Battery Wiring Shortest Cables

Discussion in 'Off Grid Living' started by CrazyJs, Jul 27, 2018.

  1. CrazyJs

    CrazyJs Monkey

    Hi All,

    New Here. New to posting on forums. New to Off Grid.

    Forgive me if this has been previously discussed. If someone wants to direct me somewhere else, feel free. But I have looked throughout this site and the google-machine and found some details lacking (and/or my understanding is lacking), so I thought I'd try a new thread:

    I have a 12v system that's aging and tired so I purchased new batteries and am ready to install. Currently, the system is running (4) L16-style batteries in series and parallel, so 12v and 2x the aH. I am replacing with (6) L16-style for 12v and 3x aH.

    The battery cabinet has space limitations so I need to run all batteries side-by-side. I found a diagram of possible wiring on this site, but wondered if one could use shorter cables (cost savings and good practice for energy flow) and spin some batteries to achieve the same thing. Probably best shown by example (below):

    Example 1, found on this site (thank you for posting), shows all batteries side by side and polarity all lining-up. Example 2 shows my new batteries sitting on the garage floor awaiting installation. I marked-up the series connections (green lines / green '12 S') to achieve 12v and the parallel connections (red and black lines / yellow 'P') to triple aH, as well as negative and positive on the way to inverter.

    Does anyone see any issue with this? It seems like I can use short cables for both series and parallel connections. In the 1st example the parallel connections would require longer cables. Anyting I am missing? Is there a problem sharing a post/terminal between series and parallel connections?

    Any help would be appreciated. If my wiring would work, is there any reason I should line up polarity anyway?



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  2. Asia-Off-Grid

    Asia-Off-Grid RIP 11-8-2018

    3M-TA3 and GrayGhost like this.
  3. Out in the woods

    Out in the woods off-grid in-the-forest beekeeper

    That should work.
    Asia-Off-Grid likes this.
  4. CrazyJs

    CrazyJs Monkey

    Paul, thanks for the link - a good resource. I will read carefully.

    Out in the Woods - Thanks!

    I sketched so many combinations trying to achieve the right combo that will fit AND use the shortest cable segments, but could find no similar wiring as an example. Good to hear from someone that I won't fry new batteries or inverter.

    Thanks guys!
    Asia-Off-Grid likes this.
  5. Asia-Off-Grid

    Asia-Off-Grid RIP 11-8-2018

    The most important thing here is, that your batteries charge as evenly as possible. Have a look at Method #4 (in the link I provided), before you decide on anything definite.
    GrayGhost likes this.
  6. CrazyJs

    CrazyJs Monkey

    Paul, After 1st read, I can see there is some nuance to battery wiring. I will need to ponder (and re-read a few times). Thanks again.
    Asia-Off-Grid likes this.
  7. BTPost

    BTPost Stumpy Old Fart,Deadman Walking, Snow Monkey Moderator

    To get the MOST POWER from a battery bank, It is wise to keep the Amps Drawn at any one time below 100 Amos... So at 12 Vdc that means 1200Watts.... If one needs more than that, you get it by Doubling the Bank Voltage to 24 Vdc, which gets you to 2400 Watts.... For big systems folks go up to 48 Vdc, and 4800 Watts... Then you need to understand if you are using LeadAcid Batteries, you do NOT want to discharge them below 50% of Rated Capacity, EVER, and usually NOT below 65% routinely...I have a Battery Bank of 12 ea L16HDs in three Strings of 4 Batteries each for 1200 AmpHours @ 24Vdc... This feeds a Trace SW4024 Inverter that runs the Cabin...I am now on the Third Set, for this Bank, and getting between 8 & 10 years out of a Set of Batteries.. I mostly use the System for fall, winter, and spring, and have a 10 Hour Cycle... Running one of my twin 20Kw Gensets from 7Am to Noon, and the from 5Pm to 10 Pm Daily. This keeps the depth of Discharge well above the 65% Rate...
  8. ghrit

    ghrit Bad company Administrator Founding Member

    Keeping cable length to a minimum is not particularly critical. Wire gauge is more important by far. IsqR loss adds up quickly with undersized wire.
    Tempstar, GrayGhost, oldawg and 3 others like this.
  9. CrazyJs

    CrazyJs Monkey

    Bruce in Alaska,
    Thanks. We don't have high demands: a few LED bulbs at night and a computer or 2 during the day (and I'm looking into using them off DC instead of from the inverter). Chest Freezer draws the most. I appreciate your advice - I had heard not to draw them down below 50%, but when I saw the literature that came with the new batteries (battery cycle life when discharged to 50%, 70%, 80%, etc) I could really see how much shorter their life would be if used hard and not recharged. During summers we should have no trouble minimizing the DoD, but during winter I will need to run our 10kw frequently to get as much lifespan as possible.

    How do you monitor the Depth of Discharge? Battery monitor? Other means?Our system came with a Tri-Metric (?) but I need to chase down the owner's manual, and I think I'll need to reset to account for the larger battery bank than currently in service.
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  10. CrazyJs

    CrazyJs Monkey

    2/0 for series and parallel connections and ground to inverter. 4/0 to inverter through fuse. Sound like enough? Inverter is 2500w Trace (U2512SB).
    Asia-Off-Grid likes this.
  11. BTPost

    BTPost Stumpy Old Fart,Deadman Walking, Snow Monkey Moderator

    I made all my interconnect Cables for the Battery Bank from Welding Lead Cable... I have. friend who owns a Welding Supply Company, and he gave me a 40’ set of welding cable, that had insulation issues.. So, I chopped it up into 8” lengths and swaged Copper connectors on the ends... Works really well... Battery Box is on the Outside Wall of my Powerhouse, and the Trace SW 4024 is on the Inside of the same Wall. Inverter Cables are less than three feet long...
  12. Cruisin Sloth

    Cruisin Sloth Special & Slow

    Loads of usage for the 12Vdc please !! Cuz I'll doo MATH
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  13. Cwmoore

    Cwmoore Totally off grid

    Hi there, Your top battery is not being utilized
  14. Cruisin Sloth

    Cruisin Sloth Special & Slow

    The Ballance is so far off , Just let them burn up a set of GC units & then after they rebuy a year later, then they might understand .. & @12 Vdc , lost in the fog.
  15. Asia-Off-Grid

    Asia-Off-Grid RIP 11-8-2018

    @CrazyJs, did ya get your issues sorted?
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