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Battery bank charging WAY slower after modification.

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  • #16
    Oh.. and just a thought.. with 10 panels at a 1000 watts.. and set up for 24v.. would you use the vmp of 18V to calculate current? Or 24V?
    1000W / 36V = 27.7amps or 1000W / 24V = 41.6amps

    my concern is I just wanna make sure I don’t push the 40amp CC?
    thanks!

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    • #17
      Originally posted by Iss_shaffer View Post
      Ok gotcha on that now.. and after looking at what I’m trying run I see I can drop down to a 2000 watt inverter. At first I was thinking, ok 2400 watt-hour system so I need a 2500 watt inverter to cover that, but now I see that is not the way to look at it. So pretty much the only cloudy area I have left now is the wire coming from the array.. it’s give or take Between a 100’-120’ run and during the tests I have conducted my input voltage coming in straight from the panels averaged between 32-33V, and that’s wired up for 24V. So with a vmp rating of 18V would you agree that’s a significant voltage drop? Looks like I made need to up that #10 to #8?
      Yes it is significant VD. With a 4 volt drop you are in the 10% range and need to be in the 2% range. The wire needs to be sized so you do not exceed a 20% VD. That may require at least a #8 .

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      • #18
        That’s a big 10/4. Well I’m gonna try and see if I can take from here. Man I really appreciate your time and patience with all the questions. You cleared a lot up for me in a short amount of time... Thanks so much!
        ✌️

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        • #19
          Originally posted by Iss_shaffer View Post
          That’s a big 10/4. Well I’m gonna try and see if I can take from here. Man I really appreciate your time and patience with all the questions. You cleared a lot up for me in a short amount of time... Thanks so much!
          ✌️
          You are welcome. I hope it all works out for you.

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          • #20
            Just a comment on panel output efficiency...I have 2 arrays with each totalling 1500 watts. Each array only put out a maximum of about 1.05KW. So you need to take into account the efficiency of panels..You need to reduce the panel output by some percentage.

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            • #21
              Citabria

              So now that I’ve revised the setup I see exactly what your talking about now with panel efficiency. It’s working way better with the 24v setup now, but needs just a little more something? It looks like my 1000w array is actually somewhere around 600w. The highest charge current I’ve seen so far has been around 25amps. I got 5 strings, each in series.. They each read around 40v but under a load they drop to around 30-32v or so? I eliminated the voltage drop between the array and the controller with the 8awg wire (150’ apart) so I’m good there now (thanks Sun Eagle!) my question now is... considering the efficiency factor, would adding a couple of more panels put me closer to what the original math calculated and still be in the safe zone?
              Thanks!

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              • #22
                If you don't keep a lead acid battery charged up all the way, it will sulfate and lose capacity. So if you're SOC is at 70% to 80% and you've been running in that range, I'm guessing your batteries are probably already damaged.

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                • #23
                  Wondering why the mppt charging current jumps around so sporadically?

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                  • #24
                    You don't have to keep buying expensive 12V panels. Since you are going to wire them in series to increase their voltage, you can add cheaper/watt grid-tie panels at lower net cost. You just need to make sure the output voltage difference is <5%. So, say you wire four of your 12V panels in series to get 18Vmp X 4 = 72VDC. You could wire that in parallel with two 72cell grid-tie panels putting out 36VDC. So, that works out to be 36Vmp X 2 = 72VDC.
                    Look on Craigslist in your local area for panels. I've made four purchases in the last year for myself and neighbors, paying only 55-59$ each for 250-260W panels. Shipping is the price killer for solar panels. When you buy new, via mail-order, ~50% of the total cost is the shipping. You can get grid-ties dirt cheap when you can drive to the seller and load them yourself on the back of the truck.

                    I like to plug numbers into formulas for people. Use this...

                    Battery capacity X charging rate X charging voltage X solar efficiency conversion = panels needed.

                    In you case, you have a 400AH battery bank, that will like being bulk charged at ~26V. Assuming you get 80% of rated output, the reciprocal of 0.80 = 1.25. 1.25 is your solar efficiency conversion factor.

                    What you need then is... 400AH X 0.1C X 26VDC X 1.25CR = 1300W of panels. So, take your 12V panels and put them in two strings of four panels. Then add two grid-tie panels wired in series. That will bring you up to ~1300W. Now, 1300W/26V =50amps, so that exceeds what your controller is rated for. With the money you save buying the grid-tie panels you could either replace the Rover with a better higher amperage controller, or add a second Rover to charge the battery bank in parallel. I personally wouldn't use two Rovers. I would buy a higher amperage controller like an Outback, Midnight, or a MorningStar.
                    Last edited by MichaelK!; 07-28-2020, 01:31 PM.

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                    • #25
                      Good stuff, thanks!

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                      • #26
                        I really recommend you do any number of voltage caculators to figure your expected voltage loss. I have a 20’ run, which requires 40 feet of wire for the calculator 20 amps out, 20 amps back, and I could use wire thinner than 10 gauge, at this distance, but if I put the panels in parallel instead of parallel, it seriously degrades the voltage loss. However, to save with voltage loss, I may go too high an input voltage to charge controller charge voltage and lose efficiency there.

                        I’m just saying there’s a lot more to attack here than just the inverter.

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