Announcement

Collapse
No announcement yet.

Swapping our 24 volt for 48 volt system

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

  • Swapping our 24 volt for 48 volt system

    I need some direction on performing a change from my old 24 volt system to a new 48 volt. This is a unique off-grid system where two small arrays combine and by using manual disconnects can toggle back-and-forth with a back-up 21kw diesel generator to use if the PV is down or when pumping water to our storage tank. Here is list of what is currently installed:
    • Trace Engineering 2524 inverter.
    • Xantrex C-40 charge controller
    • 4 Concorde AGM 6 volt batteries
    • 4 x 175 watt Siemens 24 volt PV panels
    • 4 x 52 watt ??? 24 volt PV panels
    • 60 amp fused disconnect from combined PV array
    The Trace Engineering inverter has died after 24 years of service and I could find no support for repair. This system was built by another individual and while I know it has a few problems with component matching we have made it work for us as our 2nd home. After dealing with some other unrelated challenges I ran to town and stopped at a small solar distributor/installer and discussed my problem. Very nice man and friendly staff pointed out that they recently took in a Outback VFX 3648 from a customer upgrade. They also had 4 DEKA 6 volt flooded-lead batteries at an EXTREME discount so I decided to purchase these items and switch to a 48 volt system. I do know; "Don't mix battery types" but this will work for us until I get a new system set-up, my ultimate desire for 2019. Anyways, a couple of questions about connecting the Outback inverter after reading a bit about this from the installation instructions I downloaded.
    • Outback calls this an inverter/charger but I don't see any reference to wiring from PV array. Does this mean I need to leave the C-40 charge controller in place and configure it for 48 volts?
    • What is the process to re-wire the Siemens and other panels for 48 volt output?
    • Where, in the wiring do I need lightning protection installed?
    • Will I have enough PV production to support the battery needs once I have the eight batteries wired in series?
    Any help or comments would be greatly appreciated.

  • #2
    Hello WillieRides57 and welcome to Solar Panel Talk

    To answer your questions we would first need to know a few things;

    The Ah rating of those batteries (both old and new).
    Next knowing the maximum DC input voltage (from the panels) for that Outback charge controller.
    The Vmp & Voc ratings of your panels. Just saying 24volts is not enough info. Also what are the Imp and Isc ratings?

    Comment


    • #3
      Hello SunEagle,

      Thanks for your reply.

      The older Lifetime AGM batteries are 375 ah rated. The new ones are 375 ah also.
      The Vmp from the Siemens panels are somewhere around 27.5 volts, Voc at near 29. I don't have info on the smaller 52 volt panels.
      Current is 4.1 Imp and 4.4 Isc in the Siemens panels and unknown for the others.

      Comment


      • #4
        Originally posted by WillieRides57 View Post
        Hello SunEagle,

        Thanks for your reply.

        The older Lifetime AGM batteries are 375 ah rated. The new ones are 375 ah also.
        The Vmp from the Siemens panels are somewhere around 27.5 volts, Voc at near 29. I don't have info on the smaller 52 volt panels.
        Current is 4.1 Imp and 4.4 Isc in the Siemens panels and unknown for the others.
        OK. You can wire those 4 Siemens panels in series and will get about 116V total which should be below your max DC input voltage of that charger. That gets you about 14.5 amps of charging 4 x 175w / 48V = 14.58a, (assuming the CC is a MPPT type) which is not enough for a 48V 375Ah battery system.

        You can also wire those 4 x 52watt panels in series and to get another 204 watts and then parallel wire them with the 4 Siemens, but while that comes to about 900watts will still not provide enough charging amps for that battery system.

        You need about 38amps and you will not even get 20amps. So you will need more panel wattage. I estimate you need about 1900 watts total (48V x 38A = 1824W).

        Comment


        • #5
          The C-40 charge controller is a PWM controller. Panels should be wired for 48 volt nominal . If the 52 watt panels are 36 cell panels they are 12 volt panels and should be series wired. The 24 volt siemens panels should be series wired two to a string. This would give you 3 strings that need to be combined in a fused combiner box.
          2.2kw Suntech mono, Classic 200, NEW Trace SW4024

          Comment


          • #6
            Originally posted by littleharbor View Post
            The C-40 charge controller is a PWM controller. Panels should be wired for 48 volt nominal . If the 52 watt panels are 36 cell panels they are 12 volt panels and should be series wired. The 24 volt siemens panels should be series wired two to a string. This would give you 3 strings that need to be combined in a fused combiner box.
            That Outback VFX inverter/charger can accept up to 68V DC input so even that unit could handle only 2 of those 175w panels wired in series and then 2 more in parallel for 700 watt input to charge a 48v battery system.

            Those 52 watt units may be an issue to add to the Outback so they may need to be wired to the C-40 Xantrex CC which can handle them but will lose some of the panel wattage due to being only a PWM type.

            Using 2 different spec panels to the same CC can be a hassle. But there could be issues with 2 different CC's tied to the same battery bank. Not the best plan but it may work. But I think your plan using all 8 panels wired as 3 strings to the C-40 may work.

            Comment


            • #7
              I didn't realize the Outback inverter/chargers functioned as a solar charge controller.
              2.2kw Suntech mono, Classic 200, NEW Trace SW4024

              Comment


              • #8
                Originally posted by littleharbor View Post
                I didn't realize the Outback inverter/chargers functioned as a solar charge controller.
                It may not. I could be confusing it with another Outback CC.

                Comment


                • #9
                  Originally posted by WillieRides57 View Post
                  Very nice man and friendly staff pointed out that they recently took in a Outback VFX 3648 from a customer upgrade.
                  • Outback calls this an inverter/charger but I don't see any reference to wiring from PV array. Does this mean I need to leave the C-40 charge controller in place and configure it for 48 volts?
                  Any help or comments would be greatly appreciated.
                  The OutBack VFX3648 is a 48V 3.6kW inverter/charger. it is NOT a Charge controller.
                  It can not connect solar to batteries like a charge controller.

                  The confusion here seems to be in the fact that it is an Inverter/CHARGER That means it can inverter from DC to AC and charge the batteries from AC
                  OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

                  Comment


                  • #10
                    The VFX 3648 is an inverter / charger. The charger operates from 120VAC, from the grid or a generator.
                    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


                    • #11
                      Originally posted by littleharbor View Post
                      The C-40 charge controller is a PWM controller. Panels should be wired for 48 volt nominal . If the 52 watt panels are 36 cell panels they are 12 volt panels and should be series wired. The 24 volt siemens panels should be series wired two to a string. This would give you 3 strings that need to be combined in a fused combiner box.
                      Many thanks for all your responses. I can assume the following; the need of creating 3 strings of existing PV and adding 1000 watts of PV. A new combiner disconnect is in order plus running new parallel disconnect wiring from the gen-set disconnect to Outback charger inputs. I can continue using the C-40 charge controller unless a MPPT type would be better. Any thoughts or tips on wiring the panels correctly without ruining a panel?

                      Comment


                      • #12
                        After a year I finally purchased 3 x 275 watt German Solar panels and installed a pole-mount on a Sch. 40 pole. I also am installing a MidNite Solar combiner box to bring the array strings together. Next will be a 60 amp MPPT charge controller.

                        Comment

                        Working...
                        X