Need some advice on a battery config

thermax292
thermax292 Registered Users Posts: 23 ✭
in Off Grid Solar & Battery Systems #1
I working on a grid down emergency plan to get my solar power back up and running after an EMP or CME. I have a 2000 watt Xantrex 12 volt inverter I'd like to connect to my batteries. There are 8 400 ah 6v batteries in my system giving me 48 volts. I'm thinking about purchasing another Xantrex XW-MPPT60-150 controller. My system now uses two to split up my 27 224watt Sharp panels into two groups.If the grid were to go down and I lost my inverter and controllers but my panels were still OK I'd like to connect the new controller to 1/2 the panels and supply 48 volts to my battery bank. Here's the problem. I don't have the money to purchase a new Xantrex Hybrid inverter and store it in a Faraday box. I do have a pure sine wave 2000 watt inverter that works on 12 volts. I've attached a photo to this post showing my battery config. Would it damage anything in a grid down situation if I connected the inverter at the two points I show in the drawing to get 12 volts from the 48 volt battery bank to run the 12 volt inverter? Thanks so much

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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #2
    Re: Need some advice on a battery config
    thermax292 wrote: »
    Would it damage anything in a grid down situation if I connected the inverter at the two points I show in the drawing to get 12 volts from the 48 volt battery bank to run the 12 volt inverter? Thanks so much

    It would not immediately damage anything, but you would get only 1/4 of the power available from the batteries before over-discharging that pair of batteries. And you would not be able to recharge just that pair of batteries while they were connected as part of the 48 volt bank. For the first few hours, you would be OK, but after that you would be out of luck.

    In the event of EMP damage, you would be better off modifying your battery, panel and CC wiring back to a 12 volt parallel setup for as long as you needed to use a 12 volt inverter.
    Just make sure you have the necessary additional cables and busbars on hand to do that. :-)
    SMA SB 3000, old BP panels.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #3
    Re: Need some advice on a battery config

    i think this may depend on how mickey mouse your emergency connections are to be. the biggest problem would be in connecting to the main breaker box as many inverters that are cheaper do not like this as the neutral and ground would get tied. the solution there is an inverter that can accommodate the tying, but these cost more generally. in an emergency there would be nothing wrong with having a cheaper sine wave inverter with extension cords. not good electrical practice, but hey, an emergency would be an emergency. i guess it is also rare to have such of a cheaper inverter to be at 48v that would fit your battery bank properly as tapping part of the bank for another that has a lower voltage is a big no no. you can rewire the entire battery bank to 12v or 24v to accommodate the more common cheaper inverters as was suggested and it would allow more capacity to be available to you in said emergency. basically i'm saying during an emergency anything you do is good, but the problem you may encounter is when the emergency is over will you be replacing batteries or not? this is the planning you want and need now.
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  • thermax292
    thermax292 Registered Users Posts: 23 ✭
    #4
    Re: Need some advice on a battery config

    My plan is to rewire the battery bank to 12 volts and use the Xantrex prowatt 2000 to power the house. I only plan on running 110v stuff like the lights and ref. I want to purchase a new battery controller that I can connect my PV array to. I have 27 220 watt 30 volt panels connected in groups of 3 giving me 90 volts per group. I was told also that if the panels have a blocking diode in them that after an emp/cme they my not work anyway. But in case they do, I need a good battery controller that will allow me to rewire my system and get some power out of it and yet be cheap and small enough to store in a Faraday cage. The Xantrex units (2) on my system now are the XW-MPPT60-150. I figured if I bought an extra one ( about $500.00) it would give me a spare as well as a back up for an emergency. I could replace the bad one after an emp and use 1/2 the grid as its hooked up now. My system has 9 groups of 3 panels, 4 to one controller and 5 to the other controller. I called a retailer about my Idea and the tech told me because I was going from 48v to 12v that I could only connect 3 panels ( 1 group) to the controller but I'm not sure how to figure that out. I'd like to connect the group of 5 ( 15 panels) to the battery controller to charge up a 12v battery bank consisting of 8 400ah batteries, to run my cheap Xantrex inverter.

    Thanks so much for all your responses, I know how much time and thought goes into these responses.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #5
    Re: Need some advice on a battery config

    pvs do not usually contain blocking diodes, but they do have bypass diodes. the pvs would work without them if there isn't any partial shading on the pvs, which none of us can say that that never happens. the diodes would allow power to pass around the higher resistance path posed by the shaded cells. if power is forced through the shaded cells then this creates heat and failure of the pv altogether.

    i don't recall offhand if you could wire that inverter into the utility panel with the neutral and ground tied in the utility panel or not, but the guys can make further comment on this.
    here is what i found on the users manual,

    Connect the CHASSIS GND screw to your
    system's DC grounding point using a minimum
    6 AWG wire. the systems grounding point is

    usually the AC service entrance grounding

    point or a separate ground rod. For a solar PV
    (photovoltaic) installation, this is usually the
    same rod used to ground the PV array

    of course it goes without my saying that the main breaker has to be off or sparks will fly if it should be ok with the neutral/grd connection tied.
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  • rocmor
    rocmor Registered Users Posts: 11 ✭
    #6
    Re: Need some advice on a battery config

    Just something on the side... What will be your source of water during an extended outage? Many (most?, all?) submersible pumps are 240V.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #7
    Re: Need some advice on a battery config
    rocmor wrote: »
    Many (most?, all?) submersible pumps are 240V.
    Definitely not all. But for the larger pumps and deeper wells (think longer wires), the usual current reduction advantages of 240 cause them to be by far the most common and most economical. Since the pump does not use a neutral, the number of wires is the same for either voltage.
    SMA SB 3000, old BP panels.
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  • thermax292
    thermax292 Registered Users Posts: 23 ✭
    #8
    Re: Need some advice on a battery config

    Rocmor

    I have 1500 gal on site as well as several real good purifiers and a small lake behind the house. I also have a manual well pump. thanks for asking
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