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Charge 12v bank from 48v bank with charge controller

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  • Charge 12v bank from 48v bank with charge controller

    I am putting together a 48v off grid system. During the winter the 48v bank will be maintained by a Conext XW 60 MTTP charge controller (I don't want the inverter on when I'm not there so it will be powered down). I would like to maintain my 12v bank on my travel trailer over the winter. The 12v bank won't have any loads on it and the only load on the 48v system will be the CC for the 12v bank.

    I have read the Morningstar MTTP charge controller is able to do what I want. However, I have a Windynation 30a PWM controller that can accept a VOC of 55 volts. Can I use this PWM controller connected to the 48v bank to charge the 12v bank? If an MTTP CC will work why wouldn't a PWM CC (assuming it can handle the voltage).

    Thanks for any advice.
    Conext XW5548
    Conext MPPT60-150

  • #2
    Originally posted by hammick View Post
    I am putting together a 48v off grid system.

    Can I use this PWM controller connected to the 48v bank to charge the 12v bank? If an
    MTTP CC will work why wouldn't a PWM CC (assuming it can handle the voltage).
    Don't even think of trying to use a PWM controller from a 48V battery source to charge a
    12V battery. A PWM works by letting the (solar panel) source limit the current, which is
    switched on & off for the desired average. NOTHING will limit the current that a 48V
    battery bank can supply, and you will probably let the smoke out of everything the first
    time you try. Bruce Roe

    Comment


    • #3
      PWM controllers are not self limiting on power. It would be like hooking jumper cables directly from the 48 to 12V banks.

      An MPPT controller can work but is a very poor choice as it will always run at full power.

      Google "DC-DC battery charger". You will find what you want. But since it's just a maintenance charge your looking for a small maintenance solar panel on the 12v batteries might be a better and cheaper option.

      WWW

      Comment


      • #4
        PWM will not work. not even with a ballast resistor

        MPPT would work. Cost of genuine controller vs a 12V Battery Tender run off 120VAC (I use a Battery Tender to keep the genset battery full)

        What is your charging need ? generator starting battery, 2 starts a day? Electric gate opener ? Can a 50W PV and cheap PWM keep up with your loads ?
        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


        • #5
          Thanks for the replies. I spoke with tech support at Morningstar and they told me the same thing that a PWM controller would get fried and possibly fry the 12v bank. They said the SS-MPPT 15a is a current limiting charger and would do just what I want.

          I guess what confuses me is that the Windy Nation PWM CC says it can take a panel with a VOC of 55w. So how is connecting a PWM to a 45v bank different than connecting it to a 45v panel? Does it have to do with current?

          Obviously a 120v battery tender would be the way to go. However, I don't have any grid power and the property will be vacant all winter. I need a way to keep them charged and I really don't want to install any more panels.

          I will probably just go the SS-MPPT route even though it's a little pricey for just maintaining a 12v bank.

          Can anyone tell me what size wire I should use to connect the SS-MPPT to the 48v bank? 10ga jusk my array wires?
          Conext XW5548
          Conext MPPT60-150

          Comment


          • #6
            Originally posted by hammick View Post
            Thanks for the replies. I spoke with tech support at Morningstar and they told me the same thing that a PWM controller would get fried and possibly fry the 12v bank. They said the SS-MPPT 15a is a current limiting charger and would do just what I want.

            I guess what confuses me is that the Windy Nation PWM CC says it can take a panel with a VOC of 55w. So how is connecting a PWM to a 45v bank different than connecting it to a 45v panel? Does it have to do with current?

            Obviously a 120v battery tender would be the way to go. However, I don't have any grid power and the property will be vacant all winter. I need a way to keep them charged and I really don't want to install any more panels.
            do you use a 48V inverter for AC power?



            Can anyone tell me what size wire I should use to connect the SS-MPPT to the 48v bank? 10ga jusk my array wires?
            you could use 14 ga wire, and use the right fuse for it (10A) the controller will step it down to 12V and you will want to use 10ga from the controller to the battery.

            (correction, I use a Genius charger on my starter battery - http://www.geniuschargers.com/G3500 )
            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


            • #7
              Originally posted by Mike90250 View Post
              do you use a 48V inverter for AC power?
              My off grid garage is under construction and I'm in the process of buying my solar equipment.

              Pretty sure I am going to buy the Conext SW4048 inverter. I'm not comfortable leaving it powered up for months when the property is vacant. I'll have a Conext XW 60 charging the 48v bank.
              Conext XW5548
              Conext MPPT60-150

              Comment


              • #8
                Originally posted by hammick
                So how is connecting a PWM to a 45v bank different than connecting
                it to a 45v panel? Does it have to do with current?
                I answered that question on my previous post. Bruce Roe

                Comment

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