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  • Mismatched panels in series/parallel build

    Read just a few stickys tonight and kinda understand now one of the many things I did wrong on my little 450W 12V system.
    My 12V/110V 1500W inverter is too big for only 450W of panels. So I guess I really only have only two safe options if I want to keep this system intact...

    1. Use a <450W inverter
    or
    2. Increase the amount of panels to >1500W.

    I dont like either option. I want to use the 1500W inverter and I don't want to buy 21 more 50W panels.

    New plan...

    I have 9 50W 12V panels and 6 310W 36V panels.

    I hook up 3 12V panels in series, giving me 36V on each 3 panel bank. And make three banks out of the 9 panels.
    Then hook up those three 36V banks in parallel to my 6 36V panels.

    What do you think?
    The stickys say its okay to do, but not sure which way to go.
    Do I match the volts and amps, but the watts will be 150 and 310.
    Or would it be better to hook up 6 50W panels in series parallel so the volts and watts match, but the amps will be 20A and 10A?

    I have a 60A 3000W MPPT CC for the 6 36V 10A panels already and the combined amps of all 15 panels will be 90A, so will I need a 30A MPPT CC too or do I just go with another 60A CC so the two CCs match? Or?

    Back to reading
    Attached Files
    Last edited by onesmallonebig; 05-24-2019, 04:27 AM.

  • #2
    I think you will see that your 50W 12V panels are costing you a lot more per watt than the larger 300W 36V panels, so you have made a correct choice there.
    Getting a larger CC or going to a higher battery bank voltage will give you more room to expand in the future.
    SunnyBoy 3000 US, 18 BP Solar 175B panels.

    Comment


    • #3
      you can, with proper wiring precautions, safely use your existing inverter, but it will suck the batteries down quickly.. If you only power it on when you have loads to power, the batteries would last longer
      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


      • #4
        Originally posted by inetdog View Post
        I think you will see that your 50W 12V panels are costing you a lot more per watt than the larger 300W 36V panels, so you have made a correct choice there.
        Getting a larger CC or going to a higher battery bank voltage will give you more room to expand in the future.
        Thanks to the good folks here and the wonderful stickys, I'm slowly learning the safest way to do this. At least I've disconnected everything before the fire starts lol.

        The new, improved and hopefully safe plan:
        Hook up the 9 12V panels in groups of 3 in series and parallel them to then 36V panels and buy a 100A MPPT CC.

        Hook up 3 12V batteries in series and make 6 36V battery banks.

        Or, is this gonna catch on fire too? lol

        Comment


        • #5
          Originally posted by Mike90250 View Post
          you can, with proper wiring precautions, safely use your existing inverter, but it will suck the batteries down quickly.. If you only power it on when you have loads to power, the batteries would last longer
          That's kinda what I've been doing. Off during the day to get more charge on the batteries, Only on at night.
          Im doing my best to build my own overkill monster 200A short battery cables with new marine ends.

          Comment


          • #6
            Without a hydraulic crimper. you cannot safely build even 100 A cables. Unless you are using the 48" handle crimpers.
            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


            • #7
              Your 36 volt Vmp. panels are actually considered 24 volt nominal. Your small panels are likely 12 volt, nominal. Look at the Vmp. of the small panels and you may find they are in the 17.5 - 18 volt range. That being said you really should series wire only 2 panels at a time to closely match the voltage of the large panels. Once the voltage is within 10% of the voltage of the other panels then you can parallel them together.
              36 volt, nominal systems are quite rare although 24 and 48 volt systems are quite common and finding inverters for those voltages is easy.
              2.2kw Suntech mono, Classic 200, NEW Trace SW4024

              Comment


              • #8
                Originally posted by littleharbor View Post
                Your 36 volt Vmp. panels are actually considered 24 volt nominal. Your small panels are likely 12 volt, nominal. Look at the Vmp. of the small panels and you may find they are in the 17.5 - 18 volt range. That being said you really should series wire only 2 panels at a time to closely match the voltage of the large panels. Once the voltage is within 10% of the voltage of the other panels then you can parallel them together.
                36 volt, nominal systems are quite rare although 24 and 48 volt systems are quite common and finding inverters for those voltages is easy.
                The 36V panels are right off of a 2 year old huge commercial solar farm, if that makes a difference. They are rated for 1000V Max in series.

                Vampire ratings... Vmpp? (Truth)
                Nominal (Lie)

                36V/310W panel info
                Maximum Power Point Voltage (Vmpp) 36.7V
                Open Circuit 45.3V
                Short Circuit 9.02A

                12V50W panel info
                Maximum Power Point Voltage (Vmpp) 17.5V
                Open Circuit (VOC) 22.0V
                Short Circuit (Isc) 3.17A
                Immp 2,86A

                So, I just go by the Vampire rating then.
                2 x 17.5 = 35 Pretty darn close to 36.7... within 4.64% 95.367847411444%
                Okay, ONLY two 12V (nominal) panels in series it is then. Thanks

                But in theory, wont those two panels be charging the 36V battery series banks with only 35V Max, even on a perfect day?
                Or is that safer than 3 50W panels in series that would overcharge the 36V bank with a Vmpp of 52.5V? Boom!!! Fire!!!!
                You got me all paranoid now littleharbor lol

                Also, that screws up pretty 9 50W panel array in the middle then. The little panel on the end is just for aesthetic symmetry then. Or I could buy one more 50W panel and have it stick out like a sore thumb lol

                Reliable made up a 1500W/36V/220V inverter with universal outlets for me.
                Here's a pic of the Reliable inverter on and at idle with 4 banks in series (12 so far) of those Walmart batteries... ready to plug something 220V into it (no panels attached yet).... from anywhere in the world. I've been rotating 19 batteries through the "learn the hard way" 12V system for 2 months, 8 to 12 at a time everyday... other pic taken today too. Okay, I lied the fire waiting to happen is still up and running. I'm using it now with 7 parallel batteries and 9 12V panels. Notice the voltage? Only been down to 11.1V once.My bad. It's all getting taken apart soon to finish the 36V baby monster system build though. I hope my house doesn't burn down tonight. If it does, you'll be the second person I tell, from my hotel room. I'll make sure I save the laptop, if I live
                I think what my be saving my butt with my little fire hazard 12V/110V system is that I really dont ever create very much of a load with my hermit lifestyle.
                I dont have a kiill a watt meter yet (haven't been to town in a week), but my grid meter said i was using .04 kwh today. 400 watts total with the fridge running, and a lamp, my internet box and laptop only on. Tomorrow I'll run out there with the tv, sate tv box and tv on too when the fridge kicks on. I guess I would just have to hang out by the pole waiting for the fridge to kick in to see the surge increase for a second. if that is even possible. Hell, I dont even need a kill a watt meter. I have one out on the service pole I put in in 1986?
                They installed a new fancy meter a few years ago so they can read and reset it from the office, I guess. I have used 151 Kwh this billing cycle (I think its on the 8th or the 12th. who knows I just pay the bill. I dont look at it) by mixing grid by day and solar by night.
                I have never thought about this stuff before but cant I do my average Kwh/day usage from that number?
                Just double 151 (half is solar) and divide by 16 for the 8th and then 12 for the 12th?
                302 / 16 = 18.875 Kwh/day
                or
                302 / 12 = 26.66 Kwh/day

                Can this be right? Is that a lot? I have no clue

                Edit: I just checked my power bill. My billing cycle BEGINS on the 12th.

                Thanks so much LH
                James
                Attached Files
                Last edited by onesmallonebig; 05-25-2019, 01:15 AM.

                Comment


                • #9
                  Originally posted by Mike90250 View Post
                  Without a hydraulic crimper. you cannot safely build even 100 A cables. Unless you are using the 48" handle crimpers.
                  No comment. I dont want to rile up LH again
                  Okay, I lied. I do want to rile LH up again
                  He will love these pic
                  I dont need no stinkin hydraulic crimper. Those are for rookies.
                  I'll put my cables up against anybody's.
                  I've been making 20' long copper 100A starter cables for 800HP race cars (not to mention 100 footer aluminum cables for the houses I've built) for 40 years. Long before you "Johnny come lately" Solar guys. I'm a pro NHRA drag racer. I hope LH doesn't read this
                  Attached Files
                  Last edited by onesmallonebig; 05-24-2019, 11:21 PM.

                  Comment


                  • #10
                    A starter cable @ 300A is only engaged long enough to fire the engine. An inverter sucking 95A for 2 hours on the same cable, is likely to have different results. My friend with a homemade EV, was always melting the terminals off a battery when going up hills. The battery shop would simply cast a new terminal onto the battery.
                    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 Mike90250 View Post
                      A starter cable @ 300A is only engaged long enough to fire the engine. An inverter sucking 95A for 2 hours on the same cable, is likely to have different results. My friend with a homemade EV, was always melting the terminals off a battery when going up hills. The battery shop would simply cast a new terminal onto the battery.
                      In drag racing, we turn the engine over for long periods of time before starting to build up some oil pressure before even hitting the ignition switch. Then it's still hard to get a hipo engine to fire. We run them so rich for top end end power. so they start flooded almost in hydrolock.. Plus they are extremely high compression... 13, 14 15 or more to 1 compression and they dont want to even turn over. Racing starters cost big bucks and also have two or three times more torque than regular car starters. And there's more but this is the wrong forum.

                      I had a couple old 70's electric SV-48V (8- 6V) CitIcars by Vangard back in the day. Wiki pic. Mine were yellow. They were always having lead cable end to lead post problems. Especially with a bunch of on/off golf cart solenoids controlling the voltage/speed changes. Used to keep a hammer under the seat and beat on those posts lol. With the melting point of lead around 600 degrees F, the weak link is the battery post and they start to fail long before 600.

                      I have eliminated a few of the potential problems. No lead battery cable ends. And I'm only using the steel threaded stud on the DC marine batteries

                      Every lead battery post on my system will have a minimum of 200A worth of cables (copper end to steel 5/16" stud) and as I get farther away from the inverter to cable amp capability goes up to 300A and then 400A with multiple hand built cables. Not that I will ever use 95A for 2 hours anyway, but I'm trying to reduce the external resistance, voltage drop and heat as much as I can. The batteries have enough internal resistance already.

                      I was taught by my dad, a 25 year career Navy pilot and hobby mechanic who taught me how to build my first race car 40 years ago... power cables can never be too thick and when in doubt, add redundant cables. The lead battery posts on my solar system will melt before my almost free (bought all new copper eyelet ends) redundant cables even get warm lol

                      I know a secret racer's trick to keep the lead battery posts from melting... I would tell you but I would have to kill myself if I did
                      Attached Files
                      Last edited by onesmallonebig; 05-25-2019, 02:14 AM.

                      Comment


                      • #12
                        10 days have passed. Still waiting on the new design 36V parts. Abandoned the 36v to 220v inverter idea because I cant split off one 110v from the inverter outlet like a regular 220v wall outlet. the inverter knows one side isn't drawing current, so it shuts off the other side off I'm trying to use. I watched the voltmeter voltage go from 110v to zero several times. So the stove and dryer are staying on the grid full time, for now.
                        I'm still using the small 450W 12v system. It's rock steady on sunny days. On cloudy days it pretty much useless by midnight. On sunny days I'm able to go about 48 hours on 7 batteries. Was getting over 3 days out of 12 batteries, before I stole 5 for the 36v system build. Battery voltage is never allowed to drop below 11.5V for more than a second with fridge startup surge. I'm getting so used to the little system that I can accurately predict the inverter "in" voltage late at night just by how my table lamp acts when the fridge kicks on. If it acts funky (11.3v), i just switch the cord from the solar outlet back to the grid outlet and about noon the next day plug the cord back into the solar.
                        The max charge I've seen is about 13.7v from the 3 pwm CCs. Usually 13.4 to 13.5v at the inverter. The CCs are always within 1/10v of each other. All 3 CC Temps are in the 27 to 35C range during a sunny, hot day.
                        I really cant complain about the 12v system's performance because I have nothing to compare it to... yet. The first month I was all gungho solar and my power bill was only $27 only having 300w of panels and 12 batteries. I dont use very much power anyway 10 months of the year.. The system has been offline a lot this month while working on the 36v system. I'll know this month's bill amount on the 11th.

                        The 1860w 36v system is ready to go. By next weekend the Reliable 36v to 110v 1500w inverter should be here and the 1860w system should up and running so I can use the power and test it's capabilities and duration. Building my own 10-3 cords for the final runs (12-3 for testing) and need more battery ends to finish up the battery cable Amp capabilties the way I want.

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                        • #13
                          ...
                          Last edited by onesmallonebig; 06-08-2019, 01:34 AM.

                          Comment


                          • #14
                            Have you stopped to consider that a 36 volt battery bank will need at least 43-45 volts out of the controller and with an MPPT controller that will require about 60-70 volts into the controller to maintain that 43-45 volts out!

                            Also please note that a 220 volt inverter is not a split phase 120/240 volt inverter.........they are not interchangeable!
                            Last edited by Tecnodave; 06-08-2019, 09:11 PM.

                            Comment


                            • #15
                              Originally posted by Tecnodave View Post
                              Have you stopped to consider that a 36 volt battery bank will need at least 43-45 volts out of the controller and with an MPPT controller that will require about 60-70 volts into the controller to maintain that 43-45 volts out!

                              Also please note that a 220 volt inverter is not a split phase 120/240 volt inverter.........they are not interchangeable!
                              Really? Maybe that's why I cant get my four 36v battery banks to charge higher than mid 38 volts with these panels and it takes forever (days) to charge them back up. They usually put out in the 40v range. I think I have too many batteries (12) in my banks. I tried only charging one 36v bank (disconnected the other 3 banks) and it still took almost forever.
                              Yeah, I found out the hard way that I cant split a 220v inverter into two 110s, like you can with power grid household 220v. The 110v side I'm trying to use shuts off when the inverter senses no draw on the other 110, i guess. And, I cant get my 220 dryer and oven to run of of the 220v inverter by wiring it up the "correct" way. The stove says "bad line" when I tried. So I tried wiring it a different way and nothing happened. I gave up. I'm leaving the dryer and oven on the power grid for now. I never use them much anyway. I'm going to try a 5000w (only 2500w when stepped down) 220/110v step down converter so I can at least use the 220v inverter for 110v stuff... hopefully. I can return the 220v inverter but I'm gonna keep it so I have 220v solar power available too.

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