is just that it takes 3 watch batteries to run it. That could be anywhere between 1.5V to 3V per battery or 4.5V to 9V total. The 5V USB would not be enough and a 12V source may be too much.

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                      • #12
                        Yes it's 4V I can run it off the USB Is there a controller out there that has adjustable voltage output?

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