Amp to KW?
smalltruck
Registered Users Posts: 11 ✭✭
I am not sure where this question would be best posted, so I will try here and see what happens. I am hoping that someone can either tell me or point me in the right direction. What I want to be able to figure out is how many amp hours it would require at 12 volts to produce one KW at 120 volts. I am hoping to be able to figure in loss in the batteries and going through the inverter. I do not wish to account for any lose in the system before the charge controller. If you think that you can get me started in the right direction that would be helpful I can try and put the peices together from what you give me. If you know the answer that would be even better. Thanks
Comments

Re: Amp to KW?
Starting with the math: Power = Volts * Current = Volts^2 / Resistance = I^2 * Resistance
 Energy = Power * Time = Power * Hours (for house/solar usage)
 1,000 Watts = 1 kWatt (kilo=1,000x)
 Power = Volts * Amp
 Amp*Hours = Amps * Time = Energy (Watt*Hours) / Volts = Amps*Hours
 1 kW = 1,000 Watts
 P=V*I
 I=P/V= 1,000 watts / 120 volts = 8.33 amps @ 120 VAC
 I=P/V= 1,000 watts / 120 volts =83.33 amps @ 12 VDC
 12 volt circuit current = 1,000 Watts * 1/10.5 volts * 1/0.85 efficiency = 112 amps at 12 VDC
 112 amps * 1.25 safety factor = 140 amp minimum circuit rating
Does this get you started?
BillNear San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset 
Re: Amp to KW?
This is very good. When I did the math the other day I came up with 83.33 amps for one KW as well. So that would be 83.33 Amp hours= 1 KW hour? I believe my inverter is rated at 90% efficient at 2/3 power. I am normally using it well below that 2/3 so if would be less then 90%. 85% is a good starting point. So if I understand correctly then I would take 115% of 83.33 and that would tell me how many amp hours = 1 KW hour? Or at least get me close enough. 
Re: Amp to KW?
 1,000 watts * 1/12 volt nominal * 1/0.85 * 1 Hour = 98 AH for 1,000 watts at 12 volt nominal for 1 hour
Also, I did 1,000 watts for 1 hour which is 1,000 Watt*Hours or 1 kWH.
I try to pull all the variables out and label them so you can see exactly what is going onThere is no "real difference" in the result.
BillNear San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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