PluckaPlucka Registered Users Posts: 125 ✭✭
I have 360 amp/hr 12 volt lithium battery bank   which feeds through 2500 watt 240 volt inverter and I'm thinking of buying  a aircon for cooling that states it is 1600 watt 240 volt.The question is how long would the battery last  with the solar panels charging at 40 amps for 5 hours -less for rest of the day ?  I hope to get 5 hours aircon  during the day, off at night .                            


  • BB.BB. Super Moderators, Administrators Posts: 32,216 admin
    edited April 8 #2
    It depends... I think I have read here that there are some nice Mini-Split inverter units that can run at 300 Watts (low)--Start earlier in the day (on low), and bring temp down/keep cool for evening. Other/larger AC units can easily run 1,000 watts or more.

    Say you want 8 hours per day (4 hours afternoon, and 4 hours evening):
    • 300 Watts * 8 hours * 1/0.85 AC inverter eff * 1/12 volts battery bus = 238 AH per cycle @  12 volts
    Then asking the question--If you have enough panels to charge + run the mini-split during the day (A/C on sunny duh), and only run 4 hours at evening/night:
    • 300 Watts * 4 hours evening * 1/0.85 inverter eff * 1/12 volts = 118 AH @ 12 volts
    And there is the question of how much AH you really want to use. Some BMS systems are set to 100%/0% state of charge--Some are set to 90%/20 SoC as a safety margin... If you want to be "nicer" to your battery bank:

    NOTE: Updated below--Fingers got ahead of brain. -Bill
    • 360 AH * (0.90-0.20) = 252 AH "usable" AH capacity
    • 40 amps * 12 volts = 480 Watts
    • 40 amps * 5 hours charging = 200 AH per day
    • 40 amps * 5 hours * 14.5 volts = 2,400 WH per day
    • 2,400 WH per day * 0.85 AC inverter eff  * 1/300 Watt load = 6.8 Hours of estimated runtime
    As always, the A/C unit you choose, and how you program it (if I recall correctly, one of the past popular mini-split inverter types only run at 300 watts when there is a couple degrees between programmed and actual temperature--If you have a "large spread", it may draw much more power at that point)--Details matter.

    300 Watts is probably at the very low side of A/C power usage...

    Hopefully, somebody else here can give you some actual hardware, numbers, and how to operate.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • PluckaPlucka Registered Users Posts: 125 ✭✭
    thanks  Bill
  • BB.BB. Super Moderators, Administrators Posts: 32,216 admin
    edited April 8 #4
    You are very welcome.

    By the way, click on link below ( or put the search term into duckduckgo or google:
    "site: 300 Watt mini-split" (search tag "site:" and term limiting to our forum)

    And can see some older (and newer?) posts referencing 300 Watts on a Mini-Split.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mcgivormcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    The actual run wattage will be determined by the demand, cheap single speed units are all or nothing, running at maximum power  until the setpoint is met. High efficiency inverter units may initially run at full power then slow the compressor down, top of the line may be programmed to run on ECO mode, so there is no definitive answer. My Diakin 9000 btu is substantially more efficient than a similar Samsung but cost twice as much, both inverter type, Diakin has a linear compressor and R 32 refrigerant as opposed to rotary with R 410A, it's consumption can be as low as 165W.

    The thing to consider is what the  battery current will be when running at full power, 1600W ÷ 240V  is 6.66A at 240V, the battery being 12V nominal will need to support 133.3A with the 20:1 ratio, 240V ÷ 12V, not including inefficiencies. The array would need to be sized not only to recharge what was depleted from the previous cycle but support the A/C as well.

    From an outside perspective it would seem unlikely to achieve with such a diminutive system, consider a swamp ( evaporative )cooler if there is low humidity.
    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.
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