RV FEATURE
Let ’ s say you have a 100Ah battery connected to an inverter to power a 1000W air-conditioner . How long will the air-conditioner run before the battery is completely flat ? Well , if you were relying on amp hours , you would have to figure out how many amps the air-conditioner would draw from the battery after the inverter had converted the voltage from 12V to 240V . While it ’ s possible to do , the method can vary depending on who you talk to and it ’ s prone to errors .
This is why working in watts is so easy . The power consumption rate remains constant throughout the process . And we know our 100Ah battery also has a 1200Wh capacity . All we do is divide our battery capacity by the power consumption of the air-conditioner to get a time in hours : 1200Wh battery divided by 1000Wh power consumption equals 1.2 hours of total runtime .
We can also apply the same principle to solar-charging our battery . Let ’ s say we have a 100W solar panel charging our 1200Wh battery that is at 50 per cent state of charge . That means our battery has 600Wh of remaining capacity . Assuming our solar panel is getting full sun , it will take six hours or six 100Wh ( 600Wh ).
HANG ON – IT ’ S NOT THAT SIMPLE
It ’ s around this time that all the electrical experts reading this will say that I haven ’ t taken into account a variety of factors .
Voltages are not a constant 12V and there are system inefficiencies , such as power losses through heat and resistance in the wiring . And then there ’ s the fact that solar panels rarely ever produce their rated output and , even if they did , it wouldn ’ t be constant throughout the day thanks to the changing position of the sun , not to mention cloud cover or shadows cast across them at certain times of the day .
Portable lithium power stations are becoming more popular . Their capacity is rated in watt hours .
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