Charge rate

MohammadMohammad Registered Users Posts: 7 ✭✭
I have three panels 250w 24v ... to charge two 12 v batteries connected in series (24v) ... what is the best way to connect my panels?

Comments

  • MohammadMohammad Registered Users Posts: 7 ✭✭
    I have 3000 kw inverter with 30 amp mppt charge controller
  • littleharbor2littleharbor2 Solar Expert Posts: 1,112 ✭✭✭✭
    250 watt panels are usually 60 cell panels and as such aren't 24 volt "nominal" panels You need to series wire these panels . What is the Max Voc. of your inverter/controller? Your panels are probably around 36.5 voc. so your controller needs to be capable of handling, say, 140 volts, open circuit voltage.

    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, 700 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

  • MohammadMohammad Registered Users Posts: 7 ✭✭
    Yes ... my controller is up to 120 v ... so i connected them in series ... but still i am getting only about 13 amps to batteries
  • MohammadMohammad Registered Users Posts: 7 ✭✭
    Another thing is that my two 12 v 180 amps batteries get full charged early and soon about an hour after sunset batteries voltage drops down to 23 v ... what would u recommend? Btw ... sealed batteries type
  • EstragonEstragon Registered Users Posts: 3,039 ✭✭✭✭✭
    Are there any loads on the batteries after dark? If so, what amp draw?

    A 3kw inverter is pretty big for a [email protected] bank.
    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
  • MohammadMohammad Registered Users Posts: 7 ✭✭
    They are two batteries actually ... each 180 amps ... yes little load of about 10 amps
  • EstragonEstragon Registered Users Posts: 3,039 ✭✭✭✭✭
    2 12v batteries in series would be [email protected]

    A load of 10a pulling the voltage down to 23v after an hour, plus "get fully charged early" makes me think the batteries have lost much of their capacity.
    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
  • MohammadMohammad Registered Users Posts: 7 ✭✭
    Lets say my batteries died tonight so with my three panels 250 w ... 30 a charger ... what time do i expect it to be full next morning with sun light ?!
  • oil pan 4oil pan 4 Solar Expert Posts: 759 ✭✭✭✭
    What kind of mppt controller is it?
    Sounds like it's not a real mppt cotroller.

    Solar hybrid gasoline generator, 7kw gas, 180 watts of solar, Morningstar 15 amp MPPT, group 31 AGM, 900 watt kisae inverter.

    Solar roof top GMC suburban, a normal 3/4 ton suburban with 180 watts of panels on the roof and 10 amp genasun MPPT, 2000w samlex pure sine wave inverter, 12v gast and ARB air compressors.

  • EstragonEstragon Registered Users Posts: 3,039 ✭✭✭✭✭
    > @Mohammad said:
    > Lets say my batteries died tonight so with my three panels 250 w ... 30 a charger ... what time do i expect it to be full next morning with sun light ?!
    >

    Very roughly, I would expect charging to take about an hour per 10% depth of discharge below ~85% state of charge, plus ~2-3 hours to go from 85% to near 100%.

    For example, say "died" means inverter low battery cutoff was reached at 25% state of charge. 25% to 85% is 60, so ~6 hours in decent sun to get to 85%, plus another 2-3hrs for absorb, so 8-9hrs total.

    This is a very rough guess though, based on what your 750w of pv is likely to produce in decent sun in a typical climate. Depending on conditions, it could be a couple of hours more or less.

    If the batteries appear to be fully charged after an hour or two with the 20-25a you might see from pv, the actual capacity of the batteries has likely been permanently impaired.
    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
  • BB.BB. Super Moderators, Administrators Posts: 28,184 admin
    10 amps at 24 VDC (240 Watts) or 10 amps at 120 VAC... (1,200 Watts)...
     
    A 3 kWatt AC inverter on 24 volts would "like" a minimum of ~600 Amp*Hour @ 24 volt battery bank minimum.

    Your bank would "nicely" support a maximum of ~900 Watts continuous (180 AH @ 24 volts) AC inverter...

    A 3kW inverter would want >600 AH @ 24 volts, or >300 AH @ 48 volts.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • EstragonEstragon Registered Users Posts: 3,039 ✭✭✭✭✭
    Good point. I assumed the 10a load was DC. 10a at 120vac would be > 50a at 24vdc, which would make a 180ah bank unhappy pretty fast.
    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
  • MohammadMohammad Registered Users Posts: 7 ✭✭
    I had a mistake dear friends

    The load is about 2 amp 24 v after sunset ... though my battery drops fast to 23 v ... Most likely it lost its capacity ... btw the battery was deep cycled like 5 times before ... another issue is that three panels connected in series give me about 100 v but i dud not see more than 13 amps going to the battery even when sun is pretty good
    Thanks a lot for your advice
  • MichaelKMichaelK Registered Users Posts: 79 ✭✭
    We should ask how you are actually coming up with the 13 amp number?  I'm assuming you're looking at the charge controller during the day and reading off 13 amps?  Assuming full sun at noon, with individual panels putting out 30.0Volts, you'd expect 8.33 amps of raw power.  Wiring three panels in series would give you 8.33 amps at 90 volts.  8.33A X 90V = 750W.  If your controller is transforming the voltage down to 29.6V, the amperage could theoretically go to 25amps.  That doesn't happen though in the real world.  At best, in noon-time sun you might get 80% (hot panels), so that 25amps becomes 20 amps.  So, at best, you'd expect to see no more than 20amps.  When do you see these readings?  At 9am, before getting full sun, you're likely to see only 30-40% output, or maybe 8-9amps.  By the time noon comes around, the batteries are charged and the controller drops the current to match the state of charge.  13 amps does not seem out of line with that kind of senario.

    To really find out what your panels can actually put out, you need to apply a heavy load at noon that's higher than your total solar capacity.  Things like a 1000 watt toaster, hair drier, toaster oven, ect.  With one of those running, your panels will put out their full capacity irregardless of battery charge.  
    15 Renogy 300w panels,  Midnight 200 CC, 8 Trojan L16 batteries, Schneider XW6848 NA inverter, AC-Delco 6000w gen.
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