New here, looking for info on parallel connections

xerxescct
xerxescct Registered Users Posts: 3 ✭
in Solar Beginners Corner #1
Hello everyone.

I have a 500 watt solar array running at 12 volts. I have another 500 watts of solar coming in this week. I currently have 2 100 AH AGM batteries I am charging just to run a few odds and ends around the house. These 2 batteries are being replaced with 5, 155 AH AGM batteries coming in this week to complete the setup. 

My question has to do with wiring these batteries for a near perfect balance. I know the quick and dirty way is to connect positive and negative at opposite ends of the bank but I would like to do it with as close to a perfect balance as possible. I am using 3/0 cable with copper terminals. I have no made the interconnect cables yet as I am waiting to figure out the best balance. Would someone be able to explain how this works depending on the number of batteries? I have seen a picture for a perfect balance in a 4 battery bank but not 5. So I am just trying to understand how the formula works weather it be 3 batteries or 25 batteries.

Any suggestions, website, tips, or ideas would be wonderful.

Thank you very much.

Sean
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Comments

  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    edited November 2015 #2
    You probably do NOT want to have more than 3 parallel batteries in a bank.  read here for the answer....http://smartgauge.co.uk/batt_con.html and here   http://batteryuniversity.com/learn/article/bu_002_introduction

     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
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  • xerxescct
    xerxescct Registered Users Posts: 3 ✭
    #3
    Thank you for the reply. I read over the first site a few days ago and the formula stops at 4 batteries. Would you be willing to explain the 3 battery limit? Thanks
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  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    #4
    Even with 3 batteries there is enough variance between batteries that they will not charge evenly,  At that 775 Ahr rating for the whole bank you should be considering a single string of 2V cells...  see my sig.. then there are no parallel battery issues.
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
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  • xerxescct
    xerxescct Registered Users Posts: 3 ✭
    #5
    Sounds good, I will look into the info you have provided. Thanks very much, have a good day
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  • Hamfast
    Hamfast Solar Expert Posts: 44 ✭
    #6

    Welcome to the forum Sean...  :)

    I am curious; What are you going to use this system for (odds and ends)? What are your loads? Are they AC or DC? What voltage are you going to run our system at - 24, 36, or 48volts? What voltage are your batteries?

    Four 12v, 100ah batteries in series will give you a 100ah bank @ 48v. The same four batteries in parallel will give you a 400ah bank at 12v.

    If your 155ah are 12v, you could set up 2 parallel strings (4 batteries) yielding a 310ah bank @ 24v.

    Those same four batteries in series will get you a 155ah bank @ 48v, probably a better match for the 1000W array you're going to install.    :)

    Return the 5th battery...:)

    Monte

     

    Off Grid System; 2175W array; 370ah @ 48v (8 L16 Scrubbers in series); XW MPPT60-150 CC; OutBack VFX3648, FlexNet and Mate

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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #7

    I guess you own the batteries now, I agree with what has been said above.

    Easiest way to connect them so that they have equal resistance, is to use a bus bar. This is basically a short piece of metal that all your batteries connect to. Use the same length and thickness wire for each connection. So if your farthest battery is 2 feet away, connect it with a 2 foot wire and use a 2 foot wire for the battery that's 6 inches away.

    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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