Inverters

Plucka
Plucka Registered Users Posts: 130 ✭✭
Is there a difference -Using a 1500 watt inverter  to produce 240 volts to power a 1000 watt  kettle or a 3000 watt inverter to produce the same.Is the 12 volt consumption the same  or one uses more than the other.
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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    edited August 2020 #2
    There may be slight difference depending on the efficiency curve but that shouldn't be of concern,, the greater issue, when using  high capacity inverters  with 12V nominal, is,  the high DC current encountered  and  the associated voltage drop, which in turn requires substantial conductors. For example if a 3000W inverter was at full capacity the DC current demand would be ~ 250A, which only iincreases as the battery voltage drops under such a load.
    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.  
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,606 admin
    Power = Voltage * Current

    So, in theory, a 1,500 Watt inverter will use the same amount of DC power for a 1,000 Watt kettle, as would a 3,000 Watt AC inverter.

    In practice, the 3,000 Watt inverter has larger switching transistors and such... So there is a fair amount of energy loss in the conversion from 12 VDC to 240 VAC...

    There are "curves" of inverter efficinecy... When using a only a few Watts of AC load, the 6-20 Watt "Tare" loading of the AC inverter just to "turn on" can swamp small AC loads and give you very poor efficiency (10 Watt load and 10 Watt Tare = 50% efficiency

    At higher loading many inverters can be in the 85% to 95% efficiency level.

    Other issue... For example it is very hard to get 3,000 Watts of energy from a 12 volt battery bank. Because of the high currents and voltage drops (using very heavy copper cables), I would suggest that you not try to pull much more than 1,200 to 1,800 Watts from a 12 volt battery bank. A 3kWatt inverter on a 12 volt battery bank at full AC loading would draw:
    • 3,000 Watts * 1/0.85 AC inverter eff * 1/10.5 battery cutoff voltage = 336 Amps (12 volt bank) maximum continuous current draw.
    4/0 or heavier wiring would be like 0.46 or 11.6 mm in diameter (or thicker if using heavier cable):


    Example of 4/0 cable

    WG gaugeConductor
    Diameter Inches
    Conductor
    Diameter mm
    Conductor cross section in mm2Ohms per 1000 ft.Ohms per kmMaximum amps for chassis wiringMaximum amps for
    power transmission
    Maximum frequency for
    100% skin depth for solid conductor copper
    Breaking force Soft Annealed Cu 37000 PSI
    00000.4611.6841070.0490.16072380302125 Hz6120 lbs

    If you want more Watts, look to a 24 or 48 VDC battery bank instead.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Plucka
    Plucka Registered Users Posts: 130 ✭✭
    thanks Bill