Battery wiring/configuration

jbad
jbad Registered Users Posts: 7 ✭
in Solar Beginners Corner #1
I am new to the forum but have been lurking for sometime...

I have a 4000W 24V 120/240VAC off-grid system, 10 230W panels.
I had started w/ 8 Trojan L16P-AC (420ah) 6V batteries a month ago and now adding 4 more.
I am not sure how to string the batteries. I am currently using this configuration.
Attachment not found.
I'm a bit confused since I saw this configuration as well
Attachment not found.
Any advise/enlightenment would be greatly appreciated.

Thanks!
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Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Battery wiring/configuration

    You have two connections between the positive and negative polls of each battery string. You don't want that. Take out the positive to positive on the left and the negative to negative on the right. Otherwise assuming the lengths of the wires connecting the batteries are equal it's fine.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,609 admin
    #3
    Re: Battery wiring/configuration

    And, I will add, monitor the specific gravity, the voltage across each cell/battery (under heavy charge, heavy discharge, and resting), and I would suggest (broken record time:blush:) a DC Current Clamp Meter (here is one that is not too expensive and "good enough" for the job) so you can monitor the current flow through each string (under heavy charging and discharging, the currents should be roughly similar).

    Basically, you want to look for "differences" (cell/battery with too high or too low of voltage, unbalanced current flow, etc.)... Between poor connections and the occasional failed cell (open or shorted), you want to find the problems before they can damage the rest of the battery bank (a shorted cell can cause the other cells to over charge; and open cell can take that string out of operation and eventually cause sulfation).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • jbad
    jbad Registered Users Posts: 7 ✭
    #4
    Re: Battery wiring/configuration
    Cariboocoot wrote: »
    You have two connections between the positive and negative polls of each battery string. You don't want that. Take out the positive to positive on the left and the negative to negative on the right. Otherwise assuming the lengths of the wires connecting the batteries are equal it's fine.

    Thank you for you quick response and clarification...
    Now for the real question, I am adding 4 more batteries, what would be the best way to connect them?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
    Re: Battery wiring/configuration
    jbad wrote: »
    Thank you for you quick response and clarification...
    Now for the real question, I am adding 4 more batteries, what would be the best way to connect them?

    Don't.
    You are in danger territory. For two reasons: 1). adding a third string makes it more difficult to keep current flow even throughout all (you need bus bar/common connection point. See Smart Gauge Method #3 here: http://www.smartgauge.co.uk/batt_con.html)
    2). you have a 2300 Watt array capable of about 74 Amps or an 8.8% peak charge rate. If you add another 420 Amp hours this will fall to 5.8% which is very minimal. If you add more battery you should add more panel.

    Are you sure you need more battery capacity? 1260 Amp hours @ 24 Volts is quite substantial (up to 15kW hours). If you really have need for that much power maybe you should consider the jump to a 48 Volt system.
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  • jbad
    jbad Registered Users Posts: 7 ✭
    #6
    Re: Battery wiring/configuration
    BB. wrote: »
    And, I will add, monitor the specific gravity, the voltage across each cell/battery (under heavy charge, heavy discharge, and resting), and I would suggest (broken record time:blush:) a DC Current Clamp Meter (here is one that is not too expensive and "good enough" for the job) so you can monitor the current flow through each string (under heavy charging and discharging, the currents should be roughly similar).

    Basically, you want to look for "differences" (cell/battery with too high or too low of voltage, unbalanced current flow, etc.)... Between poor connections and the occasional failed cell (open or shorted), you want to find the problems before they can damage the rest of the battery bank (a shorted cell can cause the other cells to over charge; and open cell can take that string out of operation and eventually cause sulfation).

    -Bill

    Thanks Bill for the advise...
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #7
    Re: Battery wiring/configuration

    what coot is referring to in method #3 might confuse you a bit as each battery in the drawing can also be viewed as a battery string with identical connections as the others. in other words if one string has a total of 4ft of #4/0 wire then all of the others will have to be this way too to keep balance.

    now you are probably stuck with the battery voltage needed and determined you needed more battery capacity so you can do it if you rewire to method #3, but you will have to add more pv capacity as coot said to keep a proper charge on the batteries. you can do this additional battery string and add them in parallel if you take the time to make all strings to be seen electrically equal.

    ideally, it is time to upgrade to a higher battery voltage and thus a new inverter when going 3 or more battery strings in parallel, but this isn't always economically feasible leading you to take the extra care for a 3rd battery string and more pvs to match.
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #8
    Re: Battery wiring/configuration

    Those diagrams you show are Magnum wiring diagrams. They are bizarre and wrong.
    I posted about this last November: http://forum.solar-electric.com/showthread.php?13721

    Use the Smartgauge diagrams that Cariboocoot linked to. Also, do not add a third parallel string! Parallel strings will, over time, ruin your batteries.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,609 admin
    #9
    Re: Battery wiring/configuration

    I am not sure I would go as far as saying a 3rd parallel (or more) battery string(s) will ruin your bank... It will require care and monitoring on your side to make sure that everything is functioning well--and to catch problems in time before they can damage your other batteries.

    Adding batteries is always a tough decision. Batteries age and change performance over time. Mixing batteries makes load sharing a bit more difficult and when the batteries start dieing of old age--you have the question of replacing everything at once or piecemeal as they fail.

    And there is the cost of safety... You should have have a fuse on every battery bank string (there is nothing like watching wiring turning red hot on a battery bank and no way of shutting it down--even worse if something happens at night or when you are not there). Adding a 200-300+ amp fuse + holder + wiring adds cost and more points to service too.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • jbad
    jbad Registered Users Posts: 7 ✭
    #10
    Re: Battery wiring/configuration
    BB. wrote: »
    I am not sure I would go as far as saying a 3rd parallel (or more) battery string(s) will ruin your bank... It will require care and monitoring on your side to make sure that everything is functioning well--and to catch problems in time before they can damage your other batteries.

    Adding batteries is always a tough decision. Batteries age and change performance over time. Mixing batteries makes load sharing a bit more difficult and when the batteries start dieing of old age--you have the question of replacing everything at once or piecemeal as they fail.

    And there is the cost of safety... You should have have a fuse on every battery bank string (there is nothing like watching wiring turning red hot on a battery bank and no way of shutting it down--even worse if something happens at night or when you are not there). Adding a 200-300+ amp fuse + holder + wiring adds cost and more points to service too.

    -Bill

    Thank you all for your input and advices...sorry for not getting back sooner, I was out of town and did not have access to internet.
    I will hold off with the addition and get more panels instead.
    This forum have been very help full and informational to all of us trying to survive off grid;-)
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,609 admin
    #11
    Re: Battery wiring/configuration

    I will let you off--this time. I have heard that some people actually have a life. :cry::p

    Let us know how everything continues to work for your home.

    -Bill ;)
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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