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  • #16
    Originally posted by taxer View Post
    Yes, and sounds like I have to use one of my mppt cc's too. Was hoping to set it up on the cheap for a bunkie...


    I am sorry but the words "cheap" and "solar" should never be used in the same sentence.

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    • #17
      Originally posted by taxer View Post
      Yes, and sounds like I have to use one of my mppt cc's too. Was hoping to set it up on the cheap for a bunkie...
      Ok. What equipment do you currently have? List it like this so it's clear

      1) X brand charge controller(s) @ amps, volts, watts
      2) Quantity and volts/watts of panels
      3) Inverter

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      • #18
        What I want to do is use my 50amp pwms and one of my 12v inverters- probably the 1000w for now.

        Remember this is a bunkie.
        fans, lights , electronics, pellet stove ( max 350 watts to start it - igniter, then 100w)
        Occasional 600w heater

        The pwms are generic kw2450 50amp 12v/24v
        max panel input 650w/1200w
        mav v input says 50v on label
        but poor manual translation, it says <34v
        Equalization for flood batteries is 14.6v
        Double for 24v 29.2v

        Panels are OSM off grid 235w pmax
        and as mentioned 3.65 vmp
        7.69 imp I have many

        2 panels per inverter is a waste at 12v
        But 5 at 24v is more efficient.

        Lots of 6v golf batteries
        but want to do 2 x 24v banks

        Again,

        Looking to charge batteries at 24v and discharge at 12v....

        And not looking to blow it up.

        I'm testing in theory only at this point.

        Any electrical engineers here that want to educate me on the theory behind what works and doesn't, I'm all ears. Or anyone that may have tried this before.

        I have Different scenarios I have sketched out, with switches, etc., but looking for some brain storming here.

        Previous posts discourage not taking 12v from the 24v array and discharging separately to which I fully agree.

        How can I discharge the 24v battery bank 12v at a time for my inverters?

        I questioqed discharging them by doing a parallel hook up to the inverter from the same 24v bank.
        I believe the answer was they would now become a 12v bank and fry something..
        still trying to determine the properties and principles of these arrays....

        The other possibility was to draw 12v from one bank and 12v from the other into one inverter and the remaining 12v from each bank into another inverter. The discharge connections to the inverters would be equal .

        Also, my mention of doing solar on the cheap may have been misinterpreted.
        cheap in costs is what I referred to as in mppt vs pwm. Solar does not have be expensive anymore.

        I believe proper wiring requirements is essential, but there should be many scenarios to arrive at the same solution.

        So with the equipment I mentioned anyone with an idea would be greatly appreciated.

        Switches and breakers added have given me some other solutions but they involve more manual maintenance and attention to keep the batteries at peak condition.

        Thanks

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        • #19
          Pwm input should read <34v

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          • #20
            This can be accomplished with a large bank of switches: ( I'd suggest Blue Seas marine battery switches, rugged & reliable)

            1) Switch off PV arrays

            2) disconnect charge controllers from batteries

            3) disconnect * some * of the series batteries to get 12V vs 24V

            4) parallel connect switches to parallel the 12V blocks of batteries

            5) connect inverter

            mis-perform one step and you will severely damage something, either shorting out batteries, frying your 12v inverter with 24v or
            suddenly finding out one of the 6v batteries is only 4v because of a shorted cell, and when paralleled with a batch of 12V blocks,
            you get all the good blocks discharging into the block with a dud cell.

            You will spend more on the many quality switches, than you would on a decent 24V inverter
            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


            • #21
              Taxer, you can easily do what you want to do if you don't want to charge the batteries and use the inverter at the same time, or you only want capacity of one of the batteries at a time.

              The problem is that you're going to end up with kind of a rube goldberg setup. It's simply a matter of matter of installing a couple heavy duty battery relays that allow you change your setup to 24V for charging and 12V when the inverter is on.

              When your inverter is on, you can use the power it's producing to switch a few relays that changes your battery bank to 12V. This will act as an interlock so that you never accidentally apply 24V to your inverter.

              The problem with this is that your lack of knowledge (not making fun of you) in regards to basic electrical could create problems. Once you make the necessary cables, install the relays and such, you will find that your money would have been better spent on a new inverter. I would sell some of your 6V batteries to raise cash do that instead of ending up with a band-aid system that only you know how to operate and could create a fire hazard if one of the relays goes bad or you have had a few too many cold ones and forget something.

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              • #22
                Yes, sort of Russian roulette...

                and the cost of switches/relays...

                Maintenance and attention to switch the battery banks would be tedious.


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                • #23
                  array.jpgarray.jpg

                  Has anyone ever tried this array?
                  Pulling one 12v from each 24v charging bank to power a 12v inverter A
                  Take the remaining 12v from each 24v charging bank and route it to a second B inverter.

                  Comment


                  • #24
                    That doesn’t work, you’re connecting points that have 12V between them together, causing short circuits.

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                    • #25
                      So putting the 2 12v batteries in parallel to the inverter causes the short?

                      I'm guessing only way around it is to have 4 inverters or just 1 24v bank and 2 inverters to each separate 12v...


                      Comment


                      • #26
                        Originally posted by taxer View Post
                        So putting the 2 12v batteries in parallel to the inverter causes the short?

                        I'm guessing only way around it is to have 4 inverters or just 1 24v bank and 2 inverters to each separate 12v...
                        No, use a single 24v inverter, that solves both the wiring problem and the problem of drawing unequal currents from the batteries. As you have found, you can’t have batteries wired both in series and in parallel at the same time.

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                        • #27
                          yes 24v inverter is the easy answer, but i have a few 12v 's already.,,,

                          so,the

                          4 inverters or just 1 24v bank and 2 inverters to each separate 12v

                          would work without defying principles of the wiring arrays, but excessive costs and possible uneven discharging?


                          I'm asking because there are other possible panel/cc/battery/inverter array combinations that may work with the equipment I already have.

                          I already have my mppts and inverters penciled in for my garage and cottage project. blueprints.

                          I'm not so much into efficiency for the bunkie, but to make use of my extra equipment in a safe manner.

                          Comment


                          • #28
                            Originally posted by sdold View Post
                            No, use a single 24v inverter, that solves both the wiring problem and the problem of drawing unequal currents from the batteries. As you have found, you can’t have batteries wired both in series and in parallel at the same time.
                            So here together is not considered parallel..

                            so 2 separate panels/cc/batt banks/ but sharing 12v from each sharing an inverter...is another scenario... assuming wiring a 12v from a separate system/array (separate panels/inverter/battery bank)



                            2 array.jpg2 array.jpg

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                            • #29
                              got cut off...

                              so if two separate systems sending 12v to a shared inverter is not considered parallel, this should work...

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                              • #30
                                It could work, but only until one inverter has a different load than the other inverter. Then the batteries become unbalanced and one is either undercharged, or the other is overcharged.

                                I know you are trying to economize and use the gear at hand, but while the latest scheme sort of works, it won't work with mod sine inverters and can only work with transformer isolated pure sine inverters. There are issues with the inverters AC grounding interfering with the battery grounding, Again - the easiest way is to get a 24V pure sine inverter.
                                Why pure sine :

                                fans, Pure sine required for the motor
                                lights , mod sine works for incandescent, otherwise pure sine for electronic bulbs
                                electronics, Some work with mod sine, some don't.
                                pellet stove the feed motor requires pure sine

                                Feeding mod sine into a motor causes it to consume about 20% more power that gets dissipated as 20% more waste heat. Few consumer motors have that much margin and the motors die sooner.

                                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

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