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How to wire properly, Tesla batteries, Combiner, Inverter, Panels

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  • #16
    As far as temperature concern, there is someone who has did high current testing on the Tesla batteries and they handle voltage between cells staying the same very easily, and same for temperature... it is apparently very very hard to heat up a Tesla module. Their extremely robust cells. So therefore there doesn’t have to be any cooling requirements for off grid house use. As far as LVC, HVC, I plan on keeping the battery in a 20-80% range, so whatever the voltage will come out to for 80% and for 20%... I’m assuming it’s around 42, and 47.5 volts. I think the low end cutoff 19.8 minimum, which is 3.3v a cell (they can safely go to 2.8 volts without any damage but not recommend at all). And max voltage is 25.2v which is 4.2v a cell... these are just rough numbers kinda guesstimating, but I should be pretty close, I’ll just set the parameters on the charge controller....

    also don’t have to worry about voltage differences inbetween cells with such a low amount of power going through them, especially with the amount of modules in parallel together...

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    • #17
      You have mentioned having grid power available. Why would you spend a small fortune on an off grid system when you have the option of available grid power ? You can still go solar with a grid tie system.
      2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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      • #18
        Originally posted by Brandon8791 View Post
        .....

        also don’t have to worry about voltage differences inbetween cells with such a low amount of power going through them, especially with the amount of modules in parallel together...
        What is your strategy to monitor the modules?
        9 kW solar. Driving EVs since 2012

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        • #19
          Only reason I’d rather go off grid, is because I do not want to deal with a potential bill... according to our power company, they charge $25 a month just to have a meter in place. Also to get power ran to there, I’m going to have to take down two trees which is going to cost another $1,000, plus have lines ran with the power company which will be another $600... so $1,600 plus $25 a month for the whole time it’s going, or I could just go off grid and be completely green. And then don’t have to answer to anything the power company says or wants to do, if power ever goes out, I can still have my power on.

          as far as monitoring the batteries, there is a bms board wired to the modules, I could hook up some sort of bms, but don’t think it will be worth while, not with the low loads compared to what the cells handle... there’s no way they should get imbalanced.

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          • #20
            Originally posted by Brandon8791 View Post
            ............

            as far as monitoring the batteries, there is a bms board wired to the modules, I could hook up some sort of bms, but don’t think it will be worth while, not with the low loads compared to what the cells handle... there’s no way they should get imbalanced.
            Cells age differently and their capacity differences are what cause the imbalances. . It is not the intensity of use that you are putting them through it is the unknown use that the vehicle owner may have put them through. I have a lot of confidence in the quality controls Tesla puts in place to ensure that the battery packs in their vehicles last as long as possible. . . Are you planning on getting all the modules from the same vehicle? That could increase the likelihood that they will all be similar. Your strategy of only using them between 20 and 80% will mitigate that since any differences in capacity usually shows up as imbalance at the top and bottom of the charge and discharge curves.

            You should consider some form of monitoring whether it is an occasional manual voltage check or a complex BMS. I don't put much emphasis on the balancing aspect of a BMS but the monitoring is something I pay a lot of attention to, especially with used battery modules.
            9 kW solar. Driving EVs since 2012

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            • #21
              Originally posted by Brandon8791 View Post
              Only reason I’d rather go off grid, is because I do not want to deal with a potential bill... according to our power company, they charge $25 a month just to have a meter in place. Also to get power ran to there, I’m going to have to take down two trees which is going to cost another $1,000, plus have lines ran with the power company which will be another $600... so $1,600 plus $25 a month for the whole time it’s going, or I could just go off grid and be completely green. And then don’t have to answer to anything the power company says or wants to do, if power ever goes out, I can still have my power on.
              This is penny money compared to what it'll cost you off-grid with an electric water heater (instant or not), an electric range and the rest. You'll most likely need 2 to 3 x 5000$ inverters, your solar panels at 5000$ + all the gear to rack them, 2 expensive MPPT CCs, your batteries, BMSes, a generator (to not kill your batteries) and more. Easily 20-25K$ to get started with what you have in mind.

              Plus, get that idea out of your head that "if power ever goes out, I can still have my power on." - the POCO right now does all the hard work for you to provide power to your house. Being off grid, you'll have to do it yourself, 24/7 - no one will care if your inverter dies, if one of your MPPT CC goes ape-**** or if your have issues with your BMSes. You will have to fix those to get power back. If you think your time isn't worth money, it's a false perception you have. Plus, when you go away for vacation, you'll have issues, and you'll be out of power.

              I've been off-grid for 3 years on a large property with a large high-quality solar system - it's no easy-peasy stuff.

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              • #22
                [QUOTE=Brandon8791;n412972]Only reason I’d rather go off grid, is because I do not want to deal with a potential bill...



                With a grid tied system your bill will be negligible, if sized right. I believe if you do an accurate cost analyses of off grid, over time vs. basic grid tied, you'll see the light.

                2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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