Adding to my battery bank.

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GreyMtOffGrid
GreyMtOffGrid Registered Users Posts: 5 ✭✭
in Off Grid Solar & Battery Systems #1
Here is my little set up. I have 800 (10-80W Panels) watts of solar going to my current battery bank which is 4-100ah Windy Nation Batteries in a 24 volt battery bank. My charger/Inverter is a MPP Solar all in one unit and I was curious what is the safest way to add to my battery bank? Any suggestions. 

My idea is to install a Positive and Negative bus bar to add the 2nd battery bank of 4-100ah Windy Nation batteries to my bus bar before the cables go to the MPP Solar unit. And I would connect both battery banks to the bus bar in their respective banks. So it would be 2 separate 24V 200ah battery banks to bus bars that feed to the MPP Unit. 

Obviously I would make sure both battery banks are in equal states of charge and have fuses and a manual shut off for both banks separately. Does anyone have suggestions for this or maybe if adding a 2nd charge controller would benefit my battery bank? 


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  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    #2
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    If they are connected, used and serviced at the same, it will be one battery bank....
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • GreyMtOffGrid
    GreyMtOffGrid Registered Users Posts: 5 ✭✭
    #3
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    Photowhit said:
    If they are connected, used and serviced at
    the same, it will be one battery bank....
    So there’s no issues with adding batteries as long as they’re the same brand and brought up to the same state of charge? I’ve been told by a couple people that I can’t add batteries after a month to a battery bank. 
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  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    edited February 2021 #4
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    GreyMtOffGrid said:
    Photowhit said:
    If they are connected, used and serviced at
    the same, it will be one battery bank....
    So there’s no issues with adding batteries as long as they’re the same brand and brought up to the same state of charge? I’ve been told by a couple people that I can’t add batteries after a month to a battery bank. 
    While you 'can', after about 6 months, it's not a great idea, The new set is likely to have a shortened life as the charge discharge won't b equal.

    I'm NOT saying there's no issue, I'm saying if they are charged together and discharged together, they are one battery bank. Unless you use one at a time charging and discharging, there is no practical way to have them act independently.

    In the end you have, 4 strings of 2-12 volt batteries.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #5
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    GreyMtOffGrid said:
    Photowhit said:
    If they are connected, used and serviced at
    the same, it will be one battery bank....
    So there’s no issues with adding batteries as long as they’re the same brand and brought up to the same state of charge? I’ve been told by a couple people that I can’t add batteries after a month to a battery bank. 
    The thing to be careful with is having an array incapable of charging a battery bank of too large capacity, your current setup is about ballanced in terms of array  capacity versus battery capacity. Having the additional capacity could lead to deficit charging should you have a period of poor weather or a deep discharge, which can be augmented with a secondary power source. The preferred method is to have sufficient PV to maintain the batteries, for 400Ah at 24V nominal at least 1600 W would be a better fit, more if the weather is frequently overcast for example.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
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  • Marc Kurth
    Marc Kurth Solar Expert Posts: 1,144 ✭✭✭✭
    edited February 2021 #6
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    Always be aware of your depth of discharge.

    Note the DOD vs/ Cycle life chart below is for your particular brand of batteries. These batteries appear to be better suited to occasional use as opposed to daily. Run your system accordingly.

    As seen below, running an average daily discharge of 50% for 1.5 years will result in a battery bank worn down to 60% of rated capacity.
    After 4 years with a daily DOD of only 30%, your battery bank will be down to roughly 50% of the original storage capacity.

    ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

    I always have more questions than answers. That's the nature of life.
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