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Hunting cabin with air conditioning, it's florida for God's sake

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  • Hunting cabin with air conditioning, it's florida for God's sake

    Ok, lambaste me if you like, but I'm planning to eventually run a 8000btu window shaker for 12hrs a night
    it pulls 800 watts when the compressors on and 100watts when it's off so I'm thinking about 8kwa each night
    we have a 9.5 kva generator we usually run but are trying to get off that for peace and quiet.

    my plan is an outback flexmax 60 on 48v bank
    8 trojans in series with a 438ah capacity
    maybe 3000 watts of panels
    Outback inverter/ charger 2500w,

    we only stay about 2 nights in a row, then gone for 2 weeks, if we need we can run the generator to top off batteries in the afternoon

    please let me know what you guys think
    I know , it's gonna be a big system

  • #2
    Originally posted by wetsu151 View Post
    Ok, lambaste me if you like, but I'm planning to eventually run a 8000btu window shaker for 12hrs a night
    it pulls 800 watts when the compressors on and 100watts when it's off so I'm thinking about 8kwa each night
    we have a 9.5 kva generator we usually run but are trying to get off that for peace and quiet.

    my plan is an outback flexmax 60 on 48v bank
    8 trojans in series with a 438ah capacity
    maybe 3000 watts of panels
    Outback inverter/ charger 2500w,

    we only stay about 2 nights in a row, then gone for 2 weeks, if we need we can run the generator to top off batteries in the afternoon

    please let me know what you guys think
    I know , it's gonna be a big system
    IMO that 48v 438Ah battery system should safely provide you with about 5.3 kWh a day by using 25% DOD. If your estimate for your daily load is 8kWh then I would say your battery bank may be small and will not last as long as it could because you will be discharging it about 40% each day for the two nights you use it.

    That may work for you since you are only in the cabin every couple of weeks but it still will hurt those Trojans a bit and shorten their life.

    I will say that 3000w and a 60A CC may be a little fast for that battery system but in reality you will get less than 60amp which should get you inside the C/8 charge rate. Just keep an eye on your SG values.

    I would also look into getting a kill a watt meter to measure what that AC unit will really be doing to your battery system. Estimates are fine on paper but in reality it could kill your system if you underestimate your needs.
    Last edited by SunEagle; 04-29-2018, 10:37 PM. Reason: added last sentence

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    • #3
      Yes, I have a kilo-watt meter and will test it this weekend, I can't believe how much the air conditioner is gonna cost us in battery bank cost . wow !!
      thanks for the charge info, did not think of that.

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      • #4
        Originally posted by wetsu151 View Post
        Yes, I have a kilo-watt meter and will test it this weekend, I can't believe how much the air conditioner is gonna cost us in battery bank cost . wow !!
        thanks for the charge info, did not think of that.
        And you get to replace that battery bank in 3-5 years. especially in the Florida heat.
        2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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        • #5
          8 Kwh-day at 48 volts is a 830 AH battery. A 48 volt 830 AH battery requires 4000 watts of panels and an 80 Amp MPPT charger.
          MSEE, PE

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          • #6
            Thank you guys for this info, I really appreciate your time...also dont want to be buying this stuff twice as it is expensive

            My thoughts on battery life is I will only be cycling them about 50-75 times a year. That gets me about 10+ years , No?

            Also we will be running the generator a little also

            Sunking, are your numbers rated at only a 20% discharge of the bank ?

            Also, its costing us about 1200.00 a year to run that generator currently

            Thanks
            Dave
            Last edited by wetsu151; 04-30-2018, 03:17 PM.

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            • #7
              Originally posted by wetsu151 View Post
              My thoughts on battery life is I will only be cycling them about 50-75 times a year. That gets me about 10+ years , No?
              No batteries have both cycle and calendar life. Whichever comes first.

              Originally posted by wetsu151 View Post
              Sunking, are your numbers rated at only a 20% discharge of the bank ?
              Yes

              MSEE, PE

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              • #8
                Originally posted by wetsu151 View Post
                ...its costing us about 1200.00 a year to run that generator currently
                Seems like a great deal compared to what you are thinking of spending for off-grid solar, especially with new batteries needed every 3-5 years. A 4 x 8 sheet of plywood stood on edge can really knock down the noise as long as you don't have close neighbors to deal with.

                If you cabin is often unoccupied, keep in mind thieves and vandals can spot a solar installation from miles away. A generator is easier to hide or take with you when you aren't there.

                Dave W. Gilbert AZ
                6.63kW grid-tie owner

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                • #9
                  Yes, cheaper for a smaller generator. We currently run a diesel kubota setup at 9.5kw rating. It's not loud but we just want to get away from running it all the time. I do have sun electronics here and can get modules for 50 cents a watt. Already bought a new outback flexmax 60 for 350.00 new . Big expense is those damn batteries

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                  • #10
                    If I can claim the 30% federal tax break it makes it a little bit easier, we are looking 4 peace and quite also, and 4-5 months the weather is nice enough to not need the air conditioner.
                    so my next thought is maybe set this up small now, just 4 led lights and small loads. I have found the 48volt mini-split air conditioners that look promising, maybe only pulling 4kv a night.
                    I see the tax credit is going away by 2020 though

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                    • #11
                      Originally posted by wetsu151 View Post
                      Yes, cheaper for a smaller generator. We currently run a diesel kubota setup at 9.5kw rating. It's not loud but we just want to get away from running it all the time. I do have sun electronics here and can get modules for 50 cents a watt.
                      You do not need the solar. Get a battery charger and run it off the genny like a hybrid vehicle. When the battery gets low, the generator runs and recharges the batteries and shuts off. Repeat

                      MSEE, PE

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                      • #12
                        Originally posted by wetsu151 View Post
                        Yes, cheaper for a smaller generator. We currently run a diesel kubota setup at 9.5kw rating. It's not loud but we just want to get away from running it all the time. I do have sun electronics here and can get modules for 50 cents a watt. Already bought a new outback flexmax 60 for 350.00 new . Big expense is those damn batteries
                        Yes, batteries are expensive (and heavy, and short lived.)

                        If you don't want to run the 9500 watt diesel gen, then get a smaller one that barely supports your minimum loads and use that for most of your power. Or get a slightly larger one and charge a small bank periodically as SK mentioned.

                        If you want to get solar, they can extend the times that the generator doesn't run - and can extend the life of your batteries by keeping them at a high SOC (at least for lead acid.) But it's generally not worth it to try to cover 100% of an intermittent load with solar.

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                        • #13
                          Oh boy, this gets interesting
                          I was reading the outback inverter specs for the VFXR3648A and noticed that when only pulling 500 watts from it, the efficiency is horrible.

                          It does not get to a good percentage until your pulling 1k from it.

                          That will kill my mini-split a/c draw of only 500watts idea

                          What do I need ? a much smaller inverter ?
                          Thanks

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                          • #14
                            Determine max connected load that wil be on at the same time x 1.25

                            You want the Inverter or genny to be 75% loaded.
                            MSEE, PE

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                            • #15
                              What is your recommendation on stringing these, I got a great deal on some GCL Solar panels , 325watt
                              the specs are Vmp 37.6
                              Imp 8.64
                              Voc 46
                              Isc 9.24
                              if I run 3 in series it puts me at 151 volts Voc @ 40-32
                              Last edited by wetsu151; 05-05-2018, 09:35 AM. Reason: Missed something

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