STILL confused by maths - how many AH is used if my watt meter measures 700Wh?

[hyberlut]

OK - sorry for the rookie question which I'm sure is beat to death, but I could use some feedback as to whether my math is correct.

I want to know that if I use X watt hours in an AC device, then how many Ah are being used from the 12v battery?

My killawatt meter measured my 120v fridge running off the inverter used 0.75kWh in a 24-hour period. So 750Wh/12v = 62.5Ah. Is this correct? Or do I need to convert the watt-hours (measured in AC 120V) to DC 12V first and then calculate? I have used and read countless solar calculators and used different formulas and my head is spinning, lol. I was good at theoretical math in school, but real world math isn't my forte, so some confirmation would help. 62.5Ah seems I guess about right, maybe a bit high?

I also measured only during darkness and came up with 0.17kWh. 170Wh/12v=14.1Ah, if my math above is correct.

 

[John Frum]

I want to know that if I use X watt hours in an AC device, then how many Ah are being used from the 12v battery?

750 ac watt hours * 1.15 inverter efficiency factor = 862.5 dc watt hours
862.5 dc watt hours / 12.8 nominal volts = 67.3828125 dc amp hours

 

[HOU_Castle]

For simplicity, 1A used in 120VAC system is about 10 times of Amp in 12VDC system (before adding inverter inefficiency).

 

[hyberlut]

750 ac watt hours * 1.15 inverter efficiency factor = 862.5 dc watt hours
862.5 dc watt hours / 12.8 nominal volts = 67.3828125 dc amp hours

Thank you! That was about the same number I was coming up with.

 

[hyberlut]

For simplicity, 1A used in 120VAC system is about 10 times of Amp in 12VDC system (before adding inverter inefficiency).

Thank you. Yes, I saw that formula too, I was just doubting that I had it all figured out properly, even with such a simple formula. This helps a lot to realize our 200Ah AGM bank is barely enough to get by without risking over-discharging. I see LiFePO4 in our future as we can't physically fit any more batteries than 2 in our tight space in the camp trailer.