System Critique

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  • ula
    Junior Member
    • Aug 2016
    • 18
    #1

    System Critique

    I am moving from a 12v to 24v system. Just want to check to make sure I got it correct. I have 4 330watt panels wired in series. Going to a midnite 150 (94a @ 24v) charge controller to 4-6v 235ah batteries wired in series to a 2000 watt 24v inverter. Please let me know what you think.
    thanks in advance!
    Tags: None
    • SunEagle
      Super Moderator
      • Oct 2012
      • 15123
      #2
      Originally posted by ula
      I am moving from a 12v to 24v system. Just want to check to make sure I got it correct. I have 4 330watt panels wired in series. Going to a midnite 150 (94a @ 24v) charge controller to 4-6v 235ah batteries wired in series to a 2000 watt 24v inverter. Please let me know what you think.
      thanks in advance!
      With a 1320 watt system you could end up with more than 50 amps of charging. That is about about a C/5 charge rate which is pretty aggressive for your 24V 235Ah battery system. You only need about 25amps of charging so just 2 of those 330 watt panels should provide that for you.

        Comment

        • ula
          Junior Member
          • Aug 2016
          • 18
          #3
          Thank you. Would I be able to get more power if I left it as a 12v system? I have 2 more 6v batteries available so it would be a total of 6 6v batteries.

            Comment

            • SunEagle
              Super Moderator
              • Oct 2012
              • 15123
              #4
              Originally posted by ula
              Thank you. Would I be able to get more power if I left it as a 12v system? I have 2 more 6v batteries available so it would be a total of 6 6v batteries.
              With a 12V battery system you could use all 4 of those 330 watt panels but would be hitting the maximum input for that Midnite 150 CC. Although with 90 charging amps it is still a lot for even 6 of those 235Ah batteries wired to create a 12V 705Ah system. You would be close to a C/8 charge rate which may be a little to much for the batteries you have.

              The bigger issue is you will now have parallel wired batteries which runs the risk of not charging all of them equally.

              You also will now have double the amps going through the system wires between the CC and battery as well as between the battery and inverter. With 2000 watts at 12volts the wires would need to be sized and fuse for almost 200 amps.

                Comment

                • Mike90250
                  Moderator
                  • May 2009
                  • 16020
                  #5
                  If you seldom pull your batteries down deeply, they won't try charging at +50amps for often or long, it should taper off quickly.
                  With the classic, I would set the Absorb voltage .2V lower than normal, and monitor your average charging amps, and insure you are not cooking your batteries.
                  Overpaneling will help in the winter with poor conditions
                  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

                    • ula
                      Junior Member
                      • Aug 2016
                      • 18
                      #6
                      Thank you both for the thorough responses. If I were to just purchase new batteries what would you recommend that I purchase that would work well with my current solar panel etc. system?

                        Comment

                        • SunEagle
                          Super Moderator
                          • Oct 2012
                          • 15123
                          #7
                          Originally posted by ula
                          Thank you both for the thorough responses. If I were to just purchase new batteries what would you recommend that I purchase that would work well with my current solar panel etc. system?
                          With 1320watts of panels and an MPPT CC you can get about 55 amps for a 24V battery system. So you might look for 4 x 6V 550Ah or 6 x 4V 550Ah or 12 x 2V 550Ah batteries.

                          That way you get a 550Ah system with all of the batteries wired in series.

                            Comment

                            • Mike90250
                              Moderator
                              • May 2009
                              • 16020
                              #8
                              The midnight controller is able to be programmed to limit it's output amps. I'd keep the existing batteries till they fade, and set the amps limit to 30-40A That gives you some harvest in cloudy weather. New batteries would be L-16 floor scrubber types, or L-16 $olar
                              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

                                • MichaelK!
                                  Solar Fanatic
                                  • Jul 2015
                                  • 117
                                  #9
                                  What will you winter low temperatures be? Assuming your panels have a Vmp of 37.5 volts, four in series would give you 150.0VDC. That's right at the upper edge of what the Midnight 150 is designed for. Cold winter weather could push the voltage up higher than what the controller wants. Midnight has a voltage calculator on their website http://www.midnightsolar.com/. Look for the "Classic Sizing Tool". Use the calculator to determine what voltage will be safe for your equipment. The Midnight 200 might be a better choice.

                                  Secondly, the MPPT controller is designed to transform the voltage down to the battery bank, but Midnight's graphs indicate that transforming down from a lower voltage will be slightly more efficient. You might be better served using a 2S2P panel configuration, running at 75Volts. With two parallel arrays, you could mount them in slightly different directions so each is not producing maximal amps right at noon.

                                  In my own case, I bought Renogy's 3600 watt system, but added three additional 300W panels, for a total of 4500 watts. They're wired in a 3S5P ground-mount configuration. I can rotate the ground mounts so arrays are oriented either SE or SW, so I don't need to worry about maxing the controller at noon. On paper, my system is over-paneled, but in the real world, I can start running my well pump at 8am.

                                    Comment

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