Question about battery/cable lugs and battery connections.

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spacebass
spacebass Registered Users Posts: 87 ✭✭
in Solar Beginners Corner #1
If You look at a cable lug with a 10mm hole in it , it has considerably less metal left in it to transfer the electricity than a lug with an 8mm hole in it , for often more power . Is this significant ? Will putting a washer on top help in this regard?

I am about to put 2 x 16 sqmm cables instead of one between the 12v 120ah lp04 batteries in my 48 volt series bank ,I do this because I have read the size of the cable affects the internal impedance of the batteries which is significant in charging. The same article also stated that in the bank the position of the battery/cell will affect the level of discharge relative to the others , this is something I have noticed and thought maybe I had a couple if substandard batteries.
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #2
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    Batteries in SERIES all see the same amps, charging or discharging.    As long as the interconnects are stout enough to carry the expected amps, I would not go too much overboard with dual cables.  

    If your battery bank has PARALLEL batteries, then you will have an issue with small amounts of resistance causing imbalances between the 2 banks.  So you spend a couple days getting the cables all matched up and torqued down properly and the next month a cell starts to develop some high resistance and you are back to square one trying to balance bank resistance.  It's a never ending quest, which is why a single Series string of large batteries is preferred over parallel banks.

    Some people swear that battery position in a series string affects charging, but there is no scientific evidence that allows that, unless you have tapped into a battery in the middle of the bank.   In a series circuit, all points see the same current. There are no exceptions.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #3
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     IMHO, a problem with using 2 smaller wires for battery interconnects rather than a single larger one is how do you size the  breaker/fuse?  If sized for the total ampacity of both conductors, a break in one keeps the circuit closed but with the single good conductor potentially carrying 2x design current.  
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
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  • softdown
    softdown Solar Expert Posts: 3,824 ✭✭✭✭
    #4
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    spacebass said:
    If You look at a cable lug with a 10mm hole in it , it has considerably less metal left in it to transfer the electricity than a lug with an 8mm hole in it , for often more power . Is this significant ? Will putting a washer on top help in this regard?

    I am about to put 2 x 16 sqmm cables instead of one between the 12v 120ah lp04 batteries in my 48 volt series bank ,I do this because I have read the size of the cable affects the internal impedance of the batteries which is significant in charging. The same article also stated that in the bank the position of the battery/cell will affect the level of discharge relative to the others , this is something I have noticed and thought maybe I had a couple if substandard batteries.
    You are referring to maybe a 1/4" of area for the current to pass through. Cables are important because several inches are involved. 

    Consider the safety fuse which really amounts to a much smaller cable for maybe a couple inches at most. Yet has insignificant impact because of the short length. 
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
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