Confirmation of Battery Wiring Diagram

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mjp24coho
mjp24coho Solar Expert Posts: 104 ✭✭✭
in Solar Beginners Corner #1
This may seem like a bit of a basic question, but I'm hoping you solar experts can take a look at my attached battery wiring diagram and confirm the correctness of the proposed wiring. I'm planning on wiring 16 6V 208AH Sam's Club batteries in series and then parallel to get to 24V and 832 AH. I want to make sure I have the planned wiring correct before wiring it all up.

Thanks!
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,457 admin
    #2
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    Re: Confirmation of Battery Wiring Diagram

    The one "flyover" negative lead from the top string is a bit of the unknown--But everything appears to be balanced.

    One reason I do not like lots of jumpers is because it is difficult to fuse/breaker each string (ideally done for each parallel string)--And it makes it a bit difficult to isolate a string for debugging.

    Method #3 is a bit clearer where you would fuse each string.

    But, in theory, if you could fuse at a 6 volt to 6 volt jumper (one in each string)--It would accomplish about the same thing (I am not sure that it would be well accepted--The standard being installing the fuse/breaker at the Hot Lead output from the string--But if you are trying to stop series current flow, a fuse anywhere in the system will stop high currents).

    BlueSea makes a really nice fuse holder that can be installed right on the battery flag/terminal:

    Attachment not found.Attachment not found.

    Nothing with high current, "higher voltage" DC is cheap or small...

    Batteries "scare me" and I am a big believer in fusing/breakers and well protected wiring for large battery banks.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • mtdoc
    mtdoc Solar Expert Posts: 600 ✭✭
    #3
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    Re: Confirmation of Battery Wiring Diagram

    Generally 4 parallel strings is frowned upon - and will lead to charge/discharge imbalances that will shorten battery life ( Usually Bill is one of the first to point this out!:p). But I understand sometimes ya gotta do it anyways!

    Have a look at THIS link. If you're going to have 4 parallel strings using method 3 or 4 is a better way to do it. Your current diagram is equivalent to method 2. (Note: on these diagrams one battery is equivalent to one of your strings of 4 batteries in series)
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #4
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    Re: Confirmation of Battery Wiring Diagram
    mtdoc wrote: »
    Generally 4 parallel strings is frowned upon - and will lead to charge/discharge imbalances that will shorten battery life

    And if you want to understand why, read: http://forum.solar-electric.com/showthread.php?14674

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #5
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    Re: Confirmation of Battery Wiring Diagram

    Since Paralleled Battery Banks are a fact of life you have to set up good maintenance practices to deal with them. No Battery Bank is install and forget. Paralleled Battery Banks should at least be dissembled once a year and all the connections cleaned and the bolts re-torqued. When I install a bank I number all the batteries, I like to shuffle them, like rotating the tires on your car. The batteries closest to the positive end take a larger amount of the load and use more water, so it's easy to tell they get the most wear and tear.

    In Real Life there more Banks in Parallel than in Series.
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #6
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    Re: Confirmation of Battery Wiring Diagram
    Blackcherry04 wrote: »
    The batteries closest to the positive end take a larger amount of the load and use more water, so it's easy to tell they get the most wear and tear.

    BC04, I don't doubt your observations, but... I can't think of any way to explain that except to assume that the batteries closest to the positive end are in a warmer location. I predict that if you rotated each battery 180° (but left it in the same location) and rewired the bank, the battery that had been at the positive end would now be at the negative end, but would still use more water.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #7
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    Re: Confirmation of Battery Wiring Diagram
    vtmaps wrote: »
    BC04, I don't doubt your observations, but... I can't think of any way to explain that except to assume that the batteries closest to the positive end are in a warmer location. I predict that if you rotated each battery 180° (but left it in the same location) and rewired the bank, the battery that had been at the positive end would now be at the negative end, but would still use more water.

    --vtMaps
    That would work for the first and second year, then I'd run out of ends. Most of the 50 installations I manage or own don't have that much extra 4/0 cable on them they were factory designed to be installed one way. it's the First two batteries Paralleled on the positive end. You'll also see it on batteries in series but not as much, it's always the first battery on the positive end.
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  • mjp24coho
    mjp24coho Solar Expert Posts: 104 ✭✭✭
    #8
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    Re: Confirmation of Battery Wiring Diagram
    mtdoc wrote: »
    Generally 4 parallel strings is frowned upon - and will lead to charge/discharge imbalances that will shorten battery life ( Usually Bill is one of the first to point this out!:p). But I understand sometimes ya gotta do it anyways!

    Have a look at THIS link. If you're going to have 4 parallel strings using method 3 or 4 is a better way to do it. Your current diagram is equivalent to method 2. (Note: on these diagrams one battery is equivalent to one of your strings of 4 batteries in series)

    Good points. I got carried away and completely forgot about the 2-3 parallel string rule of thumb. I was hoping to utilize cheaper Sam's Club batteries for my first battery bank, but it looks like I can't do that at 24V and still get 800+ AH with 2-3 strings. I'll have to move up to some Trojans or Surettes.

    Based on the advise here, utilizing larger Surette's, I've come up with an updated wiring diagram under Method 3 (see attached). Any thoughts on this? I would use the same size cables for all wiring. Any suggestions on what kind of terminal posts to use, and where to put the fuses? Any need to protect the terminal posts (and protect others from the terminal posts)? I'll be putting the battery bank inside a deck box (insulated with 1" foam on all sides). Thanks.
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #9
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    Re: Confirmation of Battery Wiring Diagram
    mjp24coho wrote: »
    I was hoping to utilize cheaper Sam's Club batteries for my first battery bank, but it looks like I can't do that at 24V and still get 800+ AH with 2-3 strings.

    I don't know (because you don't have a signature) whether you are building a system or just replacing the batteries on a 24 volt system. If you are building a system you can get the storage you need with 2 strings of cheap batteries at 48 volts.... four strings at 24 volts is the same storage as two strings at 48 volts.
    mjp24coho wrote: »
    I'll be putting the battery bank inside a deck box (insulated with 1" foam on all sides)

    You don't indicate your location... if you have a warm season, make sure to remove the foam insulation in the warm season. In all seasons be sure to let the hydrogen escape from the box.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • mjp24coho
    mjp24coho Solar Expert Posts: 104 ✭✭✭
    #10
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    Re: Confirmation of Battery Wiring Diagram

    I live in southern utah - warm in the summer - so I'll remove the foam in the summer.

    I already have a 24V inverter, so I'm stuck with wiring the batteries in 24V
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  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    #11
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    Re: Confirmation of Battery Wiring Diagram

    Have you considered a forklift/traction battery?

    I paid $2,525 delivered, less wiring no fuses. 800 Ah. They are big and heavy (1100lbs) but if your installing in a garage or outside it should be doable. I moved mine 2x, by myself, with a leaver and several fulcrums.

    I'll send you a link, via PM.
    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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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #12
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    Re: Confirmation of Battery Wiring Diagram
    Photowhit wrote: »
    Have you considered a forklift/traction battery?

    I paid $2,525 delivered, less wiring no fuses. 800 Ah. They are big and heavy (1100lbs) but if your installing in a garage or outside it should be doable. I moved mine 2x, by myself, with a leaver and several fulcrums.

    I'll send you a link, via PM.
    How is your Forklift battery laid out ?? 2 rows of 6 cells or 3 rows of 4 cells or 4 rows of 3 cells ?? I see a lot of combinations of them.
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