balance of my system ? I am newbie.

sullymansullyman Registered Users Posts: 2
I have 4 , 180 watt 12v panels.  (voc 21.6  vmp-18  imp-10)  a MPPT 30 amp controller. Plan on 2 strings at 24 volts,  to charge (2) 100ah 12 volt AGM batteries, in parallel.  ( as I have read that batteries is "series" do not like to be charged that way ) ?  Can a Samlex evo 2012 inverter  power this system ?  OR do I need to keep my batteries in Parallel and get the Samlex evo 2224 ?
So,  does this sound correct .?   This is for a a small hunting cabin, used only a day or two a week at most.  Loads being a few LED bulbs, 2 ceiling fans.  I have generator back up for anything else.  
Please keep it simple.....   thanks .

Comments

  • BB.BB. Super Moderators, Administrators Posts: 31,684 admin
    edited March 20 #2
    Welcome to the forum Sullyman.
    Personally, I suggest trying to prevent or reduce the usage of paralleled batteries... More cells to check electrolyte levels (if flooded cell), more electrical connections (expenses, maintenance), and needing to "balance the wiring" between strings--You want "equal" wire resistance between strings so that they better share current during charging and discharging. You can parallel strings, and here is a good website for understanding the setups:
    Regarding issues of batteries not liking series connections... For example, all lead acid batteries are made from 2 volt cells... If you have 24 volts, you need 12 cells in series. Weather that is 2x 12 volt batteries (2x 6 cells per battery = 12 cells), or 4x 6 volt batteries in series (4x 3 cells = 12 cells for 24 volts)--That is not the issue.
    What you can do with lower voltage batteries with higher AH rating--Is for example:
    • 2 x 12 volt @ 100 AH batteries in series for 24 volts * 2 parallel strings @ 200 AH = 4x 12 volt batteries (24 cells to check if FLA)
    • 4x 6 volt @ 200 AH batteries (same size/weight as [email protected]) is 24 volts @ 200 AH with one string = 4x 6 volt batteries (12 cells to check if FLA, only one series string).
    If the batteries are in series and all the cells are in good shape, they will charge just fine.
    With Flooded Cell Lead Acid Batteries (FLA), we do controlled over charging or "Equalize Charge". Basically a 12 volt bank which charges at 14.75 volts is charged for a limited time at 15-16 volts or so--This "over charging" will push current through the 100% State of Charge cells, while bringing any weak cells to 100% to. FLA batteries do not "like" EQ charging--But limited EQ charging (an hour or a few hours per month as needed) is just normal maintenance.
    AGM batteries--The cells do not "drift apart" nearly as much as FLA cells can... And AGM should not (in general) be EQ Charged at elevated voltages... There are different schools of thought, but the typical suggestion is to charge at set point voltage (say 14.4 volts) and hold that for ~8 hours or so (mild EQ charge) to level cell SoC.
    Lithium Ion batteries (we typically use LiFePO4 chemistry cells for off grid use as they are safer than some other Li Ion cells) cells do not drift in normal use... However, if they do drift, they are much easier to damage with over charging/over discharging (over/under voltage can quickly ruin cells)--Li Ion battery banks typically use a BMS (battery management system) to measure the voltages between cells and 1) alert the owner other charging/discharging equipment that there is a balance problem, 2) actually shift charging current to "low cells", and 3) turn off the battery bus if over/under voltage conditions exist or battery out of safe temperature range...
    The issue to watch is different BMS modules can mix/match the 1-3 functions above. Need to pay attention to your BMS and its limitations.
    To system design... First thing is to measure/estimate your daily loads... That defines the battery bank and the balance of system design.
    Conservation is your friend here... You do not want a pair of 200 Watt 120 VAC ceiling fans--You want something much more energy efficient... When you can get a 12 VDC fan that will use 25 Watts or less (note: will probably move less air than a 200 Watt 120 VAC ceiling fan). For example:
    Note: there are a lot of issues/complaints with many DC Ceiling fans (looking on Amazon)--Check the reviews and suppliers for "good" fans.
    If your power needs are small (lots of conservation, a few energy efficient devices)--You can look for much smaller AC inverters. The MorningStar 12 VDC TSW 300 Watt inverter has been a mainstay for many folks here. No fans, reasonbly rugged and efficient. Has remote on/off and "sleep mode" functions--Rare for smaller AC inverters:
    Samlex and Victron are now making smaller 12 volt inverters these days that do have more functions/remote options/wireless Bluetooth dongle for Victron(?).
    12 VDC is best for a "small" system (suggest 1,200 to 1,800 Watts maximum loads/AC inverter rating). But if your loads are small (such as a cabin), a 300 Watt AC inverter for some loads (cell chargers, LED lighting, laptop charger, etc.) are nice. Also you can send 120 VAC 100+ feet very easy (say remote lighting, repeater, etc.) and only use the 12 VDC power for stuff next/near the battery bank (you have to use heavier copper wiring to send 12 VDC power any significant distance--Voltage drop issues).
    Anyway... I am a bit confused about your needs... 24 VDC for a small system--Unless you have 24 VDC loads (marine or heavy truck equipment)--If you use 12 VDC appliances--Wire for 12 VDC (LED lighting, 12 VDC fridge, 12 VDC chargers for cell phone/laptop/etc.--if not using AC chargers). I really like 6 volt @ 200 AH "golf cart" batteries... Tend to be a better choice for larger battery banks...
    Let me do another post here on the design itself--Less words/confusion per post.
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.BB. Super Moderators, Administrators Posts: 31,684 admin
    2 x 12 volt @ 100 AH batteries can be configured as:
    • 1 series x 2 parallel = 12 volts @ 200 AH battery bank
    • 2 series x 1 parallel = 24 volts @ 100 AH battery bank
    Both configurations store the same amount of energy (12 volts * 200 AH = 24 volts * 100 AH = 2,400 Watt*Hours of stored energy)...
    However, if you want just 12 volts @ 200 AH, I would suggest 6 volt @ 200 AH batteries instead:
    • 1s x 2p 12 volt @ 100 AH = 12 volts @ 200 AH
    • 2s x 1p 6 volt @ 200 AH = 12 volts @ 200 AH
    Or if you want a larger bank using 4x 6 volt @ 200 AH batteries vs 4x 12 volt @ 100 AH batteries:
    • 2s x 2 parallel = 12 volts @ 400 AH (4x golf cart batteries 6 volts @ 200 AH)
    • 4s x 1 parallel = 24 volts @ 200 AH (4x golf cart batteries 6 volts @ 200 AH)
    • 1s x 4 parallel = 12 volts @ 400 AH (4x 12 volts @ 100 AH)
    • 2s x 2 parallel = 24 volts @ 200 AH (4x 12 volts @ 100 AH)
    Again, I like fewer parallel strings, and usually suggest that 3 parallel strings is about the maximum (limiting sharing issues, extra wiring, cells to check electrolyte levels on for FLA, etc.). I.e., suggest it is easier to make a larger AH battery bank with the 6 volt @ 200 AH batteries vs the 12 volt @ 100 AH sets.
    And to design... For example, say 12 VDC system with 5x 9 Watt 12 VDC LEDs for 5 hours a night and 2x 12 VDC ceiling fans at 1.2 amps for 12 hours per day/night:
    • 5x 9 Watt LED lights (12v) * 5 hours per night = 255 WH per day lighting
    • 2x 1.2 amp * 12 volt DC fans * 12 hours per day/night = 346 WH per day fans
    • 255+346=601 WH per day
    • 601 WH per day / 12 volts = 50 AH per day @ 12 volts
    For a nice/reliable cabin, suggest 2 days storage and 50% planned maximum discharge (although, perhaps 1 day storage and 50% is better for your $$$ and use genset more when needed):
    • 601 WH per day * 2 days * 1/0.50 max discharge * 1/12 VDC = 200 AH suggested @ 12 volt battery bank (2x [email protected] batteries in series)
    Two calculations for charging... One based on battery bank size (larger battery, more default charging current). And the second based on hours of sun per day by season (lots of sun, smaller solar array; not much sun larger solar array + possible genset run time).
    For charging 5% rate of charge (200 AH * 0.05 = 10 amps) can work for a weekend/summer cabin. For full time off grid 10%-13% is better:
    • 200 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 188 Watts array minimum
    • 200 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 377 Watts array nominal
    • 200 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 490 Watts array "typical" cost effective maximum
    And based on energy usage/hours of sun per day for fixed array facing south (just guessing on your location):

    Raleigh
    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 54° angle:
    (For best year-round performance)
    Jan Feb Mar Apr May Jun
    3.66
     
    4.00
     
    4.87
     
    5.29
     
    5.29
     
    5.16
     
    Jul Aug Sep Oct Nov Dec
    5.15
     
    4.93
     
    4.86
     
    4.87
     
    4.03
     
    3.67
     
    Using 4 hours of sun per day as "break even" point (use genset if needed):
    • 601 WH per day * 1/0.61 DC system eff * 1/4.0 hours of sun per day = 246 Watt array for February "break even"
    You have suggested AGM batteries--And they are a very good choice. More expensive than similar quality FLA batteries, and probably have a maximum of 5-7 year life (get deep cycle type AGMs, not "float service" batteries). Good for cold weather (freezing and below are FLA and AGM better choices vs Li Ion).
    I will stop here--Made a couple of big posts with lots of guesses about your power needs/location. Please feel free to correct my guesses and ask more questions.
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • PhotowhitPhotowhit Solar Expert Posts: 5,576 ✭✭✭✭✭
    sullyman said:
    ... to charge (2) 100ah 12 volt AGM batteries, in parallel.  ( as I have read that batteries is "series" do not like to be charged that way ) ?  Can a Samlex evo 2012 inverter  power this system ?  OR do I need to keep my batteries in Parallel and get the Samlex evo 2224 ?

    So,  does this sound correct .?  
    I think there is a reversal of understanding of Series and parallel.

    Series vs Parallel Wiring  Adventure EV
    Batteries in series are fine, in fact what we call a battery is actually usually a bank of batteries in series, each cell is a battery and they are interconnected inside of the case usually. A forklift/traction battery makes the connections on the outside between the cells;

    Forklift Battery FAQ  Maintenance and Care  Washington and California
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • sullymansullyman Registered Users Posts: 2
    BB. Thank you for the info.

    Photowhit, you are right  ! I'll keep them in series. Commonsense always wins.
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