How many batteries should I have for this app?

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xtriggerman
xtriggerman Registered Users Posts: 6 ✭✭
edited September 2017 in Solar Beginners Corner #1

 Hello all, Looks like this is the place to get educated on these sort of things so here goes. I'm getting all the parts to a small solar system of 6 100w (12v) panels to run primarily attic ventilation and a possible 12v deep well pump of 13A draw. This is a SHTF system so to speak so a string of 12v batteries will be the heart of the system with a 120v AC inverter for those outage instances on occasion. Right now, I just want to figure out how many 12v batteries I should have to be able to get them fully charged off a 300W day time input. The battery drain will for now only be from attic fans running at day/night for around 4 sun down hours discharging somewhere around 270 watts continuous. The batteries I would like to use are the Walmart Marine deep cycle 24MS rated at 1000MCA / 135AH. At 70 bucks a pop they look like the best way to go right now. I have no idea how to calculate this sort of stuff....

THANKS 

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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
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    300 w of well aimed panels, should support about 200ah @ 12V.  Look into the 6v, 200ah golf cart batteries, better practice to wire batteries in series, rather than parallel
    If your daytime loads are much more than 50-80w , you will need more panel.
    If your nightime loads total more than 1,200 watt-hours, you need more battery & more panel.

    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 ,

  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
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    @xtriggerman The batteries you refer to are not true deep cycle, to the best of my knowledge, golf cart batteries are a far better choice, and series is a better arrangement, as mentioned above.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,046 ✭✭✭✭✭
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    Could you give a link to that particular battery? I cant find it .

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
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    The proposed batteries have a CCA spec, which is not carried on true deep cycle batteries.  They are marine batteries.

    But we still have the cart before the horse.   The actual loads need to be figured out, or the system will not be the right size.
    Too small, and the batteries are always going dead, too large and you waste a lot of $$ on overbuilding,
    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 ,

  • xtriggerman
    xtriggerman Registered Users Posts: 6 ✭✭
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    https://www.walmart.com/ip/EverStart-Marine-Battery-Group-Size-24MS/16782694  This was what I was considering. On the rack at the store it stated "deep Cycle" along with RV after the marine title and the store price was 69 not 59 as in the link.

       Well, anyway If I read you guys right, I think you are saying to use 6v batteries joined in series and parallel to make the 12v? But what I don't understand is in the diagram for joining 2 6v in series, you don't get a multiple of the amp hours of the single battery where as in a 12v parallel run, each battery's AH is multiplied in the configuration.

      That being said, I understand the deep cycle idea of the bigger & heavier golf cart batteries for a most efficient discharge but heres the rub, how well will the base 6v set perform if only used 12v car & truck batteries need to be swapped in? In such a scenario, do you ditch the entire set when one or two 6 volters goes bad? In a perfect world (as today) you clean slate the entire set after so many years but I want the what if system even if I need more "common" batteries to make up for their lack of deep cycle efficiency.  Keeping this all in mind, wouldn't a parallel set of 12's be a more practical system for what I envision?  I guess I do need to get some figures together for just how much exact usage will be in the system. One thing I can trim is the night time shut down temp of the fan system if I'm over drawn at some point. There are about 9 small wattage fans in the system of 2 different kinds for I'v got some exact figuring to do yet. I'll be back with those numbers latter in the year once it cools down in the attic to do the installs. But you guys are great for the detailed help. Im just shootin from the hip with all this. 

  • bsolar
    bsolar Solar Expert Posts: 103 ✭✭✭
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    you'll need about 6 210ah golfcart batts and you can see how it goes on the panels .. get the system going and if you need more, add more .. im guessing you'll need 8 batts and 10 panels before it starts seeming like theres room to breath ..
  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,046 ✭✭✭✭✭
    edited September 2017 #8
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    The battery you describe and the one you linked to don't match at all. A 135 Ah 12 volt battery is MUCH bigger and cost MUCH more than. the one you linked. Something didn't sound right.This is why I asked.
      A 6 volt battery has double the amp hours as opposed to a physically similar sized 12 volt battery because it has 1/2 the number of cells but they are twice as large.  Example a GC2 golf cart battery of 220 amp hours has 3, 2 volt 220 amp hour cells. 12 volt batteries have 6, 2 volt cells of whatever the ah. rating of the battery is, typically in the 95 - 110 amp hour range. Flooded lead acid batteries come in 2 volt. 4 volt, 6 volt, 8 volt and 12 volt configurations. Batteries perform best when in a single series string. If you need an 1100 amp hour bank of batteries then buy 1100 amp hour 2 volt batteries. If you need a 24 volt bank but only have room for 3 batteries buy 8 volt batteries. etc. etc.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
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    Connecting in series adds voltage. Connecting in parallel adds amp-hours. As LH2 says, a single string is the ideal configuration.

    Having more than a couple strings or batteries (which are actually strings connected in a plastic case) can be a problem for a couple of reasons.

    First, keeping all the strings at an equal state of charge can be an issue. What happens is differences in resistance in the wiring causes some strings to end up chronically undercharged. If monitored closely, you can deal with this by periodically separating the strings and charging individually, but it's a PITA.

    Second, with lots of parallel strings, you have many more individual cells. The 1100ah 12v string LH2 gave as an example has 6 cells. If 110ah 12v batteries were used in parallel, you have 6 cells per battery times 10 batteries = 60 cells. That's 60 cells to check for water and to monitor specific gravity. It's also much more likely that a cell will go bad.
    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
  • xtriggerman
    xtriggerman Registered Users Posts: 6 ✭✭
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    The battery you describe and the one you linked to don't match at all. A 135 Ah 12 volt battery is MUCH bigger and cost MUCH more than. the one you linked. Something didn't sound right.This is why I asked.
      A 6 volt battery has double the amp hours as opposed to a physically similar sized 12 volt battery because it has 1/2 the number of cells but they are twice as large.  Example a GC2 golf cart battery of 220 amp hours has 3, 2 volt 220 amp hour cells. 12 volt batteries have 6, 2 volt cells of whatever the ah. rating of the battery is, typically in the 95 - 110 amp hour range. Flooded lead acid batteries come in 2 volt. 4 volt, 6 volt, 8 volt and 12 volt configurations. Batteries perform best when in a single series string. If you need an 1100 amp hour bank of batteries then buy 1100 amp hour 2 volt batteries. If you need a 24 volt bank but only have room for 3 batteries buy 8 volt batteries. etc. etc.


      Your right, I was hasty posting the link not noticing the MCA rating was different from the one in the store. I copied the MCA & AH right off the top of the battery any was surprised by the price on the front of that row of batteries and they had a full row of them on that rack labeled at $69.87. That all bugs me now Iv got to get back to the store & see whats going on and have that particular 135AH battery price checked. Some things screwy because that rating was on a 24MS size battery 

      I'm not arguing the fact that a set of 6v GC batteries are a better bank. But they also must be in series AND parallel to keep with in 12v or else I would end up with something like 96 volts as a result of only a series wiring. As for uneven parallel charging, that can be more or less over come by moving the feed cables around to the left and right in the middle of the run occasionally as pictured here as "perfectly balanced draw"  http://rvroadtrip.us/library/12v_system.php It would indeed be troublesome to have twice as many or more cells to check. I don't know, I'm split on all this. Either the efficiency of GC batteries or the find them every where 12 volters.....  Sams has Duracell 24MSHO 12v 1000MVC at 79.98 as the second cheapest 12v AH.  The simplicity of 12 volters is awfull tempting!

  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
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    A couple of 12v batteries in parallel is workable in terms of keeping them in balance and maintaining them. If the capacity of a couple of 12v batteries works for you application, great. Just be sure you're getting a true deep cycle battery, not a "dual use" or marine type. More than a couple in parallel will be a challenge.

    The main thing is to nail down your load requirement. What is the fan draw, for how long, and how many cloudy days do you need to go before charging with an alternate source of power? It would be best to actually measure this with something like a kill-a-watt meter before trying to design a system. A $10 difference in the price of a battery is going to seem pretty cheap if you end up with a system that doesn't work as expected.
    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
  • Marc Kurth
    Marc Kurth Solar Expert Posts: 1,144 ✭✭✭✭
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    Start ignoring the MCA ratings because they are useless for your needs. That only defines how many amps it will supply for 30 seconds. I would assume that you are wanting power for more than 30 seconds.

     Focus on how many deep cycles the manufacturer rates the battery to perform. True deep cycle batteries openly publish that information, and cranking amps are offered for those who are trying to do both.

    You will quickly find that a true deep cycle battery of a given size will produce 25% to 30% less cranking amps than a starting battery of the same size. Sure, deep cycle batteries can be used for starting, if that deficit is still enough. So called "marine" batteries are somewhere between the two, but cannot withstand typical off grid deep cycle use.

    Spend more time reading here and it will save you more money and headaches than you can begin to even see at this point in your journey!
    I always have more questions than answers. That's the nature of life.
  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,746 ✭✭✭✭✭✭
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    Wisdom!   Everything copacetic Marc? The derailer of threads and late happy hours!
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

  • xtriggerman
    xtriggerman Registered Users Posts: 6 ✭✭
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     OK, thanks again for all these great comments. You cant beat wisdom of experience and that's why I'm here. Funny how the SAMS marine batteries don't print AH on their batteries only MCA rates now. Thinking on all this, I think I'll have another look at the big 12v deep cycle GC units. I still want to run a parallel cable lay out to satisfy the SHTF needs of maybe some day scavenged batteries would be the only source. That way it would only be extending the cable runs. But for now, setting up with GC batteries would be my start up.

       You guys arnt rid of me yet.... I'll eventual have 2 other ways of charging this bank off grid. My controller has only one charging source.  More to chew on latter.