Help with battery bank

I am new at this, I have a cabin that is off grid. I have a sw 4024 and 7 flouresent lights, tv, 2 fans,exhaust hood and swamp cooler. I have 18 12 volt 120 ah batteries. What is the best way to connect the batteries in a bank for the 24 volt inverter? I have been studying the different suggestions on this forum, but am still a little confused about how the best way to connect the batteries. I have a 10000 watt generator that I use to pump water and charge the batteries.
Any diagrams would be greatly appreciated.

Comments

  • mike95490mike95490 Solar Expert Posts: 8,380 ✭✭✭✭✭
    Re: Help with battery bank
    phil218b wrote: »
    I have 18 12 volt 120 ah batteries. What is the best way to connect the batteries in a bank for the 24 volt inverter?

    For that many batteries ( 9 parallel strings of 2 batteries ) using a Buss Bar, with
    equal length interconnects, is the only way to do it.

    Even then, you will have problems with batteries not sharing the load equally.

    This article http://www.smartgauge.co.uk/batt_con.html will talk about the
    situation.
    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

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • TnAndyTnAndy Solar Expert Posts: 249 ✭✭✭✭✭
    Re: Help with battery bank

    Not sure how to get a diagram posted, somebody will I'm sure..

    But you have to connect pairs of the 12v batteries in series.....positive to negative on each pair, making a 24v "string".....then connect the 9 "leftover" positives together, one after another out to the end, and the same with the negative leftovers, so you have a bank of 9 strings of 2ea, ( parallel connections ).

    You'll end up with a 9x120a/h bank or 810a/h total. String adds voltage, strings in parallel add amp/hours.
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Help with battery bank

    that's a big battery bank for a cabin.
    anyway, i don't have any diagrams that you probably haven't already seen here on the forum so i'll try to take it in generalized steps.
    1> to make 24v from 2-12v batteries you need to place a single heavy wire connection from the positive of one battery to the negative of the other battery to have them be in series. if you did this to all of the connections between the 2 batteries you would short out both batteries and you don't want to do that.
    2> the remaining positive and negative post will have that same heavy wiring as the power connection points to go to the charger and/or load just like 2 batteries in a flashlight would be in series, but due to the physical size of the batteries involved you are using wire between the batteries and wires to connect the load and charger.
    3> the other 8 pairs of batteries now must have the exact same connections, wire size, and wire lengths to be identical to the first one that was made. as examples you don't want one interconnection wire to be 12 inches and another 13 inches or one positive wire 36 inches and the next one 32 inches. they have to be the same in one pair as the next pair.
    4> now these small individual battery strings of 2 batteries each must be connected together. this would be a heavy bar called a buss bar that will interconnect all of the batteries. the bar should be made extra heavy and large to account for small distances that could throw extra imbalances into the mix. with the 9 connections you'll have for the positive buss and the 9 connections you'll have for the negative buss the minimum gauge equivalent would be all of those wires together on the positive buss and then up that new gauge number by 2 places. the negative being identical will have the same.
    5> this is more just a note that you have interconnected 9 seriesed battery strings so the buss will have 9 connection points, plus a connection point for both the load and the charger for a total of 11. when getting a buss make sure it can accept that many connections and more would be better just in case. these load and charger connections will undoubtedly be for heavier gauge wire than each battery string so the buss has to be able to accept both gauges.

    now for busses for this size of a battery bank, pure copper would be best and may even be homemade from bar copper for those that like to diy. just remember that when drilling it out that this creates weak points on the bar and these weak points must be the equivalent to the minimum i spec'ed for the buss bars for their gauge and thus their resistivity.
    i probably confused you somewhat, but the key is equal and heavy.
  • icarusicarus Solar Expert Posts: 5,256 ✭✭✭✭
    Re: Help with battery bank

    The describe battery bank requires a minimum charging current of ~40 amps @ 24vdc, and could accept in excess of 100 amps. Pretty big bank for a cabin.

    That said, a 10kw genset is pretty big for a cabin too!

    Tony
  • System2System2 Posts: 6,290 admin
    Re: Help with battery bank

    Any advise on how to make a bus bar for this size bank?
  • BB.BB. Super Moderators, Administrators Posts: 29,523 admin
    Re: Help with battery bank

    I would start with a site like this company (don't know anything about them--just the first hit on google)... Lots of information and parts for sale. Obviously, solid bars of copper are not going to be cheap.

    The bigger question is the sizing of your components... How much power do you use in a day (Watt*hours or Amp*Hours), what is your peak surge current requirement (starting a well pump, etc.). When you know that information--then you can design the cabling and bus bars to your needs (and hopefully save some cash).

    Having too much battery bank (or two many small batteries made into a large bank) can be a big problem too... For example, each parallel connected string should really have a fuse/breaker on it (protects from shorts elsewhere in the battery array (or cell failures, etc.). 9 strings, 9 sets of breaker/fuse assemblies.

    Also, when you have a bunch of strings in parallel--it can become quite difficult to isolate open/shorted cells in your bank (everything is at the same voltage). You have to isolate strings (open connections/fuses) and then measure voltage/current at various points in the system to find your weak performers and move them out of service.

    Obviously, you already have the batteries -- or at least have identified a source where you can get them for "cheap" (I am guessing)--so, now you have to look at the wiring scheme that bests matches your needs. You can look through NAWS' web site for various cables, small buses, and fuse/breaker assemblies to rough out a system design and cost before you go into the details.

    You may find that the "ancillary" electrical hardware may rival the costs of the balance of your system when "properly" wiring up a large number of parallel strings.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Help with battery bank
    phil218b wrote: »
    Any advise on how to make a bus bar for this size bank?

    One of the regulars on this forum, 2manytoyz has a web site showing lots of "good stuff".

    Here's a link to his battery bank page showing how he made his buss bars:

    http://2manytoyz.com/battbank.html

    You may need thicker copper due to the sheer amperage of your battery bank, but there are numerous tables on the internet - search google for "buss bar ampacity" and you should find what you need to calculate what size copper to use.


    One thing to keep in mind - if you make the "load" connection at say, one end of the buss bars (for instance at the top in 2manytoyz rig) the battery that is *closest* to that point will do more work than the battery that is furthest (least resistance).

    The same is true of the charging - the least resistance will get the most voltage of charge.

    So, if it were me, I would probably try to balance it out a bit more...perhaps by putting the positive load connection at the top of the buss bar, and the negative at the bottom of the other buss bar.

    I might also try to mix up the battery connections to the buss bar so that no battery has *both* positive and negative closer to the load/charge than the others.
  • mike95490mike95490 Solar Expert Posts: 8,380 ✭✭✭✭✭
    Re: Help with battery bank

    McMaster-Carr has lots of copper bar stock: Part Number: 3350K22 example
    http://www.mcmaster.com

    Not sure what size you need, but it needs to be big enough to bolt through it, don't try to drill and thread it.
    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

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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