Battery Interconnects

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jcheil
jcheil Solar Expert Posts: 722 ✭✭✭
in Advanced Solar Electric Technical Forum #1
OK, so I have these 16 new Trojan L16RE-B batteries coming in next week. I'm on a 48v system so I will have 2 strings of 8.

I have been sitting here trying to figure out the best way to PHYSICALLY place them and wire them.
Does anyone have any suggestions on what layout worked best for them with the same configuration as mine? (pictures?)

I know for sure I would flip each alternating battery 180 degrees so the - and minus of each alternating battery is only about 5-6" from each other,

If I do a U shape with 4 rows of 4, that puts the final + and - all within 2' of each other, but now I have a "deep" bank making it a bit harder to get to the "back" ones. But shorter cables going to the inverter.

I really like the idea of 2 rows of 8 (so it is easy to get to all of them), but then I end up with both + at one end and both - at one end, now 6' apart.

So the other questions, is there any benefit of getting a bunch of short 1/4" thick by 1" wide, 5"-6" copper bar stock to make buss plates for the interconnects? It would seem like a perfect idea since the terminals line right up when flipping every other battery. And I think I have seen this on the fork lift batteries. They will be on a new concrete slab so I don't have to worry about anything shifting.

And then the final connection from the 2 ends (the + and -) going to the inverter breaker and NEG buss bar, do they need to be the same exact length of wire? I was thinking of having a small junction box for both + and another for both - where I could connect the 2 strings together and also put a shunt on each of the strings (before the point they are connected together), to be able to monitor the current going into and out of each string to keep an eye on potential in-balances.

If I HAVE to keep both the + and - wires the same length, using the 2 rows of 8, it looks like I would end up with (4) 5' cables (2 for the + and 2 for the -) going from each end to the wall in the vicinity of the center of the bank. From there I could have 2 cables (one + and one -) going to the inverter breaker/neg-buss, which would be mounted to the side of this long string but requiring cables about 8-10'. So in the end, the total length of each of the two cables (+ and -) would be 13-15'. Is this a problem?

PS - All the cables would be 2/0 MTW.
Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #2
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    Re: Battery Interconnects

    How about two "U" 's with the top ends facing each other and all the buss connections in the middle for each string ? I use that in Boats often, it's easy to buss them and everything is equal.
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  • jcheil
    jcheil Solar Expert Posts: 722 ✭✭✭
    #3
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    Re: Battery Interconnects
    Blackcherry04 wrote: »
    How about two "U" 's facing each other and all the buss connections in the middle for each string ? I use that in Boats often, it's easy to buss them and everything is equal.

    Ah, good idea :) That's why I am glad there are a bunch of smart people here with a lot of experience!
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #4
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    Re: Battery Interconnects
    jcheil wrote: »
    Ah, good idea :) That's why I am glad there are a bunch of smart people here with a lot of experience!
    In a boat, even a 80' one you can't put that much weight on one side, so you end up working from the middle out. I use all cables as interconnects the batteries swell and the posts will change over time and there is expansion and contraction. I do not cube the batteries without a air space between them, a 1-2" space will keep them much cooler and they will cool faster.
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #5
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    Re: Battery Interconnects
    jcheil wrote: »
    And then the final connection from the 2 ends (the + and -) going to the inverter breaker and NEG buss bar, do they need to be the same exact length of wire?

    No, they don't need to be the same length. --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • jcheil
    jcheil Solar Expert Posts: 722 ✭✭✭
    #6
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    Re: Battery Interconnects
    vtmaps wrote: »
    No, they don't need to be the same length. --vtMaps

    Thanks! And just as a refresher (to me and perhaps others) I know I read on here something important about "some" cables needing to be the exact same lengths. Perhaps that is the total cable lengths between the battery interconnects?? I can't remember.
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #7
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    Re: Battery Interconnects

    If you have two parallel battery strings--The total cable lengths in each string should be the same. But the individual sections/+/- runs do not have to match (i.e., total length of wire sets the total resistance of the string).

    What the same resistance in each string/set of interconnects so that they will all have the same voltage drop and have same/similar current flow in each string.

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