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Charge voltage needed for 24 V system

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  • Charge voltage needed for 24 V system

    What would the voltage from the solar panels need to be to charge a 24v battery system ?
    The system is charging at 26v - 200amps, but don't seem to be charging very well.

    Example: 12v car battery charges at 14-16 volts - x amps.

    Would this mean that 24v charge should be 28-30 volts - x amps ?


  • #2
    Hi Chuck welcome to the Forum. Your numbers confuse me a bit, more on that later

    For a 24 volt system the panel at max power rating needs to be 32 to 36 volts.
    Roughly 16 to 18 volts for every 12 volts of battery.

    However that rule only applies if you are using a standard PWM or shunt regulator. Using that type of regulator you will loose 30% minimum of the power from the panels.

    However with a MPPT controller those voltage rules do not apply. They still need to be at least 36 volts, but you can go as high as around 120 volts to take advantage of wiring loss efficiency at the higher voltages. At higher voltage you use less current for a given power.

    Ok lets move on to amps. Amps is the function of power and voltage from the panels. So if you have a 200 watt panel at 36 volts the current = 200 watts / 36 volts = 8.3 amps.

    You mentioned 26 volts at 200 amps. That would be one hell of a big solar panel array of 26 volts x 200 amps 5200 watts.

    Did you maybe mean you have a 200 Amp Hour Battery at 24 volts? If so that means the battery has a reserve capacity of 24 volts x 200 Amp Hours = 4800 watt hours. If that is the case, the maximum panel wattage for that size battery would be around 900 watts. At 900 watts the max charge current would be about 25 amps.

    The maximum charge rate for a lead acid battery is about 1/8 of the battery Amp Hour capacity expressed a C/8. So for a 200 Amp Hour battery = 200 / 8 = 25 amps.

    However it would be rare in most application to have a C/8 current coming from the solar panels unless you live in a real Gloomy climate like Seattle WS. Most systems run anywhere from C/10 to C/15.
    MSEE, PE

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    • #3
      Hi Chuck, welcome and thanks for joining.

      You came to the best place to learn about solar. Congrats.

      Comment


      • #4
        ~Thanks for the welcomes~

        I am very new to this solar and this place is off grid and winter is on the way. The trackers
        were damaged then replaced. Problem - they do not charge near as well as they did before.

        For charging, there are two trackers with 12 - SX60U panels each, with an out put of 26
        volts in full sun each tracker. This is wired to a Heliotrope charge controller. Then to a
        storage battery bank of 60 KS-20472 lead acid storage batteries, wire as 24 v,

        The two trackers, with 12 panels each, were installed 2 weeks ago and don't seem to be
        charging as the original did that these replace. Checking the output of each tracker, the
        voltage is 26 volts each. Should the voltage be higher in the range plus or minus 36v ?

        Comment


        • #5
          26 volts from the panel is not near enough. Where and how are you measuring the voltage. Something is wrong.

          The BP SX 60U has a Vmp (Voltage maximum power) of 16.8 volts. If used in a 24 volts system with 12 panels you should have 6 parallel strings of 2 panels wired in series which means you should be seeing 16.8 + 16.8 = 33.6 volts.

          However you did catch my attention with your Heliotrope charge controller. Last time I checked they only make two models called HPV-22 (22amps), and HPV-30 (30 amps). There are 2 things that are catching my attention.

          1. They are 12 volt charge controller, not 24.
          2. You said you have 2 two tracker with 12 panels each, wired in a 2 x 6 configuration. That tells me you should be seeing 32 volts @ 21 amps from each tracker, and when combined should be 32 volts @ 42 amps.

          If that is your model number on your controller, then you do have a problem 2 big ones. They are made for 12 volt battery systems and can only handle 30 amps.

          If you do have a Heliotrope HPV-22 or HPV 30. It will not work period. Heliotrope caters to the RV market, which is 12 volt systems. What is your model number? Is it the RV series or HPV
          MSEE, PE

          Comment


          • #6
            Originally posted by Sunking View Post
            26 volts from the panel is not near enough. Where and how are you measuring the voltage. Something is wrong.

            The BP SX 60U has a Vmp (Voltage maximum power) of 16.8 volts. If used in a 24 volts system with 12 panels you should have 6 parallel strings of 2 panels wired in series which means you should be seeing 16.8 + 16.8 = 33.6 volts.

            However you did catch my attention with your Heliotrope charge controller. Last time I checked they only make two models called HPV-22 (22amps), and HPV-30 (30 amps). There are 2 things that are catching my attention.

            1. They are 12 volt charge controller, not 24.
            2. You said you have 2 two tracker with 12 panels each, wired in a 2 x 6 configuration. That tells me you should be seeing 32 volts @ 21 amps from each tracker, and when combined should be 32 volts @ 42 amps.

            If that is your model number on your controller, then you do have a problem 2 big ones. They are made for 12 volt battery systems and can only handle 30 amps.

            If you do have a Heliotrope HPV-22 or HPV 30. It will not work period. Heliotrope caters to the RV market, which is 12 volt systems. What is your model number? Is it the RV series or HPV
            I'm getting the reading at the panels off the main pos. and neg. wires leading to the charge controller.

            I was told that the panels were wired each set of 6 parallel, than the pair of 6 each wired in series. Is that in a 2 x 6 configuration ?

            Model of the controller is a, Heliotrope CC120E

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            • #7
              Measure the panel voltage at the input of the charge controller, not at each of the trackers and see what you have.
              MSEE, PE

              Comment


              • #8
                Originally posted by Sunking View Post
                Measure the panel voltage at the input of the charge controller, not at each of the trackers and see what you have.
                The voltage at the charge controller is 25.0 volts.
                He wired something wrong, and wouldn't you know it,
                no way to get hold of him to put it rite.

                Comment


                • #9
                  Yeah Chuck from your last description 12 wired in parallel on one tracker, with 12 more wired in parallel on the other tracker, then those wired in series is just not the way I would do it. Even if he did do it that way correctly you should see 32 to 33 volts at the charge controller with about 43 amps around the noon hour. Something is wired wrong.
                  MSEE, PE

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                  • #10
                    Found a diagram of how he wired it on a paper and he wrote 24 volts at output of panels,
                    so I think I need to rewire it to get 36v out. What a mess.

                    Comment


                    • #11
                      I am curious how he came up with 24 volts, and would contest his competency if solar systems of how in the world he expects to charge 24 volt batteries with a 24 volt supply.

                      If you are using BP SX60U panels the Vmp is 16.8 volts. There is no way to configure them to get 24 volts out of them. as 16.8 does not equal 24 volts. If you wire them in series the voltage output has to be multiples of 16.8 volts. So if in a 2 x Y configuration the output voltage has to be around 33 volts. 33 volts does not equal 24 volts.

                      Next anyone who has spent more than a day reading about battery powered solar systems should have a clue that to charge a 24 volt battery, you need at least a 30 volt minimum supply.

                      Add those two items I made above and you have an incompetent installer who does not even know the bare minimum basics.

                      EDIT NOTE:

                      I tried to find your charge controller on the web. No luck, not even the manufacture list that part number. Anyway take a look in the manual for the min/max voltage input from the solar panels for a 24 volt battery system.
                      MSEE, PE

                      Comment


                      • #12
                        Heliotrope CC60/120 Charge Regulator

                        PR/HG-CC120E 120A, 12/24V Taper Charge Regulator

                        http://www.cisolar.com/catCharge.html

                        Not much of a manual, just three pieces of paper. But in one line it says 120 amp max.

                        Comment


                        • #13
                          New to this forum and the reason I joined is the knowledge that some members posses is phenomenal. I recently installed 6.3kw system with Enphase inverters and I have 8 ea. of 255 watt panels yet to install in another array. I purchased 2 1200 watt inverters from China but could not find but little reviews on them. My system is a grid tie system. I need a battery backup so I purchased a 1800 pound battery from a fellow near by. The battery appears to be in good working order. It holds a charge very well and the specific gravity is at 2.1 which is a bit low but was informed that the batteries will last longer with a low sg. I hooked a 255 watt 30+ volt 8a panel and it is charging well I think. The battery is 875 amp hours and requires 20amp to charge. will this be enough to charge the battery and how long will it take is my question? Any advise would be greatly appreciated....

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                          • #14
                            I have 6 32 volt solar panels and want to have a 24 volt system. what do I need ?

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                            • #15
                              You need to have at least 35V for full charging and equalizing functions, so you have to wire 2 panels in series to get 64V. and then use a true MPPT charge controller to charge the batteries.
                              This would give you 3 strings of 2 panels. With 3 strings, you need to use a solar Combiner Box when you wire the 3, 64v strings in parallel
                              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

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